Re: [Xenomai] Xddp protocol: question of one example

[Philippe Gerum <rpm@xenomai.org>]

On 12/19/2013 12:37 AM, Leopold Palomo-Avellaneda wrote:
> Hi,
>
> I'm developing an application that need (as always) interchange data between a realtime part and non-realtime.
>
> Looking on the documentation and surfing on the web I have found interesting for my app the examples of xddp protocol. Some time ago, there was an interesting mail about it [1].
>
> There, the original author ask one thing that I would like to be sure that I understood. On the examples, the realtime thread uses the function recvfrom() to receive data from the non-rt thread.
>
> In the mail, the original author asked about make recvfrom
> call non-blocking in xddp context, and *Philippe Gerum* answered that
> MSG_DONTWAIT should be set in flags.
>
> So, my question is that using that flag, some code like this:
>
>
> /* Read back packets echoed by the regular thread */
> ret = recvfrom(s, buf, sizeof(buf), 0, NULL, 0);
> if(ret <= 0)
>      fail("recvfrom");
>
> recvfrom will not be blocked, but it will return 0?
>
> May I understood that if there's data on the sockect recvfrom will
> return something and if no, it would not be blocked and return something?
>

Standard behavior when no data present: immediate return with ret = -1, 
errno = EWOULDBLOCK/EAGAIN.

-- 
Philippe.