Andy Galasso 480b77dfe4 AttributeError when start_event is None, and guard process faster stop (#305)
* AttributeError when start_event is None, and guard process faster stop

This commit has two related fixes that come into play when frequently
shutting down and restarting the cluster.

If a SIGINT or SIGTERM signal is received while the main process is
waiting for the sentinel process to set start_event, the signal
handler sets start_event to None, and the loop that polls start_event
will raise an unhandled AttributeError attempting to check
start_event.is_set().

The second issue is that the guard process sleeps for the guard cycle
interval in each iteration before checking the stop event, preventing
the guard cycle from terminating until the sleep completes. The
cluster can be made more responsive to a shutdown request by using
the event's wait(cycle) method rather than time.sleep(cycle) so the
process wakes immediately when the event is set.

The commit also fixes the case where the guard process sleeps for an
extra cycle when the cycle counter happens to have been reset to zero
on the loop iterations when the scheduler is called.

This fix helps in our environment where we are frequently stopping
and starting the cluster and where we have increased the guard
cycle setting to several seconds.

* Add sentinel premature death check while waiting for sentinel to start.

Suggested by github copilot [here](https://github.com/django-q2/django-q2/pull/305/changes#r3143964420)

* Add test case test_cluster_early_stop

Add a test case to validate stopping the cluster before the
sentinel has set the cluster's start_event.

The test deterministically triggers the AttributeError when
start_event is None (without the PR's fix in cluster.py).

As requested by copilot: https://github.com/django-q2/django-q2/pull/305#discussion_r3143964399

* Add test test_cluster_stop_responsive

Ensure that stopping the cluster is responsive and does not wait for a full
GUARD_CYCLE to stop the cluster.

As requested by copilot: https://github.com/django-q2/django-q2/pull/305/changes#r3143964414

* Address copilot review comments.

1. Do not raise RuntimeError if sentinel early exit was caused by
   SIGINT/SIGTERM stopping the cluster while waiting for the
   sentinel to start.
   Addresses https://github.com/django-q2/django-q2/pull/305#discussion_r3298618046

2. Ensure that the monkeypatched broker instance remains pickleable
   so the test_cluster_early_stop test will also work on platforms
   that use the spawn Process start method.
   Addresses https://github.com/django-q2/django-q2/pull/305#discussion_r3298618086

3. Do not allow the test_cluster_early_stop test to hang if the
   sentinel process or main test process terminates unexpectedly
   without setting the sentinel_event or test_event.
   Addresses https://github.com/django-q2/django-q2/pull/305#discussion_r3298618102
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2022-11-16 01:45:40 +01:00

A multiprocessing distributed task queue for Django
---------------------------------------------------

|image0| |image1| |downloads|

Django Q2 is a fork of Django Q. Big thanks to Ilan Steemers for starting this project. Unfortunately, development has stalled since June 2021. Django Q2 is the new updated version of Django Q, with dependencies updates, docs updates and several bug fixes. Original repository: https://github.com/Koed00/django-q

Features
~~~~~~~~

-  Multiprocessing worker pool
-  Asynchronous tasks
-  Scheduled, cron and repeated tasks
-  Signed and compressed packages
-  Failure and success database or cache
-  Result hooks, groups and chains
-  Django Admin integration
-  PaaS compatible with multiple instances
-  Multi cluster monitor
-  Redis, IronMQ, SQS, MongoDB or ORM
-  Rollbar and Sentry support

Changes compared to the original Django-Q:

- Dropped support for Disque (hasn't been updated in a long time)
- Dropped Redis, Arrow and Blessed dependencies
- Updated all current dependencies
- Added tests for Django 4.x and 5.x
- Added Turkish language
- Improved admin area
- Fixed a lot of issues

See the `changelog <https://github.com/GDay/django-q2/blob/master/CHANGELOG.md>`__ for all changes.

Requirements
~~~~~~~~~~~~

-  `Django <https://www.djangoproject.com>`__ > = 4.2
-  `Django-picklefield <https://github.com/gintas/django-picklefield>`__

Tested with:

* Python 3.9 to 3.13.
* Django 4.2 to 6.0.

Brokers
~~~~~~~
- `Redis <https://django-q2.readthedocs.org/en/latest/brokers.html#redis>`__
- `IronMQ <https://django-q2.readthedocs.org/en/latest/brokers.html#ironmq>`__
- `Amazon SQS <https://django-q2.readthedocs.org/en/latest/brokers.html#amazon-sqs>`__
- `MongoDB <https://django-q2.readthedocs.org/en/latest/brokers.html#mongodb>`__
- `Django ORM <https://django-q2.readthedocs.org/en/latest/brokers.html#django-orm>`__

Installation
~~~~~~~~~~~~

-  Install the latest version with pip::

    $ pip install django-q2


-  Add `django_q` to your `INSTALLED_APPS` in your projects `settings.py`::

       INSTALLED_APPS = (
           # other apps
           'django_q',
       )

-  Run Django migrations to create the database tables::

    $ python manage.py migrate

-  Choose a message `broker <https://django-q2.readthedocs.org/en/latest/brokers.html>`__, configure and install the appropriate client library.

Read the full documentation at `https://django-q2.readthedocs.org <https://django-q2.readthedocs.org>`__

Configuration
~~~~~~~~~~~~~

All configuration settings are optional. e.g:

.. code:: python

    # settings.py example
    Q_CLUSTER = {
        'name': 'myproject',
        'workers': 8,
        'recycle': 500,
        'timeout': 60,
        'compress': True,
        'cpu_affinity': 1,
        'save_limit': 250,
        'queue_limit': 500,
        'label': 'Django Q',
        'redis': {
            'host': '127.0.0.1',
            'port': 6379,
            'db': 0,
        }
    }

For full configuration options, see the `configuration documentation <https://django-q2.readthedocs.org/en/latest/configure.html>`__.

Management Commands
~~~~~~~~~~~~~~~~~~~

For the management commands to work, you will need to install Blessed: <https://github.com/jquast/blessed>

Start a cluster with::

    $ python manage.py qcluster

Monitor your clusters with::

    $ python manage.py qmonitor

Monitor your clusters' memory usage with::

    $ python manage.py qmemory

Check overall statistics with::

    $ python manage.py qinfo

Creating Tasks
~~~~~~~~~~~~~~

Use `async_task` from your code to quickly offload tasks:

.. code:: python

    from django_q.tasks import async_task, result

    # create the task
    async_task('math.copysign', 2, -2)

    # or with a reference
    import math.copysign

    task_id = async_task(copysign, 2, -2)

    # get the result
    task_result = result(task_id)

    # result returns None if the task has not been executed yet
    # you can wait for it
    task_result = result(task_id, 200)

    # but in most cases you will want to use a hook:

    async_task('math.modf', 2.5, hook='hooks.print_result')

    # hooks.py
    def print_result(task):
        print(task.result)

For more info see `Tasks <https://django-q2.readthedocs.org/en/latest/tasks.html>`__

Schedule
~~~~~~~~

Schedules are regular Django models. You can manage them through the
Admin page or directly from your code:

.. code:: python

    # Use the schedule function
    from django_q.tasks import schedule

    schedule('math.copysign',
             2, -2,
             hook='hooks.print_result',
             schedule_type=Schedule.DAILY)

    # Or create the object directly
    from django_q.models import Schedule

    Schedule.objects.create(func='math.copysign',
                            hook='hooks.print_result',
                            args='2,-2',
                            schedule_type=Schedule.DAILY
                            )

    # Run a task every 5 minutes, starting at 6 today
    # for 2 hours
    from datetime import datetime

    schedule('math.hypot',
             3, 4,
             schedule_type=Schedule.MINUTES,
             minutes=5,
             repeats=24,
             next_run=datetime.utcnow().replace(hour=18, minute=0))

    # Use a cron expression
    schedule('math.hypot',
             3, 4,
             schedule_type=Schedule.CRON,
             cron = '0 22 * * 1-5')

For more info check the `Schedules <https://django-q2.readthedocs.org/en/latest/schedules.html>`__ documentation.

Development
~~~~~~~~~~~

There is an example project that you can use to develop with. Docker (compose) is being used to set everything up.
Please note that you will have to restart the django-q container when changes have been made to tasks or django-q.
You can start the example project with:

.. code:: bash

    make dev

Create a superuser with:

.. code:: bash

    make createsuperuser

Testing
~~~~~~~

Running tests is easy with docker compose, it will also start the necessary databases. Just run:

.. code:: bash

    make test

Locale
~~~~~~

Currently available in English, German, Turkish, and French.
Translation pull requests are always welcome.

Acknowledgements
~~~~~~~~~~~~~~~~

-  Django Q was inspired by working with
   `Django-RQ <https://github.com/ui/django-rq>`__ and
   `RQ <https://github.com/ui/django-rq>`__
-  Human readable hashes by
   `HumanHash <https://github.com/zacharyvoase/humanhash>`__
-  Redditors feedback at `r/django <https://www.reddit.com/r/django/>`__

-  JetBrains for their `Open Source Support Program <https://www.jetbrains.com/community/opensource>`__

.. |image0| image:: https://github.com/GDay/django-q2/actions/workflows/test.yml/badge.svg?branche=master
   :target: https://github.com/GDay/django-q2/actions?query=workflow%3Atests
.. |image1| image:: https://coveralls.io/repos/github/GDay/django-q2/badge.svg?branch=master
   :target: https://coveralls.io/github/GDay/django-q2?branch=master
.. |downloads| image:: https://img.shields.io/pypi/dm/django-q2
   :target: https://img.shields.io/pypi/dm/django-q2
Description
A multiprocessing distributed task queue for Django based on Django-Q
Readme MIT 4.8 MiB
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