Avoiding a fork()/SIGCHLD race condition

Question

Please consider the following fork()/SIGCHLD pseudo-code.

  // main program excerpt
    for (;;) {
      if ( is_time_to_make_babie         


        

Answer 1

In addition to the existing "children" add a new data structure "early deaths". This will keep the contents of children clean.

  // main program excerpt
    for (;;) {
      if ( is_time_to_make_babies ) {

        pid = fork();
        if (pid == -1) {
          /* fail */
        } else if (pid == 0) {
          /* child stuff */
          print "child started"
          exit
        } else {
          /* parent stuff */
          print "parent forked new child ", pid
          if (!earlyDeaths.contains(pid)) {
              children.add(pid);
          } else {
              earlyDeaths.remove(pid);
          }
        }

      }
    }

  // SIGCHLD handler
  sigchld_handler(signo) {
    while ( (pid = wait(status, WNOHANG)) > 0 ) {
      print "parent caught SIGCHLD from ", pid
      if (children.contains(pid)) {
          children.remove(pid);
      } else {
          earlyDeaths.add(pid);
      }
    }
  }

EDIT: this can be simplified if your process is single threaded -- earlyDeaths doesn't have to be a container, it just has to hold one pid.