cpython-withatomic / Lib / mutex.py

The branch 'legacy-trunk' does not exist.
"""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
Tip: Filter by directory path e.g. /media app.js to search for public/media/app.js.
Tip: Use camelCasing e.g. ProjME to search for ProjectModifiedEvent.java.
Tip: Filter by extension type e.g. /repo .js to search for all .js files in the /repo directory.
Tip: Separate your search with spaces e.g. /ssh pom.xml to search for src/ssh/pom.xml.
Tip: Use ↑ and ↓ arrow keys to navigate and return to view the file.
Tip: You can also navigate files with Ctrl+j (next) and Ctrl+k (previous) and view the file with Ctrl+o.
Tip: You can also navigate files with Alt+j (next) and Alt+k (previous) and view the file with Alt+o.