[mpich-discuss] MPI_Bsend

[Pavan Balaji]

You need to allocate MPI_BSEND_OVERHEAD bytes more. See pg. 274 of the 
MPI-2.2 standard.

  -- Pavan

On 11/10/2011 01:30 PM, Wei-keng Liao wrote:
> My program using MPI_Bsend failed due to insufficient space,
> even though it did allocate exact size required, but not one byte more.
> I wonder if this is an mpich bug, or MPI requires more space than needed.
> If it is later, how much more is needed?
>
> Wei-keng
>
> error message:
> $ mpiexec -machinefile=machinefile -l -n 4 a.out
> [2] Fatal error in MPI_Bsend: Invalid buffer pointer, error stack:
> [2] MPI_Bsend(182).......: MPI_Bsend(buf=0x7fff81048a50, count=1024, MPI_BYTE, dest=0, tag=2, MPI_COMM_WORLD) failed
> [2] MPIR_Bsend_isend(318): Insufficient space in Bsend buffer; requested 1024; total buffer size is 4096
>
> ---- bsend.c -----------------------------
> #include<stdio.h>
> #include<stdlib.h>
> #include<mpi.h>
>
> int main(int argc, char **argv)
> {
>      int  i, rank, nprocs, src, bufsize;
>      char buf[1024];
>      void *bsend_buf = NULL;
>      MPI_Status status;
>
>      MPI_Init(&argc,&argv);
>      MPI_Comm_rank(MPI_COMM_WORLD,&rank);
>      MPI_Comm_size(MPI_COMM_WORLD,&nprocs);
>
>      bufsize = 1024*4;
>      // bufsize += 512; // if uncommented, the program runs successfully
>      MPI_Buffer_attach(malloc(bufsize), bufsize);
>
>      for (i=0; i<4; i++) {
>          if (rank>  0)
>              MPI_Bsend(buf, 1024, MPI_BYTE, 0, rank, MPI_COMM_WORLD);
>          else {
>              for (src=1; src<nprocs; src++)
>                  MPI_Recv(buf, 1024, MPI_BYTE, src, src, MPI_COMM_WORLD,&status);
>          }
>      }
>
>      MPI_Buffer_detach(&bsend_buf,&bufsize);
>      free(bsend_buf);
>      MPI_Finalize();
>      return 0;
> }
>
>
>
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-- 
Pavan Balaji
http://www.mcs.anl.gov/~balaji