Synchronization problem in CacheStore

This bug manifests occasionally when running the CachedTest. The AsyncStore thread suspends inside its run method on a (120 sec) timed wait because the cache is not full. When I managed to catch this case in the debugger I found that there were many writer threads (~30) suspended inside addWork in an untimed wait on the overflow lock. So, these writing threads make no progress for 120 seconds. The AsyncStore thread does notify the object on which the writers are waiting but there is clearly a window where the writers can go to sleep while the cache is full and not get notified when the AsyncStore thread has emptied it.