#include <QThread>
#include <QMutex>
#include <QWaitCondition>
#include <cstdlib>
#include <iostream>
#include <ctime>
#include <sys/time.h>
using namespace std;

class AdderThread: public QThread
{
public:
  AdderThread(int * a, int f, int l) 
  {  
    array = a;
    first = f;
    last = l;
  }
  void addElement(int v)
  {
    mutex.lock();
    sum += v;
    mutex.unlock();
  }
  void run() 
  {
    for (int cnt = first; cnt <= last; cnt ++)
      {
	addElement(array[cnt]);
      }
  }
  int getSum() const { return sum; }
private:
  QMutex mutex;
  int * array;
  int first;
  int last;
  static long sum;
};

long AdderThread::sum = 0; // initialize 

int main(int argc, char* argv[])
{
  int arraySize = 1000000; 
  int * dataArray = new int[arraySize];
  long actualSum = 0;
  for (int cnt = 0; cnt < arraySize; cnt ++)
    {
      // initialize the elements to 1, 2, 3, ...
      dataArray[cnt] = cnt;
      // cout << dataArray[cnt] << endl;
      actualSum += dataArray[cnt];
    }
  const int numThread = 4; // this is always a factor of arraySize
  AdderThread * * thrd = new AdderThread * [numThread];
  int first = 0;
  int last;
  for (int cnt = 0; cnt < numThread; cnt ++)
    {
      last = first + arraySize / numThread - 1;
      // cout << first << " " << last << endl;
      thrd[cnt] = new AdderThread(dataArray, first, last);
      first = last + 1;
    }

  for (int cnt = 0; cnt < numThread; cnt ++)
    {
      thrd[cnt] -> start();
    }

  for (int cnt = 0; cnt < numThread; cnt ++)
    {
      thrd[cnt] -> wait();
    }

  cout << "The sum by threads is " << thrd[0] -> getSum() << endl;
  cout << "The actual sum is " << actualSum << endl;
  
  for (int cnt = 0; cnt < numThread; cnt ++)
    {
      delete thrd[cnt];
    }

  delete [] thrd;
  delete [] dataArray;

  return 0;
}