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Diffstat (limited to 'lib/python2.7/mutex.py')
-rw-r--r-- | lib/python2.7/mutex.py | 55 |
1 files changed, 55 insertions, 0 deletions
diff --git a/lib/python2.7/mutex.py b/lib/python2.7/mutex.py new file mode 100644 index 0000000..3d8f428 --- /dev/null +++ b/lib/python2.7/mutex.py @@ -0,0 +1,55 @@ +"""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 acquired. +""" +from warnings import warnpy3k +warnpy3k("the mutex module has been removed in Python 3.0", stacklevel=2) +del warnpy3k + +from collections import deque + +class mutex: + def __init__(self): + """Create a new mutex -- initially unlocked.""" + self.locked = False + 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 = True + 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 = False |