switch

# File lib/irb/ext/multi-irb.rb, line 54
    def switch(key)
      th, irb = search(key)
      IRB.fail IrbAlreadyDead unless th.alive?
      IRB.fail IrbSwitchedToCurrentThread if th == Thread.current
      @current_job = irb
      th.run
      Thread.stop
      @current_job = irb(Thread.current)
    end