openstack/manila
Code Issues Proposed changes

Merge "Adjust doc about threading"

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Jenkins 2016-09-28 15:30:58 +00:00 committed by Gerrit Code Review
commit 297d8bef3b
1 changed files with 11 additions and 4 deletions

15
doc/source/devref/threading.rst

@ -32,13 +32,19 @@ delays in the case that there is only a single green thread::
...
greenthread.sleep(0)
In current code, time.sleep(0) does the same thing as greenthread.sleep(0)
if time module is patched through eventlet.monkey_patch(). To be explicit,
we recommend contributors to use ``greenthread.sleep()`` instead of
``time.sleep()``.
MySQL access and eventlet
-------------------------
Queries to the MySQL database will block the main thread of a service. This is
because OpenStack services use an external C library for accessing the MySQL
database. Since eventlet cannot use monkey-patching to intercept blocking
calls in a C library, the resulting database query blocks the thread.
There are some MySQL DB API drivers for oslo.db, like `PyMySQL`_, MySQL-python,
etc. PyMySQL is the default MySQL DB API driver for oslo.db, and it works well
with eventlet. MySQL-python uses an external C library for accessing the MySQL
database. Since eventlet cannot use monkey-patching to intercept blocking calls
in a C library, queries to the MySQL database will block the main thread of a
service.
The Diablo release contained a thread-pooling implementation that did not
block, but this implementation resulted in a `bug`_ and was removed.
@ -49,3 +55,4 @@ a discussion of the `impact on performance`_.
.. _bug: https://bugs.launchpad.net/manila/+bug/838581
.. _mailing list thread: https://lists.launchpad.net/openstack/msg08118.html
.. _impact on performance: https://lists.launchpad.net/openstack/msg08217.html
.. _PyMySQL: https://wiki.openstack.org/wiki/PyMySQL_evaluation