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I have read the documentation of uWSGI mules, and some info from other sources. But I'm confused about the differences between mules and python threads. Can anyone explain to me, what can mules do that threads cannot and why do mules even exist?

Sargsyan Grigor
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uWSGI mule can be thought of as a separate worker process, which is not accessible via sockets (eg. direct web requests). It executes an instance of your application and can be used for offloading tasks using mulefunc Python decorator for example. Also, as mentioned in the documentation, mule can be configured to execute custom logic.

On the other hand, a thread runs in its parent's (uWSGI worker) address space. So if the worker dies or is reloaded, the thread behaves the same way. It can handle requests and also can execute specified tasks (functions) via thread decorator.

Vladimir Poghosyan
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Python threads do no span on multiple CPUs, roughly said can't use all the CPU power, this is a Python GIL limitation What is the global interpreter lock (GIL) in CPython?

This is one of the reasons for using web servers, their duty is to spawn a process worker or use idle one for each task received (http request).

A mule function on the same principal, but is particular in a sense that it is intended to run tasks outside of an http request context. the idea behind, is that you could reserve some mules, each will be running in a separate process (span on multiple CPUs) as regular workers do, but they don't serve any http request, only tasks to be setup as mentioned in the uwsgi documentation.

Worth to mention that mules are also monitored by the master process of the web server, such they are respawned when killed or dead.

ollofx
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