/*
 * Toy program to demonstrate use of select for read-with-timeout.
 * You may use this in your CS143 assignment if you like.
 *
 * You can ignore these gcc errors:
 *  timeread.c: In function `timeout':
 *  timeread.c:43: warning: passing arg 2 of `select' from incompatible pointer type
 *  timeread.c:43: warning: passing arg 3 of `select' from incompatible pointer type
 *  timeread.c:43: warning: passing arg 4 of `select' from incompatible pointer type
 */

#include <sys/types.h>
#include <sys/time.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>

main()
{
  int x;

  /*
   * As a demonstration, wait up to 5 seconds for a
   * line of keyboard input.
   */
  x = timeout(0, 5000);
  if(x)
    printf("input available\n");
  else
    printf("timeout\n");
  exit(0);
}

/*
 * Wait for input to be available on file descriptor fd. But don't
 * wait longer than ms milliseconds. Return 1 if there is data to
 * be read on fd, 0 if the timeout expired.
 */
int
timeout(int fd, int ms)
{
  fd_set mask;
  int n;
  struct timeval tv;

  tv.tv_sec = ms / 1000;           /* seconds to wait */
  tv.tv_usec = (ms % 1000) * 1000; /* and additional microseconds */

  FD_ZERO(&mask);
  FD_SET(fd, &mask);

  n = select(fd + 1, &mask, (fd_set*)0, (fd_set*)0, &tv);
  if(n < 0){
    perror("select");
    exit(1);
  }
  return(n);
}