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ZmqMessage 0.1 - 21 Oct 2011

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Queueing messages for delayed sending

This feature is useful when:

• sending messages may block (ex. ZMQ_HWM is set and has been reached)
• we cannot block on sending message (it would make our thread unresponsive to other events).
• we cannot drop the message, cause it MUST be delivered when possible.

In this case we should create outgoing messages with ZmqMessage::OutOptions::NONBLOCK and ZmqMessage::OutOptions::CACHE_ON_BLOCK. If sending fails, we may 'detach' composed message and resend it later, when output socket will be available for writing.

//delayed queue
std::vector<Zmqmessage::Multipart*> queue;

zmq::socket_t s_req(ctx, ZMQ_PUSH);

//set HWM
uint64_t lim = 10;
s_req.setsockopt(ZMQ_HWM, &lim, sizeof(uint64_t));

s_req.connect("inproc://test-ep");

ZmqMessage::OutOptions opts(s_req,
  ZmqMessage::OutOptions::CACHE_ON_BLOCK | ZmqMessage::OutOptions::NONBLOCK);

ZmqMessage::Outgoing<ZmqMessage::SimpleRouting> egress(opts);

egress << "finished" << 888 << ZmqMessage::Flush;

if (egress.is_queued())
{
  queue.push_back(egress.detach());
}

See example zasync for details.

Note, that currently queueing functionality has proven working only for PUSH-PULL sockets. Request-reply patterns (REQ, RES, XREQ, XRES sockets) in many cases prevent congestion due to internal socket states.

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ZmqMessage 0.1 — open source software, support@zmqmessage.org