Using WIFSTOPPED with waitpid

It’s common to use WIFSTOPPED with waitpid when the parent process wait for a child process to stop and then the parent process sends SIGCONT to the child process to continue processing.

For this purpose, we sometimes see this kind of code:

while ($pid != ($res_pid = waitpid($pid, WUNTRACED)) || not WIFSTOPPED($?)) {
  last if -1 == $res_pid && not kill 0 => $pid;
  sleep 1;
}

But passing WIFSTOPPED to $? is actually incorrect and it may not work on some environment. You should pass ${^CHILD_ERROR_NATIVE} instead.

while ($pid != ($res_pid = waitpid($pid, WUNTRACED)) || not WIFSTOPPED(${^CHILD_ERROR_NATIVE})) {
  ..
}