/* selectchild.c - Using select to communicate with two children.
 */


#include <sys/types.h>
#include <sys/time.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#define MAXLINE 12

int main(void)
{
  int     m, n; 
  int     fd1[2];   /* pipe for communications from child1 to parent */
  int     fd2[2];   /* pipe for communications from child2 to parent */
  pid_t   pid;
  char    line[MAXLINE];
  fd_set   readset;


  if (pipe(fd1) < 0) {
    perror("pipe1");
    exit(1);}
  if (pipe(fd2) < 0) {
    perror("pipe2");
    exit(1);}
  /* child1 */
  if ( (pid = fork()) < 0) {
    perror("fork1");
    exit(1);}
  else if (pid == 0) {            
    close(fd1[0]);
    while (1) {
      write(fd1[1], "from child1\n", MAXLINE);
      sleep(1);}
    exit(0);}
  /* child2 */
  if ( (pid = fork()) < 0) {
    perror("fork2");
    exit(1);}
  else if (pid == 0) {            
    close(fd2[0]);
    while (1) {
      write(fd2[1], "from child2\n", MAXLINE);
      sleep(1.3);}
    exit(0);}
  /* parent */
  close(fd1[1]);
  close(fd2[1]);
  m = 1 + ((fd1[0]<fd2[0])?fd2[0]:fd1[0]); /*Max # of objs to wait for*/
  FD_ZERO(&readset);
  while (1) {
    FD_SET(fd1[0], &readset);
    FD_SET(fd2[0], &readset);
    if (select(m,&readset, NULL,NULL,NULL) < 0) {
      perror("select");
      exit(1);}
    if (FD_ISSET(fd1[0], &readset)) {
      n = read(fd1[0], line, MAXLINE);
      write(STDOUT_FILENO, line, n);}
    if (FD_ISSET(fd2[0], &readset)) {
      n = read(fd2[0], line, MAXLINE);
      write(STDOUT_FILENO, line, n);}
  }
  exit(0);
}