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      1 """Mutual exclusion -- for use with module sched
      2 
      3 A mutex has two pieces of state -- a 'locked' bit and a queue.
      4 When the mutex is not locked, the queue is empty.
      5 Otherwise, the queue contains 0 or more (function, argument) pairs
      6 representing functions (or methods) waiting to acquire the lock.
      7 When the mutex is unlocked while the queue is not empty,
      8 the first queue entry is removed and its function(argument) pair called,
      9 implying it now has the lock.
     10 
     11 Of course, no multi-threading is implied -- hence the funny interface
     12 for lock, where a function is called once the lock is aquired.
     13 """
     14 from warnings import warnpy3k
     15 warnpy3k("the mutex module has been removed in Python 3.0", stacklevel=2)
     16 del warnpy3k
     17 
     18 from collections import deque
     19 
     20 class mutex:
     21     def __init__(self):
     22         """Create a new mutex -- initially unlocked."""
     23         self.locked = False
     24         self.queue = deque()
     25 
     26     def test(self):
     27         """Test the locked bit of the mutex."""
     28         return self.locked
     29 
     30     def testandset(self):
     31         """Atomic test-and-set -- grab the lock if it is not set,
     32         return True if it succeeded."""
     33         if not self.locked:
     34             self.locked = True
     35             return True
     36         else:
     37             return False
     38 
     39     def lock(self, function, argument):
     40         """Lock a mutex, call the function with supplied argument
     41         when it is acquired.  If the mutex is already locked, place
     42         function and argument in the queue."""
     43         if self.testandset():
     44             function(argument)
     45         else:
     46             self.queue.append((function, argument))
     47 
     48     def unlock(self):
     49         """Unlock a mutex.  If the queue is not empty, call the next
     50         function with its argument."""
     51         if self.queue:
     52             function, argument = self.queue.popleft()
     53             function(argument)
     54         else:
     55             self.locked = False
     56