To fix an issue that a library/executable script needs to run the eventloop other than the main thread only when it is executed as a command.

[h-nagai]

When a executable Tk library script, e.g. "sample/tktextio.rb", is executed as a command, it may need to run the eventloop other than the main thread. However, when loaded as a library, it should not force the running-mode of the eventloop. "thread_tk.rb" is one solution to the problem by writing a sh-bang line like "#!/usr/bin/ruby -r thread_tk".

fix that sample/irbtkw.rbw doesn't work with the recent IRB

[jeremyevans]

This looks fine to me. I'm guessing this wasn't an issue until we made the event loop run on the main thread by default for performance reasons.

[h-nagai]

In thread_tk.rb, it is better to raise an exception if tk.rb is already loaded.
For example, add the followings at top of thread_tk.rb.
if $LOADED_FEATURES.find{|path| path =~ %r!/tk.rb$!}
raise LoadError, "thread_tk.rb must be loaded before tk.rb
end

[jeremyevans]

@h-nagai I added #53 to implement the check you requested. Instead of checking $LOADED_FEATURES, it checks to see whether the constant has already been set to true.