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A lock that prioritizes acquire()s?

Ian Kelly ian.g.kelly at gmail.com
Wed Oct 24 17:00:09 EDT 2012 
On Wed, Oct 24, 2012 at 2:19 PM, Ian Kelly <ian.g.kelly at 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()
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