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Source code

#include <qthread.h>
#include <qdatetime.h>
#include <stdlib.h>
#include <stdio.h>
#include <time.h>
#include <math.h>
 
#ifdef PROCESSES_RELEASE
  #include <unistd.h>
#endif

int **arr;
const int sz = 1000000;

void init( int na )
// Allocate na arrays and filling it random numbers
{
	srand( (unsigned)time( NULL ) );
	qWarning( "Initialize arrays" );
	arr = new int*[na];
	for ( int i=0; i < na; i++) {
		arr[i] = new int[sz];	
		for ( int j=0; j < sz; j++ ) arr[i][j] = rand();
	}
}

class Worker : public QThread
{
public:
	Worker( int begarr, int endarr ) : QThread(), ba(begarr), ea(endarr) {}
	void run() {
#ifdef PROCESSES_RELEASE
	  int pid = fork();
	  if ( ! pid ) {
#endif
			for ( int i=ba; i <= ea; i++ ) {
				double sum = 0;
				for (int j=0; j < sz; j++) sum += sin( double(arr[i][j]) );
			}
#ifdef PROCESSES_RELEASE
	  }
	  else {
	    waitpid( pid, 0, 0);
	  }	
#endif
	} 
private:
	int ba, ea;
};

int main( int argc, char** argv )
{
	if ( argc < 3 ) qFatal( "Usage : %s nArrays nThreads", argv[0] );
	const int numarr = atoi(argv[1]);
	const int numthr = atoi(argv[2]);

	init( numarr );
	QThread** threads = new QThread*[numthr];
	int cnt = 0, i, j;

	int apt = numarr / numthr;
	for ( i = 0; i < numarr; i+=apt) {
		j = i + apt - 1;
		j = j >= sz ? sz - 1 : j;
	    qDebug("Thread %d : %d - %d", cnt, i, j); 
		threads[cnt] = new Worker( i, j );
		cnt++;				
	}

	QTime tm;
	tm.start();
	qWarning( "Running threads..." );
	for ( i = 0; i < numthr; i++ ) threads[i]->start();
	for ( i = 0; i < numthr; i++ ) threads[i]->wait();
	qWarning( "Time elapsed : %d ms", tm.elapsed() );
	return 0;	
}