an example of what NOT to do from the ruby standard library

What's wrong with Ruby's implementation of conditional variables here? Hint: what's wrong has nothing to do with synchronization, concurrency, or conditional variables.

 class ConditionVariable
   class Timeout < Exception; end
 
   # Create a new timer with the argument timeout, and add the
   # current thread to the list of waiters.  Then the thread is
   # stopped.  It will be resumed when a corresponding #signal
   # occurs.
   def wait(timeout = nil)
     @monitor.instance_eval {mon_check_owner()}
     timer = create_timer(timeout)
   
     Thread.critical = true
     count = @monitor.instance_eval {mon_exit_for_cond()}
     @waiters.push(Thread.current)

     begin
   Thread.stop
       return true
     rescue Timeout
       return false
     ensure
   Thread.critical = true
   begin
   ...

--
Love,
Fritz