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:mod:`mutex` --- Mutual exclusion support
=========================================
.. module:: mutex
:synopsis: Lock and queue for mutual exclusion.
.. sectionauthor:: Moshe Zadka <moshez@zadka.site.co.il>
The :mod:`mutex` module defines a class that allows mutual-exclusion via
acquiring and releasing locks. It does not require (or imply)
:mod:`threading` or multi-tasking, though it could be useful for those
purposes.
The :mod:`mutex` module defines the following class:
.. class:: 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
:meth:`lock`, where a function is called once the lock is acquired.
.. _mutex-objects:
Mutex Objects
-------------
:class:`mutex` objects have following methods:
.. method:: mutex.test()
Check whether the mutex is locked.
.. method:: mutex.testandset()
"Atomic" test-and-set, grab the lock if it is not set, and return ``True``,
otherwise, return ``False``.
.. method:: 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 :meth:`unlock` for
explanation of when ``function(argument)`` is executed in that case.
.. method:: mutex.unlock()
Unlock the mutex if queue is empty, otherwise execute the first element in the
queue.
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