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).