[zeromq-dev] adding timeout in zmq_poll

[Pavel Gushcha]

2009/12/28 Martin Sustrik <sustrik at 250bpm.com>

> Pavel Gushcha wrote:
>
>>
>>
>> 2009/12/28 Martin Sustrik <sustrik at 250bpm.com <mailto:sustrik at 250bpm.com
>> >>
>>
>>
>>    Hi Pavel,
>>
>>
>>        I want to have timeout parameter in zmq_poll function. As i
>>        understood, It is not very difficult to implement this. But i
>>        want to ask about underwater stones:
>>
>>        1) All oses support timeout parameter? in zmq.cpp i see one part
>>        of code for windows, and one for other oses. Both parts have
>>        timeout parameter, but for windows we can set timeout with
>>        microsecond granularity. We can't get such granularity in linux?
>>
>>
>>    See Steven's discussion of the topic.
>>
>>
>> So the best solution is adding int timeout parameter to zmq_poll that mean
>> timeout in milliseconds?
>>
>
> Milliseconds is the least common denominator. However, I would suggest
> using microseconds or nanoseconds in the API even though the underlying
> infrastructure is not able to support that kind of precission. The point is
> that precise timers would arrive ultimately and at that point we would be
> able to use them without modifying 0MQ API.


Ok. If we choose nanoseconds, there is two moments:
1) Must we add two parameters to zmq_poll(): int timeout_sec, int timeout
nsec?
2) If user specified too small timeout (1 nsec) must we increase this
timeout to one ms in linux and 1microsec in windows?

How you think?


>
>
>>
>>
>>
>>        2) With adding timeout parameter in zmq_poll i must update
>>        bindings. I looked at them and found, that binding for zmq_poll
>>        present only in C,C++,Common Lisp bindings. May be i miss
>> something?
>>
>>
>>    Nope. zmq_poll is not available from python & ruby yet.
>>
>>
>> I dont found zmq_poll binding for Java too.
>>
>
> Right. No zmq_poll for Java either. In case you need it, feel free to add
> it. It should be quite straightforward.
>
>
>     One more issue: poll function inside the zmq_poll function may
>>    return before there are any actual events (say if there are messages
>>    that are going to be filtered out) so note that it is called in a
>>    loop. Adding the timeout would mean that you have to measure time
>>    spent in each poll call and subtract it from the overall timeout
>>    time as passed to zmq_poll. The alternative would be not to
>>    guarantee any events on the return from zmq_poll.
>>
>>
>> If we adding timeout to polling, in any case there is possibility that no
>> one event was fired. Measuring spent time in each poll is too complicated
>> and high resolution measurement is hard portable (i'm not sure). Now
>> poll()/select() in many cases is called twice: first with zero timeout, and
>> second with -1/NULL timeout. I prefer to add custom timeout value in second
>> parameter, and this will guarantee, that zmq_poll() will not take no longer
>> time (with some error), than specified in timeout().
>>
>
> Agreed.
>
> Martin
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.zeromq.org/pipermail/zeromq-dev/attachments/20091228/509d94ec/attachment.htm>