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v0.5.1
v0.5.1
Revision e905e957210a26804bc224f0d7577ab85b044c4a authored by Guido van Rossum on 05 September 2000, 12:42:46 UTC, committed by Guido van Rossum on 05 September 2000, 12:42:46 UTC
XXX notes for now. I could use help here!!!! Please mail me patches ASAP. We may have to put some of this off to 2.0final, but it's best to have it in shape now...
1 parent 87106b5
mutex.py
"""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:
def __init__(self):
"""Create a new mutex -- initially unlocked."""
self.locked = 0
self.queue = []
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 1
else:
return 0
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[0]
del self.queue[0]
function(argument)
else:
self.locked = 0
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