#include <poll.h>
#include <pthread.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <unistd.h>

#define	ITERATIONS 524768 
#define NUM_PAIRS 512 
#define	TIMEOUT 1000000
//#define DEBUG

int fds[NUM_PAIRS][2];	
pthread_t tid[2 * NUM_PAIRS];
int map[NUM_PAIRS];

void
write_then_poll(int *map)
{
	struct pollfd fd = { .fd = fds[*map][0], .events = POLLIN };	
	int i;
	char data;

	for (i = 0; i < ITERATIONS; i++) {	
		data = '0';
		write(fds[*map][0], &data, 1); 	
#ifdef DEBUG
		printf("Data written: %c from %ld \n", data, pthread_self());	
#endif
		if ((poll(&fd, 1, TIMEOUT)) == 0) {
			printf("No data available for %ld \n", pthread_self());
			pthread_exit(NULL);
		}	
		read(fds[*map][0], &data, 1);
#ifdef DEBUG
		printf("Data read: %c from %ld \n", data, pthread_self());		
#endif
	}
}

void
poll_then_write(int *map)
{
	struct pollfd fd = { .fd = fds[*map][1], .events = POLLIN };	
	int i;
	char data;

	for (i = 0; i < ITERATIONS; i++) {	
		if ((poll(&fd, 1, TIMEOUT)) == 0) {
			printf("No data available for %ld \n", pthread_self());
			pthread_exit(NULL);	
		}
		read(fds[*map][1], &data, 1);
#ifdef DEBUG
		printf("Data read %c from %ld \n", data, pthread_self());	
#endif
		data = '1';
		write (fds[*map][1], &data, 1);
#ifdef DEBUG
		printf("Data written: %c from %ld \n", data, pthread_self());	
#endif
	}
} 

int 
main(void)
{
	int i, ret;
	
	for (i = 0; i < NUM_PAIRS; ++i) {
		ret = socketpair(AF_UNIX, SOCK_STREAM, 0, fds[i]);
		if (ret < 0)	
			perror("Error in socketpair()\n");	
	}
	for (i = 0; i < NUM_PAIRS; i++) {
		map[i] = i;
		pthread_create(&tid[2*i], NULL, (void *) write_then_poll,
		    &map[i]);
		pthread_create(&tid[(2*i)+1], NULL, (void *) poll_then_write,
		    &map[i]); 
	}
	for (i = 0; i < 2 * NUM_PAIRS; ++i) 	
		pthread_join(tid[i], NULL);
	return (0);
}