Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.python > #32067 > unrolled thread

Re: A lock that prioritizes acquire()s?

Back to article view | Back to comp.lang.python

This discussion starts older than the indexed window; earlier articles aren't shown. The article labeled Started by below is the oldest one visible, not the original post.

Contents

  Re: A lock that prioritizes acquire()s? Ian Kelly <ian.g.kelly@gmail.com> - 2012-10-24 15:00 -0600

#32067 — Re: A lock that prioritizes acquire()s?

On Wed, Oct 24, 2012 at 2:19 PM, Ian Kelly <ian.g.kelly@gmail.com> wrote:
> I used a PriorityQueue and Conditions to get rid of the ugly while True loop.

Same things, but with Events instead of Conditions.  This is just a
bit more readable.

The PriorityQueue is also probably unnecessary, since it's always
accessed with the mutex held.  A heapq would be fine.


import threading
import Queue

class PriorityLock(object):

    def __init__(self):
        self._is_available = True
        self._mutex = threading.Lock()
        self._waiter_queue = Queue.PriorityQueue()

    def acquire(self, priority=0):
        self._mutex.acquire()
        # First, just check the lock.
        if self._is_available:
            self._is_available = False
            self._mutex.release()
            return True
        event = threading.Event()
        self._waiter_queue.put((priority, event))
        self._mutex.release()
        event.wait()
        # When the event is triggered, we have the lock.
        return True

    def release(self):
        self._mutex.acquire()
        # Notify the next thread in line, if any.
        try:
            _, event = self._waiter_queue.get_nowait()
        except Queue.Empty:
            self._is_available = True
        else:
            event.set()
        self._mutex.release()

[toc] | [standalone]

Back to top | Article view | comp.lang.python

csiph-web