mbbhalla/expirycacheimpl

A cache implementation with concurrent expired entries collector (analogous to a concurrent garbage collector)

Store list is a list of StoreListElements

StoreListElement (SLE) (also referred to as data unit (DU) => LockingMechanism Map

Each SLE is an independent mutually exclusive data structure from other SLEs There are 3 kind of threads operating on each DU

getters - gets from map possible removes also
putters - puts entries into map
collector - single thread which removes expired entries from SLE's map

collector and getters/putters are sync using count down latch (CDL) and Phaser in LockingMechanism
getters and putters are sync using synchronized over CacheEntry (value in the map)

Collector properties:

1. When collector runs on SLE getters and putters are blocked using CDL
2. Collector waits for existing get/put operations to get over using Phaser
3. When existing get/put operations on that SLE are done they deregister in phaser and collector proceeds to collect In the same time new get/put requests are blocked through CDL
4. Collector in end of operation counts down latch, thus enabling runs of waiting getters and putters

Possible Improvements on top of this:

1. checking possible Use of weakreferences so that java GC collects expired entires

2. collector thread is scheduled 1 thread. Collection can be made concurrent by multiple threads working on mutually exclusive areas of the list store.

3. optimizing collector run. Right now its scheduled. Can be possibly triggered when X % of expired entries accumulate