Main event loop thread of TkAqua (> Tk8.4.9) must be the main
application thread. So, ruby1.9 users must call Tk.mainloop on
the main application thread.

In some cases (I don't know the description of conditions),
TkAqua 8.4.7 has a same kind of hang-up trouble.
So, if 8.4.7 or later, set RUN_EVENTLOOP_ON_MAIN_THREAD to true.
When you want to control this mode, please call the following
(set true/false as you want) before "require 'tk'".
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module TkCore; RUN_EVENTLOOP_ON_MAIN_THREAD = true; end
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The value of TclTkLib::WINDOWING_SYSTEM is defined at compiling.
If it is inconsistent with linked DLL, please call the following
before "require 'tk'".
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require 'tcltklib'
module TclTkLib
  remove_const :WINDOWING_SYSTEM
  WINDOWING_SYSTEM = 'x11' # or 'aqua'
end
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