Mules are worker processes living in the uWSGI stack but not reachable via socket connections, that can be used as a generic subsystem to offload tasks. You can see them as a more primitive spooler.
They can access the entire uWSGI API and can manage signals and be communicated with through a simple string-based message system.
To start a mule (you can start an unlimited number of them), use the mule option as many times as you need.
Mules have two modes,
- Signal only mode (the default). In this mode the mules load your application as normal workers would. They can only respond to uWSGI signals.
- Programmed mode. In this mode mules load a program separate from your application. See ProgrammedMules.
By default each mule starts in signal-only mode.
uwsgi --socket :3031 --mule --mule --mule --mule
<uwsgi> <socket>:3031</socket> <mule/> <mule/> <mule/> <mule/> </uwsgi>
import uwsgi from uwsgidecorators import timer, signal, filemon # run a timer in the first available mule @timer(30, target='mule') def hello(signum): print "Hi! I am responding to signal %d, running on mule %d" % (signum, uwsgi.mule_id()) # map signal 17 to mule 2 @signal(17, target='mule2') def i_am_mule2(signum): print "Greetings! I am running in mule number two." # monitor /tmp and arouse all of the mules on modifications @filemon('/tmp', target='mules') def tmp_modified(signum): print "/tmp has been modified. I am mule %d!" % uwsgi.mule_id()
Giving a brain to mules¶
As mentioned before, mules can be programmed. To give custom logic to a mule, pass the name of a script to the mule option.
uwsgi --socket :3031 --mule=somaro.py --mule --mule --mule
This will run 4 mules, 3 in signal-only mode and one running somaro.py.
# somaro.py from threading import Thread import time def loop1(): while True: print "loop1: Waiting for messages... yawn." message = uwsgi.mule_get_msg() print message def loop2(): print "Hi! I am loop2." while True: time.sleep(2) print "This is a thread!" t = Thread(target=loop2) t.daemon = True t.start() if __name__ == '__main__': loop1()
So as you can see from the example, you can use mule_get_msg() to receive messages in a programmed mule. Multiple threads in the same programmed mule can wait for messages.
If you want to block a mule to wait on an uWSGI signal instead of a message you can use uwsgi.signal_wait().
Use uwsgi.mule_msg() to send a message to a programmed mule. Mule messages can be sent from anywhere in the uWSGI stack, including but not limited to workers, the spoolers, another mule.
# Send the string "ciuchino" to mule1. # If you do not specify a mule ID, the message will be processed by the first available programmed mule. uwsgi.mule_msg("ciuchino", 1)
As you can spawn an unlimited number of mules, you may need some form of synchronization – for example if you are developing a task management subsystem and do not want two mules to be able to start the same task simultaneously. You’re in luck – see Locks.