[mpich-discuss] uninitialized MPI_Status object

[Wei-keng Liao]

My test program can be compiled with command "mpicc get_count.c -o get_count"
and run "mpiexec -n 4 get_count". For correct (expected) result, nothing
will be printed on stdout. Otherwise, error messages will be printed. 

My point is MPI_Get_count does not report correct result because
MPI collective I/O call fails to initialize the MPI_Status object.

I found that OpenMPI and earlier version of MPICH (2-1.2.1) can run
this test code correctly.

The test failed when I ran MPICH 3.1.4 and the current from GIT repo.

Wei-keng

On Mar 26, 2016, at 3:21 PM, יוסף אלון wrote:

> בס"ד
> 
> becuse all the command confusion.
> which command should i put to run the above code?
> 
> 2016-03-26 3:31 GMT+03:00 Wei-keng Liao <wkliao at eecs.northwestern.edu>:
> 
> I notice an uninitialized MPI_Status object can make MPI_Get_count return a wrong result,
> when the data amount in the MPI operation is zero (although I only checked MPI-IO).
> Attached is a test program that uses MPI collective read where only root process has
> non-zero length data to read. The expected result from MPI_Get_count is 0 for all
> non-root process. To mimic an uninitialized MPI_Status object, I call memset to make
> the object non-zero.
> 
> Here is the code fragment.
> 
>     if (rank == 0) len = 10;
>     else len = 0;
> 
>     MPI_File_read_all(fh, buf, len, MPI_BYTE, &status);
> 
>     MPI_Get_count(&status, MPI_BYTE, &get_size);
> 
> For process rank > 0, get_size may not be 0.
> 
> 
> Wei-keng
> 
> 
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> בברכה, יוסף אלון
> 050-4916740
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