I'm attempting to spawn a thread when a user clicks a button. The thread makes a system call. If I don't do a thread.join immediately after, the app crashes (unknown software exception). Does FXRuby not like it when a child thread makes system calls? A thread in a 'standard' Ruby app (without FXRuby) can make these calls just fine. Any ideas? #--------------------------------------- require 'fox' include Fox class MyMainWindow < FXMainWindow def initialize(app) super(app, "Thread Test") #layout screen button = FXButton.new(self, "Push me.") button.connect(SEL_COMMAND, method(:onButton)) end def create super show(PLACEMENT_SCREEN) end def onButton(sender, sel, item) thread = Thread.new do `cmd /C dir` end #thread.join end end theApp = FXApp.new theApp.init(ARGV) myWindow = MyMainWindow.new(theApp) theApp.create theApp.run