#include <err.h>
#include <fcntl.h>
#include <sched.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <unistd.h>

int size = 1;
char *buf;
char synchronize[] = "Rendezvous";

void
test(int scenario)
{
	int i, fd;
	struct stat sb;

	while (stat(synchronize, &sb) == 0)
		sched_yield();

	if (scenario == 1) {
		for (i = 0; i < 100000; i++) {
			if ((fd = open("/dev/zero", O_RDONLY)) == -1)
				err(1, "open(/dev/zero)");
			if (read(fd, buf, size) != size)
				err(1, "read(/dev/zero)");
			close(fd);
		}

		for (i = 0; i < 100000; i++) {
			if ((fd = open("/dev/null", O_WRONLY)) == -1)
				err(1, "open(/dev/null)");
			if (write(fd, buf, size) != size)
				err(1, "write(/dev/null)");
			close(fd);
		}
	}

	if (scenario == 2) {
		if ((fd = open("/dev/zero", O_RDONLY)) == -1)
			err(1, "open(/dev/zero)");
		for (i = 0; i < 2000000; i++) {
			if (read(fd, buf, size) != size)
				err(1, "read(/dev/zero)");
		}
		close(fd);

		if ((fd = open("/dev/null", O_WRONLY)) == -1)
			err(1, "open(/dev/null)");
		for (i = 0; i < 2000000; i++) {
			if (write(fd, buf, size) != size)
				err(1, "write(/dev/null)");
		}
		close(fd);
	}

	if (scenario == 3) {
		for (i = 0; i < 200000; i++) {
			if ((fd = open("/dev/zero", O_RDONLY)) == -1)
				err(1, "open(/dev/zero)");
			if (read(fd, buf, size) != size)
				err(1, "read(/dev/zero)");
			close(fd);
		}
	}
	exit(0);
}

int
main(int argc, char **argv)
{
	int i, fd, scenario;

	if (argc != 2)
		errx(1, "Usage: %s {1|2|3}", argv[0]);

	scenario = atoi(argv[1]);
	if (scenario < 1 || scenario > 3)
		errx(1, "Bad scenario: %s", argv[1]);
	buf = malloc(size);

	if ((fd = open(synchronize, O_CREAT | O_TRUNC | O_RDWR, 0640)) == -1)
		err(1, synchronize);
	close(fd);
	for (i = 0; i < 20; i++) {
		if (fork() == 0) 
			test(scenario);
	}
	unlink(synchronize);
	for (i = 0; i < 20; i++)
		wait(NULL);

	return (0);
}