The snippets suggest you were storing a reference to an object on the
stack. Stack variables go out of scope when the function returns. Using a
reference to them out-of-scope is illegal but often fails
nondeterministically. Good compilers will issue a warning about this under
the right conditions (ie compiler flags).
Jeff
On Sat, Aug 10, 2019 at 10:59 AM carlos aguni via users <
users@lists.open-mpi.org> wrote:
> Hi all,
>
> Sorry no reply.
>
> I just figured out the solution.
>
> The problem was that I had a function that would MPI_Isend a message on
> every call to it. Then I'd store its request pointer to a list.
> My MPI_Isend snippet:
> MPI_Request req;
> MPI_Isend(blabla, &req)
> task_push(&req);
>
> From time to time at the beginning of that function I'd call another
> function that would iterate over that list MPI_Testing if that message
> had completed to then free the buffers used.
> The problem was that even if the flag returned from MPI_Test(&req, &flag,
> &status) previouly assigned to 0 returned 1 but my guess is that C had
> already deallocated it from the heap (idk much about C though..)
> Snippet of my clean function:
> ....
> int flag = 0;
> MPI_Test(req, &flag, &status);
> if (flag) { // then free..
> ...
>
> My solution that worked was previously malloc it before the MPI_Isend call
> like:
> MPI_Request *rr = (MPI_Request *)malloc(sizeof(MPI_Request));
> MPI_Isend(blabla...., rr);
> task_push(rr);
>
> All I know is that it's working now..
>
> Thanks to all.
>
> Regards,
> C.
>
> On Sun, Jul 28, 2019 at 11:53 AM Jeff Squyres (jsquyres) via users <
> users@lists.open-mpi.org> wrote:
>
>> On Jul 27, 2019, at 10:43 PM, Gilles Gouaillardet via users <
>> users@lists.open-mpi.org> wrote:
>> >
>> > MPI_Isend() does not automatically frees the buffer after it sends the
>> message.
>> > (it simply cannot do it since the buffer might be pointing to a global
>> > variable or to the stack).
>>
>> Gilles is correct: MPI_Isend does not free the buffer. I was wondering
>> if you had somehow used that same buffer -- or some subset of that buffer
>> -- in other non-blocking MPI API calls, and freeing it triggered Bad Things
>> because MPI was still using (some of) that buffer because of other pending
>> MPI requests.
>>
>> > Can you please extract a reproducer from your program ?
>>
>> Yes, please do this.
>>
>> > Out of curiosity, what if you insert an (useless) MPI_Wait() like this ?
>> >
>> > MPI_Test(req, &flag, &status);
>> > if (flag){
>> > MPI_Wait(req, MPI_STATUS_IGNORE);
>> > free(buffer);
>> > }
>>
>> That should be a no-op, because "req" should have been turned into
>> MPI_REQUEST_NULL if flag==true.
>>
>> --
>> Jeff Squyres
>> jsquy...@cisco.com
>>
>> _______________________________________________
>> users mailing list
>> users@lists.open-mpi.org
>> https://lists.open-mpi.org/mailman/listinfo/users
>>
> _______________________________________________
> users mailing list
> users@lists.open-mpi.org
> https://lists.open-mpi.org/mailman/listinfo/users
--
Jeff Hammond
jeff.scie...@gmail.com
http://jeffhammond.github.io/
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