Subj : Re: pthreads - cancellation
To   : comp.programming.threads
From : plinius
Date : Mon Aug 22 2005 12:07 pm

> > I'm using pthreads with a communication-librarie.
> > This librarie has blocking Recv's.
> MPI has also a non blocking receive MPI_Irecv().
>
> > When a "cummunicator" (you can see it as a radio-frequency) changes, I
> > have to repost the Recv,
> Do you mean MPI Communicator here?
>
> > The Recv function is of the following form: Recv(int number, comm
> > communicator).
> MPI_Recv() has more paramaters, actually. Is it a function of your own,
> which in turn calls MPI_Recv()?
>
Yes I know, but I suppose not everyone knows of MPI, and tried to
(maybe it didn't worked...) simplify my problem to the strict
necessary...
> > Hence I can't let the thread know it should be restarted with a
> > dummy-message,
> > because every possible value for "number" is valid.
> One possibility I see would be to extend the message. Instead of being
> one number, it would be a structure of the form:
>
> struct my_mesg {
> int   number;
> bool  restart; // true if restart message
> }
>
Yes, that's a good idea, but I have to restart allmost never (in 0,001
% of the cases...), and would like to be able to split the
"restart-code" from the rest. But I think I'll go  for your solution
indeed
> That way, you wouldn't have any problem to recognize a restart message.
> This is IMHO the "best" solution (of course, "best" is always relative
> ;-)
>
> Another possibility would be to perform a non blocking receive with
> MPI_Irecv() and poll for communicator change. But this might complicate
> message's retrieval, and you need to poll (vs. asynchronous
> notification).
>
> > Also it seems that cancellation
> I don't know the MPI internals, but I wouldn't be surprised if deferred
> cancellation works.
>
> > is really tricky (and not allways possible, and never advisable).
> Why is it never advisable?
Red this on a question in "experts-exchange.com" (a forum), and I
believed it...
> > >     Call 'shutdown' on the socket it's blocked on.
> >
> > Thanks, but the library is mpi, which doesn't has a
> > "shutdown"-operation...
> I don't know if MPI has a similar feature... But with PVM, it is
> possible to get the socket descriptors used for the communication.
> 
> 
> HTH,
> Loic.

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