Tregoreg Tregoreg - 2 months ago 8
Python Question

Stop pyzmq receiver by KeyboardInterrupt

Following this example in the ├śMQ docs, I'm trying to create a simple receiver. The example uses infinite loop. Everything works just fine. However, on MS Windows, when I hit CTRL+C to raise KeyboardInterrupt, the loop does not break. It seems that

recv()
method somehow ignores the exception. However, I'd love to exit the process by hiting CTRL+C instead of killing it. Is that possible?

Answer

A zmq.Poller object seems to help:

def poll_socket(socket, timetick = 100):
    poller = zmq.Poller()
    poller.register(socket, zmq.POLLIN)
    # wait up to 100msec
    try:
        while True:
            obj = dict(poller.poll(timetick))
            if socket in obj and obj[socket] == zmq.POLLIN:
                yield socket.recv()
    except KeyboardInterrupt:
        pass
    # Escape while loop if there's a keyboard interrupt.

Then you can do things like:

for message in poll_socket(socket):
    handle_message(message)

and the for-loop will automatically terminate on Ctrl-C. It looks like the translation from Ctrl-C to a Python KeyboardInterrupt only happens when the interpreter is active and Python has not yielded control to low-level C code; the pyzmq recv() call apparently blocks while in low-level C code, so Python never gets a chance to issue the KeyboardInterrupt. But if you use zmq.Poller then it will stop at a timeout and give the interpreter a chance to issue the KeyboardInterrupt after the timeout is complete.

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