What are some use cases for the object pool design pattern? [closed]

Question

My understanding of this is that object pools are useful when we want to work with an object but we want to use one that's already been instantiated. It's like a library book - you check out a book and you return it when you're finished reading it.

However, I struggle to see how this design pattern is used in real life. As a programmer, I have never seen a situation wherein I'd need to check out an object as opposed to creating a new one, passing it in as an argument, or defining a singleton variable containing the object.

Answer 1

It's useful if the object is re-usable and significantly more expensive to create or destroy than reuse.

Database Connections are a classic case. Connection Pools are common.

• Microsoft's ODBC implementation offers connection pools.

• Popular JDBC tools offer connection pooling. Most servlet containers have it.

• .Net Framework offers connection pooling.

Thread Pools, another popular case.

• Anything that uses Java Executors. Implementations of Executor are typically Thread Pools, or at least use a thread pool.
• Many servlet containers, web servers and app servers use thread pools.
• For example Tomcat, Glassfish, Jetty, Apache, Nginx all use thread pools (per documentation or review of source code).
• Some databases keep pools of worker threads for similar reasons. For example MySQL, MS SQLServer.

You may never find a case where you need to pool your own objects, but it is likely you will use tools that pool objects.

Answer 2

I use an object pool for acquiring images from a camera in C#. This prevents the Large Object Heap from thrashing and possibly becoming fragmented. By reusing a pool of large byte arrays, I gained a performance optimization and avoid a potential out of resources issue.

Answer 3

In game development, it comes up quite often. Even fairly simple objects that are visible (such as projectiles, boxes, etc) often have a non-trivial amount of instantiation involved, and characters even more so.

In the not-uncommon situation that you have a huge number of a given object/creature being created over the course of a level, but only a limited amount present at one time (such as waves of enemies in a vertical shooter), then pooling them is generally much better for performance.