8.9. mutex — Mutual exclusion support

Deprecated since version 2.6: The mutex module has been removed in Python 3.

The mutex module defines a class that allows mutual-exclusion via acquiring and releasing locks. It does not require (or imply) threading or multi-tasking, though it could be useful for those purposes.

The mutex module defines the following class:

class mutex.mutex

Create a new (unlocked) mutex.

A mutex has two pieces of state — a “locked” bit and a queue. When the mutex is not locked, the queue is empty. Otherwise, the queue contains zero or more (function, argument) pairs representing functions (or methods) waiting to acquire the lock. When the mutex is unlocked while the queue is not empty, the first queue entry is removed and its function(argument) pair called, implying it now has the lock.

Of course, no multi-threading is implied – hence the funny interface for lock(), where a function is called once the lock is acquired.

8.9.1. Mutex Objects

mutex objects have following methods:


Check whether the mutex is locked.


“Atomic” test-and-set, grab the lock if it is not set, and return True, otherwise, return False.

mutex.lock(function, argument)

Execute function(argument), unless the mutex is locked. In the case it is locked, place the function and argument on the queue. See unlock() for explanation of when function(argument) is executed in that case.


Unlock the mutex if queue is empty, otherwise execute the first element in the queue.