"""Mutual exclusion -- for use with module sched

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A mutex has two pieces of state -- a 'locked' bit and a queue.

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When the mutex is not locked, the queue is empty.

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Otherwise, the queue contains 0 or more (function, argument) pairs

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representing functions (or methods) waiting to acquire the lock.

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When the mutex is unlocked while the queue is not empty,

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the first queue entry is removed and its function(argument) pair called,

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implying it now has the lock.

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Of course, no multi-threading is implied -- hence the funny interface

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for lock, where a function is called once the lock is acquired.

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"""

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from warnings import warnpy3k

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warnpy3k("the mutex module has been removed in Python 3.0", stacklevel=2)

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del warnpy3k

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from collections import deque

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class mutex:

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def __init__(self):

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"""Create a new mutex -- initially unlocked."""

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self.locked = False

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self.queue = deque()

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def test(self):

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"""Test the locked bit of the mutex."""

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return self.locked

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def testandset(self):

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"""Atomic test-and-set -- grab the lock if it is not set,

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return True if it succeeded."""

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if not self.locked:

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self.locked = True

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return True

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else:

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return False

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def lock(self, function, argument):

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"""Lock a mutex, call the function with supplied argument

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when it is acquired. If the mutex is already locked, place

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function and argument in the queue."""

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if self.testandset():

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function(argument)

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else:

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self.queue.append((function, argument))

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def unlock(self):

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"""Unlock a mutex. If the queue is not empty, call the next

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function with its argument."""

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if self.queue:

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function, argument = self.queue.popleft()

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function(argument)

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else:

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self.locked = False

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