[mpich-discuss] How to make a non-MPI process to become a MPI process of MPI_COMM_WORLD?

[Huiwei Lu]

Based on my understanding, MPI_COMM_WORLD is a pre-defined
intra-communicator. I don't think you can change the size of it.

What MPI_Comm_accept and MPI_Comm_connect create is a inter-communicator,
which consist of two disjoint group of processors. (See Chap 6.6 of MPI 3.0
standard.) If you need a intra-communicator, you may use
MPI_Intercomm_merge to create one.

--
Huiwei

On Thu, Jan 22, 2015 at 6:14 PM, haozi <yidanyiji at 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 at 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 at 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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>
>
>
>
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