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

2.6 版后已移除: 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.
