sync.rb - 2 phase lock with counter
	$Release Version: 1.0$
	$Revision: 22457 $
	$Date: 2009-02-20 01:41:12 +0900 (Fri, 20 Feb 2009) $
	by Keiju ISHITSUKA(keiju@ishitsuka.com)

–

Sync_m, Synchronizer_m
Usage:
 obj.extend(Sync_m)
 or
 class Foo

include Sync_m :

end

Sync_m#sync_mode
Sync_m#sync_locked?, locked?
Sync_m#sync_shared?, shared?
Sync_m#sync_exclusive?, sync_exclusive?
Sync_m#sync_try_lock, try_lock
Sync_m#sync_lock, lock
Sync_m#sync_unlock, unlock

Sync, Synchronicer:

include Sync_m

Usage:
sync = Sync.new

Sync#mode
Sync#locked?
Sync#shared?
Sync#exclusive?
Sync#try_lock(mode) -- mode = :EX, :SH, :UN
Sync#lock(mode)     -- mode = :EX, :SH, :UN
Sync#unlock
Sync#synchronize(mode) {...}