class IRB::JobManager

def switch(key)

exception is raised.
If the given irb session is already active, an IrbSwitchedToCurrentThread

Raises an IrbAlreadyDead exception if the given +key+ is no longer alive.

Array.
Changes the current active irb session to the given +key+ in the jobs 
def switch(key)
  th, irb = search(key)
  fail IrbAlreadyDead unless th.alive?
  fail IrbSwitchedToCurrentThread if th == Thread.current
  @current_job = irb
  th.run
  Thread.stop
  @current_job = irb(Thread.current)
end