cond_var.c

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

#define TOTAL_THREADS     2
#define MAX		10

int shared = 0;
int turn = 0;
int started = 0;
pthread_mutex_t mutex;
pthread_cond_t cond;

void *increment(void *arg)
{
   int thread_no = *((int *) arg);

   pthread_mutex_lock(&mutex);
   while (1) {
     if (!started || turn != thread_no) {
       pthread_cond_wait(&cond, &mutex);
     }
     if(shared <= MAX) {
          printf("%d|%d\n", thread_no, shared++);
          turn = !turn;
          pthread_cond_signal(&cond);
     } else {
          turn = !turn;
          pthread_cond_signal(&cond);
          break;
     }
   }
   pthread_mutex_unlock(&mutex);

   return NULL;
}

int main(void)
{
   pthread_t threads[TOTAL_THREADS];
   int args[TOTAL_THREADS], index;

   pthread_mutex_init(&mutex, NULL);
   pthread_cond_init(&cond, NULL);

   for (index = 0; index < TOTAL_THREADS; ++index) {
      args[index] = index;
      pthread_create(&threads[index], NULL, increment, (void *) &args[index]);
   }

   pthread_mutex_lock(&mutex);
   started = 1;
   turn = 0;
   pthread_cond_signal(&cond); // send the first signal
   pthread_mutex_unlock(&mutex);

   for (index = 0; index < TOTAL_THREADS; ++index) {
      pthread_join(threads[index], NULL);
   }

   pthread_mutex_destroy(&mutex);
   pthread_cond_destroy(&cond);

   printf("Done!\n");
   return 0;
}