celery/celery/backends/amqp.py

# -*- coding: utf-8 -*-
"""
    celery.backends.amqp
    ~~~~~~~~~~~~~~~~~~~~

    The AMQP result backend.

    This backend publishes results as messages.

"""
from __future__ import absolute_import

import socket
import threading
import time

from collections import deque
from operator import itemgetter

from kombu import Exchange, Queue, Producer, Consumer

from celery import states
from celery.exceptions import TimeoutError
from celery.five import range
from celery.utils.log import get_logger

from .base import BaseBackend

logger = get_logger(__name__)


class BacklogLimitExceeded(Exception):
    """Too much state history to fast-forward."""


def repair_uuid(s):
    # Historically the dashes in UUIDS are removed from AMQ entity names,
    # but there is no known reason to.  Hopefully we'll be able to fix
    # this in v4.0.
    return '%s-%s-%s-%s-%s' % (s[:8], s[8:12], s[12:16], s[16:20], s[20:])


class AMQPBackend(BaseBackend):
    """Publishes results by sending messages."""
    Exchange = Exchange
    Queue = Queue
    Consumer = Consumer
    Producer = Producer

    BacklogLimitExceeded = BacklogLimitExceeded

    supports_autoexpire = True
    supports_native_join = True

    retry_policy = {
        'max_retries': 20,
        'interval_start': 0,
        'interval_step': 1,
        'interval_max': 1,
    }

    def __init__(self, app, connection=None, exchange=None, exchange_type=None,
                 persistent=None, serializer=None, auto_delete=True,
                 **kwargs):
        super(AMQPBackend, self).__init__(app, **kwargs)
        conf = self.app.conf
        self._connection = connection
        self.queue_arguments = {}
        self.persistent = (conf.CELERY_RESULT_PERSISTENT if persistent is None
                           else persistent)
        exchange = exchange or conf.CELERY_RESULT_EXCHANGE
        exchange_type = exchange_type or conf.CELERY_RESULT_EXCHANGE_TYPE
        self.exchange = self._create_exchange(exchange, exchange_type,
                                              self.persistent)
        self.serializer = serializer or conf.CELERY_RESULT_SERIALIZER
        self.auto_delete = auto_delete

        self.expires = None
        if 'expires' not in kwargs or kwargs['expires'] is not None:
            self.expires = self.prepare_expires(kwargs.get('expires'))
        if self.expires:
            self.queue_arguments['x-expires'] = int(self.expires * 1000)
        self.mutex = threading.Lock()

    def _create_exchange(self, name, type='direct', persistent=True):
        delivery_mode = persistent and 'persistent' or 'transient'
        return self.Exchange(name=name,
                             type=type,
                             delivery_mode=delivery_mode,
                             durable=self.persistent,
                             auto_delete=False)

    def _create_binding(self, task_id):
        name = task_id.replace('-', '')
        return self.Queue(name=name,
                          exchange=self.exchange,
                          routing_key=name,
                          durable=self.persistent,
                          auto_delete=self.auto_delete,
                          queue_arguments=self.queue_arguments)

    def revive(self, channel):
        pass

    def _routing_key(self, task_id):
        return task_id.replace('-', '')

    def _store_result(self, task_id, result, status, traceback=None):
        """Send task return value and status."""
        with self.mutex:
            with self.app.amqp.producer_pool.acquire(block=True) as pub:
                pub.publish({'task_id': task_id, 'status': status,
                             'result': self.encode_result(result, status),
                             'traceback': traceback,
                             'children': self.current_task_children()},
                            exchange=self.exchange,
                            routing_key=self._routing_key(task_id),
                            serializer=self.serializer,
                            retry=True, retry_policy=self.retry_policy,
                            declare=self.on_reply_declare(task_id))
        return result

    def on_reply_declare(self, task_id):
        return [self._create_binding(task_id)]

    def wait_for(self, task_id, timeout=None, cache=True, propagate=True,
                 READY_STATES=states.READY_STATES,
                 PROPAGATE_STATES=states.PROPAGATE_STATES,
                 **kwargs):
        cached_meta = self._cache.get(task_id)
        if cache and cached_meta and \
                cached_meta['status'] in READY_STATES:
            meta = cached_meta
        else:
            try:
                meta = self.consume(task_id, timeout=timeout)
            except socket.timeout:
                raise TimeoutError('The operation timed out.')

        if meta['status'] in PROPAGATE_STATES and propagate:
            raise self.exception_to_python(meta['result'])
        # consume() always returns READY_STATE.
        return meta['result']

    def get_task_meta(self, task_id, backlog_limit=1000):
        # Polling and using basic_get
        with self.app.pool.acquire_channel(block=True) as (_, channel):
            binding = self._create_binding(task_id)(channel)
            binding.declare()

            prev = latest = acc = None
            for i in range(backlog_limit):  # spool ffwd
                prev, latest, acc = latest, acc, binding.get(no_ack=False)
                if not acc:  # no more messages
                    break
                if prev:
                    # backends are not expected to keep history,
                    # so we delete everything except the most recent state.
                    prev.ack()
            else:
                raise self.BacklogLimitExceeded(task_id)

            if latest:
                payload = self._cache[task_id] = latest.payload
                latest.requeue()
                return payload
            else:
                # no new state, use previous
                try:
                    return self._cache[task_id]
                except KeyError:
                    # result probably pending.
                    return {'status': states.PENDING, 'result': None}
    poll = get_task_meta  # XXX compat

    def drain_events(self, connection, consumer,
                     timeout=None, now=time.time, wait=None):
        wait = wait or connection.drain_events
        results = {}

        def callback(meta, message):
            if meta['status'] in states.READY_STATES:
                results[meta['task_id']] = meta

        consumer.callbacks[:] = [callback]
        time_start = now()

        while 1:
            # Total time spent may exceed a single call to wait()
            if timeout and now() - time_start >= timeout:
                raise socket.timeout()
            wait(timeout=timeout)
            if results:  # got event on the wanted channel.
                break
        self._cache.update(results)
        return results

    def consume(self, task_id, timeout=None):
        wait = self.drain_events
        with self.app.pool.acquire_channel(block=True) as (conn, channel):
            binding = self._create_binding(task_id)
            with self.Consumer(channel, binding, no_ack=True) as consumer:
                while 1:
                    try:
                        return wait(conn, consumer, timeout)[task_id]
                    except KeyError:
                        continue

    def _many_bindings(self, ids):
        return [self._create_binding(task_id) for task_id in ids]

    def get_many(self, task_ids, timeout=None,
                 now=time.time, getfields=itemgetter('status', 'task_id'),
                 READY_STATES=states.READY_STATES, **kwargs):
        with self.app.pool.acquire_channel(block=True) as (conn, channel):
            ids = set(task_ids)
            cached_ids = set()
            mark_cached = cached_ids.add
            for task_id in ids:
                try:
                    cached = self._cache[task_id]
                except KeyError:
                    pass
                else:
                    if cached['status'] in READY_STATES:
                        yield task_id, cached
                        mark_cached(task_id)
            ids.difference_update(cached_ids)
            results = deque()
            push_result = results.append
            push_cache = self._cache.__setitem__

            def on_message(message):
                body = message.decode()
                state, uid = getfields(body)
                if state in READY_STATES:
                    push_result(body) \
                        if uid in task_ids else push_cache(uid, body)

            bindings = self._many_bindings(task_ids)
            with self.Consumer(channel, bindings,
                               on_message=on_message, no_ack=True):
                wait = conn.drain_events
                popleft = results.popleft
                while ids:
                    wait(timeout=timeout)
                    while results:
                        state = popleft()
                        task_id = state['task_id']
                        ids.discard(task_id)
                        push_cache(task_id, state)
                        yield task_id, state

    def reload_task_result(self, task_id):
        raise NotImplementedError(
            'reload_task_result is not supported by this backend.')

    def reload_group_result(self, task_id):
        """Reload group result, even if it has been previously fetched."""
        raise NotImplementedError(
            'reload_group_result is not supported by this backend.')

    def save_group(self, group_id, result):
        raise NotImplementedError(
            'save_group is not supported by this backend.')

    def restore_group(self, group_id, cache=True):
        raise NotImplementedError(
            'restore_group is not supported by this backend.')

    def delete_group(self, group_id):
        raise NotImplementedError(
            'delete_group is not supported by this backend.')

    def __reduce__(self, args=(), kwargs={}):
        kwargs.update(
            connection=self._connection,
            exchange=self.exchange.name,
            exchange_type=self.exchange.type,
            persistent=self.persistent,
            serializer=self.serializer,
            auto_delete=self.auto_delete,
            expires=self.expires,
        )
        return super(AMQPBackend, self).__reduce__(args, kwargs)