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Merge "Extend decision engine to support threading mode"

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Zuul
2025-08-06 15:38:31 +00:00
committed by Gerrit Code Review
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doc/source/contributor/concurrency.rst
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@@ -52,18 +52,43 @@ types of concurrency used in various services of Watcher.
.. _wait_for_any: https://docs.openstack.org/futurist/latest/reference/index.html#waiters
Concurrency modes
#################
Evenlet has been the main concurrency library within the OpenStack community
for the last 10 years since the removal of twisted. Over the last few years,
the maintenance of eventlet has decreased and the efforts to remove the GIL
from Python (PEP 703), have fundamentally changed how concurrency is making
eventlet no longer viable. While transitioning to a new native thread
solution, Watcher services will be supporting both modes, with the usage of
native threading mode initially classified as ``experimental``.
It is possible to enable the new native threading mode by setting the following
environment variable in the corresponding service configuration:
.. code:: bash
OS_WATCHER_DISABLE_EVENTLET_PATCHING=true
.. note::
The only service that supports two different concurrency modes is the
``decision engine``.
Decision engine concurrency
***************************
The concurrency in the decision engine is governed by two independent
threadpools. Both of these threadpools are GreenThreadPoolExecutor_ from the
futurist_ library. One of these is used automatically and most contributors
threadpools. These threadpools can be configured as GreenThreadPoolExecutor_
or ThreadPoolExecutor_, both from the futurist_ library, depending on the
service configuration. One of these is used automatically and most contributors
will not interact with it while developing new features. The other threadpool
can frequently be used while developing new features or updating existing ones.
It is known as the DecisionEngineThreadpool and allows to achieve performance
improvements in network or I/O bound operations.
.. _GreenThreadPoolExecutor: https://docs.openstack.org/futurist/latest/reference/index.html#executors
.. _GreenThreadPoolExecutor: https://docs.openstack.org/futurist/latest/reference/index.html#futurist.GreenThreadPoolExecutor
.. _ThreadPoolExecutor: https://docs.openstack.org/futurist/latest/reference/index.html#futurist.ThreadPoolExecutor
AuditEndpoint
#############