AspNetCore.Docs/aspnetcore/performance/ObjectPool.md

title	author	description	monikerRange	ms.author	ms.date	no-loc	uid
Object reuse with ObjectPool in ASP.NET Core	rick-anderson	Tips for increasing performance in ASP.NET Core apps using ObjectPool.	>= aspnetcore-1.1	riande	04/11/2019	Kestrel appsettings.json ASP.NET Core Identity cookie Cookie Blazor Blazor Server Blazor WebAssembly Identity Let's Encrypt Razor SignalR	performance/ObjectPool

Object reuse with ObjectPool in ASP.NET Core

By Steve Gordon, Ryan Nowak, and Günther Foidl

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.

You might want to use the object pool if the objects that are being managed are:

• Expensive to allocate/initialize.
• Represent some limited resource.
• Used predictably and frequently.

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.

Object pooling doesn't always improve performance:

• Unless the initialization cost of an object is high, it's usually slower to get the object from the pool.
• Objects managed by the pool aren't de-allocated until the pool is de-allocated.

Use object pooling only after collecting performance data using realistic scenarios for your app or library.

::: moniker range="< aspnetcore-3.0" WARNING: The ObjectPool doesn't implement IDisposable. We don't recommend using it with types that need disposal. ObjectPool in ASP.NET Core 3.0 and later supports IDisposable. ::: moniker-end

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.

Concepts

xref:Microsoft.Extensions.ObjectPool.ObjectPool`1 - the basic object pool abstraction. Used to get and return objects.

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

xref:Microsoft.Extensions.ObjectPool.ObjectPoolProvider.Create* acts as a factory for creating object pools.

The ObjectPool can be used in an app in multiple ways:

• Instantiating a pool.
• Registering a pool in Dependency injection (DI) as an instance.
• Registering the ObjectPoolProvider<> in DI and using it as a factory.

How to use ObjectPool

Call xref:Microsoft.Extensions.ObjectPool.ObjectPool`1.Get* 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.

::: moniker range=">= aspnetcore-3.0" When xref:Microsoft.Extensions.ObjectPool.DefaultObjectPoolProvider is used and T implements IDisposable:

• Items that are not returned to the pool will be disposed.
• When the pool gets disposed by DI, all items in the pool are disposed.

NOTE: After the pool is disposed:

• Calling Get throws a ObjectDisposedException.
• return disposes the given item.

::: moniker-end

ObjectPool sample

The following code:

• Adds ObjectPoolProvider to the Dependency injection (DI) container.
• Adds and configures ObjectPool<StringBuilder> to the DI container.
• Adds the BirthdayMiddleware.

[!code-csharp]

The following code implements BirthdayMiddleware

[!code-csharp]

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