home *** CD-ROM | disk | FTP | other *** search
- # 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:
- #
- # Create a new mutex -- initially unlocked
- #
- def __init__(self):
- self.locked = 0
- self.queue = []
- #
- # Test the locked bit of the mutex
- #
- def test(self):
- return self.locked
- #
- # Atomic test-and-set -- grab the lock if it is not set,
- # return true if it succeeded
- #
- def testandset(self):
- if not self.locked:
- self.locked = 1
- return 1
- else:
- return 0
- #
- # 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.
- #
- def lock(self, function, argument):
- if self.testandset():
- function(argument)
- else:
- self.queue.append((function, argument))
- #
- # Unlock a mutex. If the queue is not empty, call the next
- # function with its argument.
- #
- def unlock(self):
- if self.queue:
- function, argument = self.queue[0]
- del self.queue[0]
- function(argument)
- else:
- self.locked = 0
- #
-