[zeromq-dev] HWM and sockets blocking while in exceptional state

[Chuck Remes]

On Dec 19, 2011, at 10:34 AM, Massimiliano della Rovere wrote:

> In my tests, I :
> - run the 2 programs instantiating the sockets on the same machine
> (read below);
> - use DEALER sockets for both the sender and the receiver;
> - set RECVHWM to 1 in the receiver;
> - set SNDHWM to 1 in the sender;
> but I successfully manage to send any number of messages from the
> sender without reading any from the receiver.

I doubt this. You can probably send enough messages to fill the kernel buffers but then it should block. You are probably only testing with a few messages.

> Now having a both RECVHWM and SENDHWM set to 1, I expected that 1st
> sent message would fill the "RECVHWM slot", the 2nd sent message would
> fill the "SENDHWM slot" and a 3rd invocation of send() in the sender
> would block (it's a DEALER socket, shouldn't it)?
> 
> The strange thing is that if I use a tcp:// or ipc:// transport, the
> send() is not blocking, but trying with inproc:// transport the send
> is (correctly) blocking.
> 
> Is this difference in behaviour correct? Is the RECVHWM only working
> with inproc transport?

This is a FAQ. Please read it here:

http://www.zeromq.org/area:faq

inproc works "exactly" because there are no kernel buffers in use.

cr