/* =================================================================
   Thread example: illustrate the problem with concurrent execution
   ================================================================= */
#include <iostream>
#include <stdlib.h>
#include <pthread.h>

using namespace std;

pthread_t tid[100];
int N = 0;

pthread_mutex_t m;

/* ==============================================================
   Global variables: 1 copy - all threads use the same variable
   "shared" variable
   ============================================================== */

void *worker(void *arg)
{
   int i;    // Local variable stored on STACK
             // Each threads has its own stack
	     // Therefore: each thread has its own copy of local variable


   for (i = 0; i < 10000; i = i + 1)
   {
      pthread_mutex_lock( &m );
      N = N + 1;         // Shared N !!!
      pthread_mutex_unlock( &m );
   }

//   cout << "N = " << N << endl;

   return(NULL);     /* Thread exits (dies) */
}




/* =======================
   MAIN
   ======================= */
int main(int argc, char *argv[])
{
   int i, num_threads;

   /* -----
      Check command line
      ----- */
   if ( argc != 2 )
   {
      cout << "Usage: " << argv[0] << " Num_Threads" << endl;
      exit(1);
   }

   /* -----
      Get number of intervals and number of threads
      ----- */
   num_threads = atoi(argv[1]);

   pthread_mutex_init( &m, NULL);

   /* ------
      Create threads
      ------ */
   for (i = 0; i < num_threads; i = i + 1)
   {
      if ( pthread_create(&tid[i], NULL, worker, NULL) )
      {
	 cout << "Cannot create thread" << endl;
	 exit(1);
      }
   }

   for (i = 0; i < num_threads; i = i + 1)
      pthread_join(tid[i], NULL);

   cout << "N = " << N << endl << endl;

}