celery/celery/pool.py

"""

Process Pools.

"""
import os
import errno
import multiprocessing

from multiprocessing.pool import Pool, worker
from celery.datastructures import ExceptionInfo
from celery.utils import noop
from celery.utils.functional import curry
from operator import isNumberType


def pid_is_dead(pid):
    """Check if a process is not running by PID.

    :rtype bool:

    """
    try:
        return os.kill(pid, 0)
    except OSError, err:
        if err.errno == errno.ESRCH:
            return True # No such process.
        elif err.errno == errno.EPERM:
            return False # Operation not permitted.
        else:
            raise


def reap_process(pid):
    """Reap process if the process is a zombie.

    :returns: ``True`` if process was reaped or is not running,
        ``False`` otherwise.

    """
    if pid_is_dead(pid):
        return True

    try:
        is_dead, _ = os.waitpid(pid, os.WNOHANG)
    except OSError, err:
        if err.errno == errno.ECHILD:
            return False # No child processes.
        raise
    return is_dead


def process_is_dead(process):
    """Check if process is not running anymore.

    First it finds out if the process is running by sending
    signal 0. Then if the process is a child process, and is running
    it finds out if it's a zombie process and reaps it.
    If the process is running and is not a zombie it tries to send
    a ping through the process pipe.

    :param process: A :class:`multiprocessing.Process` instance.

    :returns: ``True`` if the process is not running, ``False`` otherwise.

    """

    # Only do this if os.kill exists for this platform (e.g. Windows doesn't
    # support it).
    if callable(getattr(os, "kill", None)) and reap_process(process.pid):
        return True

    # Then try to ping the process using its pipe.
    try:
        proc_is_alive = process.is_alive()
    except OSError:
        return True
    else:
        return not proc_is_alive


class DynamicPool(Pool):
    """Version of :class:`multiprocessing.Pool` that can dynamically grow
    in size."""

    def __init__(self, processes=None, initializer=None, initargs=()):

        if processes is None:
            try:
                processes = multiprocessing.cpu_count()
            except NotImplementedError:
                processes = 1

        super(DynamicPool, self).__init__(processes=processes,
                                          initializer=initializer,
                                          initargs=initargs)
        self._initializer = initializer
        self._initargs = initargs
        self._size = processes
        self.logger = multiprocessing.get_logger()

    def _my_cleanup(self):
        from multiprocessing.process import _current_process
        for p in list(_current_process._children):
            discard = False
            try:
                status = p._popen.poll()
            except OSError:
                discard = True
            else:
                if status is not None:
                    discard = True
            if discard:
                _current_process._children.discard(p)

    def add_worker(self):
        """Add another worker to the pool."""
        self._my_cleanup()
        w = self.Process(target=worker,
                         args=(self._inqueue, self._outqueue,
                               self._initializer, self._initargs))
        w.name = w.name.replace("Process", "PoolWorker")
        w.daemon = True
        w.start()
        self._pool.append(w)
        self.logger.debug(
            "DynamicPool: Started pool worker %s (PID: %s, Poolsize: %d)" %(
                w.name, w.pid, len(self._pool)))

    def grow(self, size=1):
        """Add workers to the pool.

        :keyword size: Number of workers to add (default: 1)

        """
        [self.add_worker() for i in range(size)]

    def _is_dead(self, process):
        """Try to find out if the process is dead.

        :rtype bool:

        """
        if process_is_dead(process):
            self.logger.info("DynamicPool: Found dead process (PID: %s)" % (
                process.pid))
            return True
        return False

    def _bring_out_the_dead(self):
        """Sort out dead process from pool.

        :returns: Tuple of two lists, the first list with dead processes,
            the second with active processes.

        """
        dead, alive = [], []
        for process in self._pool:
            if process and process.pid and isNumberType(process.pid):
                dest = dead if self._is_dead(process) else alive
                dest.append(process)
        return dead, alive

    def replace_dead_workers(self):
        """Replace dead workers in the pool by spawning new ones.

        :returns: number of dead processes replaced, or ``None`` if all
            processes are alive and running.

        """
        dead, alive = self._bring_out_the_dead()
        if dead:
            dead_count = len(dead)
            self._pool = alive
            self.grow(self._size if dead_count > self._size else dead_count)
            return dead_count


class TaskPool(object):
    """Process Pool for processing tasks in parallel.

    :param limit: see :attr:`limit` attribute.
    :param logger: see :attr:`logger` attribute.


    .. attribute:: limit

        The number of processes that can run simultaneously.

    .. attribute:: logger

        The logger used for debugging.

    """

    def __init__(self, limit, logger=None):
        self.limit = limit
        self.logger = logger or multiprocessing.get_logger()
        self._pool = None

    def start(self):
        """Run the task pool.

        Will pre-fork all workers so they're ready to accept tasks.

        """
        self._pool = DynamicPool(processes=self.limit)

    def stop(self):
        """Terminate the pool."""
        self._pool.terminate()
        self._pool = None

    def replace_dead_workers(self):
        self.logger.debug("TaskPool: Finding dead pool processes...")
        dead_count = self._pool.replace_dead_workers()
        if dead_count:
            self.logger.info(
                "TaskPool: Replaced %d dead pool workers..." % (
                    dead_count))

    def apply_async(self, target, args=None, kwargs=None, callbacks=None,
            errbacks=None, on_ack=noop):
        """Equivalent of the :func:``apply`` built-in function.

        All ``callbacks`` and ``errbacks`` should complete immediately since
        otherwise the thread which handles the result will get blocked.

        """
        args = args or []
        kwargs = kwargs or {}
        callbacks = callbacks or []
        errbacks = errbacks or []

        on_ready = curry(self.on_ready, callbacks, errbacks, on_ack)

        self.logger.debug("TaskPool: Apply %s (args:%s kwargs:%s)" % (
            target, args, kwargs))

        self.replace_dead_workers()

        return self._pool.apply_async(target, args, kwargs,
                                        callback=on_ready)

    def on_ready(self, callbacks, errbacks, on_ack, ret_value):
        """What to do when a worker task is ready and its return value has
        been collected."""
        # Acknowledge the task as being processed.
        on_ack()

        if isinstance(ret_value, ExceptionInfo):
            if isinstance(ret_value.exception, (
                    SystemExit, KeyboardInterrupt)):
                raise ret_value.exception
            [errback(ret_value) for errback in errbacks]
        else:
            [callback(ret_value) for callback in callbacks]