Programming

#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
 
#define NUM_THREADS  3
#define TCOUNT 10
#define COUNT_LIMIT 12
 
int     count = 0;
int     thread_ids[3] = {0,1,2};
pthread_mutex_t count_mutex;
pthread_cond_t count_threshold_cv;
 
void *inc_count(void *t) 
{
int i;
long my_id = (long)t;
 
for (i=0; i<TCOUNT; i++) {
  pthread_mutex_lock(&count_mutex);
  count++;
 
  /* 
  Check the value of count and signal waiting thread when condition is
  reached.  Note that this occurs while mutex is locked. 
  */
  if (count == COUNT_LIMIT) {
    pthread_cond_signal(&count_threshold_cv);
    printf("inc_count(): thread %ld, count = %d  Threshold reached.\n", 
           my_id, count);
    }
 
  printf("inc_count(): thread %ld, count = %d, unlocking mutex\n", 
  my_id, count);
  pthread_mutex_unlock(&count_mutex);
  /* Do some "work" so threads can alternate on mutex lock */
  sleep(1);
  }
pthread_exit(NULL);
}
 
void *watch_count(void *t) 
{
long my_id = (long)t;
 
printf("Starting watch_count(): thread %ld\n", my_id);
/*
Lock mutex and wait for signal.  Note that the pthread_cond_wait 
routine will automatically and atomically unlock mutex while it waits. 
Also, note that if COUNT_LIMIT is reached before this routine is run by
the waiting thread, the loop will be skipped to prevent pthread_cond_wait
from never returning. 
*/
pthread_mutex_lock(&count_mutex);
while (count<COUNT_LIMIT) {
  pthread_cond_wait(&count_threshold_cv, &count_mutex);
  printf("watch_count(): thread %ld Condition signal received.\n", my_id);
  count += 125;
  printf("watch_count(): thread %ld count now = %d.\n", my_id, count);
  }
pthread_mutex_unlock(&count_mutex);
pthread_exit(NULL);
}
 
int main (int argc, char *argv[])
{
int i, rc;
long t1=1, t2=2, t3=3;
pthread_t threads[3];
pthread_attr_t attr;
 
/* Initialize mutex and condition variable objects */
pthread_mutex_init(&count_mutex, NULL);
pthread_cond_init (&count_threshold_cv, NULL);
 
/* For portability, explicitly create threads in a joinable state */
pthread_attr_init(&attr);
pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);
pthread_create(&threads[0], &attr, watch_count, (void *)t1);
pthread_create(&threads[1], &attr, inc_count, (void *)t2);
pthread_create(&threads[2], &attr, inc_count, (void *)t3);
 
/* Wait for all threads to complete */
for (i=0; i<NUM_THREADS; i++) {
  pthread_join(threads[i], NULL);
}
printf ("Main(): Waited on %d  threads. Done.\n", NUM_THREADS);
 
/* Clean up and exit */
pthread_attr_destroy(&attr);
pthread_mutex_destroy(&count_mutex);
pthread_cond_destroy(&count_threshold_cv);
pthread_exit(NULL);
}