thwait.rb - thread synchronization class
	$Release Version: 0.9 $
	$Revision: 1.3 $
	$Date: 1998/06/26 03:19:34 $
	by Keiju ISHITSUKA(Nihpon Rational Software Co.,Ltd.)

–

feature:
provides synchronization for multiple threads.

class methods:
* ThreadsWait.all_waits(thread1,...)
  waits until all of specified threads are terminated.
  if a block is supplied for the method, evaluates it for
  each thread termination.
* th = ThreadsWait.new(thread1,...)
  creates synchronization object, specifying thread(s) to wait.

methods:
* th.threads
  list threads to be synchronized
* th.empty?
  is there any thread to be synchronized.
* th.finished?
  is there already terminated thread.
* th.join(thread1,...) 
  wait for specified thread(s).
* th.join_nowait(threa1,...)
  specifies thread(s) to wait.  non-blocking.
* th.next_wait
  waits until any of specified threads is terminated.
* th.all_waits
  waits until all of specified threads are terminated.
  if a block is supplied for the method, evaluates it for
  each thread termination.