8.9. "mutex" — Mutual exclusion support
***************************************

2.6 版後已棄用: 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:

mutex.test()

   Check whether the mutex is locked.

mutex.testandset()

   「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.

mutex.unlock()

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