[mpich-discuss] MCS lock and MPI RMA problem

[Ask Jakobsen]

Hi,

I have downloaded the source code for the MCS lock from the excellent book
"Using Advanced MPI" from
http://www.mcs.anl.gov/research/projects/mpi/usingmpi/examples-advmpi/rma2/mcs-lock.c

I have made a very simple piece of test code for testing the MCS lock but
it works at random and often never escapes the busy loops in the acquire
and release functions (see attached source code). The code appears
semantically correct to my eyes.

#include <stdio.h>
#include <mpi.h>
#include "mcs-lock.h"

int main(int argc, char *argv[])
{
  MPI_Win win;
  MPI_Init( &argc, &argv );

  MCSLockInit(MPI_COMM_WORLD, &win);

  int rank, size;
  MPI_Comm_rank(MPI_COMM_WORLD, &rank);
  MPI_Comm_size(MPI_COMM_WORLD, &size);

  printf("rank: %d, size: %d\n", rank, size);


  MCSLockAcquire(win);
  printf("rank %d aquired lock\n", rank);   fflush(stdout);
  MCSLockRelease(win);


  MPI_Win_free(&win);
  MPI_Finalize();
  return 0;
}


I have tested on several hardware platforms and mpich-3.2 and mpich-3.3a2
but with no luck.

It appears that the MPI_Win_Sync are not "refreshing" the local data or I
have a bug I can't spot.

A simple unfair lock like
http://www.mcs.anl.gov/research/projects/mpi/usingmpi/examples-advmpi/rma2/ga_mutex1.c
works perfectly.

Best regards, Ask Jakobsen
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