Question

I just got started with ZMQ. I am designing an app whose workflow is:

1. one of many clients (who have random PULL addresses) PUSH a request to a server at 5555
2. the server is forever waiting for client PUSHes. When one comes, a worker process is spawned for that particular request. Yes, worker processes can exist concurrently.
3. When that process completes it’s task, it PUSHes the result to the client.

I assume that the PUSH/PULL architecture is suited for this. Please correct me on this.

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But how do I handle these scenarios?

1. the client_receiver.recv() will wait for an infinite time when server fails to respond.
2. the client may send request, but it will fail immediately after, hence a worker process will remain stuck at server_sender.send() forever.

So how do I setup something like a timeout in the PUSH/PULL model?

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EDIT: Thanks user938949’s suggestions, I got a working answer and I am sharing it for posterity.

Answer 1

If you are using zeromq >= 3.0, then you can set the RCVTIMEO socket option:

client_receiver.RCVTIMEO = 1000 # in milliseconds

But in general, you can use pollers:

poller = zmq.Poller()
poller.register(client_receiver, zmq.POLLIN) # POLLIN for recv, POLLOUT for send

And poller.poll() takes a timeout:

evts = poller.poll(1000) # wait *up to* one second for a message to arrive.

evts will be an empty list if there is nothing to receive.

You can poll with zmq.POLLOUT, to check if a send will succeed.

Or, to handle the case of a peer that might have failed, a:

worker.send(msg, zmq.NOBLOCK)

might suffice, which will always return immediately – raising a ZMQError(zmq.EAGAIN) if the send could not complete.