celery/Changelog

================
 Change history
================

.. contents::
    :local:

.. _version-2.2.1:

2.2.1
=====
:release-date: 2011-02-02 16:00 PM CEST

.. _v221-fixes:

Fixes
-----

* Eventlet pool was leaking memory (Issue #308).

* Deprecated function ``celery.execute.delay_task`` was accidentally removed,
  now available again.

* ``BasePool.on_terminate`` stub did not exist

* celeryd detach: Adds readable error messages if user/group name does not
   exist.

* Smarter handling of unicode decod errors when logging errors.

.. _version-2.2.0:

2.2.0
=====
:release-date: 2011-02-01 10:00 AM CEST

.. _v220-important:

Important Notes
---------------

* Carrot has been replaced with `Kombu`_

    Kombu is the next generation messaging framework for Python,
    fixing several flaws present in Carrot that was hard to fix
    without breaking backwards compatibility.

    Also it adds:

    * First-class support for virtual transports; Redis, Django ORM,
      SQLAlchemy, Beanstalk, MongoDB, CouchDB and in-memory.
    * Consistent error handling with introspection,
    * The ability to ensure that an operation is performed by gracefully
      handling connection and channel errors,
    * Message compression (zlib, bzip2, or custom compression schemes).

    This means that `ghettoq` is no longer needed as the
    functionality it provided is already available in Celery by default.
    The virtual transports are also more feature complete with support
    for exchanges (direct and topic).  The Redis transport even supports
    fanout exchanges so it is able to perform worker remote control
    commands.

.. _`Kombu`: http://pypi.python.org/pypi/kombu

* Magic keyword arguments pending deprecation.

    The magic keyword arguments were responsibile for many problems
    and quirks: notably issues with tasks and decorators, and name
    collisions in keyword arguments for the unaware.

    It wasn't easy to find a way to deprecate the magic keyword arguments,
    but we think this is a solution that makes sense and it will not
    have any adverse effects for existing code.

    The path to a magic keyword argument free world is:

        * the `celery.decorators` module is deprecated and the decorators
          can now be found in `celery.task`.
        * The decorators in `celery.task` disables keyword arguments by
          default
        * All examples in the documentation have been changed to use
          `celery.task`.

        This means that the following will have magic keyword arguments
        enabled (old style):

            .. code-block:: python

                from celery.decorators import task

                @task
                def add(x, y, **kwargs):
                    print("In task %s" % kwargs["task_id"])
                    return x + y

        And this will not use magic keyword arguments (new style):

            .. code-block:: python

                from celery.task import task

                @task
                def add(x, y):
                    print("In task %s" % add.request.id)
                    return x + y

    In addition, tasks can choose not to accept magic keyword arguments by
    setting the `task.accept_magic_kwargs` attribute.

    .. admonition:: Deprecation

        Using the decorators in :mod:`celery.decorators` emits a
        :class:`PendingDeprecationWarning` with a helpful message urging
        you to change your code, in version 2.4 this will be replaced with
        a :class:`DeprecationWarning`, and in version 3.0 the
        :mod:`celery.decorators` module will be removed and no longer exist.

        Similarly, the `task.accept_magic_kwargs` attribute will no
        longer have any effect starting from version 3.0.

* The magic keyword arguments are now available as `task.request`

    This is called *the context*.  Using thread-local storage the
    context contains state that is related to the current request.

    It is mutable and you can add custom attributes that will only be seen
    by the current task request.

    The following context attributes are always available:

    =====================================  ===================================
    **Magic Keyword Argument**             **Replace with**
    =====================================  ===================================
    `kwargs["task_id"]`                    `self.request.id`
    `kwargs["delivery_info"]`              `self.request.delivery_info`
    `kwargs["task_retries"]`               `self.request.retries`
    `kwargs["logfile"]`                    `self.request.logfile`
    `kwargs["loglevel"]`                   `self.request.loglevel`
    `kwargs["task_is_eager`                `self.request.is_eager`
    **NEW**                                `self.request.args`
    **NEW**                                `self.request.kwargs`
    =====================================  ===================================

    In addition, the following methods now automatically uses the current
    context, so you don't have to pass `kwargs` manually anymore:

        * `task.retry`
        * `task.get_logger`
        * `task.update_state`

* `Eventlet`_ support.

    This is great news for I/O-bound tasks!

    To change pool implementations you use the :option:`-P|--pool` argument
    to :program:`celeryd`, or globally using the
    :setting:`CELERYD_POOL` setting.  This can be the full name of a class,
    or one of the following aliases: `processes`, `eventlet`, `gevent`.

    For more information please see the :ref:`concurrency-eventlet` section
    in the User Guide.

    .. admonition:: Why not gevent?

        For our first alternative concurrency implementation we have focused
        on `Eventlet`_, but there is also an experimental `gevent`_ pool
        available. This is missing some features, notably the ability to
        schedule ETA tasks.

        Hopefully the `gevent`_ support will be feature complete by
        version 2.3, but this depends on user demand (and contributions).

.. _`Eventlet`: http://eventlet.net
.. _`gevent`: http://gevent.org

* Python 2.4 support deprecated!

    We're happy^H^H^H^H^Hsad to announce that this is the last version
    to support Python 2.4.

    You are urged to make some noise if you're currently stuck with
    Python 2.4.  Complain to your package maintainers, sysadmins and bosses:
    tell them it's time to move on!

    Apart from wanting to take advantage of with-statements, coroutines,
    conditional expressions and enhanced try blocks, the code base
    now contains so many 2.4 related hacks and workarounds it's no longer
    just a compromise, but a sacrifice.

    If it really isn't your choice, and you don't have the option to upgrade
    to a newer version of Python, you can just continue to use Celery 2.2.
    Important fixes can be backported for as long as there is interest.

* `celeryd`: Now supports Autoscaling of child worker processes.

    The :option:`--autoscale` option can be used to configure the minimum
    and maximum number of child worker processes::

        --autoscale=AUTOSCALE
             Enable autoscaling by providing
             max_concurrency,min_concurrency.  Example:
               --autoscale=10,3 (always keep 3 processes, but grow to
              10 if necessary).

* Remote Debugging of Tasks

   ``celery.contrib.rdb`` is an extended version of :mod:`pdb` that
   enables remote debugging of processes that does not have terminal
   access.

   Example usage:

   .. code-block:: python

        from celery.contrib import rdb
        from celery.task import task

        @task
        def add(x, y):
            result = x + y
            rdb.set_trace()  # <- set breakpoint
            return result


    :func:`~celery.contrib.rdb.set_trace` sets a breakpoint at the current
    location and creates a socket you can telnet into to remotely debug
    your task.

    The debugger may be started by multiple processes at the same time,
    so rather than using a fixed port the debugger will search for an
    available port, starting from the base port (6900 by default).
    The base port can be changed using the environment variable
    :envvar:`CELERY_RDB_PORT`.

    By default the debugger will only be available from the local host,
    to enable access from the outside you have to set the environment
    variable :envvar:`CELERY_RDB_HOST`.

    When `celeryd` encounters your breakpoint it will log the following
    information::

        [INFO/MainProcess] Got task from broker:
            tasks.add[d7261c71-4962-47e5-b342-2448bedd20e8]
        [WARNING/PoolWorker-1] Remote Debugger:6900:
            Please telnet 127.0.0.1 6900.  Type `exit` in session to continue.
        [2011-01-18 14:25:44,119: WARNING/PoolWorker-1] Remote Debugger:6900:
            Waiting for client...

    If you telnet the port specified you will be presented
    with a ``pdb`` shell::

        $ telnet localhost 6900
        Connected to localhost.
        Escape character is '^]'.
        > /opt/devel/demoapp/tasks.py(128)add()
        -> return result
        (Pdb)

    Enter ``help`` to get a list of available commands,
    It may be a good idea to read the `Python Debugger Manual`_ if
    you have never used `pdb` before.

.. _`Python Debugger Manual`: http://docs.python.org/library/pdb.html


* Events are now transient and is using a topic exchange (instead of direct).

    The `CELERYD_EVENT_EXCHANGE`, `CELERYD_EVENT_ROUTING_KEY`,
    `CELERYD_EVENT_EXCHANGE_TYPE` settings are no longer in use.

    This means events will not be stored until there is a consumer, and the
    events will be gone as soon as the consumer stops.  Also it means there
    can be multiple monitors running at the same time.

    The routing key of an event is the type of event (e.g. `worker.started`,
    `worker.heartbeat`, `task.succeeded`, etc.  This means a consumer can
    filter on specific types, to only be alerted of the events it cares about.

    Each consumer will create a unique queue, meaning it is in effect a
    broadcast exchange.

    This opens up a lot of possibilities, for example the workers could listen
    for worker events to know what workers are in the neighborhood, and even
    restart workers when they go down (or use this information to optimize
    tasks/autoscaling).

    .. note::

        The event exchange has been renamed from "celeryevent" to "celeryev"
        so it does not collide with older versions.

        If you would like to remove the old exchange you can do so
        by executing the following command::

            $ camqadm exchange.delete celeryevent

* `celeryd` now starts without configuration, and configuration can be
  specified directly on the command line.

  Configuration options must appear after the last argument, separated
  by two dashes::

      $ celeryd -l info -I tasks -- broker.host=localhost broker.vhost=/app

* Configuration is now an alias to the original configuration, so changes
  to the original will reflect Celery at runtime.

* `celery.conf` has been deprecated, and modifying `celery.conf.ALWAYS_EAGER`
  will no longer have any effect.

    The default configuration is now available in the
    :mod:`celery.app.defaults` module.  The available configuration options
    and their types can now be introspected.

* Remote control commands are now provided by `kombu.pidbox`, the generic
  process mailbox.

* Internal module `celery.worker.listener` has been renamed to
  `celery.worker.consumer`, and `.CarrotListener` is now `.Consumer`.

* Previously deprecated modules `celery.models` and
  `celery.management.commands` have now been removed as per the deprecation
  timeline.

* [Security: Low severity] Removed `celery.task.RemoteExecuteTask` and
    accompanying functions: `dmap`, `dmap_async`, and `execute_remote`.

    Executing arbitrary code using pickle is a potential security issue if
    someone gains unrestricted access to the message broker.

    If you really need this functionality, then you would have to add
    this to your own project.

* [Security: Low severity] The `stats` command no longer transmits the
  broker password.

    One would have needed an authenticated broker connection to receive
    this password in the first place, but sniffing the password at the
    wire level would have been possible if using unencrypted communication.

.. _v220-news:

News
----

* The internal module `celery.task.builtins` has been removed.

* The module `celery.task.schedules` is deprecated, and
  `celery.schedules` should be used instead.

    For example if you have::

        from celery.task.schedules import crontab

    You should replace that with::

        from celery.schedules import crontab

    The module needs to be renamed because it must be possible
    to import schedules without importing the `celery.task` module.

* The following functions have been deprecated and is scheduled for
  removal in version 2.3:

    * `celery.execute.apply_async`

        Use `task.apply_async()` instead.

    * `celery.execute.apply`

        Use `task.apply()` instead.

    * `celery.execute.delay_task`

        Use `registry.tasks[name].delay()` instead.

* Importing `TaskSet` from `celery.task.base` is now deprecated.

    You should use::

        >>> from celery.task import TaskSet

    instead.

* New remote control commands:

    * `active_queues`

        Returns the queue declarations a worker is currently consuming from.

* Added the ability to retry publishing the task message in
  the event of connection loss or failure.

    This is disabled by default but can be enabled using the
    :setting:`CELERY_TASK_PUBLISH_RETRY` setting, and tweaked by
    the :setting:`CELERY_TASK_PUBLISH_RETRY_POLICY` setting.

    In addition `retry`, and `retry_policy` keyword arguments have
    been added to `Task.apply_async`.

    .. note::

        Using the `retry` argument to `apply_async` requires you to
        handle the publisher/connection manually.

* Periodic Task classes (`@periodic_task`/`PeriodicTask`) will *not* be
  deprecated as previously indicated in the source code.

    But you are encouraged to use the more flexible
    :setting:`CELERYBEAT_SCHEDULE` setting.

* Built-in daemonization support of celeryd using `celeryd-multi`
  is no longer experimental and is considered production quality.

     See :ref:`daemon-generic` if you want to use the new generic init
     scripts.

* Added support for message compression using the
  :setting:`CELERY_MESSAGE_COMPRESSION` setting, or the `compression` argument
  to `apply_async`.  This can also be set using routers.

* `celeryd`: Now logs stacktrace of all threads when receiving the
   `SIGUSR1` signal.  (Does not work on cPython 2.4, Windows or Jython).

    Inspired by https://gist.github.com/737056

* Can now remotely terminate/kill the worker process currently processing
  a task.

    The `revoke` remote control command now supports a `terminate` argument
    Default signal is `TERM`, but can be specified using the `signal`
    argument. Signal can be the uppercase name of any signal defined
    in the :mod:`signal` module in the Python Standard Library.

    Terminating a task also revokes it.

    Example::

        >>> from celery.task.control import revoke

        >>> revoke(task_id, terminate=True)
        >>> revoke(task_id, terminate=True, signal="KILL")
        >>> revoke(task_id, terminate=True, signal="SIGKILL")

* `TaskSetResult.join_native`: Backend-optimized version of `join()`.

    If available, this version uses the backends ability to retrieve
    multiple results at once, unlike `join()` which fetches the results
    one by one.

    So far only supported by the AMQP result backend.  Support for memcached
    and Redis may be added later.

* Improved implementations of `TaskSetResult.join` and `AsyncResult.wait`.

   An `interval` keyword argument have been added to both so the
   polling interval can be specified (default interval is 0.5 seconds).

    A `propagate` keyword argument have been added to `result.wait()`,
    errors will be returned instead of raised if this is set to False.

    .. warning::

        You should decrease the polling interval when using the database
        result backend, as frequent polling can result in high database load.


* The PID of the child worker process accepting a task is now sent as a field
  with the `task-started` event.

* The following fields have been added to all events in the worker class:

    * `sw_ident`: Name of worker software (e.g. celeryd).
    * `sw_ver`: Software version (e.g. 2.2.0).
    * `sw_sys`: Operating System (e.g. Linux, Windows, Darwin).

* For better accuracy the start time reported by the multiprocessing worker
  process is used when calculating task duration.

    Previously the time reported by the accept callback was used.

* `celerybeat`: New built-in daemonization support using the `--detach`
   option.

* `celeryev`: New built-in daemonization support using the `--detach`
   option.

* `TaskSet.apply_async`: Now supports custom publishers by using the
  `publisher` argument.

* Added :setting:`CELERY_SEND_TASK_SENT_EVENT` setting.

    If enabled an event will be sent with every task, so monitors can
    track tasks before the workers receive them.

* `celerybeat`: Now reuses the broker connection when applying
   scheduled tasks.

* The configuration module and loader to use can now be specified on
  the command line.

    For example::

        $ celeryd --config=celeryconfig.py --loader=myloader.Loader

* Added signals: `beat_init` and `beat_embedded_init`

    * :data:`celery.signals.beat_init`

        Dispatched when :program:`celerybeat` starts (either standalone or
        embedded).  Sender is the :class:`celery.beat.Service` instance.

    * :data:`celery.signals.beat_embedded_init`

        Dispatched in addition to the :data:`beat_init` signal when
        :program:`celerybeat` is started as an embedded process.  Sender
        is the :class:`celery.beat.Service` instance.

* Redis result backend: Removed deprecated settings `REDIS_TIMEOUT` and
  `REDIS_CONNECT_RETRY`.

* CentOS init script for :program:`celeryd` now available in `contrib/centos`.

* Now depends on `pyparsing` version 1.5.0 or higher.

    There have been reported issues using Celery with pyparsing 1.4.x,
    so please upgrade to the latest version.

* Lots of new unit tests written, now with a total coverage of 95%.

.. _v220-fixes:

Fixes
-----

* `celeryev` Curses Monitor: Improved resize handling and UI layout
  (Issue #274 + Issue #276)

* AMQP Backend: Exceptions occurring while sending task results are now
  propagated instead of silenced.

    `celeryd` will then show the full traceback of these errors in the log.

* AMQP Backend: No longer deletes the result queue after successful
  poll, as this should be handled by the
  :setting:`CELERY_AMQP_TASK_RESULT_EXPIRES` setting instead.

* AMQP Backend: Now ensures queues are declared before polling results.

* Windows: celeryd: Show error if running with `-B` option.

    Running celerybeat embedded is known not to work on Windows, so
    users are encouraged to run celerybeat as a separate service instead.

* Windows: Utilities no longer output ANSI color codes on Windows

* camqadm: Now properly handles Ctrl+C by simply exiting instead of showing
  confusing traceback.

* Windows: All tests are now passing on Windows.

* Remove bin/ directory, and `scripts` section from setup.py.

    This means we now rely completely on setuptools entrypoints.

.. _v220-experimental:

Experimental
------------

* Jython: celeryd now runs on Jython using the threaded pool.

    All tests pass, but there may still be bugs lurking around the corners.

* PyPy: celeryd now runs on PyPy.

    It runs without any pool, so to get parallel execution you must start
    multiple instances (e.g. using :program:`celeryd-multi`).

    Sadly an initial benchmark seems to show a 30% performance decrease on
    pypy-1.4.1 + JIT.  We would like to find out why this is, so stay tuned.

* :class:`PublisherPool`: Experimental pool of task publishers and
  connections to be used with the `retry` argument to `apply_async`.

  The example code below will re-use connections and channels, and
  retry sending of the task message if the connection is lost.

  .. code-block:: python

    from celery import current_app

    # Global pool
    pool = current_app().amqp.PublisherPool(limit=10)

    def my_view(request):
        with pool.acquire() as publisher:
            add.apply_async((2, 2), publisher=publisher, retry=True)


.. _version-2.1.4:

2.1.4
=====
:release-date: 2010-12-03 12:00 PM CEST

.. _v214-fixes:

Fixes
-----

* Execution options to `apply_async` now takes precedence over options
  returned by active routers.  This was a regression introduced recently
  (Issue #244).

* `celeryev` curses monitor: Long arguments are now truncated so curses
  doesn't crash with out of bounds errors.  (Issue #235).

* `celeryd`: Channel errors occurring while handling control commands no
  longer crash the worker but are instead logged with severity error.

* SQLAlchemy database backend: Fixed a race condition occurring when
  the client wrote the pending state.  Just like the Django database backend,
  it does no longer save the pending state (Issue #261 + Issue #262).

* Error email body now uses `repr(exception)` instead of `str(exception)`,
  as the latter could result in Unicode decode errors (Issue #245).

* Error e-mail timeout value is now configurable by using the
  :setting:`EMAIL_TIMEOUT` setting.

* `celeryev`: Now works on Windows (but the curses monitor won't work without
  having curses).

* Unit test output no longer emits non-standard characters.

* `celeryd`: The broadcast consumer is now closed if the connection is reset.

* `celeryd`: Now properly handles errors occurring while trying to acknowledge
  the message.

* `TaskRequest.on_failure` now encodes traceback using the current filesystem
   encoding.  (Issue #286).

* `EagerResult` can now be pickled (Issue #288).

.. _v214-documentation:

Documentation
-------------

* Adding :ref:`contributing`.

* Added :ref:`guide-optimizing`.

* Added :ref:`faq-security` section to the FAQ.

.. _version-2.1.3:

2.1.3
=====
:release-date: 2010-11-09 17:00 PM CEST

.. _v213-fixes:

* Fixed deadlocks in `timer2` which could lead to `djcelerymon`/`celeryev -c`
  hanging.

* `EventReceiver`: now sends heartbeat request to find workers.

    This means :program:`celeryev` and friends finds workers immediately
    at startup.

* celeryev cursesmon: Set screen_delay to 10ms, so the screen refreshes more
  often.

* Fixed pickling errors when pickling :class:`AsyncResult` on older Python
  versions.

* celeryd: prefetch count was decremented by eta tasks even if there
  were no active prefetch limits.


.. _version-2.1.2:

2.1.2
=====
:release-data: TBA

.. _v212-fixes:

Fixes
-----

* celeryd: Now sends the `task-retried` event for retried tasks.

* celeryd: Now honors ignore result for
  :exc:`~celery.exceptions.WorkerLostError` and timeout errors.

* celerybeat: Fixed :exc:`UnboundLocalError` in celerybeat logging
  when using logging setup signals.

* celeryd: All log messages now includes `exc_info`.

.. _version-2.1.1:

2.1.1
=====
:release-date: 2010-10-14 14:00 PM CEST

.. _v211-fixes:

Fixes
-----

* Now working on Windows again.

   Removed dependency on the pwd/grp modules.

* snapshots: Fixed race condition leading to loss of events.

* celeryd: Reject tasks with an eta that cannot be converted to a time stamp.

    See issue #209

* concurrency.processes.pool: The semaphore was released twice for each task
  (both at ACK and result ready).

    This has been fixed, and it is now released only once per task.

* docs/configuration: Fixed typo `CELERYD_SOFT_TASK_TIME_LIMIT` ->
  :setting:`CELERYD_TASK_SOFT_TIME_LIMIT`.

    See issue #214

* control command `dump_scheduled`: was using old .info attribute

* :program:`celeryd-multi`: Fixed `set changed size during iteration` bug
    occurring in the restart command.

* celeryd: Accidentally tried to use additional command line arguments.

   This would lead to an error like:

    `got multiple values for keyword argument 'concurrency'`.

    Additional command line arguments are now ignored, and does not
    produce this error.  However -- we do reserve the right to use
    positional arguments in the future, so please do not depend on this
    behavior.

* celerybeat: Now respects routers and task execution options again.

* celerybeat: Now reuses the publisher instead of the connection.

* Cache result backend: Using :class:`float` as the expires argument
  to `cache.set` is deprecated by the memcached libraries,
  so we now automatically cast to :class:`int`.

* unit tests: No longer emits logging and warnings in test output.

.. _v211-news:

News
----

* Now depends on carrot version 0.10.7.

* Added :setting:`CELERY_REDIRECT_STDOUTS`, and
  :setting:`CELERYD_REDIRECT_STDOUTS_LEVEL` settings.

    :setting:`CELERY_REDIRECT_STDOUTS` is used by :program:`celeryd` and
    :program:`celerybeat`.  All output to `stdout` and `stderr` will be
    redirected to the current logger if enabled.

    :setting:`CELERY_REDIRECT_STDOUTS_LEVEL` decides the log level used and is
    :const:`WARNING` by default.

* Added :setting:`CELERYBEAT_SCHEDULER` setting.

    This setting is used to define the default for the -S option to
    :program:`celerybeat`.

    Example:

    .. code-block:: python

        CELERYBEAT_SCHEDULER = "djcelery.schedulers.DatabaseScheduler"

* Added Task.expires: Used to set default expiry time for tasks.

* New remote control commands: `add_consumer` and `cancel_consumer`.

    .. method:: add_consumer(queue, exchange, exchange_type, routing_key,
                             **options)
        :module:

        Tells the worker to declare and consume from the specified
        declaration.

    .. method:: cancel_consumer(queue_name)
        :module:

        Tells the worker to stop consuming from queue (by queue name).


    Commands also added to :program:`celeryctl` and
    :class:`~celery.task.control.inspect`.


    Example using celeryctl to start consuming from queue "queue", in 
    exchange "exchange", of type "direct" using binding key "key"::

        $ celeryctl inspect add_consumer queue exchange direct key
        $ celeryctl inspect cancel_consumer queue

    See :ref:`monitoring-celeryctl` for more information about the
    :program:`celeryctl` program.


    Another example using :class:`~celery.task.control.inspect`:

    .. code-block:: python

        >>> from celery.task.control import inspect
        >>> inspect.add_consumer(queue="queue", exchange="exchange",
        ...                      exchange_type="direct",
        ...                      routing_key="key",
        ...                      durable=False,
        ...                      auto_delete=True)

        >>> inspect.cancel_consumer("queue")

* celerybeat: Now logs the traceback if a message can't be sent.

* celerybeat: Now enables a default socket timeout of 30 seconds.

* README/introduction/homepage: Added link to `Flask-Celery`_.

.. _`Flask-Celery`: http://github.com/ask/flask-celery

.. _version-2.1.0:

2.1.0
=====
:release-date: 2010-10-08 12:00 PM CEST

.. _v210-important:

Important Notes
---------------

* Celery is now following the versioning semantics defined by `semver`_.

    This means we are no longer allowed to use odd/even versioning semantics
    By our previous versioning scheme this stable release should have
    been version 2.2.

.. _`semver`: http://semver.org

* Now depends on Carrot 0.10.7.

* No longer depends on SQLAlchemy, this needs to be installed separately
  if the database result backend is used.

* django-celery now comes with a monitor for the Django Admin interface.
  This can also be used if you're not a Django user.  See
  :ref:`monitoring-django-admin` and :ref:`monitoring-nodjango` for more information.

* If you get an error after upgrading saying:
  `AttributeError: 'module' object has no attribute 'system'`,

    Then this is because the `celery.platform` module has been
    renamed to `celery.platforms` to not collide with the built-in
    :mod:`platform` module.

    You have to remove the old :file:`platform.py` (and maybe
    :file:`platform.pyc`) file from your previous Celery installation.

    To do this use :program:`python` to find the location
    of this module::

        $ python
        >>> import celery.platform
        >>> celery.platform
        <module 'celery.platform' from '/opt/devel/celery/celery/platform.pyc'>

    Here the compiled module is in :file:`/opt/devel/celery/celery/`,
    to remove the offending files do::

        $ rm -f /opt/devel/celery/celery/platform.py*

.. _v210-news:

News
----

* Added support for expiration of AMQP results (requires RabbitMQ 2.1.0)

    The new configuration option :setting:`CELERY_AMQP_TASK_RESULT_EXPIRES`
    sets the expiry time in seconds (can be int or float):

    .. code-block:: python

        CELERY_AMQP_TASK_RESULT_EXPIRES = 30 * 60  # 30 minutes.
        CELERY_AMQP_TASK_RESULT_EXPIRES = 0.80     # 800 ms.

* celeryev: Event Snapshots

    If enabled, :program:`celeryd` sends messages about what the worker is doing.
    These messages are called "events".
    The events are used by real-time monitors to show what the
    cluster is doing, but they are not very useful for monitoring
    over a longer period of time.  Snapshots
    lets you take "pictures" of the clusters state at regular intervals.
    This can then be stored in a database to generate statistics
    with, or even monitoring over longer time periods.

    django-celery now comes with a Celery monitor for the Django
    Admin interface. To use this you need to run the django-celery
    snapshot camera, which stores snapshots to the database at configurable
    intervals.  See :ref:`monitoring-nodjango` for information about using
    this monitor if you're not using Django.

    To use the Django admin monitor you need to do the following:

    1. Create the new database tables.

        $ python manage.py syncdb

    2. Start the django-celery snapshot camera::

        $ python manage.py celerycam

    3. Open up the django admin to monitor your cluster.

    The admin interface shows tasks, worker nodes, and even
    lets you perform some actions, like revoking and rate limiting tasks,
    and shutting down worker nodes.

    There's also a Debian init.d script for :mod:`~celery.bin.celeryev` available,
    see :doc:`cookbook/daemonizing` for more information.

    New command line arguments to celeryev:

        * :option:`-c|--camera`: Snapshot camera class to use.
        * :option:`--logfile|-f`: Log file
        * :option:`--loglevel|-l`: Log level
        * :option:`--maxrate|-r`: Shutter rate limit.
        * :option:`--freq|-F`: Shutter frequency

    The :option:`--camera` argument is the name of a class used to take
    snapshots with. It must support the interface defined by
    :class:`celery.events.snapshot.Polaroid`.

    Shutter frequency controls how often the camera thread wakes up,
    while the rate limit controls how often it will actually take
    a snapshot.
    The rate limit can be an integer (snapshots/s), or a rate limit string
    which has the same syntax as the task rate limit strings (`"200/m"`,
    `"10/s"`, `"1/h",` etc).

    For the Django camera case, this rate limit can be used to control
    how often the snapshots are written to the database, and the frequency
    used to control how often the thread wakes up to check if there's
    anything new.

    The rate limit is off by default, which means it will take a snapshot
    for every :option:`--frequency` seconds.

.. seealso::

    :ref:`monitoring-django-admin` and :ref:`monitoring-snapshots`.

* :func:`~celery.task.control.broadcast`: Added callback argument, this can be
  used to process replies immediately as they arrive.

* celeryctl: New command-line utility to manage and inspect worker nodes,
  apply tasks and inspect the results of tasks.

    .. seealso::
        The :ref:`monitoring-celeryctl` section in the :ref:`guide`.

    Some examples::

        $ celeryctl apply tasks.add -a '[2, 2]' --countdown=10

        $ celeryctl inspect active
        $ celeryctl inspect registered_tasks
        $ celeryctl inspect scheduled
        $ celeryctl inspect --help
        $ celeryctl apply --help

* Added the ability to set an expiry date and time for tasks.

    Example::

        >>> # Task expires after one minute from now.
        >>> task.apply_async(args, kwargs, expires=60)
        >>> # Also supports datetime
        >>> task.apply_async(args, kwargs,
        ...                  expires=datetime.now() + timedelta(days=1)

    When a worker receives a task that has been expired it will be
    marked as revoked (:exc:`celery.exceptions.TaskRevokedError`).

* Changed the way logging is configured.

    We now configure the root logger instead of only configuring
    our custom logger. In addition we don't hijack
    the multiprocessing logger anymore, but instead use a custom logger name
    for different applications:

    =====================================  =====================================
    **Application**                        **Logger Name**
    =====================================  =====================================
    `celeryd`                              "celery"
    `celerybeat`                           "celery.beat"
    `celeryev`                             "celery.ev"
    =====================================  =====================================

    This means that the `loglevel` and `logfile` arguments will
    affect all registered loggers (even those from 3rd party libraries).
    Unless you configure the loggers manually as shown below, that is.

    *Users can choose to configure logging by subscribing to the
    :data:`~celery.signals.setup_logging` signal:*

    .. code-block:: python

        from logging.config import fileConfig
        from celery import signals

        def setup_logging(**kwargs):
            fileConfig("logging.conf")
        signals.setup_logging.connect(setup_logging)

    If there are no receivers for this signal, the logging subsystem
    will be configured using the :option:`--loglevel`/:option:`--logfile`
    argument, this will be used for *all defined loggers*.

    Remember that celeryd also redirects stdout and stderr
    to the celery logger, if manually configure logging
    you also need to redirect the stdouts manually:

    .. code-block:: python

        from logging.config import fileConfig
        from celery import log

       def setup_logging(**kwargs):
            import logging
            fileConfig("logging.conf")
            stdouts = logging.getLogger("mystdoutslogger")
            log.redirect_stdouts_to_logger(stdouts, loglevel=logging.WARNING)

* celeryd: Added command-line option :option:`-I`/:option:`--include`:

    A comma separated list of (task) modules to be imported.

    Example::

        $ celeryd -I app1.tasks,app2.tasks

* celeryd: now emits a warning if running as the root user (euid is 0).

* :func:`celery.messaging.establish_connection`: Ability to override defaults
  used using keyword argument "defaults".

* celeryd: Now uses `multiprocessing.freeze_support()` so that it should work
  with **py2exe**, **PyInstaller**, **cx_Freeze**, etc.

* celeryd: Now includes more metadata for the :state:`STARTED` state: PID and
  host name of the worker that started the task.

    See issue #181

* subtask: Merge additional keyword arguments to `subtask()` into task keyword
  arguments.

    e.g.:

        >>> s = subtask((1, 2), {"foo": "bar"}, baz=1)
        >>> s.args
        (1, 2)
        >>> s.kwargs
        {"foo": "bar", "baz": 1}

    See issue #182.

* celeryd: Now emits a warning if there is already a worker node using the same
  name running on the same virtual host.

* AMQP result backend: Sending of results are now retried if the connection
  is down.

* AMQP result backend: `result.get()`: Wait for next state if state is not
    in :data:`~celery.states.READY_STATES`.

* TaskSetResult now supports subscription.

    ::

        >>> res = TaskSet(tasks).apply_async()
        >>> res[0].get()

* Added `Task.send_error_emails` + `Task.error_whitelist`, so these can
  be configured per task instead of just by the global setting.

* Added `Task.store_errors_even_if_ignored`, so it can be changed per Task,
  not just by the global setting.

* The crontab scheduler no longer wakes up every second, but implements
  `remaining_estimate` (*Optimization*).

* celeryd:  Store :state:`FAILURE` result if the
   :exc:`~celery.exceptions.WorkerLostError` exception occurs (worker process
   disappeared).

* celeryd: Store :state:`FAILURE` result if one of the `*TimeLimitExceeded`
  exceptions occurs.

* Refactored the periodic task responsible for cleaning up results.

    * The backend cleanup task is now only added to the schedule if
        :setting:`CELERY_TASK_RESULT_EXPIRES` is set.

    * If the schedule already contains a periodic task named
      "celery.backend_cleanup" it won't change it, so the behavior of the
      backend cleanup task can be easily changed.

    * The task is now run every day at 4:00 AM, rather than every day since
      the first time it was run (using crontab schedule instead of
      `run_every`)

    * Renamed `celery.task.builtins.DeleteExpiredTaskMetaTask`
        -> :class:`celery.task.builtins.backend_cleanup`

    * The task itself has been renamed from "celery.delete_expired_task_meta"
      to "celery.backend_cleanup"

    See issue #134.

* Implemented `AsyncResult.forget` for sqla/cache/redis/tyrant backends.
  (Forget and remove task result).

    See issue #184.

* :meth:`TaskSetResult.join <celery.result.TaskSetResult.join>`:
  Added 'propagate=True' argument.

  When set to :const:`False` exceptions occurring in subtasks will
  not be re-raised.

* Added `Task.update_state(task_id, state, meta)`
  as a shortcut to `task.backend.store_result(task_id, meta, state)`.

    The backend interface is "private" and the terminology outdated,
    so better to move this to :class:`~celery.task.base.Task` so it can be
    used.

* timer2: Set `self.running=False` in
  :meth:`~celery.utils.timer2.Timer.stop` so it won't try to join again on
  subsequent calls to `stop()`.

* Log colors are now disabled by default on Windows.

* `celery.platform` renamed to :mod:`celery.platforms`, so it doesn't
  collide with the built-in :mod:`platform` module.

* Exceptions occurring in Mediator+Pool callbacks are now caught and logged
  instead of taking down the worker.

* Redis result backend: Now supports result expiration using the Redis
  `EXPIRE` command.

* unit tests: Don't leave threads running at tear down.

* celeryd: Task results shown in logs are now truncated to 46 chars.

* `Task.__name__` is now an alias to `self.__class__.__name__`.
   This way tasks introspects more like regular functions.

* `Task.retry`: Now raises :exc:`TypeError` if kwargs argument is empty.

    See issue #164.

* timedelta_seconds: Use `timedelta.total_seconds` if running on Python 2.7

* :class:`~celery.datastructures.TokenBucket`: Generic Token Bucket algorithm

* :mod:`celery.events.state`: Recording of cluster state can now
  be paused and resumed, including support for buffering.


    .. method:: State.freeze(buffer=True)

        Pauses recording of the stream.

        If `buffer` is true, events received while being frozen will be
        buffered, and may be replayed later.

    .. method:: State.thaw(replay=True)

        Resumes recording of the stream.

        If `replay` is true, then the recorded buffer will be applied.

    .. method:: State.freeze_while(fun)

        With a function to apply, freezes the stream before,
        and replays the buffer after the function returns.

* :meth:`EventReceiver.capture <celery.events.EventReceiver.capture>`
  Now supports a timeout keyword argument.

* celeryd: The mediator thread is now disabled if
  :setting:`CELERY_RATE_LIMITS` is enabled, and tasks are directly sent to the
  pool without going through the ready queue (*Optimization*).

.. _v210-fixes:

Fixes
-----

* Pool: Process timed out by `TimeoutHandler` must be joined by the Supervisor,
  so don't remove it from the internal process list.

    See issue #192.

* `TaskPublisher.delay_task` now supports exchange argument, so exchange can be
  overridden when sending tasks in bulk using the same publisher

    See issue #187.

* celeryd no longer marks tasks as revoked if :setting:`CELERY_IGNORE_RESULT`
  is enabled.

    See issue #207.

* AMQP Result backend: Fixed bug with `result.get()` if
  :setting:`CELERY_TRACK_STARTED` enabled.

    `result.get()` would stop consuming after receiving the
    :state:`STARTED` state.

* Fixed bug where new processes created by the pool supervisor becomes stuck
  while reading from the task Queue.

    See http://bugs.python.org/issue10037

* Fixed timing issue when declaring the remote control command reply queue

    This issue could result in replies being lost, but have now been fixed.

* Backward compatible `LoggerAdapter` implementation: Now works for Python 2.4.

    Also added support for several new methods:
    `fatal`, `makeRecord`, `_log`, `log`, `isEnabledFor`,
    `addHandler`, `removeHandler`.

.. _v210-experimental:

Experimental
------------

* celeryd-multi: Added daemonization support.

    celeryd-multi can now be used to start, stop and restart worker nodes.

        $ celeryd-multi start jerry elaine george kramer

    This also creates PID files and log files (:file:`celeryd@jerry.pid`,
    ..., :file:`celeryd@jerry.log`. To specify a location for these files
    use the `--pidfile` and `--logfile` arguments with the `%n`
    format::

        $ celeryd-multi start jerry elaine george kramer \
                        --logfile=/var/log/celeryd@%n.log \
                        --pidfile=/var/run/celeryd@%n.pid

    Stopping::

        $ celeryd-multi stop jerry elaine george kramer

    Restarting. The nodes will be restarted one by one as the old ones
    are shutdown::

        $ celeryd-multi restart jerry elaine george kramer

    Killing the nodes (**WARNING**: Will discard currently executing tasks)::

        $ celeryd-multi kill jerry elaine george kramer

    See `celeryd-multi help` for help.

* celeryd-multi: `start` command renamed to `show`.

    `celeryd-multi start` will now actually start and detach worker nodes.
    To just generate the commands you have to use `celeryd-multi show`.

* celeryd: Added `--pidfile` argument.

   The worker will write its pid when it starts.  The worker will
   not be started if this file exists and the pid contained is still alive.

* Added generic init.d script using `celeryd-multi`

    http://github.com/ask/celery/tree/master/contrib/generic-init.d/celeryd

.. _v210-documentation:

Documentation
-------------

* Added User guide section: Monitoring

* Added user guide section: Periodic Tasks

    Moved from `getting-started/periodic-tasks` and updated.

* tutorials/external moved to new section: "community".

* References has been added to all sections in the documentation.

    This makes it easier to link between documents.

.. _version-2.0.3:

2.0.3
=====
:release-date: 2010-08-27 12:00 P.M CEST

.. _v203-fixes:

Fixes
-----

* celeryd: Properly handle connection errors happening while
  closing consumers.

* celeryd: Events are now buffered if the connection is down,
  then sent when the connection is re-established.

* No longer depends on the :mod:`mailer` package.

    This package had a name space collision with `django-mailer`,
    so its functionality was replaced.

* Redis result backend: Documentation typos: Redis doesn't have
  database names, but database numbers. The default database is now 0.

* :class:`~celery.task.control.inspect`:
  `registered_tasks` was requesting an invalid command because of a typo.

    See issue #170.

* :setting:`CELERY_ROUTES`: Values defined in the route should now have
  precedence over values defined in :setting:`CELERY_QUEUES` when merging
  the two.

    With the follow settings::

        CELERY_QUEUES = {"cpubound": {"exchange": "cpubound",
                                      "routing_key": "cpubound"}}

        CELERY_ROUTES = {"tasks.add": {"queue": "cpubound",
                                       "routing_key": "tasks.add",
                                       "serializer": "json"}}

    The final routing options for `tasks.add` will become::

        {"exchange": "cpubound",
         "routing_key": "tasks.add",
         "serializer": "json"}

    This was not the case before: the values
    in :setting:`CELERY_QUEUES` would take precedence.

* Worker crashed if the value of :setting:`CELERY_TASK_ERROR_WHITELIST` was
  not an iterable

* :func:`~celery.execute.apply`: Make sure `kwargs["task_id"]` is
  always set.

* `AsyncResult.traceback`: Now returns :const:`None`, instead of raising
  :exc:`KeyError` if traceback is missing.

* :class:`~celery.task.control.inspect`: Replies did not work correctly
  if no destination was specified.

* Can now store result/metadata for custom states.

* celeryd: A warning is now emitted if the sending of task error
  e-mails fails.

* celeryev: Curses monitor no longer crashes if the terminal window
  is resized.

    See issue #160.

* celeryd: On OS X it is not possible to run `os.exec*` in a process
  that is threaded.

      This breaks the SIGHUP restart handler,
      and is now disabled on OS X, emitting a warning instead.

    See issue #152.

* :mod:`celery.execute.trace`: Properly handle `raise(str)`,
  which is still allowed in Python 2.4.

    See issue #175.

* Using urllib2 in a periodic task on OS X crashed because
  of the proxy auto detection used in OS X.

    This is now fixed by using a workaround.
    See issue #143.

* Debian init scripts: Commands should not run in a sub shell

    See issue #163.

* Debian init scripts: Use the absolute path of celeryd to allow stat

    See issue #162.

.. _v203-documentation:

Documentation
-------------

* getting-started/broker-installation: Fixed typo

    `set_permissions ""` -> `set_permissions ".*"`.

* Tasks User Guide: Added section on database transactions.

    See issue #169.

* Routing User Guide: Fixed typo `"feed": -> {"queue": "feeds"}`.

    See issue #169.

* Documented the default values for the :setting:`CELERYD_CONCURRENCY`
  and :setting:`CELERYD_PREFETCH_MULTIPLIER` settings.

* Tasks User Guide: Fixed typos in the subtask example

* celery.signals: Documented worker_process_init.

* Daemonization cookbook: Need to export DJANGO_SETTINGS_MODULE in
  `/etc/default/celeryd`.

* Added some more FAQs from stack overflow

* Daemonization cookbook: Fixed typo `CELERYD_LOGFILE/CELERYD_PIDFILE`

    to `CELERYD_LOG_FILE` / `CELERYD_PID_FILE`

    Also added troubleshooting section for the init scripts.

.. _version-2.0.2:

2.0.2
=====
:release-date: 2010-07-22 11:31 A.M CEST

* Routes: When using the dict route syntax, the exchange for a task
  could disappear making the task unroutable.

    See issue #158.

* Test suite now passing on Python 2.4

* No longer have to type `PYTHONPATH=.` to use celeryconfig in the current
  directory.

    This is accomplished by the default loader ensuring that the current
    directory is in `sys.path` when loading the config module.
    `sys.path` is reset to its original state after loading.

    Adding the current working directory to `sys.path` without the user
    knowing may be a security issue, as this means someone can drop a Python module in the users
    directory that executes arbitrary commands. This was the original reason
    not to do this, but if done *only when loading the config module*, this
    means that the behavior will only apply to the modules imported in the
    config module, which I think is a good compromise (certainly better than
    just explicitly setting `PYTHONPATH=.` anyway)

* Experimental Cassandra backend added.

* celeryd: SIGHUP handler accidentally propagated to worker pool processes.

    In combination with 7a7c44e39344789f11b5346e9cc8340f5fe4846c
    this would make each child process start a new celeryd when
    the terminal window was closed :/

* celeryd: Do not install SIGHUP handler if running from a terminal.

    This fixes the problem where celeryd is launched in the background
    when closing the terminal.

* celeryd: Now joins threads at shutdown.

    See issue #152.

* Test tear down: Don't use `atexit` but nose's `teardown()` functionality
  instead.

    See issue #154.

* Debian init script for celeryd: Stop now works correctly.

* Task logger: `warn` method added (synonym for `warning`)

* Can now define a white list of errors to send error e-mails for.

    Example::

        CELERY_TASK_ERROR_WHITELIST = ('myapp.MalformedInputError')

    See issue #153.

* celeryd: Now handles overflow exceptions in `time.mktime` while parsing
  the ETA field.

* LoggerWrapper: Try to detect loggers logging back to stderr/stdout making
  an infinite loop.

* Added :class:`celery.task.control.inspect`: Inspects a running worker.

    Examples::

        # Inspect a single worker
        >>> i = inspect("myworker.example.com")

        # Inspect several workers
        >>> i = inspect(["myworker.example.com", "myworker2.example.com"])

        # Inspect all workers consuming on this vhost.
        >>> i = inspect()

        ### Methods

        # Get currently executing tasks
        >>> i.active()

        # Get currently reserved tasks
        >>> i.reserved()

        # Get the current eta schedule
        >>> i.scheduled()

        # Worker statistics and info
        >>> i.stats()

        # List of currently revoked tasks
        >>> i.revoked()

        # List of registered tasks
        >>> i.registered_tasks()

*  Remote control commands `dump_active`/`dump_reserved`/`dump_schedule`
   now replies with detailed task requests.

    Containing the original arguments and fields of the task requested.

    In addition the remote control command `set_loglevel` has been added,
    this only changes the log level for the main process.

* Worker control command execution now catches errors and returns their
  string representation in the reply.

* Functional test suite added

    :mod:`celery.tests.functional.case` contains utilities to start
    and stop an embedded celeryd process, for use in functional testing.

.. _version-2.0.1:

2.0.1
=====
:release-date: 2010-07-09 03:02 P.M CEST

* multiprocessing.pool: Now handles encoding errors, so that pickling errors
  doesn't crash the worker processes.

* The remote control command replies was not working with RabbitMQ 1.8.0's
  stricter equivalence checks.

    If you've already hit this problem you may have to delete the
    declaration::

        $ camqadm exchange.delete celerycrq

    or::

        $ python manage.py camqadm exchange.delete celerycrq

* A bug sneaked in the ETA scheduler that made it only able to execute
  one task per second(!)

    The scheduler sleeps between iterations so it doesn't consume too much CPU.
    It keeps a list of the scheduled items sorted by time, at each iteration
    it sleeps for the remaining time of the item with the nearest deadline.
    If there are no eta tasks it will sleep for a minimum amount of time, one
    second by default.

    A bug sneaked in here, making it sleep for one second for every task
    that was scheduled. This has been fixed, so now it should move
    tasks like hot knife through butter.

    In addition a new setting has been added to control the minimum sleep
    interval; :setting:`CELERYD_ETA_SCHEDULER_PRECISION`. A good
    value for this would be a float between 0 and 1, depending
    on the needed precision. A value of 0.8 means that when the ETA of a task
    is met, it will take at most 0.8 seconds for the task to be moved to the
    ready queue.

* Pool: Supervisor did not release the semaphore.

    This would lead to a deadlock if all workers terminated prematurely.

* Added Python version trove classifiers: 2.4, 2.5, 2.6 and 2.7

* Tests now passing on Python 2.7.

* Task.__reduce__: Tasks created using the task decorator can now be pickled.

* setup.py: nose added to `tests_require`.

* Pickle should now work with SQLAlchemy 0.5.x

* New homepage design by Jan Henrik Helmers: http://celeryproject.org

* New Sphinx theme by Armin Ronacher: http://celeryproject.org/docs

* Fixed "pending_xref" errors shown in the HTML rendering of the
  documentation. Apparently this was caused by new changes in Sphinx 1.0b2.

* Router classes in :setting:`CELERY_ROUTES` are now imported lazily.

    Importing a router class in a module that also loads the Celery
    environment would cause a circular dependency. This is solved
    by importing it when needed after the environment is set up.

* :setting:`CELERY_ROUTES` was broken if set to a single dict.

    This example in the docs should now work again::

        CELERY_ROUTES = {"feed.tasks.import_feed": "feeds"}

* `CREATE_MISSING_QUEUES` was not honored by apply_async.

* New remote control command: `stats`

    Dumps information about the worker, like pool process ids, and
    total number of tasks executed by type.

    Example reply::

        [{'worker.local':
             'total': {'tasks.sleeptask': 6},
             'pool': {'timeouts': [None, None],
                      'processes': [60376, 60377],
                      'max-concurrency': 2,
                      'max-tasks-per-child': None,
                      'put-guarded-by-semaphore': True}}]

* New remote control command: `dump_active`

    Gives a list of tasks currently being executed by the worker.
    By default arguments are passed through repr in case there
    are arguments that is not JSON encodable. If you know
    the arguments are JSON safe, you can pass the argument `safe=True`.

    Example reply::

        >>> broadcast("dump_active", arguments={"safe": False}, reply=True)
        [{'worker.local': [
            {'args': '(1,)',
             'time_start': 1278580542.6300001,
             'name': 'tasks.sleeptask',
             'delivery_info': {
                 'consumer_tag': '30',
                 'routing_key': 'celery',
                 'exchange': 'celery'},
             'hostname': 'casper.local',
             'acknowledged': True,
             'kwargs': '{}',
             'id': '802e93e9-e470-47ed-b913-06de8510aca2',
            }
        ]}]

* Added experimental support for persistent revokes.

    Use the `-S|--statedb` argument to celeryd to enable it::

        $ celeryd --statedb=/var/run/celeryd

    This will use the file: `/var/run/celeryd.db`,
    as the `shelve` module automatically adds the `.db` suffix.

.. _version-2.0.0:

2.0.0
=====
:release-date: 2010-07-02 02:30 P.M CEST

Foreword
--------

Celery 2.0 contains backward incompatible changes, the most important
being that the Django dependency has been removed so Celery no longer
supports Django out of the box, but instead as an add-on package
called `django-celery`_.

We're very sorry for breaking backwards compatibility, but there's
also many new and exciting features to make up for the time you lose
upgrading, so be sure to read the :ref:`News <v200-news>` section.

Quite a lot of potential users have been upset about the Django dependency,
so maybe this is a chance to get wider adoption by the Python community as
well.

Big thanks to all contributors, testers and users!

.. _v200-django-upgrade:

Upgrading for Django-users
--------------------------

Django integration has been moved to a separate package: `django-celery`_.

* To upgrade you need to install the `django-celery`_ module and change::

    INSTALLED_APPS = "celery"

  to::

    INSTALLED_APPS = "djcelery"

* If you use `mod_wsgi` you need to add the following line to your `.wsgi`
  file::

    import os
    os.environ["CELERY_LOADER"] = "django"

* The following modules has been moved to `django-celery`_:

    =====================================  =====================================
    **Module name**                        **Replace with**
    =====================================  =====================================
    `celery.models`                        `djcelery.models`
    `celery.managers`                      `djcelery.managers`
    `celery.views`                         `djcelery.views`
    `celery.urls`                          `djcelery.urls`
    `celery.management`                    `djcelery.management`
    `celery.loaders.djangoapp`             `djcelery.loaders`
    `celery.backends.database`             `djcelery.backends.database`
    `celery.backends.cache`                `djcelery.backends.cache`
    =====================================  =====================================

Importing :mod:`djcelery` will automatically setup Celery to use Django loader.
loader.  It does this by setting the :envvar:`CELERY_LOADER` environment variable to
`"django"` (it won't change it if a loader is already set.)

When the Django loader is used, the "database" and "cache" result backend
aliases will point to the :mod:`djcelery` backends instead of the built-in backends,
and configuration will be read from the Django settings.

.. _`django-celery`: http://pypi.python.org/pypi/django-celery

.. _v200-upgrade:

Upgrading for others
--------------------

.. _v200-upgrade-database:

Database result backend
~~~~~~~~~~~~~~~~~~~~~~~

The database result backend is now using `SQLAlchemy`_ instead of the
Django ORM, see `Supported Databases`_ for a table of supported databases.

The `DATABASE_*` settings has been replaced by a single setting:
:setting:`CELERY_RESULT_DBURI`. The value here should be an
`SQLAlchemy Connection String`_, some examples include:

.. code-block:: python

    # sqlite (filename)
    CELERY_RESULT_DBURI = "sqlite:///celerydb.sqlite"

    # mysql
    CELERY_RESULT_DBURI = "mysql://scott:tiger@localhost/foo"

    # postgresql
    CELERY_RESULT_DBURI = "postgresql://scott:tiger@localhost/mydatabase"

    # oracle
    CELERY_RESULT_DBURI = "oracle://scott:tiger@127.0.0.1:1521/sidname"

See `SQLAlchemy Connection Strings`_ for more information about connection
strings.

To specify additional SQLAlchemy database engine options you can use
the :setting:`CELERY_RESULT_ENGINE_OPTIONS` setting::

    # echo enables verbose logging from SQLAlchemy.
    CELERY_RESULT_ENGINE_OPTIONS = {"echo": True}

.. _`SQLAlchemy`:
    http://www.sqlalchemy.org
.. _`Supported Databases`:
    http://www.sqlalchemy.org/docs/dbengine.html#supported-databases
.. _`SQLAlchemy Connection String`:
    http://www.sqlalchemy.org/docs/dbengine.html#create-engine-url-arguments
.. _`SQLAlchemy Connection Strings`:
    http://www.sqlalchemy.org/docs/dbengine.html#create-engine-url-arguments

.. _v200-upgrade-cache:

Cache result backend
~~~~~~~~~~~~~~~~~~~~

The cache result backend is no longer using the Django cache framework,
but it supports mostly the same configuration syntax::

    CELERY_CACHE_BACKEND = "memcached://A.example.com:11211;B.example.com"

To use the cache backend you must either have the `pylibmc`_ or
`python-memcached`_ library installed, of which the former is regarded
as the best choice.

.. _`pylibmc`: http://pypi.python.org/pypi/pylibmc
.. _`python-memcached`: http://pypi.python.org/pypi/python-memcached

The support backend types are `memcached://` and `memory://`,
we haven't felt the need to support any of the other backends
provided by Django.

.. _v200-incompatible:

Backward incompatible changes
-----------------------------

* Default (python) loader now prints warning on missing `celeryconfig.py`
  instead of raising :exc:`ImportError`.

    celeryd raises :exc:`~celery.exceptions.ImproperlyConfigured` if the configuration
    is not set up. This makes it possible to use `--help` etc., without having a
    working configuration.

    Also this makes it possible to use the client side of celery without being
    configured::

        >>> from carrot.connection import BrokerConnection
        >>> conn = BrokerConnection("localhost", "guest", "guest", "/")
        >>> from celery.execute import send_task
        >>> r = send_task("celery.ping", args=(), kwargs={}, connection=conn)
        >>> from celery.backends.amqp import AMQPBackend
        >>> r.backend = AMQPBackend(connection=conn)
        >>> r.get()
        'pong'

* The following deprecated settings has been removed (as scheduled by
  the `deprecation timeline`_):

    =====================================  =====================================
    **Setting name**                       **Replace with**
    =====================================  =====================================
    `CELERY_AMQP_CONSUMER_QUEUES`          `CELERY_QUEUES`
    `CELERY_AMQP_EXCHANGE`                 `CELERY_DEFAULT_EXCHANGE`
    `CELERY_AMQP_EXCHANGE_TYPE`            `CELERY_DEFAULT_EXCHANGE_TYPE`
    `CELERY_AMQP_CONSUMER_ROUTING_KEY`     `CELERY_QUEUES`
    `CELERY_AMQP_PUBLISHER_ROUTING_KEY`    `CELERY_DEFAULT_ROUTING_KEY`
    =====================================  =====================================

.. _`deprecation timeline`:
    http://ask.github.com/celery/internals/deprecation.html

* The `celery.task.rest` module has been removed, use :mod:`celery.task.http`
  instead (as scheduled by the `deprecation timeline`_).

* It's no longer allowed to skip the class name in loader names.
  (as scheduled by the `deprecation timeline`_):

    Assuming the implicit `Loader` class name is no longer supported,
    if you use e.g.::

        CELERY_LOADER = "myapp.loaders"

    You need to include the loader class name, like this::

        CELERY_LOADER = "myapp.loaders.Loader"

* :setting:`CELERY_TASK_RESULT_EXPIRES` now defaults to 1 day.

    Previous default setting was to expire in 5 days.

*  AMQP backend: Don't use different values for `auto_delete`.

    This bug became visible with RabbitMQ 1.8.0, which no longer
    allows conflicting declarations for the auto_delete and durable settings.

    If you've already used celery with this backend chances are you
    have to delete the previous declaration::

        $ camqadm exchange.delete celeryresults

* Now uses pickle instead of cPickle on Python versions <= 2.5

    cPickle is broken in Python <= 2.5.

    It unsafely and incorrectly uses relative instead of absolute imports,
    so e.g.::

          exceptions.KeyError

    becomes::

          celery.exceptions.KeyError

    Your best choice is to upgrade to Python 2.6,
    as while the pure pickle version has worse performance,
    it is the only safe option for older Python versions.

.. _v200-news:

News
----

* **celeryev**: Curses Celery Monitor and Event Viewer.

    This is a simple monitor allowing you to see what tasks are
    executing in real-time and investigate tracebacks and results of ready
    tasks. It also enables you to set new rate limits and revoke tasks.

    Screenshot:

    .. figure:: images/celeryevshotsm.jpg

    If you run `celeryev` with the `-d` switch it will act as an event
    dumper, simply dumping the events it receives to standard out::

        $ celeryev -d
        -> celeryev: starting capture...
        casper.local [2010-06-04 10:42:07.020000] heartbeat
        casper.local [2010-06-04 10:42:14.750000] task received:
            tasks.add(61a68756-27f4-4879-b816-3cf815672b0e) args=[2, 2] kwargs={}
            eta=2010-06-04T10:42:16.669290, retries=0
        casper.local [2010-06-04 10:42:17.230000] task started
            tasks.add(61a68756-27f4-4879-b816-3cf815672b0e) args=[2, 2] kwargs={}
        casper.local [2010-06-04 10:42:17.960000] task succeeded:
            tasks.add(61a68756-27f4-4879-b816-3cf815672b0e)
            args=[2, 2] kwargs={} result=4, runtime=0.782663106918

        The fields here are, in order: *sender hostname*, *timestamp*, *event type* and
        *additional event fields*.

* AMQP result backend: Now supports `.ready()`, `.successful()`,
  `.result`, `.status`, and even responds to changes in task state

* New user guides:

    * :doc:`userguide/workers`
    * :doc:`userguide/tasksets`
    * :doc:`userguide/routing`

* celeryd: Standard out/error is now being redirected to the log file.

* :mod:`billiard` has been moved back to the celery repository.

    =====================================  =====================================
    **Module name**                        **celery equivalent**
    =====================================  =====================================
    `billiard.pool`                        `celery.concurrency.processes.pool`
    `billiard.serialization`               `celery.serialization`
    `billiard.utils.functional`            `celery.utils.functional`
    =====================================  =====================================

    The :mod:`billiard` distribution may be maintained, depending on interest.

* now depends on :mod:`carrot` >= 0.10.5

* now depends on :mod:`pyparsing`

* celeryd: Added `--purge` as an alias to `--discard`.

* celeryd: Ctrl+C (SIGINT) once does warm shutdown, hitting Ctrl+C twice
  forces termination.

* Added support for using complex crontab-expressions in periodic tasks. For
  example, you can now use::

    >>> crontab(minute="*/15")

  or even::

    >>> crontab(minute="*/30", hour="8-17,1-2", day_of_week="thu-fri")

  See :doc:`userguide/periodic-tasks`.

* celeryd: Now waits for available pool processes before applying new
  tasks to the pool.

    This means it doesn't have to wait for dozens of tasks to finish at shutdown
    because it has applied prefetched tasks without having any pool
    processes available to immediately accept them.

    See issue #122.

* New built-in way to do task callbacks using
  :class:`~celery.task.sets.subtask`.

  See :doc:`userguide/tasksets` for more information.

* TaskSets can now contain several types of tasks.

  :class:`~celery.task.sets.TaskSet` has been refactored to use
  a new syntax, please see :doc:`userguide/tasksets` for more information.

  The previous syntax is still supported, but will be deprecated in
  version 1.4.

* TaskSet failed() result was incorrect.

    See issue #132.

* Now creates different loggers per task class.

    See issue #129.

* Missing queue definitions are now created automatically.

    You can disable this using the :setting:`CELERY_CREATE_MISSING_QUEUES`
    setting.

    The missing queues are created with the following options::

        CELERY_QUEUES[name] = {"exchange": name,
                               "exchange_type": "direct",
                               "routing_key": "name}

   This feature is added for easily setting up routing using the `-Q`
   option to `celeryd`::

       $ celeryd -Q video, image

   See the new routing section of the User Guide for more information:
   :doc:`userguide/routing`.

* New Task option: `Task.queue`

    If set, message options will be taken from the corresponding entry
    in :setting:`CELERY_QUEUES`. `exchange`, `exchange_type` and `routing_key`
    will be ignored

* Added support for task soft and hard time limits.

    New settings added:

    * :setting:`CELERYD_TASK_TIME_LIMIT`

        Hard time limit. The worker processing the task will be killed and
        replaced with a new one when this is exceeded.

    * :setting:`CELERYD_SOFT_TASK_TIME_LIMIT`

        Soft time limit. The :exc:`celery.exceptions.SoftTimeLimitExceeded`
        exception will be raised when this is exceeded.  The task can catch
        this to e.g. clean up before the hard time limit comes.

    New command line arguments to celeryd added:
    `--time-limit` and `--soft-time-limit`.

    What's left?

    This won't work on platforms not supporting signals (and specifically
    the `SIGUSR1` signal) yet. So an alternative the ability to disable
    the feature all together on nonconforming platforms must be implemented.

    Also when the hard time limit is exceeded, the task result should
    be a `TimeLimitExceeded` exception.

* Test suite is now passing without a running broker, using the carrot
  in-memory backend.

* Log output is now available in colors.

    =====================================  =====================================
    **Log level**                          **Color**
    =====================================  =====================================
    `DEBUG`                                Blue
    `WARNING`                              Yellow
    `CRITICAL`                             Magenta
    `ERROR`                                Red
    =====================================  =====================================

    This is only enabled when the log output is a tty.
    You can explicitly enable/disable this feature using the
    :setting:`CELERYD_LOG_COLOR` setting.

* Added support for task router classes (like the django multi-db routers)

    * New setting: :setting:`CELERY_ROUTES`

    This is a single, or a list of routers to traverse when
    sending tasks. Dictionaries in this list converts to a
    :class:`celery.routes.MapRoute` instance.

    Examples:

        >>> CELERY_ROUTES = {"celery.ping": "default",
                             "mytasks.add": "cpu-bound",
                             "video.encode": {
                                 "queue": "video",
                                 "exchange": "media"
                                 "routing_key": "media.video.encode"}}

        >>> CELERY_ROUTES = ("myapp.tasks.Router",
                             {"celery.ping": "default})

    Where `myapp.tasks.Router` could be:

    .. code-block:: python

        class Router(object):

            def route_for_task(self, task, args=None, kwargs=None):
                if task == "celery.ping":
                    return "default"

    route_for_task may return a string or a dict. A string then means
    it's a queue name in :setting:`CELERY_QUEUES`, a dict means it's a custom route.

    When sending tasks, the routers are consulted in order. The first
    router that doesn't return `None` is the route to use. The message options
    is then merged with the found route settings, where the routers settings
    have priority.

    Example if :func:`~celery.execute.apply_async` has these arguments::

       >>> Task.apply_async(immediate=False, exchange="video",
       ...                  routing_key="video.compress")

    and a router returns::

        {"immediate": True,
         "exchange": "urgent"}

    the final message options will be::

        immediate=True, exchange="urgent", routing_key="video.compress"

    (and any default message options defined in the
    :class:`~celery.task.base.Task` class)

* New Task handler called after the task returns:
  :meth:`~celery.task.base.Task.after_return`.

* :class:`~celery.datastructures.ExceptionInfo` now passed to
   :meth:`~celery.task.base.Task.on_retry`/
   :meth:`~celery.task.base.Task.on_failure` as einfo keyword argument.

* celeryd: Added :setting:`CELERYD_MAX_TASKS_PER_CHILD` /
  :option:`--maxtasksperchild`

    Defines the maximum number of tasks a pool worker can process before
    the process is terminated and replaced by a new one.

* Revoked tasks now marked with state :state:`REVOKED`, and `result.get()`
  will now raise :exc:`~celery.exceptions.TaskRevokedError`.

* :func:`celery.task.control.ping` now works as expected.

* `apply(throw=True)` / :setting:`CELERY_EAGER_PROPAGATES_EXCEPTIONS`:
  Makes eager execution re-raise task errors.

* New signal: :data:`~celery.signals.worker_process_init`: Sent inside the
  pool worker process at init.

* celeryd :option:`-Q` option: Ability to specify list of queues to use,
  disabling other configured queues.

    For example, if :setting:`CELERY_QUEUES` defines four
    queues: `image`, `video`, `data` and `default`, the following
    command would make celeryd only consume from the `image` and `video`
    queues::

        $ celeryd -Q image,video

* celeryd: New return value for the `revoke` control command:

    Now returns::

        {"ok": "task $id revoked"}

    instead of `True`.

* celeryd: Can now enable/disable events using remote control

    Example usage:

        >>> from celery.task.control import broadcast
        >>> broadcast("enable_events")
        >>> broadcast("disable_events")

* Removed top-level tests directory. Test config now in celery.tests.config

    This means running the unit tests doesn't require any special setup.
    `celery/tests/__init__` now configures the :envvar:`CELERY_CONFIG_MODULE`
    and :envvar:`CELERY_LOADER` environment variables, so when `nosetests`
    imports that, the unit test environment is all set up.

    Before you run the tests you need to install the test requirements::

        $ pip install -r contrib/requirements/test.txt

    Running all tests::

        $ nosetests

    Specifying the tests to run::

        $ nosetests celery.tests.test_task

    Producing HTML coverage::

        $ nosetests --with-coverage3

    The coverage output is then located in `celery/tests/cover/index.html`.

* celeryd: New option `--version`: Dump version info and exit.

* :mod:`celeryd-multi <celeryd.bin.celeryd_multi>`: Tool for shell scripts
  to start multiple workers.

 Some examples::

        # Advanced example with 10 workers:
        #   * Three of the workers processes the images and video queue
        #   * Two of the workers processes the data queue with loglevel DEBUG
        #   * the rest processes the default' queue.
        $ celeryd-multi start 10 -l INFO -Q:1-3 images,video -Q:4,5:data
            -Q default -L:4,5 DEBUG

        # get commands to start 10 workers, with 3 processes each
        $ celeryd-multi start 3 -c 3
        celeryd -n celeryd1.myhost -c 3
        celeryd -n celeryd2.myhost -c 3
        celeryd- n celeryd3.myhost -c 3

        # start 3 named workers
        $ celeryd-multi start image video data -c 3
        celeryd -n image.myhost -c 3
        celeryd -n video.myhost -c 3
        celeryd -n data.myhost -c 3

        # specify custom hostname
        $ celeryd-multi start 2 -n worker.example.com -c 3
        celeryd -n celeryd1.worker.example.com -c 3
        celeryd -n celeryd2.worker.example.com -c 3

        # Additionl options are added to each celeryd',
        # but you can also modify the options for ranges of or single workers

        # 3 workers: Two with 3 processes, and one with 10 processes.
        $ celeryd-multi start 3 -c 3 -c:1 10
        celeryd -n celeryd1.myhost -c 10
        celeryd -n celeryd2.myhost -c 3
        celeryd -n celeryd3.myhost -c 3

        # can also specify options for named workers
        $ celeryd-multi start image video data -c 3 -c:image 10
        celeryd -n image.myhost -c 10
        celeryd -n video.myhost -c 3
        celeryd -n data.myhost -c 3

        # ranges and lists of workers in options is also allowed:
        # (-c:1-3 can also be written as -c:1,2,3)
        $ celeryd-multi start 5 -c 3  -c:1-3 10
        celeryd-multi -n celeryd1.myhost -c 10
        celeryd-multi -n celeryd2.myhost -c 10
        celeryd-multi -n celeryd3.myhost -c 10
        celeryd-multi -n celeryd4.myhost -c 3
        celeryd-multi -n celeryd5.myhost -c 3

        # lists also works with named workers
        $ celeryd-multi start foo bar baz xuzzy -c 3 -c:foo,bar,baz 10
        celeryd-multi -n foo.myhost -c 10
        celeryd-multi -n bar.myhost -c 10
        celeryd-multi -n baz.myhost -c 10
        celeryd-multi -n xuzzy.myhost -c 3

* The worker now calls the result backends `process_cleanup` method
  *after* task execution instead of before.

* AMQP result backend now supports Pika.

.. _version-1.0.6:

1.0.6
=====
:release-date: 2010-06-30 09:57 A.M CEST

* RabbitMQ 1.8.0 has extended their exchange equivalence tests to
  include `auto_delete` and `durable`. This broke the AMQP backend.

  If you've already used the AMQP backend this means you have to
  delete the previous definitions::

      $ camqadm exchange.delete celeryresults

  or::

      $ python manage.py camqadm exchange.delete celeryresults

.. _version-1.0.5:

1.0.5
=====
:release-date: 2010-06-01 02:36 P.M CEST

.. _v105-critical:

Critical
--------

* SIGINT/Ctrl+C killed the pool, abruptly terminating the currently executing
  tasks.

    Fixed by making the pool worker processes ignore :const:`SIGINT`.

* Should not close the consumers before the pool is terminated, just cancel
  the consumers.

    See issue #122.

* Now depends on :mod:`billiard` >= 0.3.1

* celeryd: Previously exceptions raised by worker components could stall startup,
  now it correctly logs the exceptions and shuts down.

* celeryd: Prefetch counts was set too late. QoS is now set as early as possible,
  so celeryd can't slurp in all the messages at start-up.

.. _v105-changes:

Changes
-------

* :mod:`celery.contrib.abortable`: Abortable tasks.

    Tasks that defines steps of execution, the task can then
    be aborted after each step has completed.

* :class:`~celery.events.EventDispatcher`: No longer creates AMQP channel
  if events are disabled

* Added required RPM package names under `[bdist_rpm]` section, to support building RPMs
  from the sources using setup.py

* Running unit tests: :envvar:`NOSE_VERBOSE` environment var now enables verbose output from Nose.

* :func:`celery.execute.apply`: Pass log file/log level arguments as task kwargs.

    See issue #110.

* celery.execute.apply: Should return exception, not :class:`~celery.datastructures.ExceptionInfo`
  on error.

    See issue #111.

* Added new entries to the :doc:`FAQs <faq>`:

    * Should I use retry or acks_late?
    * Can I execute a task by name?

.. _version-1.0.4:

1.0.4
=====
:release-date: 2010-05-31 09:54 A.M CEST

* Changelog merged with 1.0.5 as the release was never announced.

.. _version-1.0.3:

1.0.3
=====
:release-date: 2010-05-15 03:00 P.M CEST

.. _v103-important:

Important notes
---------------

* Messages are now acknowledged *just before* the task function is executed.

    This is the behavior we've wanted all along, but couldn't have because of
    limitations in the multiprocessing module.
    The previous behavior was not good, and the situation worsened with the
    release of 1.0.1, so this change will definitely improve
    reliability, performance and operations in general.

    For more information please see http://bit.ly/9hom6T

* Database result backend: result now explicitly sets `null=True` as
  `django-picklefield` version 0.1.5 changed the default behavior
  right under our noses :(

    See: http://bit.ly/d5OwMr

    This means those who created their celery tables (via syncdb or
    celeryinit) with picklefield versions >= 0.1.5 has to alter their tables to
    allow the result field to be `NULL` manually.

    MySQL::

        ALTER TABLE celery_taskmeta MODIFY result TEXT NULL

    PostgreSQL::

        ALTER TABLE celery_taskmeta ALTER COLUMN result DROP NOT NULL

* Removed `Task.rate_limit_queue_type`, as it was not really useful
  and made it harder to refactor some parts.

* Now depends on carrot >= 0.10.4

* Now depends on billiard >= 0.3.0

.. _v103-news:

News
----

* AMQP backend: Added timeout support for `result.get()` /
  `result.wait()`.

* New task option: `Task.acks_late` (default: :setting:`CELERY_ACKS_LATE`)

    Late ack means the task messages will be acknowledged **after** the task
    has been executed, not *just before*, which is the default behavior.

    .. note::

        This means the tasks may be executed twice if the worker
        crashes in mid-execution. Not acceptable for most
        applications, but desirable for others.

* Added crontab-like scheduling to periodic tasks.

    Like a cron job, you can specify units of time of when
    you would like the task to execute. While not a full implementation
    of cron's features, it should provide a fair degree of common scheduling
    needs.

    You can specify a minute (0-59), an hour (0-23), and/or a day of the
    week (0-6 where 0 is Sunday, or by names: sun, mon, tue, wed, thu, fri,
    sat).

    Examples:

    .. code-block:: python

        from celery.schedules import crontab
        from celery.decorators import periodic_task

        @periodic_task(run_every=crontab(hour=7, minute=30))
        def every_morning():
            print("Runs every morning at 7:30a.m")

        @periodic_task(run_every=crontab(hour=7, minute=30, day_of_week="mon"))
        def every_monday_morning():
            print("Run every monday morning at 7:30a.m")

        @periodic_task(run_every=crontab(minutes=30))
        def every_hour():
            print("Runs every hour on the clock. e.g. 1:30, 2:30, 3:30 etc.")

    .. note::
        This a late addition. While we have unittests, due to the
        nature of this feature we haven't been able to completely test this
        in practice, so consider this experimental.

* `TaskPool.apply_async`: Now supports the `accept_callback` argument.

* `apply_async`: Now raises :exc:`ValueError` if task args is not a list,
  or kwargs is not a tuple (Issue #95).

* `Task.max_retries` can now be `None`, which means it will retry forever.

* Celerybeat: Now reuses the same connection when publishing large
  sets of tasks.

* Modified the task locking example in the documentation to use
  `cache.add` for atomic locking.

* Added experimental support for a *started* status on tasks.

    If `Task.track_started` is enabled the task will report its status
    as "started" when the task is executed by a worker.

    The default value is `False` as the normal behaviour is to not
    report that level of granularity. Tasks are either pending, finished,
    or waiting to be retried. Having a "started" status can be useful for
    when there are long running tasks and there is a need to report which
    task is currently running.

    The global default can be overridden by the :setting:`CELERY_TRACK_STARTED`
    setting.

* User Guide: New section `Tips and Best Practices`.

    Contributions welcome!

.. _v103-remote-control:

Remote control commands
-----------------------

* Remote control commands can now send replies back to the caller.

    Existing commands has been improved to send replies, and the client
    interface in `celery.task.control` has new keyword arguments: `reply`,
    `timeout` and `limit`. Where reply means it will wait for replies,
    timeout is the time in seconds to stop waiting for replies, and limit
    is the maximum number of replies to get.

    By default, it will wait for as many replies as possible for one second.

    * rate_limit(task_name, destination=all, reply=False, timeout=1, limit=0)

        Worker returns `{"ok": message}` on success,
        or `{"failure": message}` on failure.

            >>> from celery.task.control import rate_limit
            >>> rate_limit("tasks.add", "10/s", reply=True)
            [{'worker1': {'ok': 'new rate limit set successfully'}},
             {'worker2': {'ok': 'new rate limit set successfully'}}]

    * ping(destination=all, reply=False, timeout=1, limit=0)

        Worker returns the simple message `"pong"`.

            >>> from celery.task.control import ping
            >>> ping(reply=True)
            [{'worker1': 'pong'},
             {'worker2': 'pong'},

    * revoke(destination=all, reply=False, timeout=1, limit=0)

        Worker simply returns `True`.

            >>> from celery.task.control import revoke
            >>> revoke("419e46eb-cf6a-4271-86a8-442b7124132c", reply=True)
            [{'worker1': True},
             {'worker2'; True}]

* You can now add your own remote control commands!

    Remote control commands are functions registered in the command
    registry. Registering a command is done using
    :meth:`celery.worker.control.Panel.register`:

    .. code-block:: python

        from celery.task.control import Panel

        @Panel.register
        def reset_broker_connection(panel, **kwargs):
            panel.consumer.reset_connection()
            return {"ok": "connection re-established"}

    With this module imported in the worker, you can launch the command
    using `celery.task.control.broadcast`::

        >>> from celery.task.control import broadcast
        >>> broadcast("reset_broker_connection", reply=True)
        [{'worker1': {'ok': 'connection re-established'},
         {'worker2': {'ok': 'connection re-established'}}]

    **TIP** You can choose the worker(s) to receive the command
    by using the `destination` argument::

        >>> broadcast("reset_broker_connection", destination=["worker1"])
        [{'worker1': {'ok': 'connection re-established'}]

* New remote control command: `dump_reserved`

    Dumps tasks reserved by the worker, waiting to be executed::

        >>> from celery.task.control import broadcast
        >>> broadcast("dump_reserved", reply=True)
        [{'myworker1': [<TaskRequest ....>]}]

* New remote control command: `dump_schedule`

    Dumps the workers currently registered ETA schedule.
    These are tasks with an `eta` (or `countdown`) argument
    waiting to be executed by the worker.

        >>> from celery.task.control import broadcast
        >>> broadcast("dump_schedule", reply=True)
        [{'w1': []},
         {'w3': []},
         {'w2': ['0. 2010-05-12 11:06:00 pri0 <TaskRequest
                    {name:"opalfeeds.tasks.refresh_feed_slice",
                     id:"95b45760-4e73-4ce8-8eac-f100aa80273a",
                     args:"(<Feeds freq_max:3600 freq_min:60
                                   start:2184.0 stop:3276.0>,)",
                     kwargs:"{'page': 2}"}>']},
         {'w4': ['0. 2010-05-12 11:00:00 pri0 <TaskRequest
                    {name:"opalfeeds.tasks.refresh_feed_slice",
                     id:"c053480b-58fb-422f-ae68-8d30a464edfe",
                     args:"(<Feeds freq_max:3600 freq_min:60
                                   start:1092.0 stop:2184.0>,)",
                     kwargs:"{\'page\': 1}"}>',
                '1. 2010-05-12 11:12:00 pri0 <TaskRequest
                    {name:"opalfeeds.tasks.refresh_feed_slice",
                     id:"ab8bc59e-6cf8-44b8-88d0-f1af57789758",
                     args:"(<Feeds freq_max:3600 freq_min:60
                                   start:3276.0 stop:4365>,)",
                     kwargs:"{\'page\': 3}"}>']}]

.. _v103-fixes:

Fixes
-----

* Mediator thread no longer blocks for more than 1 second.

    With rate limits enabled and when there was a lot of remaining time,
    the mediator thread could block shutdown (and potentially block other
    jobs from coming in).

* Remote rate limits was not properly applied (Issue #98).

* Now handles exceptions with Unicode messages correctly in
  `TaskRequest.on_failure`.

* Database backend: `TaskMeta.result`: default value should be `None`
  not empty string.

.. _version-1.0.2:

1.0.2
=====
:release-date: 2010-03-31 12:50 P.M CET

* Deprecated: :setting:`CELERY_BACKEND`, please use
  :setting:`CELERY_RESULT_BACKEND` instead.

* We now use a custom logger in tasks. This logger supports task magic
  keyword arguments in formats.

    The default format for tasks (:setting:`CELERYD_TASK_LOG_FORMAT`) now
    includes the id and the name of tasks so the origin of task log messages
    can easily be traced.

    Example output::
        [2010-03-25 13:11:20,317: INFO/PoolWorker-1]
            [tasks.add(a6e1c5ad-60d9-42a0-8b24-9e39363125a4)] Hello from add

    To revert to the previous behavior you can set::

        CELERYD_TASK_LOG_FORMAT = """
            [%(asctime)s: %(levelname)s/%(processName)s] %(message)s
        """.strip()

* Unit tests: Don't disable the django test database tear down,
  instead fixed the underlying issue which was caused by modifications
  to the `DATABASE_NAME` setting (Issue #82).

* Django Loader: New config :setting:`CELERY_DB_REUSE_MAX` (max number of
  tasks to reuse the same database connection)

    The default is to use a new connection for every task.
    We would very much like to reuse the connection, but a safe number of
    reuses is not known, and we don't have any way to handle the errors
    that might happen, which may even be database dependent.

    See: http://bit.ly/94fwdd

* celeryd: The worker components are now configurable: :setting:`CELERYD_POOL`,
  :setting:`CELERYD_CONSUMER`, :setting:`CELERYD_MEDIATOR`, and
  :setting:`CELERYD_ETA_SCHEDULER`.

    The default configuration is as follows:

    .. code-block:: python

        CELERYD_POOL = "celery.concurrency.processes.TaskPool"
        CELERYD_MEDIATOR = "celery.worker.controllers.Mediator"
        CELERYD_ETA_SCHEDULER = "celery.worker.controllers.ScheduleController"
        CELERYD_CONSUMER = "celery.worker.consumer.Consumer"

    The :setting:`CELERYD_POOL` setting makes it easy to swap out the
    multiprocessing pool with a threaded pool, or how about a
    twisted/eventlet pool?

    Consider the competition for the first pool plug-in started!


* Debian init scripts: Use `-a` not `&&` (Issue #82).

* Debian init scripts: Now always preserves `$CELERYD_OPTS` from the
  `/etc/default/celeryd` and `/etc/default/celerybeat`.

* celery.beat.Scheduler: Fixed a bug where the schedule was not properly
  flushed to disk if the schedule had not been properly initialized.

* celerybeat: Now syncs the schedule to disk when receiving the :sig:`SIGTERM`
  and :sig:`SIGINT` signals.

* Control commands: Make sure keywords arguments are not in Unicode.

* ETA scheduler: Was missing a logger object, so the scheduler crashed
  when trying to log that a task had been revoked.

* management.commands.camqadm: Fixed typo `camqpadm` -> `camqadm`
  (Issue #83).

* PeriodicTask.delta_resolution: Was not working for days and hours, now fixed
  by rounding to the nearest day/hour.

* Fixed a potential infinite loop in `BaseAsyncResult.__eq__`, although
  there is no evidence that it has ever been triggered. 

* celeryd: Now handles messages with encoding problems by acking them and
  emitting an error message.

.. _version-1.0.1:

1.0.1
=====
:release-date: 2010-02-24 07:05 P.M CET

* Tasks are now acknowledged early instead of late.

    This is done because messages can only be acknowledged within the same
    connection channel, so if the connection is lost we would have to refetch
    the message again to acknowledge it.

    This might or might not affect you, but mostly those running tasks with a
    really long execution time are affected, as all tasks that has made it
    all the way into the pool needs to be executed before the worker can
    safely terminate (this is at most the number of pool workers, multiplied
    by the :setting:`CELERYD_PREFETCH_MULTIPLIER` setting.)

    We multiply the prefetch count by default to increase the performance at
    times with bursts of tasks with a short execution time. If this doesn't
    apply to your use case, you should be able to set the prefetch multiplier
    to zero, without sacrificing performance.

    .. note::

        A patch to :mod:`multiprocessing` is currently being
        worked on, this patch would enable us to use a better solution, and is
        scheduled for inclusion in the `2.0.0` release.

* celeryd now shutdowns cleanly when receiving the :sig:`SIGTERM` signal.

* celeryd now does a cold shutdown if the :sig:`SIGINT` signal is received (Ctrl+C),
  this means it tries to terminate as soon as possible.

* Caching of results now moved to the base backend classes, so no need
  to implement this functionality in the base classes.

* Caches are now also limited in size, so their memory usage doesn't grow
  out of control.
  
    You can set the maximum number of results the cache
    can hold using the :setting:`CELERY_MAX_CACHED_RESULTS` setting (the
    default is five thousand results). In addition, you can refetch already
    retrieved results using `backend.reload_task_result` +
    `backend.reload_taskset_result` (that's for those who want to send
    results incrementally).

* `celeryd` now works on Windows again.

    .. warning::

        If you're using Celery with Django, you can't use `project.settings`
        as the settings module name, but the following should work::

        $ python manage.py celeryd --settings=settings

* Execution: `.messaging.TaskPublisher.send_task` now
  incorporates all the functionality apply_async previously did.
  
    Like converting countdowns to eta, so :func:`celery.execute.apply_async` is
    now simply a convenient front-end to
    :meth:`celery.messaging.TaskPublisher.send_task`, using
    the task classes default options.

    Also :func:`celery.execute.send_task` has been
    introduced, which can apply tasks using just the task name (useful
    if the client does not have the destination task in its task registry).

    Example:

        >>> from celery.execute import send_task
        >>> result = send_task("celery.ping", args=[], kwargs={})
        >>> result.get()
        'pong'

* `camqadm`: This is a new utility for command line access to the AMQP API.

    Excellent for deleting queues/bindings/exchanges, experimentation and
    testing::

        $ camqadm
        1> help

    Gives an interactive shell, type `help` for a list of commands.

    When using Django, use the management command instead::

        $ python manage.py camqadm
        1> help

* Redis result backend: To conform to recent Redis API changes, the following
  settings has been deprecated:

        * `REDIS_TIMEOUT`
        * `REDIS_CONNECT_RETRY`

    These will emit a `DeprecationWarning` if used.

    A `REDIS_PASSWORD` setting has been added, so you can use the new
    simple authentication mechanism in Redis.

* The redis result backend no longer calls `SAVE` when disconnecting,
  as this is apparently better handled by Redis itself.

* If `settings.DEBUG` is on, celeryd now warns about the possible
  memory leak it can result in.

* The ETA scheduler now sleeps at most two seconds between iterations.

* The ETA scheduler now deletes any revoked tasks it might encounter.

    As revokes are not yet persistent, this is done to make sure the task
    is revoked even though it's currently being hold because its eta is e.g.
    a week into the future.

* The `task_id` argument is now respected even if the task is executed 
  eagerly (either using apply, or :setting:`CELERY_ALWAYS_EAGER`).

* The internal queues are now cleared if the connection is reset.

* New magic keyword argument: `delivery_info`.

    Used by retry() to resend the task to its original destination using the same
    exchange/routing_key.

* Events: Fields was not passed by `.send()` (fixes the UUID key errors
  in celerymon)

* Added `--schedule`/`-s` option to celeryd, so it is possible to
  specify a custom schedule filename when using an embedded celerybeat
  server (the `-B`/`--beat`) option.

* Better Python 2.4 compatibility. The test suite now passes.

* task decorators: Now preserve docstring as `cls.__doc__`, (was previously
  copied to `cls.run.__doc__`)

* The `testproj` directory has been renamed to `tests` and we're now using
  `nose` + `django-nose` for test discovery, and `unittest2` for test
  cases.

* New pip requirements files available in `contrib/requirements`.

* TaskPublisher: Declarations are now done once (per process).

* Added `Task.delivery_mode` and the :setting:`CELERY_DEFAULT_DELIVERY_MODE`
  setting.

    These can be used to mark messages non-persistent (i.e. so they are
    lost if the broker is restarted).

* Now have our own `ImproperlyConfigured` exception, instead of using the
  Django one.

* Improvements to the Debian init scripts: Shows an error if the program is
  not executable.  Does not modify `CELERYD` when using django with
  virtualenv.

.. _version-1.0.0:

1.0.0
=====
:release-date: 2010-02-10 04:00 P.M CET

.. _v100-incompatible:

Backward incompatible changes
-----------------------------

* Celery does not support detaching anymore, so you have to use the tools
  available on your platform, or something like Supervisord to make
  celeryd/celerybeat/celerymon into background processes.

    We've had too many problems with celeryd daemonizing itself, so it was
    decided it has to be removed. Example startup scripts has been added to
    `contrib/`:

    * Debian, Ubuntu, (start-stop-daemon)

        `contrib/debian/init.d/celeryd`
        `contrib/debian/init.d/celerybeat`

    * Mac OS X launchd

        `contrib/mac/org.celeryq.celeryd.plist`
        `contrib/mac/org.celeryq.celerybeat.plist`
        `contrib/mac/org.celeryq.celerymon.plist`

    * Supervisord (http://supervisord.org)

        `contrib/supervisord/supervisord.conf`

    In addition to `--detach`, the following program arguments has been
    removed: `--uid`, `--gid`, `--workdir`, `--chroot`, `--pidfile`,
    `--umask`. All good daemonization tools should support equivalent
    functionality, so don't worry.

    Also the following configuration keys has been removed:
    `CELERYD_PID_FILE`, `CELERYBEAT_PID_FILE`, `CELERYMON_PID_FILE`.

* Default celeryd loglevel is now `WARN`, to enable the previous log level
  start celeryd with `--loglevel=INFO`.

* Tasks are automatically registered.

    This means you no longer have to register your tasks manually.
    You don't have to change your old code right away, as it doesn't matter if
    a task is registered twice.

    If you don't want your task to be automatically registered you can set
    the `abstract` attribute

    .. code-block:: python

        class MyTask(Task):
            abstract = True

    By using `abstract` only tasks subclassing this task will be automatically
    registered (this works like the Django ORM).

    If you don't want subclasses to be registered either, you can set the
    `autoregister` attribute to `False`.

    Incidentally, this change also fixes the problems with automatic name
    assignment and relative imports. So you also don't have to specify a task name
    anymore if you use relative imports.

* You can no longer use regular functions as tasks.

    This change was added
    because it makes the internals a lot more clean and simple. However, you can
    now turn functions into tasks by using the `@task` decorator:

    .. code-block:: python

        from celery.decorators import task

        @task
        def add(x, y):
            return x + y

    .. seealso::

        :ref:`guide-tasks` for more information about the task decorators.

* The periodic task system has been rewritten to a centralized solution.

    This means `celeryd` no longer schedules periodic tasks by default,
    but a new daemon has been introduced: `celerybeat`.

    To launch the periodic task scheduler you have to run celerybeat::

        $ celerybeat

    Make sure this is running on one server only, if you run it twice, all
    periodic tasks will also be executed twice.

    If you only have one worker server you can embed it into celeryd like this::

        $ celeryd --beat # Embed celerybeat in celeryd.

* The supervisor has been removed.

    This means the `-S` and `--supervised` options to `celeryd` is
    no longer supported. Please use something like http://supervisord.org
    instead.

* `TaskSet.join` has been removed, use `TaskSetResult.join` instead.

* The task status `"DONE"` has been renamed to `"SUCCESS"`.

* `AsyncResult.is_done` has been removed, use `AsyncResult.successful`
  instead.

* The worker no longer stores errors if `Task.ignore_result` is set, to
  revert to the previous behaviour set
  :setting:`CELERY_STORE_ERRORS_EVEN_IF_IGNORED` to `True`.

* The statistics functionality has been removed in favor of events,
  so the `-S` and --statistics` switches has been removed.

* The module `celery.task.strategy` has been removed.

* `celery.discovery` has been removed, and it's `autodiscover` function is
  now in `celery.loaders.djangoapp`. Reason: Internal API.

* The :envvar:`CELERY_LOADER` environment variable now needs loader class name
  in addition to module name,

    E.g. where you previously had: `"celery.loaders.default"`, you now need
    `"celery.loaders.default.Loader"`, using the previous syntax will result
    in a `DeprecationWarning`.

* Detecting the loader is now lazy, and so is not done when importing
  `celery.loaders`.

    To make this happen `celery.loaders.settings` has
    been renamed to `load_settings` and is now a function returning the
    settings object. `celery.loaders.current_loader` is now also
    a function, returning the current loader.

    So::

        loader = current_loader

    needs to be changed to::

        loader = current_loader()

.. _v100-deprecations:

Deprecations
------------

* The following configuration variables has been renamed and will be
  deprecated in v2.0:

    * CELERYD_DAEMON_LOG_FORMAT -> CELERYD_LOG_FORMAT
    * CELERYD_DAEMON_LOG_LEVEL -> CELERYD_LOG_LEVEL
    * CELERY_AMQP_CONNECTION_TIMEOUT -> CELERY_BROKER_CONNECTION_TIMEOUT
    * CELERY_AMQP_CONNECTION_RETRY -> CELERY_BROKER_CONNECTION_RETRY
    * CELERY_AMQP_CONNECTION_MAX_RETRIES -> CELERY_BROKER_CONNECTION_MAX_RETRIES
    * SEND_CELERY_TASK_ERROR_EMAILS -> CELERY_SEND_TASK_ERROR_EMAILS

* The public API names in celery.conf has also changed to a consistent naming
  scheme.

* We now support consuming from an arbitrary number of queues.

    To do this we had to rename the configuration syntax. If you use any of
    the custom AMQP routing options (queue/exchange/routing_key, etc.), you
    should read the new FAQ entry: http://bit.ly/aiWoH.

    The previous syntax is deprecated and scheduled for removal in v2.0.

* `TaskSet.run` has been renamed to `TaskSet.apply_async`.

    `TaskSet.run` has now been deprecated, and is scheduled for
    removal in v2.0.

.. v100-news:

News
----

* Rate limiting support (per task type, or globally).

* New periodic task system.

* Automatic registration.

* New cool task decorator syntax.

* celeryd now sends events if enabled with the `-E` argument.

    Excellent for monitoring tools, one is already in the making
    (http://github.com/ask/celerymon).

    Current events include: worker-heartbeat,
    task-[received/succeeded/failed/retried],
    worker-online, worker-offline.

* You can now delete (revoke) tasks that has already been applied.

* You can now set the hostname celeryd identifies as using the `--hostname`
  argument.

* Cache backend now respects the :setting:`CELERY_TASK_RESULT_EXPIRES` setting.

* Message format has been standardized and now uses ISO-8601 format
  for dates instead of datetime.

* `celeryd` now responds to the :sig:`SIGHUP` signal by restarting itself.

* Periodic tasks are now scheduled on the clock.

    I.e. `timedelta(hours=1)` means every hour at :00 minutes, not every
    hour from the server starts.  To revert to the previous behaviour you
    can set `PeriodicTask.relative = True`.

* Now supports passing execute options to a TaskSets list of args, e.g.:

    >>> ts = TaskSet(add, [([2, 2], {}, {"countdown": 1}),
    ...                   ([4, 4], {}, {"countdown": 2}),
    ...                   ([8, 8], {}, {"countdown": 3})])
    >>> ts.run()

* Got a 3x performance gain by setting the prefetch count to four times the 
  concurrency, (from an average task round-trip of 0.1s to 0.03s!).

    A new setting has been added: :setting:`CELERYD_PREFETCH_MULTIPLIER`, which
    is set to `4` by default.

* Improved support for webhook tasks.

    `celery.task.rest` is now deprecated, replaced with the new and shiny
    :mod:`celery.task.http`. With more reflective names, sensible interface,
    and it's possible to override the methods used to perform HTTP requests.

* The results of task sets are now cached by storing it in the result
  backend.

.. _v100-changes:

Changes
-------

* Now depends on carrot >= 0.8.1

* New dependencies: billiard, python-dateutil, django-picklefield

* No longer depends on python-daemon

* The `uuid` distribution is added as a dependency when running Python 2.4.

* Now remembers the previously detected loader by keeping it in
  the :envvar:`CELERY_LOADER` environment variable.

    This may help on windows where fork emulation is used.

* ETA no longer sends datetime objects, but uses ISO 8601 date format in a
  string for better compatibility with other platforms.

* No longer sends error mails for retried tasks.

* Task can now override the backend used to store results.

* Refactored the ExecuteWrapper, `apply` and :setting:`CELERY_ALWAYS_EAGER`
  now also executes the task callbacks and signals.

* Now using a proper scheduler for the tasks with an ETA.

    This means waiting eta tasks are sorted by time, so we don't have
    to poll the whole list all the time.

* Now also imports modules listed in :setting:`CELERY_IMPORTS` when running
  with django (as documented).

* Log level for stdout/stderr changed from INFO to ERROR

* ImportErrors are now properly propagated when autodiscovering tasks.

* You can now use `celery.messaging.establish_connection` to establish a
  connection to the broker.

* When running as a separate service the periodic task scheduler does some
  smart moves to not poll too regularly.

    If you need faster poll times you can lower the value
    of :setting:`CELERYBEAT_MAX_LOOP_INTERVAL`.

* You can now change periodic task intervals at runtime, by making
  `run_every` a property, or subclassing `PeriodicTask.is_due`.

* The worker now supports control commands enabled through the use of a
  broadcast queue, you can remotely revoke tasks or set the rate limit for
  a task type. See :mod:`celery.task.control`.

* The services now sets informative process names (as shown in `ps`
  listings) if the :mod:`setproctitle` module is installed.

* :exc:`celery.exceptions.NotRegistered` now inherits from :exc:`KeyError`,
  and `TaskRegistry.__getitem__`+`pop` raises `NotRegistered` instead

* You can set the loader via the :envvar:`CELERY_LOADER` environment variable.

* You can now set :setting:`CELERY_IGNORE_RESULT` to ignore task results by
  default (if enabled, tasks doesn't save results or errors to the backend used).

* celeryd now correctly handles malformed messages by throwing away and
  acknowledging the message, instead of crashing.

.. _v100-bugs:

Bugs
----

* Fixed a race condition that could happen while storing task results in the
  database.

.. _v100-documentation:

Documentation
-------------

* Reference now split into two sections; API reference and internal module
  reference.

.. _version-0.8.4:

0.8.4
=====
:release-date: 2010-02-05 01:52 P.M CEST

* Now emits a warning if the --detach argument is used.
  --detach should not be used anymore, as it has several not easily fixed
  bugs related to it. Instead, use something like start-stop-daemon,
  Supervisord or launchd (os x).


* Make sure logger class is process aware, even if running Python >= 2.6.


* Error e-mails are not sent anymore when the task is retried.

.. _version-0.8.3:

0.8.3
=====
:release-date: 2009-12-22 09:43 A.M CEST

* Fixed a possible race condition that could happen when storing/querying
  task results using the database backend.

* Now has console script entry points in the setup.py file, so tools like
  Buildout will correctly install the programs celeryd and celeryinit.

.. _version-0.8.2:

0.8.2
=====
:release-date: 2009-11-20 03:40 P.M CEST

* QOS Prefetch count was not applied properly, as it was set for every message
  received (which apparently behaves like, "receive one more"), instead of only 
  set when our wanted value changed.

.. _version-0.8.1:

0.8.1
=================================
:release-date: 2009-11-16 05:21 P.M CEST

.. _v081-very-important:

Very important note
-------------------

This release (with carrot 0.8.0) enables AMQP QoS (quality of service), which
means the workers will only receive as many messages as it can handle at a
time. As with any release, you should test this version upgrade on your
development servers before rolling it out to production!

.. _v081-important:

Important changes
-----------------

* If you're using Python < 2.6 and you use the multiprocessing backport, then
  multiprocessing version 2.6.2.1 is required.

* All AMQP_* settings has been renamed to BROKER_*, and in addition
  AMQP_SERVER has been renamed to BROKER_HOST, so before where you had::

        AMQP_SERVER = "localhost"
        AMQP_PORT = 5678
        AMQP_USER = "myuser"
        AMQP_PASSWORD = "mypassword"
        AMQP_VHOST = "celery"

  You need to change that to::

        BROKER_HOST = "localhost"
        BROKER_PORT = 5678
        BROKER_USER = "myuser"
        BROKER_PASSWORD = "mypassword"
        BROKER_VHOST = "celery"

* Custom carrot backends now need to include the backend class name, so before
  where you had::

        CARROT_BACKEND = "mycustom.backend.module"

  you need to change it to::

        CARROT_BACKEND = "mycustom.backend.module.Backend"

  where `Backend` is the class name. This is probably `"Backend"`, as
  that was the previously implied name.

* New version requirement for carrot: 0.8.0

.. _v081-changes:

Changes
-------

* Incorporated the multiprocessing backport patch that fixes the
  `processName` error.

* Ignore the result of PeriodicTask's by default.

* Added a Redis result store backend

* Allow /etc/default/celeryd to define additional options for the celeryd init
  script.

* MongoDB periodic tasks issue when using different time than UTC fixed.

* Windows specific: Negate test for available os.fork (thanks miracle2k)

* Now tried to handle broken PID files.

* Added a Django test runner to contrib that sets
  `CELERY_ALWAYS_EAGER = True` for testing with the database backend.

* Added a :setting:`CELERY_CACHE_BACKEND` setting for using something other
  than the django-global cache backend.

* Use custom implementation of functools.partial (curry) for Python 2.4 support
  (Probably still problems with running on 2.4, but it will eventually be
  supported)

* Prepare exception to pickle when saving :state:`RETRY` status for all backends.

* SQLite no concurrency limit should only be effective if the database backend
  is used.


.. _version-0.8.0:

0.8.0
=====
:release-date: 2009-09-22 03:06 P.M CEST

.. _v080-incompatible:

Backward incompatible changes
-----------------------------

* Add traceback to result value on failure.

    .. note::

        If you use the database backend you have to re-create the
        database table `celery_taskmeta`.

        Contact the :ref:`mailing-list` or :ref:`irc-channel` channel
        for help doing this.

* Database tables are now only created if the database backend is used,
  so if you change back to the database backend at some point,
  be sure to initialize tables (django: `syncdb`, python: `celeryinit`).

  .. note::

     This is only applies if using Django version 1.1 or higher.

* Now depends on `carrot` version 0.6.0.

* Now depends on python-daemon 1.4.8

.. _v080-important:

Important changes
-----------------

* Celery can now be used in pure Python (outside of a Django project).

    This means celery is no longer Django specific.

    For more information see the FAQ entry
    :ref:`faq-is-celery-for-django-only`.

* Celery now supports task retries.

    See `Cookbook: Retrying Tasks`_ for more information.

.. _`Cookbook: Retrying Tasks`:
    http://ask.github.com/celery/cookbook/task-retries.html

* We now have an AMQP result store backend.

    It uses messages to publish task return value and status. And it's
    incredibly fast!

    See issue #6 for more info!

* AMQP QoS (prefetch count) implemented:

    This to not receive more messages than we can handle.

* Now redirects stdout/stderr to the celeryd log file when detached

* Now uses `inspect.getargspec` to only pass default arguments
    the task supports.

* Add Task.on_success, .on_retry, .on_failure handlers
    See :meth:`celery.task.base.Task.on_success`,
        :meth:`celery.task.base.Task.on_retry`,
        :meth:`celery.task.base.Task.on_failure`,

* `celery.utils.gen_unique_id`: Workaround for
    http://bugs.python.org/issue4607

* You can now customize what happens at worker start, at process init, etc.,
    by creating your own loaders. (see :mod:`celery.loaders.default`,
    :mod:`celery.loaders.djangoapp`, :mod:`celery.loaders`.)

* Support for multiple AMQP exchanges and queues.

    This feature misses documentation and tests, so anyone interested 
    is encouraged to improve this situation.

* celeryd now survives a restart of the AMQP server!

  Automatically re-establish AMQP broker connection if it's lost.

  New settings:

    * AMQP_CONNECTION_RETRY
        Set to `True` to enable connection retries.

    * AMQP_CONNECTION_MAX_RETRIES.
        Maximum number of restarts before we give up. Default: `100`.

.. _v080-news:

News
----

*  Fix an incompatibility between python-daemon and multiprocessing,
    which resulted in the `[Errno 10] No child processes` problem when
    detaching.

* Fixed a possible DjangoUnicodeDecodeError being raised when saving pickled
    data to Django`s memcached cache backend.

* Better Windows compatibility.

* New version of the pickled field (taken from
    http://www.djangosnippets.org/snippets/513/)

* New signals introduced: `task_sent`, `task_prerun` and
    `task_postrun`, see :mod:`celery.signals` for more information.

* `TaskSetResult.join` caused `TypeError` when `timeout=None`.
    Thanks Jerzy Kozera.  Closes #31

* `views.apply` should return `HttpResponse` instance.
    Thanks to Jerzy Kozera. Closes #32

* `PeriodicTask`: Save conversion of `run_every` from `int`
    to `timedelta` to the class attribute instead of on the instance.

* Exceptions has been moved to `celery.exceptions`, but are still
    available in the previous module.

* Try to rollback transaction and retry saving result if an error happens
    while setting task status with the database backend.

* jail() refactored into :class:`celery.execute.ExecuteWrapper`.

* `views.apply` now correctly sets mime-type to "application/json"

* `views.task_status` now returns exception if state is :state:`RETRY`

* `views.task_status` now returns traceback if state is :state:`FAILURE`
    or :state:`RETRY`

* Documented default task arguments.

* Add a sensible __repr__ to ExceptionInfo for easier debugging

* Fix documentation typo `.. import map` -> `.. import dmap`.
    Thanks to mikedizon

.. _version-0.6.0:

0.6.0
=====
:release-date: 2009-08-07 06:54 A.M CET

.. _v060-important:

Important changes
-----------------

* Fixed a bug where tasks raising unpickleable exceptions crashed pool
    workers. So if you've had pool workers mysteriously disappearing, or
    problems with celeryd stopping working, this has been fixed in this
    version.

* Fixed a race condition with periodic tasks.

* The task pool is now supervised, so if a pool worker crashes,
    goes away or stops responding, it is automatically replaced with
    a new one.

* Task.name is now automatically generated out of class module+name, e.g.
    `"djangotwitter.tasks.UpdateStatusesTask"`. Very convenient. No idea why
    we didn't do this before. Some documentation is updated to not manually
    specify a task name.

.. _v060-news:

News
----

* Tested with Django 1.1

* New Tutorial: Creating a click counter using carrot and celery

* Database entries for periodic tasks are now created at `celeryd`
    startup instead of for each check (which has been a forgotten TODO/XXX
    in the code for a long time)

* New settings variable: :setting:`CELERY_TASK_RESULT_EXPIRES`
    Time (in seconds, or a `datetime.timedelta` object) for when after
    stored task results are deleted. For the moment this only works for the
    database backend.

* `celeryd` now emits a debug log message for which periodic tasks
    has been launched.

* The periodic task table is now locked for reading while getting
    periodic task status. (MySQL only so far, seeking patches for other
    engines)

* A lot more debugging information is now available by turning on the
    `DEBUG` log level (`--loglevel=DEBUG`).

* Functions/methods with a timeout argument now works correctly.

* New: `celery.strategy.even_time_distribution`: 
    With an iterator yielding task args, kwargs tuples, evenly distribute
    the processing of its tasks throughout the time window available.

* Log message `Unknown task ignored...` now has log level `ERROR`

* Log message `"Got task from broker"` is now emitted for all tasks, even if
    the task has an ETA (estimated time of arrival). Also the message now
    includes the ETA for the task (if any).

* Acknowledgement now happens in the pool callback. Can't do ack in the job
    target, as it's not pickleable (can't share AMQP connection, etc.)).

* Added note about .delay hanging in README

* Tests now passing in Django 1.1

* Fixed discovery to make sure app is in INSTALLED_APPS

* Previously overridden pool behavior (process reap, wait until pool worker
    available, etc.) is now handled by `multiprocessing.Pool` itself.

* Convert statistics data to Unicode for use as kwargs. Thanks Lucy!

.. _version-0.4.1:

0.4.1
=====
:release-date: 2009-07-02 01:42 P.M CET

* Fixed a bug with parsing the message options (`mandatory`,
  `routing_key`, `priority`, `immediate`)

.. _version-0.4.0:

0.4.0
=====
:release-date: 2009-07-01 07:29 P.M CET

* Adds eager execution. `celery.execute.apply`|`Task.apply` executes the
  function blocking until the task is done, for API compatibility it
  returns an `celery.result.EagerResult` instance. You can configure
  celery to always run tasks locally by setting the
  :setting:`CELERY_ALWAYS_EAGER` setting to `True`.

* Now depends on `anyjson`.

* 99% coverage using python `coverage` 3.0.

.. _version-0.3.20:

0.3.20
======
:release-date: 2009-06-25 08:42 P.M CET

* New arguments to `apply_async` (the advanced version of
  `delay_task`), `countdown` and `eta`;

    >>> # Run 10 seconds into the future.
    >>> res = apply_async(MyTask, countdown=10);

    >>> # Run 1 day from now
    >>> res = apply_async(MyTask,
    ...                   eta=datetime.now() + timedelta(days=1))

* Now unlinks stale PID files

* Lots of more tests.

* Now compatible with carrot >= 0.5.0.

* **IMPORTANT** The `subtask_ids` attribute on the `TaskSetResult`
  instance has been removed. To get this information instead use:

        >>> subtask_ids = [subtask.task_id for subtask in ts_res.subtasks]

* `Taskset.run()` now respects extra message options from the task class.

* Task: Add attribute `ignore_result`: Don't store the status and
  return value. This means you can't use the
  `celery.result.AsyncResult` to check if the task is
  done, or get its return value. Only use if you need the performance
  and is able live without these features. Any exceptions raised will
  store the return value/status as usual.

* Task: Add attribute `disable_error_emails` to disable sending error
  emails for that task.

* Should now work on Windows (although running in the background won't
  work, so using the `--detach` argument results in an exception
  being raised.)

* Added support for statistics for profiling and monitoring.
  To start sending statistics start `celeryd` with the
  `--statistics option. Then after a while you can dump the results
  by running `python manage.py celerystats`. See
  `celery.monitoring` for more information.

* The celery daemon can now be supervised (i.e. it is automatically
  restarted if it crashes). To use this start celeryd with the
  --supervised` option (or alternatively `-S`).

* views.apply: View applying a task. Example

    ::

        http://e.com/celery/apply/task_name/arg1/arg2//?kwarg1=a&kwarg2=b


    .. warning::

        Use with caution! Do not expose this URL to the public
        without first ensuring that your code is safe!

* Refactored `celery.task`. It's now split into three modules:

    * celery.task

        Contains `apply_async`, `delay_task`, `discard_all`, and task
        shortcuts, plus imports objects from `celery.task.base` and
        `celery.task.builtins`

    * celery.task.base

        Contains task base classes: `Task`, `PeriodicTask`,
        `TaskSet`, `AsynchronousMapTask`, `ExecuteRemoteTask`.

    * celery.task.builtins

        Built-in tasks: `PingTask`, `DeleteExpiredTaskMetaTask`.

.. _version-0.3.7:

0.3.7
=====
:release-date: 2008-06-16 11:41 P.M CET

* **IMPORTANT** Now uses AMQP`s `basic.consume` instead of
  `basic.get`. This means we're no longer polling the broker for
  new messages.

* **IMPORTANT** Default concurrency limit is now set to the number of CPUs
  available on the system.

* **IMPORTANT** `tasks.register`: Renamed `task_name` argument to
  `name`, so

        >>> tasks.register(func, task_name="mytask")

  has to be replaced with:

        >>> tasks.register(func, name="mytask")

* The daemon now correctly runs if the pidlock is stale.

* Now compatible with carrot 0.4.5

* Default AMQP connection timeout is now 4 seconds.
* `AsyncResult.read()` was always returning `True`.

*  Only use README as long_description if the file exists so easy_install
   doesn't break.

* `celery.view`: JSON responses now properly set its mime-type. 

* `apply_async` now has a `connection` keyword argument so you
  can re-use the same AMQP connection if you want to execute
  more than one task.

* Handle failures in task_status view such that it won't throw 500s.

* Fixed typo `AMQP_SERVER` in documentation to `AMQP_HOST`.

* Worker exception e-mails sent to administrators now works properly.

* No longer depends on `django`, so installing `celery` won't affect
  the preferred Django version installed.

* Now works with PostgreSQL (psycopg2) again by registering the
  `PickledObject` field.

* `celeryd`: Added `--detach` option as an alias to `--daemon`, and
  it's the term used in the documentation from now on.

* Make sure the pool and periodic task worker thread is terminated
  properly at exit. (So `Ctrl-C` works again).

* Now depends on `python-daemon`.

* Removed dependency to `simplejson`

* Cache Backend: Re-establishes connection for every task process
  if the Django cache backend is memcached/libmemcached.

* Tyrant Backend: Now re-establishes the connection for every task
  executed.

.. _version-0.3.3:

0.3.3
=====
:release-date: 2009-06-08 01:07 P.M CET

* The `PeriodicWorkController` now sleeps for 1 second between checking
  for periodic tasks to execute.

.. _version-0.3.2:

0.3.2
=====
:release-date: 2009-06-08 01:07 P.M CET

* celeryd: Added option `--discard`: Discard (delete!) all waiting
  messages in the queue.

* celeryd: The `--wakeup-after` option was not handled as a float.

.. _version-0.3.1:

0.3.1
=====
:release-date: 2009-06-08 01:07 P.M CET

* The `PeriodicTask` worker is now running in its own thread instead
  of blocking the `TaskController` loop.

* Default `QUEUE_WAKEUP_AFTER` has been lowered to `0.1` (was `0.3`)

.. _version-0.3.0:

0.3.0
=====
:release-date: 2009-06-08 12:41 P.M CET

.. warning::

    This is a development version, for the stable release, please
    see versions 0.2.x.

**VERY IMPORTANT:** Pickle is now the encoder used for serializing task
arguments, so be sure to flush your task queue before you upgrade.

* **IMPORTANT** TaskSet.run() now returns a celery.result.TaskSetResult
  instance, which lets you inspect the status and return values of a
  taskset as it was a single entity.

* **IMPORTANT** Celery now depends on carrot >= 0.4.1.

* The celery daemon now sends task errors to the registered admin e-mails.
  To turn off this feature, set `SEND_CELERY_TASK_ERROR_EMAILS` to
  `False` in your `settings.py`. Thanks to Grégoire Cachet.

* You can now run the celery daemon by using `manage.py`::

        $ python manage.py celeryd

  Thanks to Grégoire Cachet.

* Added support for message priorities, topic exchanges, custom routing
  keys for tasks. This means we have introduced
  `celery.task.apply_async`, a new way of executing tasks.

  You can use `celery.task.delay` and `celery.Task.delay` like usual, but
  if you want greater control over the message sent, you want
  `celery.task.apply_async` and `celery.Task.apply_async`.

  This also means the AMQP configuration has changed. Some settings has
  been renamed, while others are new::

        CELERY_AMQP_EXCHANGE
        CELERY_AMQP_PUBLISHER_ROUTING_KEY
        CELERY_AMQP_CONSUMER_ROUTING_KEY
        CELERY_AMQP_CONSUMER_QUEUE
        CELERY_AMQP_EXCHANGE_TYPE

  See the entry `Can I send some tasks to only some servers?`_ in the
  `FAQ`_ for more information.

.. _`Can I send some tasks to only some servers?`:
        http://bit.ly/celery_AMQP_routing
.. _`FAQ`: http://ask.github.com/celery/faq.html

* Task errors are now logged using log level `ERROR` instead of `INFO`,
  and stacktraces are dumped. Thanks to Grégoire Cachet.

* Make every new worker process re-establish it's Django DB connection,
  this solving the "MySQL connection died?" exceptions.
  Thanks to Vitaly Babiy and Jirka Vejrazka.

* **IMPORTANT** Now using pickle to encode task arguments. This means you
  now can pass complex python objects to tasks as arguments.

* Removed dependency to `yadayada`.

* Added a FAQ, see `docs/faq.rst`.

* Now converts any Unicode keys in task `kwargs` to regular strings.
  Thanks Vitaly Babiy.

* Renamed the `TaskDaemon` to `WorkController`.

* `celery.datastructures.TaskProcessQueue` is now renamed to
  `celery.pool.TaskPool`.

* The pool algorithm has been refactored for greater performance and
  stability.

.. _version-0.2.0:

0.2.0
=====
:release-date: 2009-05-20 05:14 P.M CET

* Final release of 0.2.0

* Compatible with carrot version 0.4.0.

* Fixes some syntax errors related to fetching results
  from the database backend.

.. _version-0.2.0-pre3:

0.2.0-pre3
==========
:release-date: 2009-05-20 05:14 P.M CET

* *Internal release*. Improved handling of unpickleable exceptions,
  `get_result` now tries to recreate something looking like the
  original exception.

.. _version-0.2.0-pre2:

0.2.0-pre2
==========
:release-date: 2009-05-20 01:56 P.M CET

* Now handles unpickleable exceptions (like the dynamically generated
  subclasses of `django.core.exception.MultipleObjectsReturned`).

.. _version-0.2.0-pre1:

0.2.0-pre1
==========
:release-date: 2009-05-20 12:33 P.M CET

* It's getting quite stable, with a lot of new features, so bump
  version to 0.2. This is a pre-release.

* `celery.task.mark_as_read()` and `celery.task.mark_as_failure()` has
  been removed. Use `celery.backends.default_backend.mark_as_read()`, 
  and `celery.backends.default_backend.mark_as_failure()` instead.

.. _version-0.1.15:

0.1.15
======
:release-date: 2009-05-19 04:13 P.M CET

* The celery daemon was leaking AMQP connections, this should be fixed,
  if you have any problems with too many files open (like `emfile`
  errors in `rabbit.log`, please contact us!

.. _version-0.1.14:

0.1.14
======
:release-date: 2009-05-19 01:08 P.M CET

* Fixed a syntax error in the `TaskSet` class.  (No such variable
  `TimeOutError`).

.. _version-0.1.13:

0.1.13
======
:release-date: 2009-05-19 12:36 P.M CET

* Forgot to add `yadayada` to install requirements.

* Now deletes all expired task results, not just those marked as done.

* Able to load the Tokyo Tyrant backend class without django
  configuration, can specify tyrant settings directly in the class
  constructor.

* Improved API documentation

* Now using the Sphinx documentation system, you can build
  the html documentation by doing ::

        $ cd docs
        $ make html

  and the result will be in `docs/.build/html`.

.. _version-0.1.12:

0.1.12
======
:release-date: 2009-05-18 04:38 P.M CET

* `delay_task()` etc. now returns `celery.task.AsyncResult` object,
  which lets you check the result and any failure that might have
  happened.  It kind of works like the `multiprocessing.AsyncResult`
  class returned by `multiprocessing.Pool.map_async`.

* Added dmap() and dmap_async(). This works like the 
  `multiprocessing.Pool` versions except they are tasks
  distributed to the celery server. Example:

        >>> from celery.task import dmap
        >>> import operator
        >>> dmap(operator.add, [[2, 2], [4, 4], [8, 8]])
        >>> [4, 8, 16]

        >>> from celery.task import dmap_async
        >>> import operator
        >>> result = dmap_async(operator.add, [[2, 2], [4, 4], [8, 8]])
        >>> result.ready()
        False
        >>> time.sleep(1)
        >>> result.ready()
        True
        >>> result.result
        [4, 8, 16]

* Refactored the task metadata cache and database backends, and added
  a new backend for Tokyo Tyrant. You can set the backend in your django
  settings file. E.g.::

        CELERY_RESULT_BACKEND = "database"; # Uses the database
        CELERY_RESULT_BACKEND = "cache"; # Uses the django cache framework
        CELERY_RESULT_BACKEND = "tyrant"; # Uses Tokyo Tyrant
        TT_HOST = "localhost"; # Hostname for the Tokyo Tyrant server.
        TT_PORT = 6657; # Port of the Tokyo Tyrant server.

.. _version-0.1.11:

0.1.11
======
:release-date: 2009-05-12 02:08 P.M CET

* The logging system was leaking file descriptors, resulting in
  servers stopping with the EMFILES (too many open files) error. (fixed)

.. _version-0.1.10:

0.1.10
======
:release-date: 2009-05-11 12:46 P.M CET

* Tasks now supports both positional arguments and keyword arguments.

* Requires carrot 0.3.8.

* The daemon now tries to reconnect if the connection is lost.

.. _version-0.1.8:

0.1.8
=====
:release-date: 2009-05-07 12:27 P.M CET

* Better test coverage
* More documentation
* celeryd doesn't emit `Queue is empty` message if
  `settings.CELERYD_EMPTY_MSG_EMIT_EVERY` is 0.

.. _version-0.1.7:

0.1.7
=====
:release-date: 2009-04-30 1:50 P.M CET

* Added some unit tests

* Can now use the database for task metadata (like if the task has
  been executed or not). Set `settings.CELERY_TASK_META`

* Can now run `python setup.py test` to run the unit tests from
  within the `tests` project.

* Can set the AMQP exchange/routing key/queue using
  `settings.CELERY_AMQP_EXCHANGE`, `settings.CELERY_AMQP_ROUTING_KEY`,
  and `settings.CELERY_AMQP_CONSUMER_QUEUE`.

.. _version-0.1.6:

0.1.6
=====
:release-date: 2009-04-28 2:13 P.M CET

* Introducing `TaskSet`. A set of subtasks is executed and you can
  find out how many, or if all them, are done (excellent for progress
  bars and such)

* Now catches all exceptions when running `Task.__call__`, so the
  daemon doesn't die. This doesn't happen for pure functions yet, only
  `Task` classes.

* `autodiscover()` now works with zipped eggs.

* celeryd: Now adds current working directory to `sys.path` for
  convenience.

* The `run_every` attribute of `PeriodicTask` classes can now be a
  `datetime.timedelta()` object.

* celeryd: You can now set the `DJANGO_PROJECT_DIR` variable
  for `celeryd` and it will add that to `sys.path` for easy launching.

* Can now check if a task has been executed or not via HTTP.

* You can do this by including the celery `urls.py` into your project,

        >>> url(r'^celery/$', include("celery.urls"))

  then visiting the following url,::

        http://mysite/celery/$task_id/done/

  this will return a JSON dictionary like e.g:

        >>> {"task": {"id": $task_id, "executed": true}}

* `delay_task` now returns string id, not `uuid.UUID` instance.

* Now has `PeriodicTasks`, to have `cron` like functionality.

* Project changed name from `crunchy` to `celery`. The details of
  the name change request is in `docs/name_change_request.txt`.

.. _version-0.1.0:

0.1.0
=====
:release-date: 2009-04-24 11:28 A.M CET

* Initial release