[mpich-discuss] Question reg usage with MPI_THREAD_MULTIPLE

[Ramesh Vinayagam]

Hello,


I having a question regarding the usage of MPI_THREAD_MULTIPLE.

I was wondering whether this scenario works with MPI

Process 0
Thread 1 -> probes and receives
Thread 2 -> Sends to  process 0

Process 1

Thread 1 -> probes and receives
Thread 2 -> Sends to  process 1

I wrote a simple code, and it seems to hang with mpich2. I am not sure
whether or not this feature is supported with MPI, can anyone let me know
whether what I do here is correct or wrong?


Here is the code.. This code hangs when I use it with two processes. It
works with one process.

Thanks
Ramesh
____________________________________________________________________________________________________________________________________________________
#include <stdio.h>
#include <stdlib.h>
#include <mpi.h>
#include <string.h>
#include <assert.h>

typedef struct
{
  int thread;
  MPI_Comm comm;
  int rank;
} thdata;

void probe_recv (void *ptr){
  thdata *data;
  data = (thdata *) ptr;
  int count, flag = 0;
  MPI_Status status;
  char buf[256];

  printf("%d :Thread :%d Prbes and receives \n", data->rank, data->thread);
  while (!flag){
    MPI_Iprobe(data->rank, 0, data->comm, &flag, &status);
  }
  MPI_Get_count( &status, MPI_CHAR, &count);
  printf("%d :Thread :%d count : %d \n", data->rank, data->thread, count);

  MPI_Recv( &buf,
    count,
    MPI_CHAR,
    data->rank,
    status.MPI_TAG,
    data->comm,
    MPI_STATUS_IGNORE);

  printf("%d Message : %s \n", data->rank,buf);
}

void send(void *ptr){
  thdata *data;
  char buffer[256];
  data = (thdata *) ptr;
  printf("%d: Thread :%d Sends \n", data->rank, data->thread);
  strcpy(buffer,"Hello World");
  MPI_Send(&buffer,256, MPI_CHAR, data->rank, 0, data->comm);
  printf("%d: Thread :%d send completed \n",
 data->rank,
 data->thread);
}


int main(int argc, char *argv[]){

  int provided, i[2], rank, size;
  MPI_Status  status;
  pthread_t thread_a, thread_b;
  MPI_Comm communicator[2];
  thdata data1, data2;

  MPI_Init_thread(&argc, &argv, MPI_THREAD_MULTIPLE, &provided);

  if (provided != MPI_THREAD_MULTIPLE){
printf("Error\n");
MPI_Abort(911, MPI_COMM_WORLD);
  }
  MPI_Comm_rank(MPI_COMM_WORLD, &rank);
  MPI_Comm_size(MPI_COMM_WORLD, &size);
  assert (size == 2);
  MPI_Comm_dup(MPI_COMM_WORLD,&communicator[rank]);

  data1.comm = communicator[rank];
  data1.thread = 1;
  data1.rank = rank;
  pthread_create (&thread_a, NULL, (void *) &probe_recv, (void *)&data1);

  data2.comm = communicator[rank];
  data2.thread = 2;
  data2.rank = rank;
  pthread_create (&thread_b, NULL, (void *) &send, (void *)&data2);

  pthread_join(thread_a, NULL);
  pthread_join(thread_b, NULL);
  MPI_Finalize();
}
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