Using a Reentrant lock instead of the intrinsic synchronization lock
permits limiting the blocking time to acquire a lock.
Useful on a very busy Cache concurrently accessed by many threads : when
the time to acquire a lock is too high, getting/storing content on the
cache becomes inefficient, and it is then better to fall back to loading
remote resources.
Illustrated by the CacheTest stress test and some traces reported in
mantis 751 ( http://mantis.tokeek.de/view.php?id=751 )
Michael Peter Christen