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======
PyMongo supports `Gevent <http://www.gevent.org/>`_. Simply call Gevent's
``monkey.patch_all()`` before loading any other modules:
.. doctest::
>>> # You must call patch_all() *before* importing any other modules
>>> from gevent import monkey
>>> monkey.patch_all()
>>> from pymongo import MongoClient
>>> client = MongoClient()
PyMongo uses thread and socket functions from the Python standard library.
Gevent's monkey-patching replaces those standard functions so that PyMongo
does asynchronous I/O with non-blocking sockets, and schedules operations
on greenlets instead of threads.
Avoid blocking in Hub.join
--------------------------
By default, PyMongo uses threads to discover and monitor your servers' topology
(see :ref:`health-monitoring`). If you execute ``monkey.patch_all()`` when
your application first begins, PyMongo automatically uses greenlets instead
of threads.
When shutting down, if your application calls :meth:`~gevent.hub.Hub.join` on
Gevent's :class:`~gevent.hub.Hub` without first terminating these background
greenlets, the call to :meth:`~gevent.hub.Hub.join` blocks indefinitely. You
therefore **must close or dereference** any active
:class:`~pymongo.mongo_client.MongoClient` before exiting.
An example solution to this issue in some application frameworks is a signal
handler to end background greenlets when your application receives SIGHUP:
.. code-block:: python
import signal
def graceful_reload(signum, traceback):
"""Explicitly close some global MongoClient object."""
client.close()
signal.signal(signal.SIGHUP, graceful_reload)
Applications using uWSGI prior to 1.9.16 are affected by this issue,
or newer uWSGI versions with the ``-gevent-wait-for-hub`` option.
See `the uWSGI changelog for details
<http://uwsgi-docs.readthedocs.org/en/latest/Changelog-1.9.16.html#important-change-in-the-gevent-plugin-shutdown-reload-procedure>`_.
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