Introduction to Concurrency in Programming Languages

OpenMP Quick Reference 289

Listing A.6: Demonstrating a parallel for-loop.

# inclu de < stdlib .h>

# inclu de < omp .h >

int main ( int argc , char ** argv ) {

int i , j;

double mean = 0.0 , * x ;

int N = 20 000000;

x = ( double *) malloc ( sizeof ( double )*N );

/* populate x on main thread ... */

for ( i =0; i <N ; i ++)

x[i] = ( double ) rand () / ( double ) RAND_MAX ;

/* compute mean in pa rallel */

# pragma omp p arallel shared ( mean ) private (i )

{

# pragma omp for r eduction (+: mean )

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

mean = mean + x[i] / ( double ) N;

}

}

}

290 Introduction to Concurrency in Programming Languages

to compute the mean of an array of numbers,