Perhaps I am doing something wrong. The childrens' calls to
MPI_Intercomm_merge never return.
Here's the chronology (with 2 children):
parent calls MPI_Init
parent calls MPI_Comm_spawn
child calls MPI_Init
child calls MPI_Init
parent call to MPI_Comm_spawn returns
(long pause inserted)
parent calls MPI_Intercomm_merge
child MPI_Init returns
child calls MPI_Intercomm_merge
child MPI_Init returns
child calls MPI_Intercomm_merge
parent MPI_Intercomm_merge returns
... but the child processes never return from the MPI_InterComm_merge
function.
Here are some code snippets:
############# parent:
MPI_Init(NULL,NULL);
int nkids=2;
int errs[nkids];
MPI_Comm kid;
cerr << "parent calls MPI_Comm_spawn" << endl;
CHECK_MPI_CODE(
MPI_Comm_spawn("test_mpi",NULL,nkids,MPI_INFO_NULL,0,MPI_COMM_WORLD,&kid,errs)
);
cerr << "parent call to MPI_Comm_spawn returns" << endl;
for (k=0;k<nkids;++k)
CHECK_MPI_CODE( errs[k] );
MPI_Comm allmpi;
cerr << "(long pause)" << endl;
sleep(3);
cerr << "parent calls MPI_Intercomm_merge\n";
CHECK_MPI_CODE( MPI_Intercomm_merge( kid, 0, &allmpi) );
cerr << "parent MPI_Intercomm_merge returns\n";
############### child:
fprintf(stderr,"child calls MPI_Init \n");
CHECK_MPI_CODE( MPI_Init(NULL,NULL) );
fprintf(stderr,"child MPI_Init returns\n");
MPI_Comm parent;
CHECK_MPI_CODE( MPI_Comm_get_parent(&parent) );
fprintf(stderr,"child calls MPI_Intercomm_merge \n");
MPI_Comm allmpi;
CHECK_MPI_CODE( MPI_Intercomm_merge( parent, 1, &allmpi) );
fprintf(stderr,"child call to MPI_Intercomm_merge returns\n");
(the above line never gets executed)
Aurélien Bouteiller wrote:
MPI_Intercomm_merge is what you are looking for.
Aurelien
Le 26 juil. 08 à 13:23, Mark Borgerding a écrit :
Okay, so I've gotten a little bit closer.
I'm using MPI_Comm_spawn to start several children processes. The
problem is that the children are in their own group, separate from
the parent (just the like the documentation says). I want to merge
the children's group with the parent group so I can efficiently
Send/Recv data between them..
Is this possible?
Plan B: I guess if there is no elegant way to merge all those
processes into one group, I can connect sockets and make intercomms
to talk from the parent directly to each child.
-- Mark
Mark Borgerding wrote:
I am writing a code module that plugs into a larger application
framework. That framework loads my code module as a shared object.
So I do not control how the first process gets started, but I still
want it to be able to start and participate in an MPI group.
Here's roughly what I want to happen ( I think):
framework app running (not under my control)
-> framework loads mycode.so shared object into its process
-> mycode.so starts mpi programs on several hosts (e.g.
via system call to mpiexec )
-> initial mycode.so process participates in the group
he just started (e.g. he shows up in MPI_Comm_group, can use
MPI_Send, MPI_Recv, etc. )
Can this be done?
I am running under Centos 5.2
Thanks,
Mark
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