ISPN-4424 Synchronize updating cache entry and making a copy
ISPN-4424 Synchronize updating cache entry and making a copy
- making the CacheEntry immutable is not enough, the whole CacheEntry hierarchy needs to be made immutable
- using clone is simpler that making the hierarchy immutable
ISPN-3938 AdvancedAsyncCacheLoader.process() concurrency issues

Simplify ExecutorAllCompletionService to track the tasks itself instead of
using an ExecutorCompletionService.