Requirements :

1. Read your own writes
2. Multiple write policies , write back and write through
3. Expiration time
4. Multiple replacements policy - LRU , LFU
5. Ansyc processing
6. Request collapsing policy

Should allow:

1. listeners on load and evict
2. hot loading elements on startup
3. multiple eviction algorithms like LRU and LFU
4. expiration time
5. multiple fetch algorithms like write back and write through
6. return futures
7. request collapsing
8. Avoid thrashing with rate limiting