=====MPI-Beispiel ring.c=====

C-Programm
%%(c;;ring.c:)
/* MPI-Beispiel
R0 sendet zu R1
R1 empfängt und sendet zu R2
R2 empfängt und sendet zu R3

... empfängt und sendet zu R0
R0 empfängt und sendet zu R1
usw.

http://www.tnotes.de/MpiBeispielRing

Compile: mpicc -o ring ring.c
Start: mpiexec -n 6 ./ring

@author Andreas Tobola
@since 06.12.2008
*/
#include "mpi.h"
#include <stdio.h>
#include <string.h>

int main(int argc, char** argv)
{
int size, rank, prank, nrank;
char sdata[] = "Wir spielen mit MPI!";
char rdata[30];
int data_size;
int i;
MPI_Status stat;

data_size = sizeof(sdata);

MPI_Init(&argc, &argv);
MPI_Comm_size( MPI_COMM_WORLD, &size );
MPI_Comm_rank( MPI_COMM_WORLD, &rank );


// Calcualte previous prozess rank
prank = rank-1;
if (prank==-1)
prank = size-1;

// Calcualte next prozess rank
nrank = (rank+1) % size;

// If we are the first (rank 0), first token has to be send
if (rank==0)
{
sleep(2);
MPI_Send(sdata, data_size, MPI_CHAR, 1, 1, MPI_COMM_WORLD );
printf ("R%d sent data to R%d.\n", rank, nrank );
}


for(i=0; i<10; i++)
{

// Wait and receive data form prank
printf ("R%d is waiting for R%d...\n", rank, prank);
memset(rdata, 0 , 30);
MPI_Recv(rdata, data_size, MPI_CHAR, prank , 1, MPI_COMM_WORLD, &stat);

// Print and forward data to nrank
printf( "R%d received from R%d: %s\n", rank, prank, rdata);
usleep(100000);
MPI_Send(rdata, data_size, MPI_CHAR, nrank , 1, MPI_COMM_WORLD );
printf ("R%d sent data to R%d.\n", rank, nrank );

}

//printf( "Finalize %d/%d\n", rank, size );
MPI_Finalize();
return 0;
}


%%

Kompilieren
%%(bash)
mpicc ring.c -o ring
%%

Mit vier Prozessen auf einem Rechner testen
%%
mpiexec -n 4 ring
%%

Ausgabe
%%
R1 is waiting for R0...
R2 is waiting for R1...
R3 is waiting for R2...
R0 sent data to R1.
R0 is waiting for R3...
R1 received from R0: Wir spielen mit MPI!
R1 sent data to R2.
R1 is waiting for R0...
R2 received from R1: Wir spielen mit MPI!
R2 sent data to R3.
R2 is waiting for R1...
R3 received from R2: Wir spielen mit MPI!
R0 received from R3: Wir spielen mit MPI!
R3 sent data to R0.
R3 is waiting for R2...
R0 sent data to R1.
R0 is waiting for R3...
R1 received from R0: Wir spielen mit MPI!
R2 received from R1: Wir spielen mit MPI!
R1 sent data to R2.
R1 is waiting for R0...
R2 sent data to R3.
R2 is waiting for R1...
R3 received from R2: Wir spielen mit MPI!
R0 received from R3: Wir spielen mit MPI!
R3 sent data to R0.
R3 is waiting for R2...
R0 sent data to R1.
R0 is waiting for R3...
R1 received from R0: Wir spielen mit MPI!
R2 received from R1: Wir spielen mit MPI!
R1 sent data to R2.
R1 is waiting for R0...
R2 sent data to R3.
R2 is waiting for R1...
R3 received from R2: Wir spielen mit MPI!
R0 received from R3: Wir spielen mit MPI!
R3 sent data to R0.
R3 is waiting for R2...
...

%%


Mit drei Rechnern testen
%%(bash)
mpiexec -n 1 -host amygdala ~/code/mpi/04_ring/ring : -n 1 -host IBM ~/mpi/ring : -n 1 -host Medusa ~/mpi/ring
%%

%%
R2 is waiting for R1...
R1 is waiting for R0...
R0 sent data to R1.
R0 is waiting for R2...
R1 received from R0: Wir spielen mit MPI!
R2 received from R1: Wir spielen mit MPI!
R1 sent data to R2.
R1 is waiting for R0...
R0 received from R2: Wir spielen mit MPI!
R2 sent data to R0.
R2 is waiting for R1...
...
%%



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