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- #include <pthread.h>
- #include <stdio.h>
- #include <stdlib.h>
- #define NTHREADS 4
- #define ARRAYSIZE 1000000
- #define ITERATIONS ARRAYSIZE / NTHREADS
- double sum=0.0, a[ARRAYSIZE];
- pthread_mutex_t sum_mutex;
- void *do_work(void *tid)
- {
- int i, start, *mytid, end;
- double mysum=0.0;
- /* Initialize my part of the global array and keep local sum */
- mytid = (int *) tid;
- start = (*mytid * ITERATIONS);
- end = start + ITERATIONS;
- printf ("Thread %d doing iterations %d to %dn",*mytid,start,end-1);
- for (i=start; i < end ; i++) {
- a[i] = i * 1.0;
- mysum = mysum + a[i];
- }
- /* Lock the mutex and update the global sum, then exit */
- pthread_mutex_lock (&sum_mutex);
- sum = sum + mysum;
- pthread_mutex_unlock (&sum_mutex);
- pthread_exit(NULL);
- }
- int main(int argc, char *argv[])
- {
- int i, start, tids[NTHREADS];
- pthread_t threads[NTHREADS];
- pthread_attr_t attr;
- /* Pthreads setup: initialize mutex and explicitly create threads in a
- joinable state (for portability). Pass each thread its loop offset */
- pthread_mutex_init(&sum_mutex, NULL);
- pthread_attr_init(&attr);
- pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);
- for (i=0; i<NTHREADS; i++) {
- tids[i] = i;
- pthread_create(&threads[i], &attr, do_work, (void *) &tids[i]);
- }
- /* Wait for all threads to complete then print global sum */
- for (i=0; i<NTHREADS; i++) {
- pthread_join(threads[i], NULL);
- }
- printf ("Done. Sum= %e n", sum);
- sum=0.0;
- for (i=0;i<ARRAYSIZE;i++){
- a[i] = i*1.0;
- sum = sum + a[i]; }
- printf("Check Sum= %en",sum);
- /* Clean up and exit */
- pthread_attr_destroy(&attr);
- pthread_mutex_destroy(&sum_mutex);
- pthread_exit (NULL);
- }
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