On Wed, Oct 24, 2012 at 12:54 PM, David M Chess <ch...@us.ibm.com> wrote:
> Seeking any thoughts on other/better ways to do this, or whether the
> inefficiency will be too eyerolling if we get say one request per second
> with an average service time a bit under a second but maximum service time
> well over a second, and most of them are importance zero, but every (many)
> seconds there will be one or two with higher importance.
I used a PriorityQueue and Conditions to get rid of the ugly while True loop.
import threading
from Queue import PriorityQueue, Empty
class PriorityLock(object):
def __init__(self):
self._is_available = True
self._mutex = threading.Lock()
self._waiter_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
condition = threading.Condition()
condition.acquire()
self._waiter_queue.put((priority, condition))
self._mutex.release()
condition.wait()
condition.release()
return True
def release(self):
self._mutex.acquire()
# Notify the next thread in line, if any.
try:
_, condition = self._waiter_queue.get_nowait()
except Empty:
self._is_available = True
else:
condition.acquire()
condition.notify()
condition.release()
self._mutex.release()
def test():
import random, time
def thread(lock, priority):
lock.acquire(priority)
print("Thread %d running" % priority)
time.sleep(1)
lock.release()
lock = PriorityLock()
threads = [threading.Thread(target=thread, args=(lock, x)) for x
in range(10)]
random.shuffle(threads)
for thread in threads:
thread.start()
for thread in threads:
thread.join()
if __name__ == "__main__":
test()
Output:
Thread 9 running
Thread 0 running
Thread 1 running
Thread 2 running
Thread 3 running
Thread 4 running
Thread 5 running
Thread 6 running
Thread 7 running
Thread 8 running
Note that with the PriorityQueue, lower priority values are retrieved
first. Thread 9 ran first just by virtue of being first to the gate,
and after that you can see that everything went in order.
Cheers,
Ian
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