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SF bug #690377: Dud footnote reference in distutils docs
author Raymond Hettinger <python@rcn.com>
date Fri, 21 Feb 2003 02:47:09 +0000
parents 37ffce2d9c3c
children 63fa60f2d61c
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1 """Mutual exclusion -- for use with module sched
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2
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3 A mutex has two pieces of state -- a 'locked' bit and a queue.
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4 When the mutex is not locked, the queue is empty.
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5 Otherwise, the queue contains 0 or more (function, argument) pairs
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6 representing functions (or methods) waiting to acquire the lock.
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7 When the mutex is unlocked while the queue is not empty,
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8 the first queue entry is removed and its function(argument) pair called,
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9 implying it now has the lock.
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10
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11 Of course, no multi-threading is implied -- hence the funny interface
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12 for lock, where a function is called once the lock is aquired.
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13 """
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14
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15 class mutex:
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16 def __init__(self):
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17 """Create a new mutex -- initially unlocked."""
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18 self.locked = 0
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19 self.queue = []
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20
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21 def test(self):
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22 """Test the locked bit of the mutex."""
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23 return self.locked
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24
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25 def testandset(self):
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26 """Atomic test-and-set -- grab the lock if it is not set,
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27 return True if it succeeded."""
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28 if not self.locked:
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29 self.locked = 1
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30 return True
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31 else:
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32 return False
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33
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34 def lock(self, function, argument):
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35 """Lock a mutex, call the function with supplied argument
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36 when it is acquired. If the mutex is already locked, place
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37 function and argument in the queue."""
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38 if self.testandset():
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39 function(argument)
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40 else:
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41 self.queue.append((function, argument))
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42
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43 def unlock(self):
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44 """Unlock a mutex. If the queue is not empty, call the next
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45 function with its argument."""
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46 if self.queue:
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47 function, argument = self.queue.pop(0)
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48 function(argument)
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49 else:
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50 self.locked = 0