The following code fails during runtime because of the MPI Scatter Error which I am not able to fix. When following documentation and other similar error pages, I didn't see any issue. Please help. I am using openmpi/4.0.5-gcc.
#include <stdio.h>
#include <stdlib.h>
#include "mpi.h"
#define UPPER_LIMIT 4
#define master 0
int main(int argc, char *argv[])
{
int *data;
int process_id, total_process, temp_result;
int i, tag, final_result;
MPI_Init(&argc, &argv);
MPI_Comm_rank(MPI_COMM_WORLD, &process_id);
MPI_Comm_size(MPI_COMM_WORLD, &total_process);
MPI_Status status;
if ( total_process > UPPER_LIMIT )
{
if ( process_id == 0 )
printf("max allowed processes limit [%d] exceeded.\n", UPPER_LIMIT);
exit(0);
}
final_result = 0;
for ( i = 0; i < total_process; i ){
data[i] = (int)i;
}
int j;
for(j = 0; j < total_process; j ) {
printf("%d ", data[j]);
if(j==total_process-1)
printf("*** %d\n", process_id);
}
MPI_Scatter(data, total_process, MPI_INT, &temp_result, 1, MPI_INT, 0, MPI_COMM_WORLD);
if(process_id!=master){
temp_result = temp_result/process_id;
MPI_Reduce(&temp_result, &final_result, 1, MPI_INT, MPI_SUM, 1, MPI_COMM_WORLD);
}
if(final_result>0){
tag = process_id;
MPI_Send(&final_result, 1, MPI_INT, 0, tag, MPI_COMM_WORLD);
}
if(process_id==master){
MPI_Recv(&final_result, 1, MPI_INT, MPI_ANY_SOURCE, MPI_ANY_TAG, MPI_COMM_WORLD, &status);
}
MPI_Finalize();
return 0;
}
Error Log
0 1 2 3 *** 0
0 1 2 3 *** 1
0 1 2 3 *** 2
0 1 2 3 *** 3
*** An error occurred in MPI_Scatter
*** reported by process [1855324161,0]
*** on communicator MPI_COMM_WORLD
*** MPI_ERR_TRUNCATE: message truncated
*** MPI_ERRORS_ARE_FATAL (processes in this communicator will now abort,
*** and potentially your MPI job)
MPI_Scatter Documentation
MPI_Scatter Sends data from one process to all other processes in a communicator
Synopsis int MPI_Scatter(const void *sendbuf, int sendcount, MPI_Datatype sendtype, void *recvbuf, int recvcount, MPI_Datatype recvtype, int root, MPI_Comm comm)
Input Parameters
sendbuf - address of send buffer (choice, significant only at root)
sendcount - number of elements sent to each process (integer, significant only at root)
sendtype - data type of send buffer elements (significant only at root) (handle)
recvcount - number of elements in receive buffer (integer)
recvtype - data type of receive buffer elements (handle)
root - rank of sending process (integer)
comm - communicator (handle)
Output Parameters
recvbuf - address of receive buffer (choice)
Update
After updating the MPI_Scatter send count to 1, The above-mentioned error goes away but the program stays ideal and it didn't print anything that was placed after the MPI_Scatter line.
MPI_Scatter(data, 1, MPI_INT, &temp_result, 1, MPI_INT, 0, MPI_COMM_WORLD);
CodePudding user response:
You quote the relevant line: "sendcount - number of elements sent to each process (integer". So if you send 1 element to each process, you need to set the sendcount to 1, not total_process
.