[.Net] .NET Core中如何实现或使用对象池？

• 前言
  
• 池化策略
  
• 对象池的使用
  
• 指定对象池容量
  
• 在 ASP.NET Core 中使用
  
• 总结
  

public class FooPooledObjectPolicy : IPooledObjectPolicy<Foo>
{
  public Foo Create()
  {
    return new Foo();
  }
  public bool Return(Foo obj)
  {
    return true;
  }
}

var policy = new DefaultPooledObjectPolicy<Foo>();
var pool = new DefaultObjectPool<Foo>(policy);

using Microsoft.Extensions.ObjectPool;
using System;
var policy = new DefaultPooledObjectPolicy<Foo>();
var pool = new DefaultObjectPool<Foo>(policy);
// 借
var item1 = pool.Get();
// 还
pool.Return(item1);
Console.WriteLine("item 1: {0}", item1.Id);
// 借
var item2 = pool.Get();
// 还
pool.Return(item2);
Console.WriteLine("item 2: {0}", item2.Id);
Console.ReadKey();
public class Foo
{
  public string Id { get; set; } = Guid.NewGuid().ToString("N");
}

// ...
// 借
var item1 = pool.Get();
Console.WriteLine("item 1: {0}", item1.Id);
// 再借
var item2 = pool.Get();
Console.WriteLine("item 2: {0}", item2.Id);
// ...

using Microsoft.Extensions.ObjectPool;
using System;
var policy = new DefaultPooledObjectPolicy<Foo>();
// 指定容量为 2。
var pool = new DefaultObjectPool<Foo>(policy, 2);
// 借走 3 个
var item1 = pool.Get();
Console.WriteLine("item 1: {0}", item1.Id);
var item2 = pool.Get();
Console.WriteLine("item 2: {0}", item2.Id);
var item3 = pool.Get();
Console.WriteLine("item 3: {0}", item3.Id);
// 再还会 3 个
pool.Return(item1);
pool.Return(item2);
pool.Return(item3);

// 再借走 3 个
var item4 = pool.Get();
Console.WriteLine("item 4: {0}", item4.Id);
var item5 = pool.Get();
Console.WriteLine("item 5: {0}", item5.Id);
var item6 = pool.Get();
Console.WriteLine("item 6: {0}", item6.Id);
Console.ReadKey();

https://docs.microsoft.com/en-us/aspnet/core/performance/objectpool

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");
      // 其它处理
      await context.Response.WriteAsync(stringBuilder.ToString());
    }
    finally // 即使出错也要保证归还对象
    {
      builderPool.Return(stringBuilder);
    }
  }
}

public class Startup
{
  public void ConfigureServices(IServiceCollection services)
  {
    services.TryAddSingleton<ObjectPoolProvider, DefaultObjectPoolProvider>();
    services.TryAddSingleton<ObjectPool<StringBuilder>>(serviceProvider =>
    {
      var provider = serviceProvider.GetRequiredService<ObjectPoolProvider>();
      var policy = new StringBuilderPooledObjectPolicy();
      return provider.Create(policy);
    });
  }
  public void Configure(IApplicationBuilder app, IHostingEnvironment env)
  {
    app.UseMiddleware<BirthdayMiddleware>();
  }
}