/*****************************************************************************
* FILE: bug6fix.c
* DESCRIPTION:
*   This solution uses a mutex variable to protect the global sum while each
*   thread updates it. A much more efficient method would be that used in the
*   dotprod_mutex.c example.
* SOURCE: 07/06/05 Blaise Barney
* LAST REVISED: 07/06/05 Blaise Barney
******************************************************************************/
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>

/* Define global data where everyone can see them */
#define NUMTHRDS 8
#define VECLEN 10000
pthread_mutex_t mutexsum;
int *a, *b; 
long sum=0.0;

void *dotprod(void *arg)
{
  /* Each thread works on a different set of data.
   * The offset is specified by the arg parameter. The size of
   * the data for each thread is indicated by VECLEN.
   */
   int i, start, end, offset, len, tid;
   tid = (int)arg;
   offset = tid;
   len = VECLEN;
   start = offset*len;
   end   = start + len;

/* Perform my section of the dot product */
   printf("thread: %d starting. start=%d end=%d\n",tid,start,end-1);
   for (i=start; i<end ; i++) {
      pthread_mutex_lock(&mutexsum);
      sum += (a[i] * b[i]);
      pthread_mutex_unlock(&mutexsum);
      }
   printf("thread: %d done. Global sum now is=%li\n",tid,sum);

   pthread_exit((void*) 0);
}

int main (int argc, char *argv[])
{
int i;
void *status;
pthread_t threads[NUMTHRDS];
pthread_attr_t attr;

/* Assign storage and initialize values */
a = (int*) malloc (NUMTHRDS*VECLEN*sizeof(int));
b = (int*) malloc (NUMTHRDS*VECLEN*sizeof(int));
  
for (i=0; i<VECLEN*NUMTHRDS; i++)
  a[i]=b[i]=1;

/* Initialize mutex variable */
pthread_mutex_init(&mutexsum, NULL);
         
/* Create threads as joinable, each of which will execute the dot product
 * routine. Their offset into the global vectors is specified by passing
 * the "i" argument in pthread_create().
 */
pthread_attr_init(&attr);
pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);
for(i=0;i<NUMTHRDS;i++)
   pthread_create(&threads[i], &attr, dotprod, (void *)i); 

pthread_attr_destroy(&attr);

/* Wait on the other threads for final result */

for(i=0;i<NUMTHRDS;i++) {
  pthread_join(threads[i], &status);
  }
/* After joining, print out the results and cleanup */
printf ("Final Global Sum=%li\n",sum);
free (a);
free (b);
pthread_mutex_destroy(&mutexsum);
pthread_exit(NULL);
}