[MPICH] Possible Race condition between Test() and Cancel

[Rajeev Thakur]

If the request is completed by a test or wait, it is set to
MPI_REQUEST_NULL. See if adding an "if (request != MPI_REQUEST_NULL)" around
the MPI_Cancel helps.

Rajeev
 

> -----Original Message-----
> From: owner-mpich-discuss at mcs.anl.gov 
> [mailto:owner-mpich-discuss at mcs.anl.gov] On Behalf Of David Minor
> Sent: Tuesday, January 31, 2006 1:22 AM
> To: mpich-discuss at mcs.anl.gov
> Subject: [MPICH] Possible Race condition between Test() and Cancel
> 
> There appears to be a problem with MPI_Cancel. At least under 
> Red Hat 9
> with the the g++ 3.4.3 compiler.
> 
> If you Cancel a completed receive request, you will get an 
> MPI abort or
> seg fault.
> But if you Test() the request before calling cancel on it there is
> always the possibility that between the Test() and the Cancel() the
> request will be completed thus causing an abort.  What is the 
> solution?
> Shouldn't Cancel() simply return an error if the request is already
> completed?
> 
> My specific problem is:
> 
> I'w waiting with WaitAll on a set of receive requests. I want to wait
> until either 1) They all complete or 2) another thread 
> decides to cancel
> the requests.
> 
> The problem is that the thread that cancels the requests has no way of
> assuring that it doesn't call Cancel() on an already 
> completed request.
> 
> Please advise,
> 
> Regards,
> David Minor Orbotech
> 
>