[MPICH2-dev] Truncated messages

[Rob Ross]

Hi,

Ok.  First, please send the error stack, because it will be interesting 
to see what error is happening.

It's not legal to send something with a typemap of 3 chars and try to 
receive it with a typemap of 3 integers.  So the code is erroneous.

However, we don't normally do checking to see if the typemaps match.  So 
my guess is that the code is inferring that there is a problem because 
only three bytes are sent, but 4 bytes (assuming 32-bit platform) would 
be necessary to constitute a complete integer.

Rob

duncan.thomas at quadrics.com wrote:
> Hi
> 
> I've got some code that behaves differently between mpich 1 & 2 when handling truncated messages. Specifically it runs fine on mpich1, but errors out on mpich2.1.3. I was wondering if anybody could tell me if the code is valid, and if this change in behaviour is intentional?
> 
> #include <stdio.h>
> #include <stdlib.h>
> #include <string.h>
>     
> #include <mpi.h>
> 
> #define BUFSIZE 128
>     
> #define FAIL_ERROR       123
> #define RESFAIL_ERROR    123
> #define INTERNAL_ERROR   123
> 
> void
> if_error(char *function, char *data, int ret)
> {
>     if (ret == 0)
>         return;
> 
>     if (data)
>         printf("%s for %s returned %d (%#x)\n", function, data, ret, ret);
>     else
>         printf("%s returned %d (%#x)\n", function, ret, ret);
> 
>     exit(INTERNAL_ERROR);
> }
> 
> int 
> main (int argc, char *argv[])
> {
>     int ret;
>     char *src, *sendrec;
>     int bufsize = BUFSIZE;
> 
>     int myrank, nprocs;
>     int i;
>     MPI_Status status;
> 
>     int small_non_contig_struct_count = 3;
>     int small_non_contig_struct_blocklens[] = {1, 1, 1};
>     MPI_Aint small_non_contig_struct_disps[] = {0, 2, 4};
>     MPI_Datatype small_non_contig_struct_types[] = {MPI_CHAR, MPI_CHAR, MPI_CHAR};
>     MPI_Datatype small_non_contig_struct_type;
> 
>     int contig_indexed_count = 3;
>     int contig_indexed_blocklens[] = {1, 2, 1};
>     int contig_indexed_indices[] = {4, 8, 16};
>     int contig_indexed_inner_type = MPI_INT;
>     int contig_indexed_type;
>     
>     ret = MPI_Init(&argc, &argv);
>     ret = MPI_Comm_rank(MPI_COMM_WORLD, &myrank);
>     ret = MPI_Comm_size(MPI_COMM_WORLD, &nprocs);
> 
>     if (nprocs < 2) {
>         printf("Need at least 2 procs\n");
>         exit(RESFAIL_ERROR);
>     }
> 
>     ret = MPI_Type_struct(small_non_contig_struct_count, small_non_contig_struct_blocklens, small_non_contig_struct_disps, small_non_contig_struct_types, &small_non_contig_struct_type);
>     if_error("MPI_Type_struct", "small_non_contig_struct_type", ret);
>     
>     ret = MPI_Type_commit(&small_non_contig_struct_type);
>     if_error("MPI_Type_commit", "small_non_contig_struct_type", ret);
> 
>     ret = MPI_Type_indexed(contig_indexed_count, contig_indexed_blocklens, contig_indexed_indices, contig_indexed_inner_type, &contig_indexed_type);
>     if_error("MPI_Type_indexed", "contig_indexed_type", ret);
> 
>     ret = MPI_Type_commit(&contig_indexed_type);
>     if_error("MPI_Type_commit", "contig_indexed_type", ret);
> 
> 
>     ret = MPI_Alloc_mem(bufsize, MPI_INFO_NULL, &src);
> 
>     if (ret != 0) {
>         printf("MPI_Alloc_mem src = #%x\n", ret);
>         exit(INTERNAL_ERROR);
>     }
> 
>     ret = MPI_Alloc_mem(bufsize, MPI_INFO_NULL, &sendrec);
> 
>     if (ret != 0) {
>         printf("MPI_Alloc_mem sendrec buf = #%x\n", ret);
>         exit(INTERNAL_ERROR);
>     }
> 
> 
>     for (i=0; i<bufsize; i++) {
>         src[i] = (char) i+1;
>     }
> 
>     memset(sendrec, 0, bufsize);
> 
>     MPI_Barrier(MPI_COMM_WORLD);
>     if (myrank == 1) {
>         MPI_Send(src, 1, small_non_contig_struct_type, 0, 0xabc, MPI_COMM_WORLD);
>     } else {
>         MPI_Recv(sendrec, 1, contig_indexed_type, 1, 0xabc, MPI_COMM_WORLD, &status);
>     }
> 
>     MPI_Barrier(MPI_COMM_WORLD);
> 
>     MPI_Free_mem(src);
>     MPI_Free_mem(sendrec);
> 
>     return 0;
> }
> 
> 
> Under mpich1 it completes silently, under mpich2 I get an error stack.
> 
> Thanks
>