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 = 0

    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 = 1

    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 = 0