On 12/20/2013 01:42 PM, Leopold Palomo-Avellaneda wrote:
A Divendres, 20 de desembre de 2013, Philippe Gerum va escriure:
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.
Ok,
if you are writing some data (some bytes) in the socket, can I trust that
recvfrom will return -1 until ALL data is transferred?
Yes, guaranteed for all nrt -> rt transfers. This also applies the other
way, unless MSG_MORE is given to sendmsg() with streaming mode enabled
for the socket, and the message spans multiple output buffers (see
setsockopt(XDDP_BUFSZ) for enabling streaming mode).
--
Philippe.
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