Doubt about sockets

[Eric Norum]

Why not just use the message queues that RTEMS provides?
It seems like a lot of extra work to go through the network stack for this.

On Jun 22, 2010, at 10:04 AM, Vinu Rajashekhar wrote:

> 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
> 
> 

-- 
Eric Norum
wenorum at lbl.gov

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