/* -*- mode:c; c-file-style:"k&r"; c-basic-offset: 4; tab-width:4; indent-tabs-mode:nil; mode:auto-fill; fill-column:78; -*- */
/* vim: set ts=4 sw=4 et tw=78 fo=cqt wm=0: */

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

pthread_mutex_t count_mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t condvar = PTHREAD_COND_INITIALIZER;

void * function1();
void * function2();
int count = 0;

#define COUNT_DONE  10
#define COUNT_HALT1  3
#define COUNT_HALT2  6

int main (int argc, const char ** argv)
{
   pthread_t thread1, thread2;

   pthread_create(&thread1, NULL, &function1, NULL);
   pthread_create(&thread2, NULL, &function2, NULL);

   pthread_join(thread1, NULL);
   pthread_join(thread2, NULL);

   printf("Final count: %d\n", count);
   return 0;
}

void * function1 (void)
{
   for(;;) {
      // Lock mutex and then wait for signal to relase mutex
      pthread_mutex_lock(&count_mutex);

      // Wait while functionCount2() operates on count
      // mutex unlocked if condition varialbe in functionCount2() signaled.
      pthread_cond_wait(&condvar, &count_mutex);
      count++;
      printf("Counter value in function1: %d\n", count);

      pthread_mutex_unlock(&count_mutex);

      if (count >= COUNT_DONE)
          return NULL;
   }
}

void * function2 (void)
{
    for(;;) {
       pthread_mutex_lock(&count_mutex);

       if (count < COUNT_HALT1 || count > COUNT_HALT2) {
            // Condition of if statement has been met.
            // Signal to free waiting thread by freeing the mutex.
            // Note: functionCount1() is now permitted to modify "count".
            pthread_cond_signal(&condvar);
       } else {
            count++;
            printf("Counter value function2: %d\n", count);
       }

       pthread_mutex_unlock(&count_mutex);

       if (count >= COUNT_DONE)
           return NULL;
    }
}