PP(pp_waitpid)
{
    ...
    if (PL_signals & PERL_SIGNALS_UNSAFE_FLAG)
        result = wait4pid(pid, &argflags, optype);
    else {
        while ((result = wait4pid(pid, &argflags, optype)) == -1 && errno == EINTR) {
	  PERL_ASYNC_CHECK();
        }
    }
    ...