Q. Determine what part of global array to work on thread number?
#include < omp.h >
void subdomain(float x[ ], int istart, int ipoints)
{
int i;
for (i = 0; i < ipoints; i++)
x[istart+i] = 123.456;
}
void sub(float x[ 10000], int npoints)
{
int t_num, num_t, ipoints, istart;
#pragma omp parallel default(shared) private(t_num , num_t, ipoints, istart)
{
t_num = omp_get_thread_num(); //thread number of current thread
num_t = omp_get_num_threads(); //number of threads
ipoints = npoints / num_t; /* size of partition */
istart = t_num * ipoints; /* starting array index */
if (t_num == num_t-1) /* last thread may do more */
ipoints = npoints - istart;
subdomain(x, istart, ipoints);
}
}
int main()
{
float array[10000];
sub(array, 10000);
return 0;
}
In this illustration we used two library methods : omp_get_num_threads() and omp_get_thread_num().
omp_get_num_threads() returns number of threads which are currently being used in parallel directive.
omp_get_thread_num() returns thread number (an integer from 0 to omp_get_num_threads() - 1 where thread 0 is master thread).