Python iterable Queue

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感情败类 2021-02-14 12:21

I need to know when a Queue is closed and wont have more items so I can end the iteration.

I did it by putting a sentinel in the queue:

from Queue import         


        
2条回答
  •  长发绾君心
    2021-02-14 12:27

    The multiprocessing module has its own version of Queue that does include a close method. I am not sure how it works in threading, but its worth a try. I don't see why it shouldn't work the same:

    from multiprocessing import Queue
    
    q = Queue()
    q.put(1)
    q.get_nowait()
    # 1
    q.close()
    q.get_nowait()
    # ...
    # IOError: handle out of range in select()
    

    You could just catch the IOError as the close signal.

    TEST

    from multiprocessing import Queue
    from threading import Thread
    
    def worker(q):
        while True:
            try:
                item = q.get(timeout=.5)
            except IOError:
                print "Queue closed. Exiting thread."
                return
            except:
                continue
            print "Got item:", item
    
    q = Queue()
    for i in xrange(3):
        q.put(i)
    t = Thread(target=worker, args=(q,))
    t.start()
    # Got item: 0
    # Got item: 1
    # Got item: 2
    q.close()
    # Queue closed. Exiting thread.
    

    Though to be honest, its not too much different than setting a flag on the Queue.Queue. The multiprocessing.Queue is just using a closed file descriptor as a flag:

    from Queue import Queue
    
    def worker2(q):
        while True:
            if q.closed:
                print "Queue closed. Exiting thread."
                return
            try:
                item = q.get(timeout=.5)
            except:
                continue
            print "Got item:", item
    
    q = Queue()
    q.closed = False
    for i in xrange(3):
        q.put(i)
    t = Thread(target=worker2, args=(q,))
    t.start()
    # Got item: 0
    # Got item: 1
    # Got item: 2
    q.closed = True
    # Queue closed. Exiting thread.
    

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