Showing content from http://svn.python.org/projects/python/tags/r14beta2/Lib/mutex.py below:
# Mutual exclusion -- for use with module sched # 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 0 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 aquired. # class mutex: # # Create a new mutex -- initially unlocked # def __init__(self): self.locked = 0 self.queue = [] # # Test the locked bit of the mutex # def test(self): return self.locked # # Atomic test-and-set -- grab the lock if it is not set, # return true if it succeeded # def testandset(self): if not self.locked: self.locked = 1 return 1 else: return 0 # # Lock a mutex, call the function with supplied argument # when it is acquired. # If the mutex is already locked, place function and argument # in the queue. # def lock(self, function, argument): if self.testandset(): function(argument) else: self.queue.append(function, argument) # # Unlock a mutex. If the queue is not empty, call the next # function with its argument. # def unlock(self): if self.queue: function, argument = self.queue[0] del self.queue[0] function(argument) else: self.locked = 0 #
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