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68 lines
2.9 KiB
Markdown
68 lines
2.9 KiB
Markdown
# Object Pooling
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Object pooling is an optimization pattern. It's used to improve performance, in certain cases, by re-using objects instead of allocating memory for them on demand. In C/C++, one the things object pooling has to offer is a solution to avoid [memory fragmentation](http://stackoverflow.com/questions/3770457/what-is-memory-fragmentation). In C#, we don't have to worry about memory fragmentation thanks to [garbage collection](https://msdn.microsoft.com/en-us/library/ee787088). However, garbage collection can be still be too expensive for certain parts of real-time applications, especially on mobile devices with slower CPUs and simpler garbage collectors. [More details on object pooling here](http://gameprogrammingpatterns.com/object-pool.html).
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# IMPORTANT
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Always profile the game for performance problems!
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Using a `Pool<T>` without first profiling for the need of one may result in a *decrease* in performance in certain cases. If you are unsure, don't use the object pooling pattern.
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# Creating a Pool-able Object
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All objects which can be pooled need to implement the `IPoolable` interface.
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The following is a code snippet with comments demonstrating how to implement the interface.
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```csharp
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private class MyPoolable : IPoolable
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{
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private ReturnToPoolDelegate _returnAction;
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void IPoolable.Initialize(ReturnToPoolDelegate returnAction)
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{
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// copy the instance reference of the return function so we can call it later
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_returnAction = returnAction;
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}
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public void Return()
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{
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// check if this instance has already been returned
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if (_returnAction != null)
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{
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// not yet returned, return it now
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_returnAction.Invoke(this);
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// set the delegate instance reference to null, so we don't accidentally return it again
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_returnAction = null;
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}
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}
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}
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```
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# Using Pooled Objects
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## Creating a Pool
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Instantiating a `Pool<T>` is similar to any generic collection, i.e `List<T>`, but the pool does require 2 parameters for it's constructor. `T` also has to implement `IPoolable`.
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```csharp
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var pool = new Pool<MyPoolable>(50, index => new MyPoolable());
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```
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The first parameter is the _capacity_ of the pool; the maximum number of object instances the pool has reference to. The second parameter is the delegate responsible for creating each object instance.
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### NOTE
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Having too large of a capacity will waste memory, but having too small of a capacity will limit the number of object instances that can be pooled.
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All object instances are created when the pool is instantiated.
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## Getting a Pooled Object
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A free pooled object instance can be requested from the pool instance.
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```csharp
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var myPoolable = pool.Request();
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```
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### NOTE
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If the pool is empty, the result will be `null`.
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## Returning a Object to the Pool
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When the object instance is no longer needed it should be returned to the pool so it can be re-used.
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```csharp
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myPoolable.Return();
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```
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