[zeromq-dev] Can zmq_pollitem_t contain an item with a NULL socket ?
Lindley French
lindleyf at gmail.com
Thu Jan 30 13:29:22 CET 2014
No particular objection to the union idea (although it should be carefully profiled for speed against the existing code!) but I am curious, what possible benefit there could be to have NULL sockets in the poller? This seems contrary to "expected" workings in C-like languages.
> On Jan 30, 2014, at 5:20 AM, Laurent Alebarde <l.alebarde at free.fr> wrote:
>
> IMHO, it is a bad design of zmq_pollitem_t. It should not have one attribute for socket and another one for file-descriptor with this unrobust behaviour to use the second one when the first one is NULL, but one for the type (socket or fd), and a union containing one or the other.
>
> Implemented:
> typedef struct
> {
> void *socket;
> #if defined _WIN32
> SOCKET fd;
> #else
> int fd;
> #endif
> short events;
> short revents;
> } zmq_pollitem_t;
>
> Should be:
>
> typedef struct
> {
> int type; // ZMQ_SOCKET | ZMQ_FD
> union {
> void *socket;
> #if defined _WIN32
> SOCKET fd;
> #else
> int fd;
> #endif
> } dev;
> short events;
> short revents;
> } zmq_pollitem_t;
>
> But it would break the ABI to change it, isn't it ?
>
>
> Le 30/01/2014 10:56, Laurent Alebarde a écrit :
>> In fact, it is in src/zmq.cpp / "int zmq_poll (zmq_pollitem_t *items_, int nitems_, long timeout_)"
>>
>> When the socket is NULL, zmq_poll takes the second attribute of the zmq_pollitem_t structure which is a file descriptor. So, I cannot do anything here, as "socket == NULL and fd == 0" is legitimate.
>>
>> Conclusion: I have to deal myself with the complexity of not having NULL sockets in my zmq_pollitem_t array.
>>
>> Le 30/01/2014 09:23, Laurent Alebarde a écrit :
>>> Thanks Pieter.
>>>
>>> Personnaly, I would prefer "ignore", in order to build zmq_pollitem_t arrays with more ease, when they are built by the application itself, and not hardwritten in the code.
>>>
>>> Any objection ?
>>>
>>> Le 29/01/2014 20:20, Pieter Hintjens a écrit :
>>>> Undefined, by the man page. It should probably assert in such a case.
>>>>
>>>> On Wed, Jan 29, 2014 at 12:07 PM, Laurent Alebarde <l.alebarde at free.fr> wrote:
>>>>> Hi Devs,
>>>>>
>>>>> What is the zmq_poll behaviour when the zmq_pollitem_t array contains an
>>>>> item with a NULL socket ? ignored, undefined, error ?
>>>>>
>>>>> If it is in src/poll.cpp / "void zmq::poll_t::loop ()" / "for
>>>>> (pollset_t::size_type i = 0; i != pollset.size (); i++)", it seems there is
>>>>> no NULL test with a continue.
>>>>>
>>>>> Cheers,
>>>>>
>>>>>
>>>>> Laurent
>>>>>
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