[zeromq-dev] poll does not return on a SUB socket

Sven Koebnick sven.koebnick at t-online.de
Thu Dec 16 20:00:35 CET 2010

Hi Martin,

the main issue is, that poll(... ,-1) does not at all return despite  
the fact that there is a message available!
The usage of timeout value is a current workaround, because the second  
call to poll (the first returned zero) successfully returns a number  
greater one.

sent by the iPhone

Am 16.12.2010 um 13:33 schrieb Martin Sustrik <sustrik at 250bpm.com>:

> Hi Sven,
>> In addition, a poll with 180 seconds (an 18 and 7 zeros) does NEVER  
>> wait
>> so long, but return immediately. If there is no message available, it
>> returns 0 as expected, but sometimes the ERRNO is set to 0  
>> (SUCCESS) and
>> sometimes ERRNO is set to 11 (Ressource temporarily not available).  
>> What
>> do theese different ERRNOs mean? Can I understand ERRNO=11 as  
>> "there is
>> no PUB socket connected"? (I bind the SUB and connect the PUB!)
> If you have a look at zmq_poll man page you'll find out that zmq_poll
> waits *up to* specified number of microseconds. So yes, it can return
> prematurely. However, new version of 0MQ (2.1) honour the timeout  
> precisely.
> When timeout is reached, zmq_poll returns 0 but does not set the  
> error.
> That means that errno can contain an error returned by some previous
> function or somesuch.
> Martin
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