Thanks. I thought those threads will not interfere with each other since they have no common variables except std IO. 
 

Date: Thu, 3 Sep 2009 09:01:28 -0700
From: Eugene.Loh@sun.com
To: users@open-mpi.org
Subject: Re: [OMPI users] Help!

guosong wrote:
I am new to open MPI
I am not, but I'm not real familiar with thread-safe MPI programming.  Still, I saw no other replies to your question, so I'll make an attempt to answer.

MPI does not guarantee thread safety.  E.g., see http://www.mpi-forum.org/docs/mpi-20-html/node162.htm#Node162 and the ensuing pages.

To do what you want to do, you need to make sure you have thread safety.  There is a standard MPI interface for doing so.  I'm not good at C++, so here is a C example:



#include <stdio.h>
#include <mpi.h>

int main(int argc, char **argv) {
  int provided;

  /* start MPI, asking for support for multiple threads */
  MPI_Init_thread(&argc,&argv,MPI_THREAD_MULTIPLE,&provided);

  /* report what level of support is actually provided */
  if ( MPI_THREAD_SINGLE     == provided ) printf(" MPI_THREAD_SINGLE\n");
  if ( MPI_THREAD_FUNNELED   == provided ) printf(" MPI_THREAD_FUNNELED\n");
  if ( MPI_THREAD_SERIALIZED == provided ) printf(" MPI_THREAD_SERIALIZED\n");
  if ( MPI_THREAD_MULTIPLE   == provided ) printf(" MPI_THREAD_MULTIPLE\n");

  /* exit */
  MPI_Finalize();

  return 0;
}



Run this program.  If the program does not print out "MPI_THREAD_MULTIPLE", you're not getting the level of thread support you require and your program is not guaranteed to run properly.  You have to make sure you're using a thread-safe MPI before you can expect your program to work.

The next question is whether Open MPI is thread safe, and I'll leave you with this:
http://www.open-mpi.org/faq/?category=supported-systems#thread-support

G ood luck.  Again, I'm not experienced with thread-safe MPI programming (though I understand the general concepts).


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