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collective.taskqueue 0.5.1

Latest Version: 0.7.1

collective.taskqueue

Yet another way to queue and execute asynchronous tasks in Plone.

This is an experiment. Not yet battle tested.

collective.taskqueue enables asynchronous tasks in Plone add-ons by providing a small framework for asynchronously queueing requests to ZPublisher. With this aproachasynchronous tasks are just normal calls to normally registered browser views (or other traversable callables) and they authenticated using PAS as all the other requests.

In addition, it’s possible to configure views so that they are visible only for asynchronous requests. Also, collective.taskqueue ships with a special PAS-plugin, which authenticates each request as the user who queued it.

Minimal configuration:

zope-conf-additional =
    %import collective.taskqueue
    <taskqueue />
    <taskqueue-server />

Minimal configuration gives you one volatile instance-local queue and consumer, but no guarantee on delivery.

Minimal configuration with multiple queues:

zope-conf-additional =
    %import collective.taskqueue
    <taskqueue />
    <taskqueue-server />

    <taskqueue>
    queue mailhost
    </taskqueue>
    <taskqueue-server>
    queue mailhost
    </taskqueue-server>

Preferred minimal configration with Redis:

eggs =
    collective.taskqueue [redis]

zope-conf-additional =
    %import collective.taskqueue
    <taskqueue>
      type redis
      unix_socket_path ${buildout:directory}/var/redis.sock
    </taskqueue>
    <taskqueue-server>
      name ${:_buildout_section_name_}
    </taskqueue-server>

Redis-support gives you distributable queues, which can be shared between instances. All instances should have queue-specific <taskqueue />, but only the consuming instance requires <taskqueue-server />.

Example Redis configuration with multiple queues:

eggs =
    collective.taskqueue [redis]

zope-conf-additional =
    %import collective.taskqueue
    <taskqueue>
      type redis
      unix_socket_path ${buildout:directory}/var/redis.sock
    </taskqueue>
    <taskqueue-server>
      name ${:_buildout_section_name_}
    </taskqueue-server>
    <taskqueue>
      type redis
      queue mailhost
      unix_socket_path ${buildout:directory}/var/redis.sock
    </taskqueue>
    <taskqueue-server>
      queue mailhost
      name ${:_buildout_section_name_}
    </taskqueue-server>

It’s recommended to only use local Redis-installations, because remote connections can be killed by firewalls (there’s no ping or heartbeat to keep the connection alive thorugh enterprise firewalls).

Queue a task:

from collective.taskqueue import taskqueue
taskqueue.add('/Plone/path/to/my/view')

Tasks are queued (and consumed) after a successful transaction.

To make views visible only for asynchronous requests, views can be registered for a special layer collective.taskqueue.interfaces.ITaskQueueLayer, which is only found from requests dispatched by collective.taskqueue.

By default, taskqueue.add copies headers from the current requests to the asynchronous request. That should be enough to authenticate the requests in exactly the the same way as the current request was authenticated.

More robust authentication can be implemented with a custom PAS-plugin. collective.taskqueue ships with an optionally installable PAS-plugin, which authenticates each request as the user who queued it. To achieve this, collective.taskqueue appends X-Task-User-Id-header into the queued request.

Advanced configuration

Supported <taskqueue />-settings are:

queue (default=default)
Unique task queue name.
type (default=local)
Task queue type (‘local’ or ‘redis’) or full class path to a custom type.
unix_socket_path
Redis server unix socket path (use instead of host and port).

Other supported Redis-queue options are: host, port, db and password.

Supported <taskqueue-server />-settings are:

name (default=default)
Consumer name, preferably instance name. Consumer is name used by Redis-queues for reserving messages from queue to achieve quaranteed delivery.
queue (default=default)
Queue name for this consumer (consuming server). There must be a <taskqueue/> with matching queue-value registered.
concurrent_limit (default=1)
Maximum concurrent task limit for this consumer. It’s recommend to set this smaller than zserver-thread-count. Leaving this to the default (1) should give the best results in terms of minimal ConflictErrors.
retry_max_count (default=10)

Maximum ZPublisher retry count for requests dispatched by this consumer.

Note

Once this limit has been exceeded by ZPublisher, the conflicting task is permanently trashed. (An alternative behavior is possible by implementing a custom queue class.)

Advanced usage

taskqueue.add accepts the following arguments (with default value):

url (required, no default)
Target path representing the task to be called.
method (optional, default=GET)
HTTP-method for the call. Must be either GET or POST.
params (optional, default=None)
A dictionary of optional task arguments, which are appended as query string after the given url. (When params are provided, url must not already include any querystring).
headers (optional, default=None)
A dictionary of optional HTTP-headers to be appended to (or used to replace) the headers copied from the active request.
payload (optional, default=current)
An optional payload for POST-request. Payload from the active request will be copied by default. Copying the active payload can be prevented with payload=None.
queue (optional, default=alphabetically-first-registered-queue)
An optional queue name, when more than one queue is registered.

How Redis queueing works

  1. taskqueue.add prepares a message, which will be pushed (lpush) into key collective.taskqueue.%(queue)s (where %(queue)s` is the name of the queue) at the end of the transaction. If Redis connection is down during the transaction vote, the whole transaction is aborted.
  2. <taskqueue-server /> reads each message (rpoplpush) from queue so that they will remain in key collective.taskqueue.%(queue)s.%(name)s (where %(name)s is the name of the <taskqueue-server/>) until each asynchronous processing request has returned a HTTP response.
  3. On startup, and when all known messages have been processed, <taskqueue-server/> purges collective.taskqueue.%(queue)s.%(name)s into collective.taskqueue.%(queue)s (with rpoplpush) and those tasks are processed again. (E.g. if Plone was forced to restart in middle of task handling request.)

Redis integration uses PubSub to notify itself about new messages in queue (and get as instant handling as possible in terms of Plone’s asyncore-loop).

Changelog

0.5.1 (2014-05-14)

  • Fix issue where concurrent task counter mutex was not released due to uncaught exception [Asko Soukka]
  • Fix issue where a socket in asyncore.map was closed during asyncore.poll [Asko Soukka]

0.5.0 (2014-04-03)

  • Fix threading and execution order related issue where currently active Redis tasks were requeued (and processed more than once) [Asko Soukka]
  • Add ‘X-Task-Id’-header to help keeping track of tasks n consuming views [Asko Soukka]

0.4.4 (2013-11-25)

  • Fix regression where redis+msgpack where accidentally always required [#7] [Asko Soukka]
  • Update docs [Dylan Jay]
  • Fix default for ‘unix_socket_path’ [fixes #8] [Dylan Jay]

0.4.3 (2013-11-15)

  • Update README [Asko Soukka]

0.4.2 (2013-11-15)

  • Updated README [Asko Soukka]

0.4.1 (2013-11-14)

  • Updated README [Asko Soukka]

0.4.0 (2013-11-14)

  • Refactor configuration by replacing explicit utilities and <product-configuration/> with <taskqueue/>-component [Asko Soukka]

0.3.1 (2013-11-13)

  • Enhance acceptance testing support with the first acceptance tests [Asko Soukka]

0.3.0 (2013-11-10)

  • Fix TaskQueueServer to re-connect to Redis after Redis restart [Asko Soukka]
  • Fix to ping Redis on Zope start only in development mode [Asko Soukka]
  • Add optional Task Queue PAS plugin to independently authenticate queued tasks as their creator [Asko Soukka]

0.2.2 (2013-11-09)

  • Fix to flush Redis pub-notifications only when queue has been emptied to ensure that all messages will be processed [Asko Soukka]

0.2.1 (2013-11-09)

  • Fix taskqueue socket to be not readable by default [Asko Soukka]

0.2.0 (2013-11-09)

  • Enhance Redis-integration to connect redis notification pubsub-socket directly to asyncore on instant message handling [Asko Soukka]
  • Fix to require redis >= 2.4.10 [fixes #2] [Asko Soukka]
  • Fix to not start with clear error when clearly intending to use RedisTaskQueues without redis-dependencies. Also crash when cannot connect to Redis. [fixes #1] [Asko Soukka]

0.1.0 (2013-11-03)

  • First release for experimental use.
 
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