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annotate Lib/mutex.py @ 80661:94de77bd0b4b 2.7

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Issue #16194: document imp.load_dynamic problems when read several extension modules from the same binary object file.
author Andrew Svetlov <andrew.svetlov@gmail.com>
date Thu, 29 Nov 2012 19:51:28 +0200
parents b674706f3b10
children
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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 from warnings import warnpy3k
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15 warnpy3k("the mutex module has been removed in Python 3.0", stacklevel=2)
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16 del warnpy3k
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17
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18 from collections import deque
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19
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20 class mutex:
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21 def __init__(self):
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22 """Create a new mutex -- initially unlocked."""
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23 self.locked = False
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24 self.queue = deque()
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25
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26 def test(self):
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27 """Test the locked bit of the mutex."""
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28 return self.locked
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29
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30 def testandset(self):
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31 """Atomic test-and-set -- grab the lock if it is not set,
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32 return True if it succeeded."""
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33 if not self.locked:
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34 self.locked = True
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35 return True
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36 else:
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37 return False
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38
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39 def lock(self, function, argument):
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40 """Lock a mutex, call the function with supplied argument
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41 when it is acquired. If the mutex is already locked, place
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42 function and argument in the queue."""
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43 if self.testandset():
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44 function(argument)
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45 else:
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46 self.queue.append((function, argument))
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47
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48 def unlock(self):
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49 """Unlock a mutex. If the queue is not empty, call the next
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50 function with its argument."""
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51 if self.queue:
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52 function, argument = self.queue.popleft()
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53 function(argument)
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54 else:
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55 self.locked = False