[zeromq-dev] level-triggered FD

[Doron Somech]

the FD must be read-only, it might be possible in some OS but I won't be
portable.

Regarding the Command FD, it must be used, otherwise the Recv/Send FD won't
work.

So in your case you need to be add the event-loop both the command FD
(which is the regular FD) and Recv/Send FD.

When command FD is signaled you must call zmq_process_comands, which
currently doesn't exist.
When recv/send FD is signaled you can call recv/send.
zmq_process_command it what causing the other FDs to get signaled.

The bottom line, this is kind of syntactic sugar, it will be the equivalent
of calling has_in or has_out immediately after FD is signaled and only then
call recv/send.





On Fri, Jan 22, 2016 at 5:54 PM, MinRK <benjaminrk at gmail.com> wrote:

>
>
> On Fri, Jan 22, 2016 at 4:19 PM, Doron Somech <somdoron at gmail.com> wrote:
>
>> The FD today is signalled when ever a command should be processes. What
>> we can do is split it to 3 different FD:
>>
>> * Command FD : The one being used right now, this still must be used,
>> when ever signalled call process commands (which we should expose in API).
>> * Recv FD: use as level triggered to receive.
>> * Send FD: use as level triggered to send.
>>
>> Only issue with this solution, you should include in your event loop
>> minimum two FD, one for processing commands and one for send/ recv.
>>
> I think two FDs would be fine; certainly better than what we have now. It
> would eliminate the significant problem of one signal for separate events.
> Perhaps this is a naïve question: Is it not possible to have an FD signal
> writable when the socket becomes writable and readable when the socket
> becomes readable? If they both have to be read-only FDs, that seems fine,
> as long as the signaling for send and recv are separated somehow. I'm not
> sure what users would do with the Command FD.
>
> -MinRK
>
>
>> For thread safe sockets this is a little simpler as we can make one FD
>> for all sockets for processing commands.
>> On Jan 22, 2016 2:52 PM, "Pieter Hintjens" <ph at imatix.com> wrote:
>>
>>> Yes, the edge triggered FD in libzmq has been a constant source of
>>> annoyance. Maybe someone on this list knows how to fix it.
>>>
>>> On Fri, Jan 22, 2016 at 1:40 PM, MinRK <benjaminrk at gmail.com> wrote:
>>> > Hi all,
>>> >
>>> > I've implemented yet another eventloop integration in pyzmq (asyncio,
>>> this
>>> > time), and this is only nontrivial because of the edge-triggered
>>> read-only
>>> > zmq.FD. Integrating into existing eventloops would be much easier if
>>> we had
>>> > a more traditional level-triggered FD to work with.
>>> >
>>> > Is there a technical reason why we can't add a zmq.LEVEL_FD that would
>>> > behave in a more conventional manner:
>>> >
>>> > - level-triggered
>>> > - signal write when socket is writable
>>> > - signal read when socket is readable
>>> >
>>> > I would work on this myself, but unfortunately I don't think I have the
>>> > relevant expertise.
>>> >
>>> > -MinRK
>>> >
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