Staging
v0.5.0
v0.5.0
https://github.com/python/cpython
Tip revision: 413a49145e35c7a2d3a7de27c5a1828449c9b2e5 authored by Benjamin Peterson on 02 March 2019, 18:17:42 UTC
Set version to 2.7.16 final.
Set version to 2.7.16 final.
Tip revision: 413a491
mutex.py
"""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 acquired.
"""
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