Wow, this is a really interesting (and effective) solution. Reading the
docs on IO.pipe (http://www.ruby-doc.org/core-1.9.3/IO.html) this looks
pretty safe. And it works on Ruby 1.9.3 and 2.0.0-preview2.

My objective was to clean up my resources when the program receives a
SIGTERM. (As a counter example, calling "exit!" inside the original trap
context in my gist would have successfully killed my program without
throwing an exception but would not have cleaned up the utilized
resources.) There is the ominous "does not work on all systems" warning
with this method, but if I can test it out on some of the major ones
successfully, I'll go with it.

For what it's worth, I've filed my issue with ruby-core here:
http://bugs.ruby-lang.org/issues/7648. It hasn't gained any traction yet,
but if you want to post your own experience with Queue#enq it might be an
addendum to this bug report or a new bug altogether.

Thanks for your help! This was educational.

Joe

On Fri, Jan 4, 2013 at 8:44 AM, Sean O'Halpin <sean.ohalpin / gmail.com>wrote:

> On Tue, Jan 1, 2013 at 4:20 PM, Joe Leo <joseph.leo3 / gmail.com> wrote:
> > I'm working on updating a gem to be compatible with Ruby 2.0 and am
> > currently using Ruby 2.0.0-preview2. I'm running into trouble with a
> > class which inherits from GServer and I think it's related to this bug
> and
> > subsequent patch. Please look at the gist:
> > https://gist.github.com/4424479
> >
> > Using Ruby <= 1.9.3, when sending an interrupt signal this code would
> > exit cleanly. Using Ruby 2.0, an exception is thrown on launcher.stop:
> >
> > ~/.rvm/rubies/ruby-2.0.0-preview2/lib/ruby/2.0.0/gserver.rb:116:in
> > `synchronize': can't be called from trap context (ThreadError)
> >     from
> > ~/.rvm/rubies/ruby-2.0.0-preview2/lib/ruby/2.0.0/gserver.rb:116:in
> > `stop'
> >
>
> I can confirm this is new behaviour in 2.0.0-preview2 - it also
> happens when you use Queue#enq from within a trap handler (which is an
> issue for me unfortunately).
>
> You could use a variant of the self-pipe trick to signal a thread as
> in the example below. Regards, Sean.
>
> # CODE
>
> require "gserver"
>
> # example server
> class MyServer < GServer
>   def initialize(port=10001, *args)
>     super(port, *args)
>   end
>   def serve(io)
>     io.puts(Time.now.to_s)
>   end
> end
>
> class Launcher
>   def initialize(servers)
>     @servers = servers
>   end
>
>   def start
>     @servers.each { |server| server.start }
>   end
>
>   def join
>     @servers.each { |server| server.join }
>   end
>
>   def stop
>     @servers.each { |server| server.stop }
>   end
> end
>
> servers = [MyServer.new]
> launcher = Launcher.new(servers)
>
> # create self-pipe
> p_read, p_write = IO.pipe
>
> Thread.start(launcher, p_read) do |l, pr|
>   pr.read # blocks until write end closed
>   pr.close
>   l.stop
>   exit
> end
>
> launcher.start
> trap("SIGINT") { p_write.close } # close pipe to signal thread
> launcher.join
>
>