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-rw-r--r--Lib/mutex.py52
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diff --git a/Lib/mutex.py b/Lib/mutex.py
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-"""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.
-"""
-
-from collections import deque
-
-class mutex:
- def __init__(self):
- """Create a new mutex -- initially unlocked."""
- self.locked = 0
- self.queue = deque()
-
- def test(self):
- """Test the locked bit of the mutex."""
- return self.locked
-
- def testandset(self):
- """Atomic test-and-set -- grab the lock if it is not set,
- return True if it succeeded."""
- if not self.locked:
- self.locked = 1
- return True
- else:
- return False
-
- def lock(self, function, argument):
- """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."""
- if self.testandset():
- function(argument)
- else:
- self.queue.append((function, argument))
-
- def unlock(self):
- """Unlock a mutex. If the queue is not empty, call the next
- function with its argument."""
- if self.queue:
- function, argument = self.queue.popleft()
- function(argument)
- else:
- self.locked = 0