>Note from my first mail on this thread:
Thank you again for the attention and for your answer,
>"As per MPI-2 p84, the command, argv, maxprocs, and info arguments to
>MPI_COMM_SPAWN are only significant in the root process."
>Specifically: MPI says that it doesn't matter what you put in argv on
>any process other than the root. The argv from the root is the only
>argv that matters.
Now I really understood the function of the root, but the problem,
using the MPI_Comm_spawn function is that: for example, using my program
below, for the rank (mon_rang) equal to 0, it will execute 8 times with
for the process which corresponds to the rank 0 and seven more times to
the othes 7 processes and not just one time for each process. How can I
remedy that ?
>By changing your application to use MPI_COMM_SELF, this effectively
>makes every process the root, and therefore it launches 8 different
>processes (each with their own MPI_COMM_WORLD). That's why you see 8
>"rank 0"s. Yes, they're all rank 0, but from different
>MPI_COMM_WORLD's. Additionally, none of those processes can communicate
>with each other -- they can only communicate with their parent, which,
>in this case, is one process from the original MPI application that
>you ran (probably via mpirun).
Yes, I'm using mpirun.
>Also note from my previous mail:
>"If you want to launch N processes, each with different arguments, then
>you need to use either multiple calls to MPI_COMM_SPAWN (i.e., each
>one with a different argv), or MPI_COMM_SPAWN_MULTIPLE, where you can
>specify an array of argv."
But what I want, is to launch a new process from every process existing,
and try to merge all worlds after that. And for that, I can't employ
MPI_comm_spawn_multiple, because if I start the program with 8
processes, just the root process will launch the new processes and
it isn't the purpose of the program.
>If you want these 8 processes to share a common MPI_COMM_WORLD, and you
>only want one launch command, then you really need to use
>MPI_COMM_SPAWN_MULTIPLE.
Thank you again,
Gabriel Paillard
On Dec 6, 2004, at 11:32 AM, Gabriel Antoine Louis Paillard wrote:
Now, after some modifications in the same code, finally I have
the desired output (all processes received their argument), but
the rank
0 executed 8 times the same thing.
#include <stdio.h>
#include <mpi.h>
int slave ();
int main(int argc,char *argv[])
{
int myrank;
double starttime,endtime;
MPI_Init(&argc, &argv);
starttime = MPI_Wtime();
MPI_Comm_rank(MPI_COMM_WORLD, &myrank);
switch(myrank) {
case 0:
slave(1);
break;
case 1:
slave(7);
break;
case 2:
slave(11);
break;
case 3:
slave(13);
break;
case 4:
slave(17);
break;
case 5:
slave(19);
break;
case 6:
slave(23);
break;
case 7:
slave(29);
break;
}
endtime = MPI_Wtime();
printf("time: %1.15f\n", endtime-starttime);
MPI_Finalize();
exit(0);
}
int slave (unsigned long int argument)
{
char command[] = "Program";
char **argv;
int errcode;
int err,mon_rang;
MPI_Comm nouveau_monde;
mon_rang=MPI_Comm_rank(MPI_COMM_WORLD, &mon_rang);
argv=(char **)malloc(2*sizeof(char *));
argv[0]=(char*)malloc(100*sizeof(char));
sprintf(argv[0],"%ld",argument);
argv[1] = NULL;
MPI_Comm_set_errhandler(MPI_COMM_WORLD,MPI_ERRORS_RETURN);
err=MPI_Comm_spawn(command,argv,8,MPI_INFO_NULL,mon_rang,MPI_COMM_SELF, &nouveau_monde,&errcode);
return(0);
}
Thanks again,
Gabriel Paillard
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{+} http://www.lam-mpi.org/
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