From: Paul Brannan <paul@...>
Date: 2002-03-25T23:37:34+09:00
Subject: Restoring old signal handlers

If I install a new signal handler for, say, SIGCHLD, I can make sure the
original gets called with:

  old_handler = trap("CLD") do
    old_handler.call() if not old_handler.nil?
    # ...
  end

If I do this twice, then when SIGCHLD is received:

  handler2 -> calls handler1 -> calls original handler

How can I remove handler1 in such a way that when SIGCHLD is recieved:

  handler2 -> calls original handler

(it occurred to me to install a new handler temporarily just to get
handler2, then to re-install handler2 as the original handler, but this
seems somewhat klunky).

Paul