67 lines
3.3 KiB
Markdown
67 lines
3.3 KiB
Markdown
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---
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title: Object reuse with ObjectPool in ASP.NET Core
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author: rick-anderson
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description: Tips for increasing performance in ASP.NET Core apps using ObjectPool.
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monikerRange: '>= aspnetcore-1.1'
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ms.author: riande
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ms.date: 4/11/2019
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uid: performance/ObjectPool
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---
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# Object reuse with ObjectPool in ASP.NET Core
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By [Steve Gordon](https://twitter.com/stevejgordon), [Ryan Nowak](https://github.com/rynowak), and [Rick Anderson](https://twitter.com/RickAndMSFT)
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<xref:Microsoft.Extensions.ObjectPool> is part of the ASP.NET Core infrastructure that supports keeping a group of objects in memory for reuse rather than allowing the objects to be garbage collected.
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You might want to use the object pool if the objects that are being managed are:
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- Expensive to allocate/initialize.
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- Represent some limited resource.
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- Used predictably and frequently.
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For example, the ASP.NET Core framework uses the object pool in some places to reuse <xref:System.Text.StringBuilder> instances. `StringBuilder` allocates and manages its own buffers to hold character data. ASP.NET Core regularly uses `StringBuilder` to implement features, and reusing them provides a performance benefit.
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Object pooling doesn't always improve performance:
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- Unless the initialization cost of an object is high, it's usually slower to get the object from the pool.
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- Objects managed by the pool aren't de-allocated until the pool is de-allocated.
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Use object pooling only after collecting performance data using realistic scenarios for your app or library.
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**WARNING: The `ObjectPool` doesn't implement `IDisposable`. We don't recommend using it with types that need disposal.**
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**NOTE: The ObjectPool doesn't place a limit on the number of objects that it will allocate, it places a limit on the number of objects it will retain.**
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## Concepts
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<xref:Microsoft.Extensions.ObjectPool.ObjectPool`1> - the basic object pool abstraction. Used to get and return objects.
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<xref:Microsoft.Extensions.ObjectPool.PooledObjectPolicy%601> - implement this to customize how an object is created and how it is *reset* when returned to the pool. This can be passed into an object pool that you construct directly.... OR
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<xref:Microsoft.Extensions.ObjectPool.ObjectPoolProvider.Create*> acts as a factory for creating object pools.
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<!-- REview, there is no ObjectPoolProvider<T> -->
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The ObjectPool can be used in an app in multiple ways:
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* Instantiating a pool.
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* Registering a pool in [Dependency injection](xref:fundamentals/dependency-injection) (DI) as an instance.
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* Registering the `ObjectPoolProvider<>` in DI and using it as a factory.
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## How to use ObjectPool
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Call <xref:Microsoft.Extensions.ObjectPool.ObjectPool`1> to get an object and <xref:Microsoft.Extensions.ObjectPool.ObjectPool`1.Return*> to return the object. There's no requirement that you return every object. If you don't return an object, it will be garbage collected.
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## ObjectPool sample
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The following code:
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* Adds `ObjectPoolProvider` to the [Dependency injection](xref:fundamentals/dependency-injection) (DI) container.
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* Adds and configures `ObjectPool<StringBuilder>` to the DI container.
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* Adds the `BirthdayMiddleware`.
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[!code-csharp[](ObjectPool/ObjectPoolSample/Startup.cs?name=snippet)]
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The following code implements `BirthdayMiddleware`
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[!code-csharp[](ObjectPool/ObjectPoolSample/BirthdayMiddleware.cs?name=snippet)]
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