diff options
| -rw-r--r-- | Lib/mutex.py | 59 |
1 files changed, 59 insertions, 0 deletions
diff --git a/Lib/mutex.py b/Lib/mutex.py new file mode 100644 index 0000000..38983fc --- /dev/null +++ b/Lib/mutex.py @@ -0,0 +1,59 @@ +# 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 = [] + return self + # + # 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 + # |