ASP.NET Core中的对象池化技术详解

写在前面

Microsoft.Extensions.ObjectPool 是 ASP.NET Core 基础结构的一部分，当对象的初始化成本较高，并且可能被频繁使用时，才适合采用对象池技术；被ObjectPool管理的对象不会进入垃圾回收，使用时通过由实例对象实现的Get()方法，从对象池中借出对象，用完之后调用Return(T obj)方法，将对象还回去。也可以在Return(T obj)方法中设置判断条件，仅允许特定的对象进入对象池。

通过NuGet 获取 Microsoft.Extensions.ObjectPool 类库

代码实现

using Microsoft.Extensions.DependencyInjection.Extensions;
using Microsoft.Extensions.ObjectPool;
using System.Security.Cryptography;
using System.Text;

var builder = WebApplication.CreateBuilder(args);

// DefaultPooledObjectPolicy: 默认的策略，继承抽象类PooledObjectPolicy
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);
});

builder.Services.TryAddSingleton<ObjectPool<Person>>(serviceProvider => {
var provider = serviceProvider.GetRequiredService<ObjectPoolProvider>();
var policy = new PersonPoolPolicy();
return provider.Create(policy);
});

builder.Services.TryAddSingleton<ObjectPool<StringBuilder>>(serviceProvider =>
{
var provider = serviceProvider.GetRequiredService<ObjectPoolProvider>();
var policy = new StringBuilderPooledObjectPolicy();
return provider.Create(policy);
});

var app = builder.Build();

// config middleware
app.UseMiddleware<BirthdayMiddleware>();

app.MapGet(\”/\”, () => \”Hello rjcql!\”);

// return the SHA256 hash of a word
http://localhost:5128/hash/xxxx
app.MapGet(\”/hash/{word}\”, (string word, ObjectPool<ReusableBuffer> bufferPool) =>
{

var buffer = bufferPool.Get();
try
{
// Set the buffer data to the ASCII values of a word
for (var i = 0; i < word.Length; i++)
{
buffer.Data[i] = (byte)word[i];
}

Span<byte> hash = stackalloc byte[32];
SHA256.HashData(buffer.Data.AsSpan(0, word.Length), hash);
return \”Hash: \” + Convert.ToHexString(hash);
}
finally
{
// Data is automatically reset because this type implemented IResettable
bufferPool.Return(buffer);
}
});

app.MapGet(\”/create/{name}\”, (string name, ObjectPool<Person> personPool) =>
{
var person = personPool.Get();
try
{
person.Id = Guid.NewGuid().ToString(\”N\”);
var lastName = person.Name; // 这个是上一个对象的值
person.Name = name;
return $\”{person.Id}:{person.Name}, {lastName}\”;
}
finally
{
// 根据条件回收
personPool.Return(person);
}
});

app.Run();

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

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

public class Person
{
public string Id { get; set; }

public string Name { get; set; }
}

public class PersonPoolPolicy : PooledObjectPolicy<Person>
{
public override Person Create()
{
return new Person { Id = \”\”, Name = \”rjcql\” };
}

public override bool Return(Person p)
{
if (p.Name != \”rjcql\”)
{
// 不允许其他名称的对象放入对象池
return false;
}
return true;
}
}

/// <summary>
/// 创建中间件
/// </summary>
public class BirthdayMiddleware
{
private readonly RequestDelegate _next;

public BirthdayMiddleware(RequestDelegate next)
{
_next = next;
}

public async Task InvokeAsync(HttpContext context, ObjectPool<StringBuilder> builderPool)
{
var stringBuilder = builderPool.Get();
try
{
stringBuilder.Append(\”Hi\”);
// 在中间干点啥别的
// await context.Response.WriteAsync(stringBuilder.ToString());
await _next.Invoke(context);
}
finally // 即使出错也要保证归还对象
{
builderPool.Return(stringBuilder);
}
}
}