[zeromq-dev] ZMQ_FD and inproc:// socket

[Max Kozlovsky]

Hi,

It is kind of tricky.

The availability of data on the file descriptor returned with ZMQ_FD
signals that there is a zmq socket state change, i.e. the receive queue
goes from empty to non-empty. Any operation on the socket
(send/receive/getsockopt with ZMQ_EVENTS) may clear the notification. No
further notifications will be received until there is another state change.
This means the application has to continue sending/receiving data until
getsockopt with ZMQ_EVENTS says further operations are not possible. The
application should not access the file descriptor directly beyond using it
as poll/epoll file descriptor.

I am not familiar with boost::aio, but you'll need to do at least the
following:
1) define your own read handler which is called when the file descriptor
signals data availability, which will call zmq_msg_recv() on corresponding
zmq socket.
2) either exhaust the incoming data completely each time read handler is
called, or somehow mark the file descriptor as having the data available so
your read handler is called again when the control is returned to the
library.

Max



On Tue, Nov 15, 2016 at 5:06 AM, Arnaud Kapp <kapp.arno at gmail.com> wrote:

> Hello,
>
> I'm using zmqpp in my project, and I have a special case where I need to
> integrate
> with boost::asio (this is what azmq does, but for now I just need it once,
> so I don't want
> to switch libraries).
>
> The idea was to rely on ZMQ_FD and add the corresponding FD to ASIO's
> event loop.
> However, I've found that async_read_some() wasn't triggered. It turns out
> it's likely an issue
> in libzmq: https://github.com/zeromq/libzmq/issues/1434
>
> After taking a quick look at AZQM it seems it's also using ZMQ_FD.
> Can anyone tell me what's the trick to get them to work?
>
> Thanks,
>
> --
> Kapp Arnaud - Xaqq
>
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>
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