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

http://www.mcs.anl.gov/~huiweilu/

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

Hi, guys.

This web page (http://wiki.mpich.org/mpich/index.php/PMI_v2_Design_Thoughts) says:

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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