Object Pool Pattern in ASP.NET Core

: Boost Performance and Manage Resources

The Object Pool Pattern in ASP.NET Core is a powerful technique to improve app performance and manage resources efficiently. Here's what you need to know:

Reuses objects instead of creating new ones
Great for expensive objects or limited resources
Built-in support via Microsoft.Extensions.ObjectPool

Key benefits:

Reduces object creation/destruction overhead
Improves performance for frequently used objects
Manages limited resources effectively

When to use:

Creating objects is expensive
Objects represent limited resources
Frequent and predictable object usage

How it works:

Create a pool of objects
Get an object from the pool when needed
Return the object to the pool when done

Important considerations:

Measure performance before implementing
Watch out for state leakage and thread safety
Reset objects properly before returning to pool

Scenario	Benefit
Database connections	Faster setup
Thread management	Better responsiveness
Memory-heavy objects	Less memory use
High-concurrency	Improved performance

Remember: Object pooling isn't always the answer. Use it wisely and only after collecting real performance data for your app or library.

What is the Object Pool Pattern?

The Object Pool Pattern is a smart way to manage resources in ASP.NET Core apps. Instead of creating new objects every time, it reuses a pool of existing ones.

How it works

Create a pool of objects
Grab an object from the pool when needed
Return it to the pool when done

This pattern is great when:

Creating objects takes a lot of time or resources
You have limited resources
Your app frequently uses and releases objects

When to use it

Object pooling works well in specific cases:

Scenario	Benefit
Database connections	Faster setup
Thread management	Better responsiveness
Memory-heavy objects	Less memory use
High-concurrency	Better performance

Take a web server handling tons of requests. Using an object pool for database connections can speed things up BIG TIME. Why? It reuses connections instead of making new ones for each request.

Even Microsoft uses object pooling in ASP.NET Core. They pool StringBuilder instances to make string operations faster.

But here's the thing: it's not always the answer. Microsoft says:

Only use object pooling after you've collected real performance data for your app or library.

In other words: measure first, implement later.

When done right, object pooling can:

Speed up object creation
Reduce memory issues
Manage resources better

But it's not all sunshine and rainbows. You'll need to juggle pool size and handle cases when all objects are in use. It's a trade-off between efficiency and complexity.

What you need to know first

Before we jump into the Object Pool Pattern in ASP.NET Core, let's cover the basics:

You'll need a good grasp of:

C# programming
ASP.NET Core fundamentals
Multithreading concepts
.NET memory management

Here's what you should have:

Latest .NET SDK
An IDE (Visual Studio, VS Code, or JetBrains Rider)
Microsoft.Extensions.ObjectPool NuGet package

Key skills and their importance:

Skill	Importance	Focus
C#	High	Generics, interfaces
ASP.NET Core	High	Dependency injection
Concurrency	Medium	Thread safety
Performance profiling	Low	Measuring impact

Remember:

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

Object pooling isn't always the answer. You'll need to implement PooledObjectPolicy for custom object handling. Consider IResettable for automatic object resets.

How to use Object Pool in ASP.NET Core

Let's set up an Object Pool in ASP.NET Core. We'll cover the basics, create a reusable class, and walk through a step-by-step guide.

Basic Object Pool setup

You'll need:

Microsoft.Extensions.ObjectPool NuGet package
A class to pool
An object pool provider and policy

Here's a quick setup:

var builder = WebApplication.CreateBuilder(args);
builder.Services.TryAddSingleton<ObjectPoolProvider, DefaultObjectPoolProvider>();
builder.Services.TryAddSingleton<ObjectPool<MyClass>>(serviceProvider =>
{
    var provider = serviceProvider.GetRequiredService<ObjectPoolProvider>();
    var policy = new DefaultPooledObjectPolicy<MyClass>();
    return provider.Create(policy);
});

This adds the ObjectPoolProvider to the DI container and sets up a pool for MyClass.

Reusable Object Pool class

Here's a generic Object Pool class:

public class ObjectPool<T> where T : new()
{
    private readonly ConcurrentBag<T> _objects;
    private readonly Func<T> _objectGenerator;
    private readonly int _maxSize;

    public ObjectPool(Func<T> objectGenerator, int maxSize)
    {
        _objects = new ConcurrentBag<T>();
        _objectGenerator = objectGenerator;
        _maxSize = maxSize;
    }

    public T Get() => _objects.TryTake(out T item) ? item : _objectGenerator();

    public void Return(T item)
    {
        if (_objects.Count < _maxSize)
            _objects.Add(item);
    }
}

This class uses a ConcurrentBag for thread-safety and lets you set a maximum pool size.

Step-by-step guide

Create the pooled object class

public class MyFtpClient
{
    public MyFtpClient()
    {
        // Expensive setup operations
    }

    public void Upload(string file) { /* ... */ }
}

Set up the Object Pool

In your Program.cs:

builder.Services.AddSingleton(sp =>
    new ObjectPool<MyFtpClient>(() => new MyFtpClient(), 100));

Use the Object Pool

In a service:

public class FtpService
{
    private readonly ObjectPool<MyFtpClient> _pool;

    public FtpService(ObjectPool<MyFtpClient> pool) => _pool = pool;

    public void UploadFile(string file)
    {
        var client = _pool.Get();
        try
        {
            client.Upload(file);
        }
        finally
        {
            _pool.Return(client);
        }
    }
}

This setup manages expensive resources like FTP clients, improving app performance by reusing objects.

Note: Object pooling isn't always the best solution. Use it for expensive-to-create objects that are used frequently and predictably.

Tips for using Object Pool correctly

Object pooling can boost your ASP.NET Core app's performance. But it's not all sunshine and rainbows. Here's how to use it right:

1. Return objects to the pool

Don't forget to put objects back when you're done. If you don't, you'll have memory issues that won't show up right away.

2. Reset object state

Clear out all the fields when you put an object back. Otherwise, you'll have data from one use showing up in another.

3. Watch those references

Keep an eye on how many things are pointing to your pooled objects. Mess this up, and you'll get memory leaks or weird behavior.

4. Be careful with collections

Arrays and lists are tricky to pool. They change size, which makes pooling hard. Think about using something else instead.

5. Consider the costs

Object pools aren't free. They use memory and CPU. Make sure the benefits are worth it for your specific situation.

6. Make it thread-safe

If you're using multiple threads, add locks. This stops race conditions that can mess everything up.

7. Set pool limits

Decide on minimum and maximum pool sizes. This helps balance how much stuff you're using with how fast things run.

Here's a basic thread-safe object pool with a size limit:

public class ObjectPool<T> where T : new()
{
    private readonly ConcurrentBag<T> _objects;
    private readonly int _maxSize;

    public ObjectPool(int maxSize)
    {
        _objects = new ConcurrentBag<T>();
        _maxSize = maxSize;
    }

    public T Get() => _objects.TryTake(out T item) ? item : new T();

    public void Return(T item)
    {
        if (_objects.Count < _maxSize)
            _objects.Add(item);
    }
}

"If you forget to do any of this then the object's state will 'leak' between uses of it." - Jackson Dunstan, Author at JacksonDunstan.com

Object pooling works best when creating objects is expensive and you use them a lot but for short times. Think database connections in busy web apps.

Finally, use tools like PerfView to find where object pooling will help most. Don't just guess - let the data guide you.

More complex Object Pool techniques

Let's explore advanced object pooling in ASP.NET Core.

Thread safety

Microsoft.Extensions.ObjectPool handles thread safety for you:

using Microsoft.Extensions.ObjectPool;

public class ThreadSafeObjectPool<T> where T : class, new()
{
    private readonly DefaultObjectPool<T> _pool;

    public ThreadSafeObjectPool(int maximumRetained)
    {
        var policy = new DefaultPooledObjectPolicy<T>();
        var provider = new DefaultObjectPoolProvider();
        _pool = (DefaultObjectPool<T>)provider.Create(policy);
    }

    public T Get() => _pool.Get();
    public void Return(T obj) => _pool.Return(obj);
}

Managing pool size

Control resource usage with a size-limited pool:

public class SizeLimitedObjectPool<T> where T : class, new()
{
    private readonly ConcurrentBag<T> _objects;
    private readonly int _maxSize;
    private int _count;

    public SizeLimitedObjectPool(int maxSize)
    {
        _objects = new ConcurrentBag<T>();
        _maxSize = maxSize;
        _count = 0;
    }

    public T Get()
    {
        if (_objects.TryTake(out T item))
        {
            Interlocked.Decrement(ref _count);
            return item;
        }
        return new T();
    }

    public void Return(T item)
    {
        if (Interlocked.Increment(ref _count) <= _maxSize)
        {
            _objects.Add(item);
        }
        else
        {
            Interlocked.Decrement(ref _count);
        }
    }
}

Object lifetime management

Handle disposable objects to prevent memory leaks:

public class DisposableObjectPool<T> where T : class, IDisposable, new()
{
    private readonly ConcurrentBag<T> _objects;
    private bool _isDisposed;

    public DisposableObjectPool()
    {
        _objects = new ConcurrentBag<T>();
    }

    public T Get()
    {
        if (_isDisposed)
            throw new ObjectDisposedException(nameof(DisposableObjectPool<T>));

        return _objects.TryTake(out T item) ? item : new T();
    }

    public void Return(T item)
    {
        if (_isDisposed)
        {
            item.Dispose();
            return;
        }
        _objects.Add(item);
    }

    public void Dispose()
    {
        if (_isDisposed) return;
        _isDisposed = true;

        while (_objects.TryTake(out T item))
        {
            item.Dispose();
        }
    }
}

Custom object reset

Implement a custom PooledObjectPolicy for specific reset logic:

public class CustomObjectPolicy<T> : PooledObjectPolicy<T> where T : class, new()
{
    public override T Create() => new T();

    public override bool Return(T obj)
    {
        if (obj is IResettable resettable)
        {
            resettable.Reset();
            return true;
        }
        return false;
    }
}

Use this policy when creating your pool to reset objects before returning them.

Making your app faster with Object Pool

Object pooling can speed up your ASP.NET Core app. But it's not always the answer. Here's how to check if it'll help and how to use it right:

Find the slow spots

First, profile your app. Use Visual Studio Profiler or dotTrace to see where object creation is slowing things down.

Check if it's working

After you set up object pooling:

Compare before and after: Use BenchmarkDotNet.
Watch memory use: Is garbage collection happening less?
Time user requests: Are they faster now?

Get the pool size right

Too small? No speed boost. Too big? Wasted memory.

Start small and slowly make the pool bigger. Watch what happens:

var pool = new DefaultObjectPool<ExpensiveObject>(
    new DefaultPooledObjectPolicy<ExpensiveObject>(),
    maxCapacity: 100);

Change maxCapacity and see how it affects your app.

Custom object policies

For tricky objects, make your own PooledObjectPolicy:

public class CustomObjectPolicy : IPooledObjectPolicy<ExpensiveObject>
{
    public ExpensiveObject Create() => new ExpensiveObject();

    public bool Return(ExpensiveObject obj)
    {
        obj.Reset(); // Your reset logic here
        return true;
    }
}

This resets objects properly before they go back in the pool.

Thread-safe pools

If your app does many things at once, use this:

var provider = new DefaultObjectPoolProvider();
var pool = provider.Create(new CustomObjectPolicy());

It's safe for multi-threaded apps.

Keep an eye on things

Check your app's speed often:

Look for memory leaks
See if the pool is being used fully
Check if objects are still slow to create

If things change, adjust your pooling setup.

Using Object Pool with Dependency Injection

Object Pool and Dependency Injection (DI) in ASP.NET Core? They're a match made in heaven. Here's how to make them work together:

Set Up Your Pool

First, add this to your Startup.cs or Program.cs:

builder.Services.TryAddSingleton<ObjectPoolProvider, DefaultObjectPoolProvider>();
builder.Services.TryAddSingleton<ObjectPool<ReusableBuffer>>(serviceProvider =>
{
    var provider = serviceProvider.GetRequiredService<ObjectPoolProvider>();
    var policy = new DefaultPooledObjectPolicy<ReusableBuffer>();
    return provider.Create(policy);
});

This creates a pool for ReusableBuffer objects.

Use It in Controllers

Now, let's put that pool to work in your controllers:

public class HashController : Controller
{
    private readonly ObjectPool<ReusableBuffer> _bufferPool;

    public HashController(ObjectPool<ReusableBuffer> bufferPool)
    {
        _bufferPool = bufferPool;
    }

    [HttpGet("/hash/{name}")]
    public IActionResult GetHash(string name)
    {
        var buffer = _bufferPool.Get();
        try
        {
            // Use the buffer
            for (var i = 0; i < name.Length; i++)
            {
                buffer.Data[i] = (byte)name[i];
            }
            Span<byte> hash = stackalloc byte[32];
            SHA256.HashData(buffer.Data.AsSpan(0, name.Length), hash);
            return Ok("Hash: " + Convert.ToHexString(hash));
        }
        finally
        {
            _bufferPool.Return(buffer);
        }
    }
}

Scoped Services? No Problem

You can use pooled objects as scoped services too:

services.AddPool<MyService>()
        .AddScoped<Consumer>();

public class Consumer
{
    private readonly MyService _myService;
    public Consumer(ObjectPool<MyService> myServicePool)
    {
        _myService = myServicePool.Get();
        // Use _myService
    }

    // Don't forget to return the service to the pool when done
}

Auto-Reset Objects

Make your pooled objects reset themselves:

public class ReusableBuffer : IResettable
{
    public byte[] Data { get; } = new byte[1024 * 1024]; // 1 MB

    public bool TryReset()
    {
        Array.Clear(Data);
        return true;
    }
}

This clears the buffer when it goes back to the pool.

Control Pool Size

Set how many objects your pool keeps:

builder.Services.AddPooled<MyPooledClass>(options => options.Capacity = 64);

This caps the pool at 64 objects.

Thread Safety? Built-In

Object pools in ASP.NET Core are already thread-safe. No extra locks needed in multi-threaded code.

Real examples of Object Pool use

Let's look at how Object Pool patterns work in the real world:

Database Connection Pooling

ADO.NET uses connection pooling to speed things up:

using (var conn1 = new SqlConnection("Server=myServer;Database=myDb1;User Id=myUser;Password=myPass;"))
using (var conn2 = new SqlConnection("Server=myServer;Database=myDb2;User Id=myUser;Password=myPass;"))
using (var conn3 = new SqlConnection("Server=myServer;Database=myDb1;User Id=myUser;Password=myPass;"))
{
    conn1.Open();
    conn2.Open();
    conn3.Open();
}

This code creates two connection pools:

One for conn1 and conn3 (same connection string)
Another for conn2 (different database)

Web Crawler Speed Boost

Object Pooling can seriously speed up web crawling:

Metric	Without Pool	With Pool	Improvement
Processing Time	9.7 hours	4 hours	242% faster
URLs Processed	5,000	5,000	Same

Here's a BrowserPool class that manages Selenium WebDriver instances:

public class BrowserPool
{
    private readonly ConcurrentQueue<IWebDriver> _pool = new ConcurrentQueue<IWebDriver>();
    private readonly SemaphoreSlim _semaphore;

    public BrowserPool(int size)
    {
        _semaphore = new SemaphoreSlim(size, size);
        for (int i = 0; i < size; i++)
        {
            _pool.Enqueue(new ChromeDriver());
        }
    }

    public async Task<IWebDriver> GetBrowserAsync()
    {
        await _semaphore.WaitAsync();
        _pool.TryDequeue(out var browser);
        return browser;
    }

    public void ReleaseBrowser(IWebDriver browser)
    {
        _pool.Enqueue(browser);
        _semaphore.Release();
    }
}

This approach cuts down on the time spent creating and destroying browser instances for each URL.

HTTP Client Pooling

ASP.NET Core's HttpClientFactory manages pools of HttpClient instances:

services.AddHttpClient("github", c =>
{
    c.BaseAddress = new Uri("https://api.github.com/");
    c.DefaultRequestHeaders.Add("Accept", "application/vnd.github.v3+json");
    c.DefaultRequestHeaders.Add("User-Agent", "HttpClientFactory-Sample");
});

This setup creates a pool of HttpClient instances, which helps avoid socket exhaustion and boosts performance.

Fixing problems with Object Pool

Object Pools can speed things up, but they come with their own set of issues. Let's look at some common problems and how to fix them:

Forgetting to return objects

This is a big one. If you don't put objects back in the pool, you'll run out of resources fast.

Fix: Use a using statement:

using (var obj = pool.Get())
{
    // Do stuff with obj
}
// obj goes back to the pool automatically

State leakage

Objects might keep data from their last use. That's bad news.

Fix: Reset objects when you're done:

public void Release(MyObject obj)
{
    obj.ResetAllProperties();
    _pool.Return(obj);
}

Thread safety

Object pools aren't thread-safe out of the box. This can cause problems.

Fix: Use ConcurrentBag<T> and lock things down:

private readonly ConcurrentBag<MyObject> _pool = new ConcurrentBag<MyObject>();
private readonly SemaphoreSlim _semaphore;

public MyObject Get()
{
    _semaphore.Wait();
    return _pool.TryTake(out var item) ? item : new MyObject();
}

Memory leaks from static references

Static references can stop objects from being garbage collected.

Fix: Use WeakReference for caching:

private static WeakReference<MyObject> _cachedObject;

public MyObject GetCachedObject()
{
    if (_cachedObject.TryGetTarget(out var obj))
        return obj;

    obj = new MyObject();
    _cachedObject.SetTarget(obj);
    return obj;
}

Too much memory use

If you're not careful, pools can eat up a lot of memory.

Fix: Set a size limit:

private const int MaxPoolSize = 100;

public void Return(MyObject obj)
{
    if (_pool.Count < MaxPoolSize)
        _pool.Add(obj);
    else
        obj.Dispose();
}

HttpClient issues

Using HttpClient wrong can cause port exhaustion.

Fix: Reuse HttpClient instances:

private static readonly HttpClient _httpClient = new HttpClient();

public async Task<int> GetStatusCode(string url)
{
    var result = await _httpClient.GetAsync(url);
    return (int)result.StatusCode;
}

Wrap-up

The Object Pool Pattern in ASP.NET Core can boost performance and manage resources effectively. Here's what you need to know:

It reuses objects instead of creating new ones
It's great for expensive objects or limited resources
ASP.NET Core has built-in support via Microsoft.Extensions.ObjectPool

But it's not perfect. Remember:

Measure performance first
Watch out for state leakage and thread safety issues
Reset objects properly

What's next? Microsoft might improve ObjectPool<T> with:

Better DI integration
Smarter pooling strategies
Enhanced monitoring tools

Object pooling in ASP.NET Core is powerful, but use it wisely.

FAQs

What is an object pool in .NET?

An object pool in .NET is a container that holds reusable objects in memory. It's part of ASP.NET Core and helps boost performance by cutting down on object creation and destruction.

Here's what you need to know:

It keeps objects in memory instead of letting them get garbage collected
It's great for objects that are costly to create or represent limited resources
You'll find it in the Microsoft.Extensions.ObjectPool namespace

How does an object pool work in .NET?

Let's break it down with a quick example:

using Microsoft.Extensions.ObjectPool;

public class ExpensiveObject
{
    // Costly initialization logic here
}

// Set up the pool
ObjectPool<ExpensiveObject> pool = new DefaultObjectPool<ExpensiveObject>(
    new DefaultPooledObjectPolicy<ExpensiveObject>());

// Grab an object from the pool
ExpensiveObject obj = pool.Get();

// Use the object
// ...

// Put it back in the pool
pool.Return(obj);

This pattern shines when dealing with things like database connections or network sockets.

Is ObjectPool thread-safe?

You bet. ObjectPool in ASP.NET Core is built to handle multiple threads. All its methods (both static and instance) are safe to use in multi-threaded scenarios.

As Jon Skeet, a big name in software engineering, puts it:

"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."

So, you can use ObjectPool without worrying about thread-related headaches.

Object Pool Pattern in ASP.NET Core

Related video from YouTube

What is the Object Pool Pattern?

How it works

When to use it

What you need to know first

How to use Object Pool in ASP.NET Core

Basic Object Pool setup

Reusable Object Pool class

Step-by-step guide

Tips for using Object Pool correctly

More complex Object Pool techniques

Thread safety

Managing pool size

Object lifetime management

Custom object reset

sbb-itb-29cd4f6

Making your app faster with Object Pool

Find the slow spots

Check if it's working

Get the pool size right

Custom object policies

Thread-safe pools

Keep an eye on things

Using Object Pool with Dependency Injection

Set Up Your Pool

Use It in Controllers

Scoped Services? No Problem

Auto-Reset Objects

Control Pool Size

Thread Safety? Built-In

Real examples of Object Pool use

Database Connection Pooling

Web Crawler Speed Boost

HTTP Client Pooling

Fixing problems with Object Pool

Forgetting to return objects

State leakage

Thread safety

Memory leaks from static references

Too much memory use

HttpClient issues

Wrap-up

FAQs

What is an object pool in .NET?

How does an object pool work in .NET?

Is ObjectPool thread-safe?

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