#include <mpi.h>
#include <pthread.h>
float *x, *y;
#define PROC (8)
float e_vec[PROC];
int n_thread0, n_thread1;
void *thread1(void *arg) {
int p = (int)arg;
int n0 = n_thread0 + (p * (n_thread1-n_thread0)) / PROC;
int n1 = n_thread0 + ((p+1) * (n_thread1-n_thread0)) / PROC;
// do computation
float e = 0;
for (int i=n0; i<n1; ++i) {
x[i] += ( y[i+1] + y[i-1] )*.5;
e += y[i] * y[i];
}
e_vec[p] = e;
return (void*) 0;
}
int main(int argc, char *argv[]) {
int n = ...;
MPI_Init(&argc, &argv);
int numproc, me;
MPI_Comm_size(MPI_COMM_WORLD, &numproc);
MPI_Comm_rank(MPI_COMM_WORLD, &me);
int p_left = -1, p_right = -1;
if (me > 0)
p_left = me-1;
if (me < numproc-1)
p_right = me+1;
int n_local0 = 1 + (me * (n-1)) / numproc;
int n_local1 = 1 + ((me+1) * (n-1)) / numproc;
// allocate only local part + ghost zone of the arrays x,y
MPI_Alloc_mem(sizeof(float) * (n_local1 - n_local0 + 2),
MPI_INFO_NULL, &x);
MPI_Alloc_mem(sizeof(float) * (n_local1 - n_local0 + 2),
MPI_INFO_NULL, &y);
x -= (n_local0 - 1);
y -= (n_local0 - 1);
MPI_Win win;
MPI_Win_create(&y[n_local0], sizeof(float) * (n_local1-n_local0+2),
sizeof(float), MPI_INFO_NULL, MPI_COMM_WORLD, &win);
... // fill x, y
// fill ghost zone
MPI_Win_fence(0, win);
if (p_left != -1)
MPI_Put(&y[n_local0], 1, MPI_FLOAT, p_left,
n_local1-n_local0+1, 1, MPI_FLOAT, win);
if (p_right != -1)
MPI_Put(&y[n_local1-1], 1, MPI_FLOAT, p_right,
0, 1, MPI_FLOAT, win);
MPI_Win_fence(0, win);
pthread_t threads[PROC];
pthread_attr_t attr;
pthread_attr_init(&attr);
n_thread0 = n_local0;
n_thread1 = n_local1;
float e = 0;
// start threads and wait for termination
for (int p=0; p<PROC; ++p)
pthread_create(&threads[p], &attr, thread1, (void *)p);
for (int p=0; p<PROC; ++p) {
pthread_join(threads[p], NULL);
e += e_vec[p];
}
float e_local = e;
MPI_Allreduce(&e_local, &e, 1, MPI_FLOAT, MPI_SUM, MPI_COMM_WORLD);
... // output x, e
MPI_Win_free(&win);
x += (n_local0 - 1);
y += (n_local0 - 1);
MPI_Free_mem(y);
MPI_Free_mem(x);
MPI_Finalize();
return 0;
}
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