/*
 *	CSE451 Section Pthread Example Code
 *	April 16, 2009
 */

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

#define MAXCOUNT 500
#define SIGNALCOUNT 3

void *count_up(void *args);
void *subtract(void *args);

pthread_mutex_t *mutex;
pthread_cond_t *done;

int main ()
{
	//thread handles
	pthread_t cu, s;
	
	//shared variable between the two threads
	int shared_int = 0;
	
	//allocate and init the mutex
	mutex = (pthread_mutex_t *) malloc (sizeof (pthread_mutex_t));
	if(!mutex)
	{
		exit(1);
	}
	pthread_mutex_init (mutex, NULL);
	
	//allocate and init the condition variable
	done = (pthread_cond_t *) malloc (sizeof (pthread_cond_t));
	if(!done)
	{
		exit(1);
	}
	pthread_cond_init (done, NULL);

	//do work son
	pthread_create (&cu, NULL, count_up, &shared_int);
	pthread_create (&s, NULL, subtract, &shared_int);
	
	//wait for threads to finish
	pthread_join (cu, NULL);
	pthread_join (s, NULL);

	//clean up
	pthread_mutex_destroy(mutex);
	pthread_cond_destroy(done);
	return 0;
}

void *count_up (void *args)
{
	int i;
	int *count = (int*)args;
	for(i=0;i<SIGNALCOUNT*MAXCOUNT;i++)
	{
		//lock the mutex and increment the counter
		pthread_mutex_lock(mutex);
		if(++(*count) == MAXCOUNT)
		{
			printf("Count maxed at %d, Signal Subtract\n", *count);
			//tell the other thread this thread is done
			pthread_cond_signal(done);
		}

		pthread_mutex_unlock(mutex);
		//sleep to let the other thread get scheduled
		usleep(10);
	}

}

void *subtract (void *args)
{
	int i;
	int *count = (int*)args;

	for(i=0;i<SIGNALCOUNT;i++)
	{
		pthread_mutex_lock(mutex);
		if(*count < MAXCOUNT)
		{
			//Count has not reached MAXCOUNT so wait until it does
			pthread_cond_wait(done, mutex);
			printf("Subtract was signalled!, Now subtracting!\n");
			*count -= MAXCOUNT;
			printf("Count now is %d\n\n", *count);
		}
		pthread_mutex_unlock(mutex);
	}
}