Hi.
The following server/client example is selected from OpenMPI. 
I compile and run the example by using OpenMPI, everything is OK.
BUT, I compile and run it by mpich(3.1.3), which is BLOCKED as my example!

This is a bug?

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <mpi.h>

/*

   LOGIC:

     - the 'server' opens a port and write the info to a file
     - the 'clients' open the file and connect to the port
     - after each accept, the server and client do a merge to
       convert the intercomm to an intracomm

   DETAIL STEPS:

     - server open port
     - server does accept
     - client #1 does connect
     - server and client #1 do merge
     - server does accept
     - client #2 does connect
     - server, client #1 and client #2 do merge
     - server does accept
     - client #3 does connect
     - server, client #1, client #2 and client #3 do merge

*/

#define TAG 0

#define CHK(code) do                            \
  {                                             \
    int retval = code ;                         \
    if (retval != MPI_SUCCESS)                  \
    {                                           \
      fprintf(stderr, "Error: " #code "\n") ;   \
      exit(1) ;                                 \
    }                                           \
  } while(0)

int main(int argc, char *argv[])
{
  char hostname[255] ;
  char buff[255] ;

  int role ;
  int num_clients ;
  int size, rank ;

  FILE *fp ;
  char server_port_name[MPI_MAX_PORT_NAME] ;

  MPI_Comm intercomm, intracomm ;
  MPI_Status status ;
  int msg_count ;
  int i ;

  /* sanity check the args */
  if(argc != 3)
  {
    fprintf(stderr, "usage %s <num clients> <1:server | 0:client>\n", argv[0]) ;
    exit(1) ;
  }

  num_clients = atoi(argv[1]) ;
  role = atoi(argv[2]) ;

  if (num_clients <= 0 || (role != 0 && role != 1))
  {
    fprintf(stderr, "usage %s <num clients> <1:server | 0:client>\n", argv[0]) ;
    exit(1) ;
  }

  /* initialize MPI  */
  CHK(MPI_Init(&argc, &argv)) ;

  /* get the node name */
  {
    int retval = gethostname(hostname, 255) ;
    if(retval == -1)
    {
      fprintf(stderr, "gethostname failed: %s\n", strerror(errno)) ;
      exit(1) ;
    }
  }

  /* server */
  if(role == 1)
  {
    printf("SERVER: on node '%s'\n", hostname) ;

    /* open port to establish connections */
    CHK(MPI_Open_port(MPI_INFO_NULL, server_port_name)) ;

    printf("SERVER: opened port=%s\n", server_port_name) ;

    /* store the port name */
    fp = fopen("server_port_name.txt", "w") ;
    if(fp == NULL)
    {
      fprintf(stderr, "fopen failed: %s\n", strerror(errno)) ;
      exit(1) ;
    }
    fprintf(fp, "%s", server_port_name) ;
    fclose(fp) ;

    /* the server accepts connections from all the clients */
    for(i = 0 ; i < num_clients ; i++ )
    {
      /* accept connections at this port */
      CHK(MPI_Comm_accept(server_port_name, MPI_INFO_NULL, 0,
                          i == 0 ? MPI_COMM_WORLD : intracomm,
                          &intercomm)) ;

      printf("SERVER: accepted connection from client %d\n", i+1) ;

      /* merge, to form one intra communicator */
      CHK(MPI_Intercomm_merge(intercomm, 0, &intracomm)) ;

      printf("SERVER: merged with client %d\n", i+1) ;

      CHK(MPI_Comm_size(intracomm, &size)) ;
      CHK(MPI_Comm_rank(intracomm, &rank)) ;

      printf("SERVER: after merging with client %d: size=%d rank=%d\n", i+1, size, rank) ;
    }
  } /* end server */

  /* client */
  if(role == 0)
  {
    printf("CLIENT: on node '%s'\n", hostname) ;

    fp = fopen("server_port_name.txt", "r") ;
    if(fp == NULL)
    {
      fprintf(stderr, "fopen failed: %s\n", strerror(errno)) ;
      exit(1) ;
    }
    fscanf(fp, "%s", server_port_name) ;
    fclose(fp) ;

    printf("CLIENT: attempting to connect to server on port=%s\n", server_port_name) ;

    /* connect to the server */
    CHK(MPI_Comm_connect (server_port_name, MPI_INFO_NULL, 0, MPI_COMM_WORLD, &intercomm)) ;

    printf("CLIENT: connected to server on port\n") ;

    /* merge the server and client to one intra communicator */
    CHK(MPI_Intercomm_merge(intercomm, 1, &intracomm)) ;

    printf("CLIENT: merged with existing intracomm\n") ;

    CHK(MPI_Comm_size(intracomm, &size)) ;
    CHK(MPI_Comm_rank(intracomm, &rank)) ;

    printf("CLIENT: after merging, new comm: size=%d rank=%d\n", size, rank) ;

    for (i = rank ; i < num_clients ; i++)
    {
      /* client performs a collective accept */
      CHK(MPI_Comm_accept(server_port_name, MPI_INFO_NULL, 0, intracomm, &intercomm)) ;

      printf("CLIENT: connected to server on port\n") ;

      /* merge the two intra comms back to one communicator */
      CHK(MPI_Intercomm_merge(intercomm, 0, &intracomm)) ;

      printf("CLIENT: merged with existing members\n") ;

      CHK(MPI_Comm_size(intracomm, &size)) ;
      CHK(MPI_Comm_rank(intracomm, &rank)) ;

      printf("CLIENT: new size after merging with existing members: size=%d rank=%d\n", size, rank) ;
    }

  } /* end client */

  CHK(MPI_Comm_size(intracomm, &size)) ;
  CHK(MPI_Comm_rank(intracomm, &rank)) ;

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

  if(rank == 0)
  {
    msg_count = num_clients ;

    while(msg_count)
    {
      CHK(MPI_Recv(buff, 255, MPI_CHAR, MPI_ANY_SOURCE,
                   MPI_ANY_TAG, intracomm, &status)) ;

      printf("Received hello msg from '%s'\n", buff) ;
      msg_count-- ;
    }
  }
  else
  {
    /* all ranks > 0 */

    CHK(MPI_Send(hostname, strlen(hostname) + 1, MPI_CHAR, 0, TAG, intracomm)) ;
  }

  CHK(MPI_Finalize()) ;

  fprintf(stderr, "Rank %d is exiting\n", rank);
  return 0 ;
}


At 2015-01-24 10:43:07, "haozi" <yidanyiji@163.com> wrote:
Thanks, Bland and Lu.

You are right.
These functions (such as MPI_Comm_accept, MPI_Comm_connect, MPI_Intercomm_merge) can help me to get a new intra-communicator which contains ALL MPI processes.

Now, I have a more complicated example:
    I have a server and a client. 
    After they merge into an intra-communicator by using connect/accept/merge fucntions, another client would plant to join them, too.
    I thought that the code is simular, but the code CAN'T work: Second client CAN'T connect. The new comm CAN'T accept. They all BLOCK.

    As you see, the second client BLOCKs at MPI_Comm_connect, and processes of newcomm BLOCK at MPI_Comm_accept.
    What's Wrong with my code? 

//server
#include "mpi.h"
int main(int argc, char *argv[])
{
MPI_Comm client, client2, newcomm, newcomm2;
MPI_Status status;
char port_name[MPI_MAX_PORT_NAME];
char port_name2[MPI_MAX_PORT_NAME];
int size, again, rank, myrank;

MPI_Init(&argc, &argv);
MPI_Open_port(MPI_INFO_NULL, port_name);//OK

MPI_Comm_accept(port_name, MPI_INFO_NULL, 0, MPI_COMM_WORLD,&client);//OK

MPI_Intercomm_merge(client,11,&newcomm);//OK

    MPI_Barrier(newcomm);//OK

MPI_Open_port(MPI_INFO_NULL, port_name2);// OK

MPI_Comm_accept(port_name2, MPI_INFO_NULL, 0, newcomm,&client2);// BLOCK here, Wath's wrong?

MPI_Intercomm_merge(client2,12,&newcomm2);

    MPI_Barrier(newcomm2);

    MPI_Close_port(port_name);
MPI_Comm_disconnect(&client);
    MPI_Close_port(port_name2);
MPI_Comm_disconnect(&client2);

MPI_Finalize();
return 0;
}

//first client
#include "mpi.h"
int main( int argc, char **argv )
{
MPI_Comm server,newcomm,newcomm2,client2;
char port_name[MPI_MAX_PORT_NAME];
char port_name2[MPI_MAX_PORT_NAME];
int size,rank;

MPI_Init( &argc, &argv );
strcpy( port_name, argv[1] );
MPI_Comm_connect( port_name, MPI_INFO_NULL, 0, MPI_COMM_SELF,&server );//OK

MPI_Intercomm_merge(server,11,&newcomm);//OK

MPI_Barrier(newcomm);//OK

MPI_Open_port(MPI_INFO_NULL, port_name2);//OK
MPI_Comm_accept(port_name2, MPI_INFO_NULL, 0, newcomm,&client2);// BLOCK here, Wath's wrong?

MPI_Intercomm_merge(client2,12,&newcomm2);

MPI_Barrier(newcomm2);

    MPI_Close_port(port_name2);
MPI_Comm_disconnect(&client2);
MPI_Comm_disconnect( &server );
MPI_Finalize();
return 0;
}

//second client
#include "mpi.h"
int main( int argc, char **argv )
{
MPI_Comm server,newcomm;
char port_name[MPI_MAX_PORT_NAME];
int size,rank;

MPI_Init( &argc, &argv );
strcpy( port_name, argv[1] );//OK
MPI_Comm_connect( port_name, MPI_INFO_NULL, 0, MPI_COMM_SELF,&server );// BLOCK here, Wath's wrong?
MPI_Comm_size(MPI_COMM_WORLD, &size);

MPI_Intercomm_merge(server,11,&newcomm);

MPI_Barrier(newcomm);
MPI_Comm_disconnect( &server );
MPI_Finalize();
return 0;
}




At 2015-01-23 23:14:06, "Wesley Bland" <wbland@anl.gov> wrote:

The size of MPI_COMM_WORLD will never change. That communicator is set at initialization time and is not ever modified. However, when you finish connect/accept, you get a new communicator which you can merge into an intra-communicator which functions exactly like MPI_COMM_WORLD. Don’t be attached to the variable name MPI_COMM_WORLD. It’s just a variable and you can use a different one with very little extra work.

Thanks,
Wesley


On Thu, Jan 22, 2015 at 6:14 PM, haozi <yidanyiji@163.com> wrote:
Thanks, Lu.
My simple code is as following.
//server
#include "mpi.h"

int main(int argc, char *argv[])
{
MPI_Comm client;
MPI_Status status;
char port_name[MPI_MAX_PORT_NAME];
int size, again;

MPI_Init(&argc, &argv);
MPI_Comm_size(MPI_COMM_WORLD, &size);
MPI_Open_port(MPI_INFO_NULL, port_name);
printf("server port_name is %s\n\n", port_name);
MPI_Comm_accept(port_name, MPI_INFO_NULL, 0, MPI_COMM_WORLD,&client);
MPI_Comm_size(MPI_COMM_WORLD, &size);
printf("At server, comm_size=%d @ MPI_COMM_WORLD=%x, Client_World=%x\n",size,MPI_COMM_WORLD, client);
MPI_Comm_size(client, &size);
printf("At server, client_size=%d @ MPI_COMM_WORLD=%x, Client_World=%x\n",size,MPI_COMM_WORLD, client);

MPI_Comm_disconnect(&client);
MPI_Finalize();
return 0;
}

//client
#include "mpi.h"

int main( int argc, char **argv )
{
MPI_Comm server;
char port_name[MPI_MAX_PORT_NAME];
int size;

MPI_Init( &argc, &argv );
strcpy( port_name, argv[1] );
printf("server port name:%s\n",port_name);
MPI_Comm_connect( port_name, MPI_INFO_NULL, 0, MPI_COMM_WORLD,&server );
MPI_Comm_size(MPI_COMM_WORLD, &size);
printf("At client, comm_size=%d @ MPI_COMM_WORLD=%x, Server_World=%x\n",size,MPI_COMM_WORLD,server);
MPI_Comm_size(server, &size);
printf("At client, server_size=%d @ MPI_COMM_WORLD=%x, Server_World=%x\n",size,MPI_COMM_WORLD,server);

MPI_Comm_disconnect( &server );
MPI_Finalize();
return 0;
}

The run command is as following.
mpiexec -n 1 ./server
mpiexec -n 1 ./client

BUT, the SIZE is 1, NOT 2.

My question is as before: How does the size of MPI_COMM_WORLD change to 2 ?


At 2015-01-23 00:30:43, "Huiwei Lu" <huiweilu@mcs.anl.gov> wrote:
You may take a look at MPI_Comm_accept and MPI_Comm_connect, which will connect a new client process to a server process. See Chap. 10 of MPI 3.0 standard (www.mpi-forum.org/docs/mpi-3.0/mpi30-report.pdf) for a detail example.

--
Huiwei Lu
Postdoc Appointee
Mathematics and Computer Science Division
Argonne National Laboratory

On Thu, Jan 22, 2015 at 9:41 AM, haozi <yidanyiji@163.com> wrote:
Hi, guys.

              Singleton init. This is the process by which a program that was not started with mpiexec can become an MPI process and make use of all MPI features, including MPI_Comm_spawn, needs to be designed and documented, with particular attention to the disposition of standard I/O. Not all process managers will want to or even be able to create a new mpiexec process, so this needs to be negotiated. Similarly, the dispostion of stdio needs to be negotiated between the singleton process and the process manager. To address these issues, a new singleton init protocol has been implemented and tested with the gforker process manager.

I am very interested in this function.
Can this function solve the following question:
              At beginning, the MPI job uses the mpiexec commond to start three MPI processes. That is to say, there are three MPI processes in MPI_COMM_WORLD. At some time, the job find itself to need another MPI process to cooperate the three MPI processes. So the question is: Could PMI help an non-MPI process to become a MPI process of the current MPI_COMM_WORLD? That is to say, Could the non-MPI process use the PMI function to become a member process of the current MPI job which would have FOUR MPI processes in MPI_COMM_WORLD?

Is there some method to solve question?
Is anybody have some example?

Thandks!!!



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