Ruby/Tk does NOT support forking the process on which Tk interpreter
is running (unless NEVER control Tk interpreter under the forked child 
process). In the library 'tk.rb', a Tk interpreter is initialized. 
Therefore, if you want running Tk under a child process, please call
"require 'tk'" in the child process. 

For example, the following sample1 will NOT work, and sample2 will
work properly.

---<sample1: NOT work>---------------------------------------
require 'tk'  ## init Tk interpreter under parent process

exit! if fork ## exit parent process

## child process
TkButton.new(:text=>'QUIT', :command=>proc{exit}).pack
Tk.mainloop
-------------------------------------------------------------

---<sample2: will work>--------------------------------------
exit! if fork ## exit main process

## child process
require 'tk'  ## init Tk interpreter under child process
TkButton.new(:text=>'QUIT', :command=>proc{exit}).pack
Tk.mainloop
-------------------------------------------------------------

                                         2004/04/20  Hidetoshi NAGAI