How to implement ConcurrentHashMap with features similar in LinkedHashMap?

Question

I have used LinkedHashMap with accessOrder true along with allowing a maximum of 500 entries at any time as the LRU cache for data. But due to scalabil

Answer 1

You mention wanting to solve scalability problems with a "thread-safe" alternative. "Thread safety" here means that the structure is tolerant of attempts at concurrent access, in that it won't suffer corruption by concurrent use without external synchronization. However, such tolerance does not necessarily help to improve "scalability". In the simplest -- though usually misguided -- approach, you'll try to synchronize your structure internally and still leave non-atomic check-then-act operations unsafe.

LRU caches require at least some awareness of the total structure. They need something like a count of the members or the size of the members to decide when to evict, and then they need to be able to coordinate the eviction with concurrent attempts to read, add, or remove elements. Trying to reduce the synchronization necessary for concurrent access to the "main" structure fights against your eviction mechanism, and forces your eviction policy to be less precise in its guarantees.

The currently accepted answer mentions "when you want to evict an entry". Therein lies the rub. How do you know when you want to evict an entry? Which other operations do you need to pause in order to make this decision?