C/Zombies

The code below will quickly tidy up after zombie children, and at the same time check for incoming data.

• Assume sock is the file descriptor that you wish to read from
  
• children is incremented when you call fork()

/* tidy up after children, but accept new data if its there! */
while (children) {
  int pid, status, read;
  struct timeval timeout;
  fd_set toset;
 
  /* check if any children have become zombies! */
  pid = waitpid(-1,&status,WNOHANG | WUNTRACED);
  if (pid > 0) {
    children--;
    printf("*** Child Died ***  PID: %-6d    Status: %-3d    Children: %-2d\n",pid,WEXITSTATUS(status),children);
    /* if there are no children left, will break
       if there are more zombie children will tidy up before looking for data */
    continue;
  }
 
  /* timeout on the socket every 0.5sec */
  memset(&timeout,0,sizeof(timeout));
  timeout.tv_usec = 500000;
 
  FD_ZERO(&toset);
  FD_SET(sock,&toset);
 
  /* check if there is data in the socket to be read... */
  if ((read = select(sock+1,&toset,NULL,NULL,&timeout)) == -1) {
    perror("select()");
    break;
  } else if (read != 0) {
    /* something can be read! */
    break;
  }
}