The Gevent loop engine
======================
`Gevent`_ is an amazing non-blocking Python network library built on top of
``libev`` and ``greenlet``. Even though uWSGI supports Greenlet as
suspend-resume/greenthread/coroutine library, it requires a lot of effort and
code modifications to work with gevent. The gevent plugin requires gevent
1.0.0 and :doc:`Async` mode.
.. _Gevent: http://www.gevent.org
Notes
-----
* The :doc:`SignalFramework` is fully working with Gevent mode. Each handler
will be executed in a dedicated greenlet. Look at :file:`tests/ugevent.py` for
an example.
* uWSGI multithread mode (``threads`` option) will not work with Gevent.
Running Python threads in your apps is supported.
* Mixing uWSGI's Async API with gevent's is **EXPLICITLY FORBIDDEN**.
Building the plugin (uWSGI >= 1.4)
----------------------------------
The gevent plugin is compiled in by default when the default profile is used.
Doing the following will install the python plugin as well as the gevent one:
.. code-block:: sh
pip install uwsgi
Building the plugin (uWSGI < 1.4)
---------------------------------
A 'gevent' build profile can be found in the :file:`buildconf` directory.
.. code-block:: sh
python uwsgiconfig --build gevent
# or...
UWSGI_PROFILE=gevent make
# or...
UWSGI_PROFILE=gevent pip install git+git://github.com/unbit/uwsgi.git
# or...
python uwsgiconfig --plugin plugins/gevent # external plugin
Running uWSGI in gevent mode
----------------------------
.. code-block:: sh
uwsgi --gevent 100 --socket :3031 --module myapp
or for a modular build:
.. code-block:: sh
uwsgi --plugins python,gevent --gevent 100 --socket :3031 --module myapp
the argument of --gevent is the number of async cores to spawn
A crazy example
---------------
The following example shows how to sleep in a request, how to make asynchronous
network requests and how to continue doing logic after a request has been
closed.
.. code-block:: python
import gevent
import gevent.socket
def bg_task():
for i in range(1,10):
print "background task", i
gevent.sleep(2)
def long_task():
for i in range(1,10):
print i
gevent.sleep()
def application(e, sr):
sr('200 OK', [('Content-Type','text/html')])
t = gevent.spawn(long_task)
t.join()
yield "sleeping for 3 seconds...
"
gevent.sleep(3)
yield "done
"
yield "getting some ips...
"
urls = ['www.google.com', 'www.example.com', 'www.python.org', 'projects.unbit.it']
jobs = [gevent.spawn(gevent.socket.gethostbyname, url) for url in urls]
gevent.joinall(jobs, timeout=2)
for j in jobs:
yield "ip = %s
" % j.value
gevent.spawn(bg_task) # this task will go on after request end
Monkey patching
---------------
uWSGI uses native gevent api, so it does not need monkey patching. That said,
your code may need it, so remember to call ``gevent.monkey.patch_all()`` at the
start of your app. As of uWSGI 1.9, the convenience option
``--gevent-monkey-patch`` will do that for you.
Please note that uWSGI does monkey patching before your application **starts**,
not before your application **loads**. So if you are loading other modules
while loading your application you may still need to call
``gevent.monkey.patch_all()`` yourself.
A common example is using ``psycopg2_gevent`` with django. Django will make a
connection to postgres for each thread (storing it in thread locals).
As the uWSGI gevent plugin runs on a single thread this approach will lead to a
deadlock in psycopg. Enabling monkey patch will allow you to map thread locals
to greenlets (though you could avoid full monkey patching and only call
``gevent.monkey.patch_thread()``) and solves the issue:
.. code-block:: python
import gevent.monkey
gevent.monkey.patch_thread()
import gevent_psycopg2
gevent_psycopg2.monkey_patch()
or (to monkey patch everything)
.. code-block:: python
import gevent.monkey
gevent.monkey.patch_all()
import gevent_psycopg2
gevent_psycopg2.monkey_patch()
Notes on clients and frontends
------------------------------
* If you're testing a WSGI application that generates a stream of data, you
should know that ``curl`` by default buffers data until a newline. So make sure
you either disable curl's buffering with the ``-N`` flag or have regular
newlines in your output.
* If you are using Nginx in front of uWSGI and wish to stream data from your
app, you'll probably want to disable Nginx's buffering.
.. code-block:: nginx
uwsgi_buffering off;