Doubt about sockets

[Vinu Rajashekhar]

On Tue, Jun 22, 2010 at 10:11 PM, Eric Norum <wenorum at lbl.gov> wrote:

>
> On Jun 22, 2010, at 9:21 AM, Vinu Rajashekhar wrote:
>
> On Tue, Jun 22, 2010 at 9:48 PM, Eric Norum <wenorum at lbl.gov> wrote:
>
>> You can read and write a socket from different threads.
>> Just don't have multiple threads trying to read at the same time or trying
>> to write at the same time.
>>
>>
> Yes, what if that happens, I don't care about the data being transferred.
> I just want to wakeup select using the socket, then ?
>
>
> Are you doing a select waiting for read data to appear?
> or are you doing a select waiting for space to become ready in a write
> queue?
>
> Do you mean you do a write on one machine and want the 'select read' to
> wake up on the other machine?
>
> It's not clear to me what you have in mind.
>
>
Ok. What I need to do is to wakeup a select call, that's all, on the same
machine.

The original code, had a pipe whose read end would go into the set of fds in
select.
But with RTEMS, since select can't wait on file descriptors, I can't use
this. I can't
use socketpairs in place of the pipe, by the way, since RTEMS doesn't
support that.

So the solution is to use a plain sockets. I will write something into one
socket, sw,
which should wakeup select, because it would be waiting on the socket at the
other
end of the connection, socket sr. Basically replicating something like a
pipe, but I don't
care about the data, just need to wakeup the select.

Now, this write into sw, can happen from more than one thread, at the same
time.
 that is a potential problem in RTEMS. So what is the solution for this
problem ?
Is there a better solution to my problem ?

As an aside, is implementing socketpairs() in RTEMS very difficult at this
point in time ?

>
>
>> On Jun 22, 2010, at 9:03 AM, Vinu Rajashekhar wrote:
>>
>> > From the networking documentation, it seems that one cannot
>> > share the same socket across threads/tasks for the same operation, like
>> > read or write.
>> >
>> > What is the exact problem if I use the same socket to write something
>> > across different threads, is data corruption the only problem? More
>> specifically,
>> > if I have run a select call on a socket, and if I write something into
>> the socket,
>> > from different threads, does the select wakeup for sure ?
>> > _______________________________________________
>> > rtems-users mailing list
>> > rtems-users at rtems.org
>> > http://www.rtems.org/mailman/listinfo/rtems-users
>>
>> --
>> Eric Norum
>> wenorum at lbl.gov
>>
>>
>
> --
>
> Eric Norum
> wenorum at lbl.gov
>
>
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