.NET Core 1.1迁移至3.1：如何注册Autofac容器释放回调？

问题背景 #

从.NET Core 1.1升级至3.1后，原1.1中通过appLifetime.ApplicationStopped.Register(() => this.ApplicationContainer.Dispose())实现的应用停止时Autofac容器释放逻辑，在新的Startup结构下不知如何适配。

.NET Core 1.1 原有代码 #

public class Startup
{
  public Startup(IHostingEnvironment env)
  {
    var builder = new ConfigurationBuilder()
        .SetBasePath(env.ContentRootPath)
        .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
        .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true)
        .AddEnvironmentVariables();
    this.Configuration = builder.Build();
  }

  public IContainer ApplicationContainer { get; private set; }

  public IConfigurationRoot Configuration { get; private set; }

  public IServiceProvider ConfigureServices(IServiceCollection services)
  {
    services.AddMvc();
    var builder = new ContainerBuilder();
    builder.RegisterType<MyType>().As<IMyType>();
    builder.Populate(services);
    this.ApplicationContainer = builder.Build();
    return new AutofacServiceProvider(this.ApplicationContainer);
  }

  public void Configure(
    IApplicationBuilder app,
    ILoggerFactory loggerFactory,
    IApplicationLifetime appLifetime)
  {
      loggerFactory.AddConsole(this.Configuration.GetSection("Logging"));
      loggerFactory.AddDebug();

      app.UseMvc();

      appLifetime.ApplicationStopped.Register(() => this.ApplicationContainer.Dispose());
  }
}

.NET Core 3.1 当前Startup结构 #

public class Startup
{
  public Startup(IConfiguration configuration)
  {
    this.Configuration = configuration;
  }

  public IConfiguration Configuration { get; private set; }

  public ILifetimeScope AutofacContainer { get; private set; }

  public void ConfigureServices(IServiceCollection services)
  {
    services.AddOptions();
  }

  public void ConfigureContainer(ContainerBuilder builder)
  {
    builder.RegisterModule(new MyApplicationModule());
  }

  public void Configure(
    IApplicationBuilder app,
    ILoggerFactory loggerFactory,
    IApplicationLifetime appLifetime)
  {
    this.AutofacContainer = app.ApplicationServices.GetAutofacRoot();

    loggerFactory.AddConsole(this.Configuration.GetSection("Logging"));
    loggerFactory.AddDebug();
    app.UseMvc();
  }
}

解决方案 #

1. 替换过时的生命周期接口 #

.NET Core 3.0+ 中IApplicationLifetime已被标记为过时，官方推荐使用IHostApplicationLifetime，两者事件定义一致，直接替换参数类型即可。

2. 注册容器释放逻辑 #

在Configure方法中，获取到Autofac根容器后，将其释放逻辑注册到应用停止事件中，和原1.1逻辑一致：

修改后的Configure方法代码：

public void Configure(
    IApplicationBuilder app,
    ILoggerFactory loggerFactory,
    IHostApplicationLifetime appLifetime)
{
    this.AutofacContainer = app.ApplicationServices.GetAutofacRoot();

    loggerFactory.AddConsole(this.Configuration.GetSection("Logging"));
    loggerFactory.AddDebug();
    app.UseMvc();

    // 注册应用停止时的容器释放逻辑
    appLifetime.ApplicationStopped.Register(() => this.AutofacContainer.Dispose());
}

补充说明 #

实际上，使用Autofac官方的.NET Core集成包时，主机停止过程中会自动释放Autofac根容器，因此手动注册上述释放逻辑并非必须。但如果你的业务场景中有额外资源需要和容器同步释放，或者需要确保自定义的释放逻辑执行，保留这段代码是完全可行的。

内容的提问来源于stack exchange，提问作者hng