#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/select.h>
#include <string.h>
#include <errno.h>
#include <sys/time.h>
#include <time.h>

#define WARN(...) do { fprintf(stderr, __VA_ARGS__); fputc('\n', stderr); } while(0)
#define ERROR(...) do { WARN(__VA_ARGS__); exit(1); } while(0)

void nonblock(int fd, int nb)
{
	int flags = fcntl(fd, F_GETFL);
	flags &= ~O_NONBLOCK;
	if (nb)
		flags |= O_NONBLOCK;
	if (fcntl(fd, F_SETFL, flags) == -1)
		ERROR("failed: fcntl: %s", strerror(errno));
}

fd_set canread_fds;
int canread(int fd) {
	int count;
	int fd_max = fd + 1;
	struct timeval timeout = { 0, 0 };
	fd_set *s = &canread_fds;
	FD_SET(fd, s);
	count = select(fd_max, &canread_fds, NULL, NULL, &timeout);
	FD_CLR(fd, s);
	return count > 0;
}

int main(void)
{
	int fd;
	int n;
	char *msg = "hello world!";
	int i;
	long delay = 1;
	FD_ZERO(&canread_fds);
	fd = open("fifo", O_RDWR|O_NONBLOCK);
//	fd = open("fifo", O_WRONLY);
	WARN("opened %d", fd);
	nonblock(fd, 0);
	WARN("made blocking");
	for (i=0; i<10; ++i) {
		n = write(fd, msg, strlen(msg)+1);
		WARN("%d", n);
	}
	WARN("wrote");
	
	while (canread(fd)) {
		if (delay > (int)1e9) {
			sleep(1);
		} else {
			struct timespec d = { 0, delay };
			nanosleep(&d, NULL);
			delay *= 2;
		}
	}
	WARN("final delay: %ld", delay);
	close(fd);
	WARN("closed");
	return 0;
}