Re: [mpich-discuss] MCS lock and MPI RMA problem

5 Mar 2017


      Hi Richard,

The window is initialised in MCSLockInit (see book author's code
http://www.mcs.anl.gov/research/projects/mpi/usingmpi/examples-advmpi/rma2/m...)

void MCSLockInit(MPI_Comm comm, MPI_Win *win)
{
  int      *lmem, rank;
  MPI_Aint winsize;
  MPI_Comm_rank(comm,&rank);

  if (MCS_LOCKRANK == MPI_KEYVAL_INVALID)
    MPI_Win_create_keyval(MPI_WIN_NULL_COPY_FN,
			  MPI_WIN_NULL_DELETE_FN,
			  &MCS_LOCKRANK, (void*)0);

  winsize = 2 * sizeof(int);
  if (rank == 0) winsize += sizeof(int);
  MPI_Win_allocate(winsize, sizeof(int), MPI_INFO_NULL, comm,
                   &lmem, win);
  lmem[nextRank] = -1;
  lmem[blocked]  = 0;
  if (rank == 0) {
    lmem[lockTail] = -1;
  }
  MPI_Win_set_attr(*win, MCS_LOCKRANK, (void*)(MPI_Aint)rank);
  MPI_Barrier(comm);
}

Best regards, Ask

Date: Sat, 4 Mar 2017 19:03:13 +0000
...
From: Richard Warren <[email protected]>
To: "[email protected]" <[email protected]>
Subject: Re: [mpich-discuss] MCS lock and MPI RMA problem
Message-ID:
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namprd17.prod.outlook.com>
Content-Type: text/plain; charset="us-ascii"
I don't see that you've actually created an MPI_Win object anywhere.  My
guess is that you need to use MPI_Win_create to initialize your window
before you can do any locks or other RMA operations with it.
________________________________
From: Ask Jakobsen <[email protected]>
Sent: Saturday, March 4, 2017 3:30:09 AM
To: [email protected]
Subject: [mpich-discuss] MCS lock and MPI RMA problem
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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