[zeromq-dev] Possible bug in ZMQ HWM handling?

Francesco francesco.montorsi at gmail.com
Fri Aug 31 19:36:32 CEST 2018

I forgot to specify: this happens with ZeroMQ 4.2.3 on Linux.

Il giorno ven 31 ago 2018 alle ore 18:54 Francesco <
francesco.montorsi at gmail.com> ha scritto:

> Hi all,
> I spent quite a bit of time to look into a weird issue.
> Here's my setup:
>      1 PUB socket  connected to a STEERABLE PROXY FRONTED socket, using
> INPROC transport
>      1 SUB socket  connected to the STEERABLE PROXY BACKEND socket, using
> TCP transport
> Before starting stuff (i.e. calling zmq_connect() or zmq_bind()) I lower
> all HWMs (for both TX/RX) of all sockets to just "10".  Moreover I set
> Now my expected behaviour is that after 20 messages sent from the PUB
> socket, the zmq_send() on that PUB becomes blocking.
> You may argue that since I have the XPUB/XSUB sockets of the proxy in the
> middle, the value after it becomes blocking is 40. That's ok.
> The experimental result I found is that the PUB NEVER becomes blocking.
> If I send 10000 messages from the PUB they all go through.
> In the SUB I sleep 1 second after EVERY message received. It takes a while
> but in the end the SUB receives all the 10000 messages...
> Is there an explanation for this? Who buffered all those messages (against
> my will) ?
> Thanks for any hint!
> Francesco
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