Could you test the following script?
----------------------------------------------------------
module TkCore; RUN_EVENTLOOP_ON_MAIN_THREAD = true; end
require 'tk'
Tk.mainloop
----------------------------------------------------------
If it works, a bug may exist on handling a Thread.

From: "edmccard (Ed McCardell)" <edmccard / hotmail.com>
Subject: [ruby-core:53226] [ruby-trunk - Bug #8000] "require 'tk'" segfaults on 64-bit linux with Tk 8.6
Date: Fri, 8 Mar 2013 17:55:30 +0900
Message-ID: <redmine.journal-37386.20130308175529 / ruby-lang.org>

> 
> Issue #8000 has been updated by edmccard (Ed McCardell).
> 
> File bt-debug.txt added
> 
> Now that I've tried a few more ruby/tk scripts, I see that only a limited subset of tk works on 32-bit under Tk8.6. But in case it's still useful, I've attached a backtrace from gdb using ruby1.9.3p392/tcl8.6/tk8.6 with debug info on 64-bit.
> ----------------------------------------
> Bug #8000: "require 'tk'" segfaults on 64-bit linux with Tk 8.6
> https://bugs.ruby-lang.org/issues/8000#change-37386
> 
> Author: edmccard (Ed McCardell)
> Status: Open
> Priority: Normal
> Assignee: 
> Category: 
> Target version: 
> ruby -v: ruby 1.9.3p392 (2013-02-22 revision 39386) [x86_64-linux]
> 
> 
> Using ruby 1.9.3p392 and Tk 8.6.0 on 64-bit Arch Linux, attempting to "require 'tk'" causes a segfault.
> 
> To reproduce:
>     ruby -e "require 'tk'"
> 
> The crash log is in the attached file.
> 
> Notes:
> - I've heard from a Gentoo user who is having the same problem.
> - On 32-bit Arch Linux, there is no problem.
> 
> 
> -- 
> http://bugs.ruby-lang.org/
>