Object Pool Design Pattern

Object Pool design pattern is also known as
- Resource Pool
- N-ton
Performance gains become visible when:
- Initializing a Reusable class instance is expensive operation.
- Rate of instantiation is high; time of use by clients - low.

A Reusable Pool class manages a cache of concrete Reusable Objects.
A Reusable Object is often referred to as a subject of the pool.
Generally the pool will be a growing pool:
1. Pool can be empty at the beginning, or pre-populated with a number of subjects.
2. Pool can create new subjects.
3. Pool may restrict the maximum number of subjects created.

Reusable Pool design implements a facility to periodically clean up the unused objects, for example, with the help of a time measuring proxy.

Clients collaborate with the ReusablePool class in a very limited manner:


    Reusable obj = ReusablePool.getInstance().acquireReusable();

Consider TCP/IP Sequence Diagrams at
http://www.eventhelix.com/RealtimeMantra/Networking/
The DHCP Sequence Diagram explains how a DHCP client obtains dynamic IP address from the DHCP server.
The DHCP server maintains a cache of leased and available IP addresses.
It is likely that DHCP server implementation could benefit from a Reusable Pool of IP records.
Since the network protocol requires DHCP lease time maintenance, a time measuring proxy may be required to accommodate the lease duration and its operations.