[Xenomai] Xddp protocol: question of one example

[Leopold Palomo-Avellaneda <leo@alaxarxa.net>]

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?

Thanks in advance,

Leopold

[1] http://www.xenomai.org/pipermail/xenomai/2010-February/019364.html

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