Implementing a concurrent LinkedHashMap

Question

I\'m trying to create a concurrent LinkedHashMap for a multithreaded architecture.

If I use Collections#synchronizedMap(), I would have to use synchroni

Answer 1

A LinkedHashMap has a doubly linked list running through a hashtable. A FIFO only mutates the links on a write (insertion or removal). This makes implementing a version fairly straightforward.

1. Write a LHM with only insertion order allowed.
2. Switch to a ConcurrentHashMap as the hashtable.
3. Protect #put() / #putIfAbsent() / #remove() with a lock.
4. Make the "next" field volatile.

On iteration, no lock is needed as you can safely follow the "next" field. Reads can be lock-free by just delegating to the CHM on a #get().