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

struct CarInfo {
	int id;
	int dir;
};
pthread_mutex_t m = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t s_n = PTHREAD_COND_INITIALIZER;
pthread_cond_t n_s = PTHREAD_COND_INITIALIZER;
pthread_cond_t *cq[2] = { &s_n, &n_s };

char *sdir[] = { "south", "north" };

int cars_on_bridge = 0;
int dir_on_bridge = -1; //0: south->north; 1:north->south; -1:bridge empty

void *car_thread (void *p) {
	struct CarInfo *car = p;
	
	pthread_mutex_lock(&m);
	
	while (cars_on_bridge > 2 || (dir_on_bridge != -1 && 
					dir_on_bridge != car->dir))
		pthread_cond_wait(cq[car->dir], &m);

	cars_on_bridge++;
	dir_on_bridge = car->dir;
	
	printf("Car %2d  on bridge, going %s, on bridge %d car(s) (to %s)\n",
		car->id, sdir[car->dir],
		cars_on_bridge, sdir[dir_on_bridge]);

	pthread_mutex_unlock(&m);

	usleep(5000000);
	
	pthread_mutex_lock(&m);
	
	cars_on_bridge--;

	printf("Car %2d off bridge, going %s, on bridge %d car(s) (to %s)\n",
		car->id, sdir[car->dir],
		cars_on_bridge, sdir[dir_on_bridge]);

	if (cars_on_bridge > 0) {
		pthread_cond_signal(cq[car->dir]);
	}
	else {
		dir_on_bridge = -1;
		pthread_cond_broadcast(cq[1 - car->dir]);
	}
	
	pthread_mutex_unlock(&m);
	
	free(car);
}

int main () {
	pthread_t thr_id;
	pthread_attr_t attr;
	int car_id = 0;
	struct CarInfo *car;

	pthread_attr_init(&attr);
	pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);

	while (1) {
		car = malloc(sizeof(struct CarInfo));
		car->id = ++car_id;
		car->dir = rand() & 1;
		
		printf("New car %d arrived from %s\n", car_id, sdir[1 - car->dir]);
		
		pthread_create(&thr_id, &attr, car_thread, (void *) car);
		
		usleep(2000000);
	}

	return 0;
}