[ruby-core:86655] cross-thread IO#close semantics

[Eric Wong <normalperson@yhbt.net>]

Related to the discussion on [Bug #14681]

I found an old Ruby 1.8 installation, and the following code
exits after 100ms with: [IOError, "stream closed"]
1.9 and later hangs forever:

  r, w = IO.pipe
  th = Thread.new do
    begin
      IO.select([r])
    rescue => e
      warn [ e.class, e.message ].inspect
    end
  end
  sleep 0.1
  r.close
  th.join

Of course I know why: it's not implemented in 1.9+;
rb_thread_io_blocking_region only cares for operations on the
single FD case, multiplexing functions like select aren't
supported.  I could implement it, but it has overhead and maybe
nobody cares for this feature.  IO.select is an inefficient API
anyways

This also pertains to [Feature #13618] for auto-fiber/green thread
support or whatever it will be called.

If I replace IO.select with single FD operation which hits
rb_thread_io_blocking_region in 1.9+ such as "r.read", then Ruby
behaves consistently in 1.8/1.9/2.x