On Aug 28, 2010, at 9:44 AM, Jon Dyte wrote:
Hi
I am considering adding a new socket option, in order to get the
number
of subscriptions on the sub side socket.
This is because in the dynamic subscribe/unsubscribe scenario it is
possible to receive a message whilst in a loop
while (true)
{
zmq::message_t msg;
sm.recv(&msg);
// do an unsubscribe of last remaining subscription for this
socket
// whoops return to the loop and we will block forever
}
If we could query the number of subscriptions from the socket,
the program could terminate cleanly.
Thoughts?
Jon
It would seem rational to be able to enumerate the subscriptions, but
there aren't enough args in setsockopt, and a lot of the solutions are
pretty crufty (like specially formatted buffers).
One thought would be to be able to ship socket info messages:
// next msg group will have subscriptions
s.setsockopt(... ZMQ_RECVSUBS ...)
for (;;) {
...
s.recv(&msg); // get a subscription
...
if (! more)
break;
}
Haven't looked to see how ugly this would be.
Perhaps set/getsockopt are obsolete, maybe message based control is
the future :-) ---
// per context control ?
ctl_socket = zmq_socket(ctx, ZMQ_CTXCTL);
...
zmq_identity(socket, ... ...); // get my socket's identity
...
zmq_send(ctl_socket, ... command ..., ZMQ_SNDMORE);
zmq_send(ctl_socket, ... identity ..., ZMQ_SNDMORE);
zmq_send(ctl_socket, ... arg1 ..., ZMQ_SNDMORE);
zmq_send(ctl_socket, ... arg2 ..., 0);
for (;;) {
// get responses....
zmq_recv(ctl_socket, &msg, 0);
...
// do something useful
...
if (! more)
break;
}
This looks pretty easy to wrap, is generalizable, stays in the
paradigm, and I can't *wait* to write the DEVICE for this one :-)
Anyway, those are thoughts ;-)
Best.
Matt
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