using mutex [pthreads]

gistfile1.c

#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>

typedef struct
{
   double *a;
   double *b;
   double sum;
   int veclen;
} DOTDATA;

#define NUMTHRDS 4
#define VECLEN 100

DOTDATA dotstr;
pthread_t callThd[NUMTHRDS];
pthread_mutex_t mutexsum;

void *dotprod(void *arg)
{
   int i, start, end, len;
   long offset;
   double mysum, *x, *y;
   offset = (long) arg;

   len = dotstr.veclen;
   start = offset*len;
   end = start + len;
   x = dotstr.a;
   y = dotstr.b;

   mysum = 0;
   for(i=start; i < end; i++)
      mysum += (x[i] * y[i]);

   pthread_mutex_lock (&mutexsum);
   dotstr.sum += mysum;
   pthread_mutex_unlock(&mutexsum);

   pthread_exit((void*) 0);
}

int main(int argc, char **argv)
{
   long i;
   double *a, *b;
   void *status;
   pthread_attr_t attr;

   a = (double *) malloc(NUMTHRDS * VECLEN * sizeof(double));
   b = (double *) malloc(NUMTHRDS * VECLEN * sizeof(double));

   for (i = 0; i < VECLEN * NUMTHRDS; i++)
   {
      a[i] = 1.0;
      b[i] = a[i];
   }

   dotstr.veclen = VECLEN;
   dotstr.a = a;
   dotstr.b = b;
   dotstr.sum = 0;

   pthread_mutex_init(&mutexsum, NULL);

   pthread_attr_init(&attr);
   pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);

   for(i=0; i< NUMTHRDS; i++)
      pthread_create(&callThd[i], &attr, dotprod, (void *) i);

   pthread_attr_destroy(&attr);
   for(i = 0; i < NUMTHRDS; i++)
      pthread_join(callThd[i], &status);

   printf("Sum = %f \n", dotstr.sum);
   free(a);
   free(b);
   pthread_mutex_destroy(&mutexsum);
   pthread_exit(NULL);
}