Hello Jeff and Hristo, Now I am completely confused:
So, let's say, the complete reception requires 8192 bytes. And, I have: MPI_Irecv( (void*)this->receivebuffer,/* the receive buffer */ this->receive_packetsize, /* 80 */ MPI_BYTE, /* The data type expected */ this->transmittingnode, /* The node from which to receive */ this->uniquetag, /* Tag */ MPI_COMM_WORLD, /* Communicator */ &Irecv_request /* request handle */ ); That means, the the MPI_Test will tell me that the reception is complete when I have received the first 80 bytes. Correct? Next, let[s say that I have a receive buffer with a capacity of 160 bytes, then, will overflow error occur here? Even if I have decided to receive a large payload in chunks of 80 bytes? I am sorry, the manual and the API reference was too vague for me. Thanks a lot Devendra ________________________________ From: "Iliev, Hristo" <il...@rz.rwth-aachen.de> To: Open MPI Users <us...@open-mpi.org> Cc: devendra rai <rai.deven...@yahoo.co.uk> Sent: Tuesday, 21 August 2012, 9:48 Subject: Re: [OMPI users] MPI_Irecv: Confusion with <<int count>> inputy parameter Jeff, >> Or is it the number of elements that are expected to be received, and hence >> MPI_Test will tell me that the receive is not complete untill "count" number >> of elements have not been received? > > Yes. Answering "Yes" this question might further the confusion there. The "count" argument specifies the *capacity* of the receive buffer and the receive operation (blocking or not) will complete successfully for any matching message with size up to "count", even for an empty message with 0 elements, and will produce an overflow error if the received message was longer and data truncation has to occur. On 20.08.2012, at 16:32, Jeff Squyres <jsquy...@cisco.com> wrote: > On Aug 20, 2012, at 5:51 AM, devendra rai wrote: > >> Is it the number of elements that have been received *thus far* in the >> buffer? > > No. > >> Or is it the number of elements that are expected to be received, and hence >> MPI_Test will tell me that the receive is not complete untill "count" number >> of elements have not been received? > > Yes. > >> Here's the reason why I have a problem (and I think I may be completely >> stupid here, I'd appreciate your patience): > [snip] >> Does anyone see what could be going wrong? > > Double check that the (sender_rank, tag, communicator) tuple that you issued > in the MPI_Irecv matches the (rank, tag, communicator) tuple from the sender > (tag and communicator are arguments on the sending side, and rank is the rank > of the sender in that communicator). > > When receives block like this without completing like this, it usually means > a mismatch between the tuples. > > -- > Jeff Squyres > jsquy...@cisco.com > For corporate legal information go to: > http://www.cisco.com/web/about/doing_business/legal/cri/ > > > _______________________________________________ > users mailing list > us...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/users -- Hristo Iliev, Ph.D. -- High Performance Computing, RWTH Aachen University, Center for Computing and Communication Seffenter Weg 23, D 52074 Aachen (Germany) Tel: +49 241 80 24367 -- Fax/UMS: +49 241 80 624367
