| """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. |
| """ |
| 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 |
