ASP.NET Core – 选项系统之源码介绍

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摘要

.NET Core 选项系统的主要实现在 Microsoft.Extensions.Options 和 Microsoft.Extensions.Options.ConfigurationExtensions 两个 Nuget 包。对于一个框架的源码进行解读,我们可以从我们常用的框架中的类或方法入手,这些类或方法就是我们解读的入口。

.NET Core 选项系统的主要实现在 Microsoft.Extensions.Options 和 Microsoft.Extensions.Options.ConfigurationExtensions 两个 Nuget 包。对于一个框架的源码进行解读,我们可以从我们常用的框架中的类或方法入手,这些类或方法就是我们解读的入口。

从上面对选项系统的介绍中,大家也可以看出,日常对选项系统的使用涉及到的主要有 Configure 方法,有 IOptions、IOptionsSnapshot、IOptionMonitor 等接口。

Configure

首先看选项注册,也就是 Configure 方法,注册相关的方法都是扩展方法,上面也讲到 Configure 方法有多个扩展来源,其中最常用的是 OptionsConfigurationServiceCollectionExtensions 中的 Configure 方法,该方法用于从配置信息中读取配置并绑定为选项,如下,这里将相应的方法单独摘出来了。

点击查看代码 OptionsConfigurationServiceCollectionExtensions.Configure
public static class OptionsConfigurationServiceCollectionExtensions { 	/// <summary> 	/// Registers a configuration instance which TOptions will bind against. 	/// </summary> 	/// <typeparam name="TOptions">The type of options being configured.</typeparam> 	/// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param> 	/// <param name="config">The configuration being bound.</param> 	/// <returns>The <see cref="IServiceCollection"/> so that additional calls can be chained.</returns> 	[RequiresUnreferencedCode(OptionsBuilderConfigurationExtensions.TrimmingRequiredUnreferencedCodeMessage)] 	public static IServiceCollection Configure<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)] TOptions>(this IServiceCollection services, IConfiguration config) where TOptions : class 		=> services.Configure<TOptions>(Options.Options.DefaultName, config);  	/// <summary> 	/// Registers a configuration instance which TOptions will bind against. 	/// </summary> 	/// <typeparam name="TOptions">The type of options being configured.</typeparam> 	/// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param> 	/// <param name="name">The name of the options instance.</param> 	/// <param name="config">The configuration being bound.</param> 	/// <returns>The <see cref="IServiceCollection"/> so that additional calls can be chained.</returns> 	[RequiresUnreferencedCode(OptionsBuilderConfigurationExtensions.TrimmingRequiredUnreferencedCodeMessage)] 	public static IServiceCollection Configure<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)] TOptions>(this IServiceCollection services, string name, IConfiguration config) where TOptions : class 		=> services.Configure<TOptions>(name, config, _ => { });  	/// <summary> 	/// Registers a configuration instance which TOptions will bind against. 	/// </summary> 	/// <typeparam name="TOptions">The type of options being configured.</typeparam> 	/// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param> 	/// <param name="config">The configuration being bound.</param> 	/// <param name="configureBinder">Used to configure the <see cref="BinderOptions"/>.</param> 	/// <returns>The <see cref="IServiceCollection"/> so that additional calls can be chained.</returns> 	[RequiresUnreferencedCode(OptionsBuilderConfigurationExtensions.TrimmingRequiredUnreferencedCodeMessage)] 	public static IServiceCollection Configure<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)] TOptions>(this IServiceCollection services, IConfiguration config, Action<BinderOptions> configureBinder) 		where TOptions : class 		=> services.Configure<TOptions>(Options.Options.DefaultName, config, configureBinder);  	/// <summary> 	/// Registers a configuration instance which TOptions will bind against. 	/// </summary> 	/// <typeparam name="TOptions">The type of options being configured.</typeparam> 	/// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param> 	/// <param name="name">The name of the options instance.</param> 	/// <param name="config">The configuration being bound.</param> 	/// <param name="configureBinder">Used to configure the <see cref="BinderOptions"/>.</param> 	/// <returns>The <see cref="IServiceCollection"/> so that additional calls can be chained.</returns> 	[RequiresUnreferencedCode(OptionsBuilderConfigurationExtensions.TrimmingRequiredUnreferencedCodeMessage)] 	public static IServiceCollection Configure<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)] TOptions>(this IServiceCollection services, string name, IConfiguration config, Action<BinderOptions> configureBinder) 		where TOptions : class 	{ 		if (services == null) 		{ 			throw new ArgumentNullException(nameof(services)); 		}  		if (config == null) 		{ 			throw new ArgumentNullException(nameof(config)); 		}  		services.AddOptions(); 		services.AddSingleton<IOptionsChangeTokenSource<TOptions>>(new ConfigurationChangeTokenSource<TOptions>(name, config)); 		return services.AddSingleton<IConfigureOptions<TOptions>>(new NamedConfigureFromConfigurationOptions<TOptions>(name, config, configureBinder)); 	} } 

其中 IOptionsChangeTokenSource 接口是用来监听配置变化的服务,这个后面讲。

另外还有 OptionsServiceCollectionExtensions 中的 Configure 方法,用于直接通过委托对选项类进行配置。

点击查看代码 OptionsServiceCollectionExtensions.Configure
public static class OptionsServiceCollectionExtensions {  	public static IServiceCollection Configure<TOptions>(this IServiceCollection services, Action<TOptions> configureOptions) where TOptions : class 		=> services.Configure(Options.Options.DefaultName, configureOptions);  	public static IServiceCollection Configure<TOptions>(this IServiceCollection services, string name, Action<TOptions> configureOptions) 		where TOptions : class 	{ 		if (services == null) 		{ 			throw new ArgumentNullException(nameof(services)); 		}  		if (configureOptions == null) 		{ 			throw new ArgumentNullException(nameof(configureOptions)); 		}  		services.AddOptions(); 		services.AddSingleton<IConfigureOptions<TOptions>>(new ConfigureNamedOptions<TOptions>(name, configureOptions)); 		return services; 	} } 

可以看出,其实选项系统中的选项都是命名模式的,默认名称为 Options.Options.DefaultName,实际就是 string.Empty。当我们调用 Configure 方法对选项进行配置的时候,实际上时调用了 AddOptions 方法,并且往容器中添加了一个单例的实现了 IConfigureOptions 接口的实现。

IConfigureOptions、IConfigureNamedOptions、IPostConfigureOptions

其中 IConfigureOptions 是选项配置行为服务接口,ConfigureOptions 是它的默认实现,该类的内容很简单,它的内部主要就是保存了一个委托,用于记录使用者对选项的配置操作。

点击查看代码 ConfigureOptions
public class ConfigureOptions<TOptions> : IConfigureOptions<TOptions> where TOptions : class { 	/// <summary> 	/// Constructor. 	/// </summary> 	/// <param name="action">The action to register.</param> 	public ConfigureOptions(Action<TOptions> action) 	{ 		Action = action; 	}  	/// <summary> 	/// The configuration action. 	/// </summary> 	public Action<TOptions> Action { get; }  	/// <summary> 	/// Invokes the registered configure <see cref="Action"/>. 	/// </summary> 	/// <param name="options">The options instance to configure.</param> 	public virtual void Configure(TOptions options) 	{ 		if (options == null) 		{ 			throw new ArgumentNullException(nameof(options)); 		}  		Action?.Invoke(options); 	} } 

IConfigureNamedOptions 继承了 IConfigureNamedOptions 接口,默认实现是 ConfigureNamedOptions ,作用一样,只不过多了一个方法用于应对命名选项模式。它有多个重载泛型重载,也是之前的文章ASP.NET Core - 选型系统之选型配置 中讲到的“使用DI服务配置选项”的具体实现。

点击查看代码 ConfigureNamedOptions

```csharp public class ConfigureNamedOptions : IConfigureNamedOptions where TOptions : class { ///

/// Constructor. ///

/// The name of the options. /// The action to register. public ConfigureNamedOptions(string name, Action action) { Name = name; Action = action; }

/// <summary> /// The options name. /// </summary> public string Name { get; }  /// <summary> /// The configuration action. /// </summary> public Action<TOptions> Action { get; }  /// <summary> /// Invokes the registered configure <see cref="Action"/> if the <paramref name="name"/> matches. /// </summary> /// <param name="name">The name of the options instance being configured.</param> /// <param name="options">The options instance to configure.</param> public virtual void Configure(string name, TOptions options) { 	if (options == null) 	{ 		throw new ArgumentNullException(nameof(options)); 	}  	// Null name is used to configure all named options. 	if (Name == null || name == Name) 	{ 		Action?.Invoke(options); 	} }  /// <summary> /// Invoked to configure a <typeparamref name="TOptions"/> instance with the <see cref="Options.DefaultName"/>. /// </summary> /// <param name="options">The options instance to configure.</param> public void Configure(TOptions options) => Configure(Options.DefaultName, options); 

}

</details>  而 NamedConfigureFromConfigurationOptions<TOptions> 类是 IConfigureNamedOptions<TOptions> 的另一个实现,继承了ConfigureNamedOptions<TOptions> 类,重写了一些行为,最终是通过之前讲到的 ConfigurationBuilder的 Bind 方法将配置绑定到选项类而已。  <details> <summary>点击查看代码 NamedConfigureFromConfigurationOptions<TOptions></summary>  ```csharp public class NamedConfigureFromConfigurationOptions<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)] TOptions> : ConfigureNamedOptions<TOptions> 	where TOptions : class { 	/// <summary> 	/// Constructor that takes the <see cref="IConfiguration"/> instance to bind against. 	/// </summary> 	/// <param name="name">The name of the options instance.</param> 	/// <param name="config">The <see cref="IConfiguration"/> instance.</param> 	[RequiresUnreferencedCode(OptionsBuilderConfigurationExtensions.TrimmingRequiredUnreferencedCodeMessage)] 	public NamedConfigureFromConfigurationOptions(string name, IConfiguration config) 		: this(name, config, _ => { }) 	{ }  	/// <summary> 	/// Constructor that takes the <see cref="IConfiguration"/> instance to bind against. 	/// </summary> 	/// <param name="name">The name of the options instance.</param> 	/// <param name="config">The <see cref="IConfiguration"/> instance.</param> 	/// <param name="configureBinder">Used to configure the <see cref="BinderOptions"/>.</param> 	[RequiresUnreferencedCode(OptionsBuilderConfigurationExtensions.TrimmingRequiredUnreferencedCodeMessage)] 	public NamedConfigureFromConfigurationOptions(string name, IConfiguration config, Action<BinderOptions> configureBinder) 		: base(name, options => BindFromOptions(options, config, configureBinder)) 	{ 		if (config == null) 		{ 			throw new ArgumentNullException(nameof(config)); 		} 	}  	[UnconditionalSuppressMessage("ReflectionAnalysis", "IL2026:RequiresUnreferencedCode", 		Justification = "The only call to this method is the constructor which is already annotated as RequiresUnreferencedCode.")] 	private static void BindFromOptions(TOptions options, IConfiguration config, Action<BinderOptions> configureBinder) => config.Bind(options, configureBinder); } 

其他的 IPostConfigureOptions 接口也是一样套路,当我们通过相应的方法传入委托对选项类进行配置的时候,会向容器中注入一个单例服务,将配置行为保存起来。

接着往下看 AddOptions 方法,AddOptions 方法有两个重载:

点击查看代码 AddOptions

```csharp public static class OptionsServiceCollectionExtensions { public static IServiceCollection AddOptions(this IServiceCollection services) { if (services == null) { throw new ArgumentNullException(nameof(services)); }

	services.TryAdd(ServiceDescriptor.Singleton(typeof(IOptions<>), typeof(UnnamedOptionsManager<>))); 	services.TryAdd(ServiceDescriptor.Scoped(typeof(IOptionsSnapshot<>), typeof(OptionsManager<>))); 	services.TryAdd(ServiceDescriptor.Singleton(typeof(IOptionsMonitor<>), typeof(OptionsMonitor<>))); 	services.TryAdd(ServiceDescriptor.Transient(typeof(IOptionsFactory<>), typeof(OptionsFactory<>))); 	services.TryAdd(ServiceDescriptor.Singleton(typeof(IOptionsMonitorCache<>), typeof(OptionsCache<>))); 	return services; } public static OptionsBuilder<TOptions> AddOptions<TOptions>(this IServiceCollection services, string name) 	where TOptions : class { 	if (services == null) 	{ 		throw new ArgumentNullException(nameof(services)); 	}  	services.AddOptions(); 	return new OptionsBuilder<TOptions>(services, name); } 

}

</details>  这里可以看出两者的返回值不同,而且第二个方法也调用了第一个方法,第一个方法中主要就是向容器中添加我们常用的IOptions<TOptions>、IOptionsSnapshot<TOptions>、IOptionsMonitor<TOptions> 服务接口,这里也可以看到不同服务接口对于的生命周期。除此之外还有工厂服务IOptionsFactory<>和缓存服务IOptionsMonitorCache<>,这两个就是选项体系的关键。每个选项进行配置的时候都会同时注入这些服务,所以每一个选项我们都能使用三个不同接口去解析。  # OptionsBuilder  上面第二个 AddOptions 方法返回 OptionsBuilder<TOptions> 对象。之前讲过 OptionsBuilder<TOptions> 类中也有 Configure 方法,其实不止 Configure 方法,其他的 PostConfigure 方法等也有,它其实就是最终的选项系统配置类,我们所有的选项配置其实都可以通过调用第二个 AddOptions 方法,再通过 OptionsBuilder<TOptions> 对象中的方法来完成配置。其他各个扩展方法的配置方式不过是进行了使用简化而已。  <details> <summary>点击查看代码 OptionsBuilder<TOptions></summary>  ```csharp public class OptionsBuilder<TOptions> where TOptions : class { 	private const string DefaultValidationFailureMessage = "A validation error has occurred."; 	 	public string Name { get; } 	 	public IServiceCollection Services { get; } 	 	public OptionsBuilder(IServiceCollection services, string name) 	{ 		Services = services; 		Name = name ?? Options.DefaultName; 	} 	 	public virtual OptionsBuilder<TOptions> Configure(Action<TOptions> configureOptions) 	{ 		Services.AddSingleton<IConfigureOptions<TOptions>>(new ConfigureNamedOptions<TOptions>(Name, configureOptions)); 		return this; 	} 	 	public virtual OptionsBuilder<TOptions> PostConfigure(Action<TOptions> configureOptions) 	{ 		Services.AddSingleton<IPostConfigureOptions<TOptions>>(new PostConfigureOptions<TOptions>(Name, configureOptions)); 		return this; 	} 	 	public virtual OptionsBuilder<TOptions> Validate(Func<TOptions, bool> validation) 		=> Validate(validation: validation, failureMessage: DefaultValidationFailureMessage); 		 	public virtual OptionsBuilder<TOptions> Validate(Func<TOptions, bool> validation, string failureMessage) 	{ 		Services.AddSingleton<IValidateOptions<TOptions>>(new ValidateOptions<TOptions>(Name, validation, failureMessage)); 		return this; 	} } 

IValidateOptions

我们除了可以对选项进行配置绑定之外,还可以对选项进行验证。验证规则是通过上面的第二个 AddOptions 方法返回的 OptionsBuilder 方法进行添加的。

验证规则配置有三种方式,最后其实都是通过 IValidateOptions 的实现类来完成。我们自己实现的自定义验证类就不用说了,最后我们会将其注入到容器中,而从上面的代码中可以看到,当我们通过委托的方式自定义验证规则的时候,它会被构建成一个 ValidateOptions 类对象,并注入到容器中作为一个服务。

ValidateOptions 是 IValidateOptions 的一个实现类,构造函数中接收委托,通过委托返回的 bool 结构判断验证是否通过。

点击查看代码 ValidateOptions
public class ValidateOptions<TOptions> : IValidateOptions<TOptions> where TOptions : class { 	/// <summary> 	/// Constructor. 	/// </summary> 	/// <param name="name">Options name.</param> 	/// <param name="validation">Validation function.</param> 	/// <param name="failureMessage">Validation failure message.</param> 	public ValidateOptions(string name, Func<TOptions, bool> validation, string failureMessage) 	{ 		Name = name; 		Validation = validation; 		FailureMessage = failureMessage; 	}  	/// <summary> 	/// The options name. 	/// </summary> 	public string Name { get; }  	/// <summary> 	/// The validation function. 	/// </summary> 	public Func<TOptions, bool> Validation { get; }  	/// <summary> 	/// The error to return when validation fails. 	/// </summary> 	public string FailureMessage { get; }  	/// <summary> 	/// Validates a specific named options instance (or all when <paramref name="name"/> is null). 	/// </summary> 	/// <param name="name">The name of the options instance being validated.</param> 	/// <param name="options">The options instance.</param> 	/// <returns>The <see cref="ValidateOptionsResult"/> result.</returns> 	public ValidateOptionsResult Validate(string name, TOptions options) 	{ 		// null name is used to configure all named options 		if (Name == null || name == Name) 		{ 			if ((Validation?.Invoke(options)).Value) 			{ 				return ValidateOptionsResult.Success; 			} 			return ValidateOptionsResult.Fail(FailureMessage); 		}  		// ignored if not validating this instance 		return ValidateOptionsResult.Skip; 	} } 

我们可以通过重载方法传入相应的验证失败提醒文本。

Options、UnnamedOptionsManager

接下来看选项使用相关的内容,其中 IOptions 中的选项类一经创建一直保持不变,默认实现类 UnnamedOptionsManager

点击查看代码 UnnamedOptionsManager
internal sealed class UnnamedOptionsManager<[DynamicallyAccessedMembers(Options.DynamicallyAccessedMembers)] TOptions> : 	IOptions<TOptions> 	where TOptions : class { 	private readonly IOptionsFactory<TOptions> _factory; 	private volatile object _syncObj; 	private volatile TOptions _value;  	public UnnamedOptionsManager(IOptionsFactory<TOptions> factory) => _factory = factory;  	public TOptions Value 	{ 		get 		{ 			if (_value is TOptions value) 			{ 				return value; 			}  			lock (_syncObj ?? Interlocked.CompareExchange(ref _syncObj, new object(), null) ?? _syncObj) 			{ 				return _value ??= _factory.Create(Options.DefaultName); 			} 		} 	} } 

IOptions 接口只有一个 Value 属性,实现类中通过锁确保创建的 Value 值不会因为线程问题导致不同,且该服务被注册为单例生命周期,所以对象不销毁,后续一直会读取内存中的 Value 值。具体选项类对象的创建由工厂服务负责。

IOptionsSnapshot、OptionsManager

IOptionsSnapshot 的实现类是 OptionsManager,该类中有一个私有的 OptionsCache 属性,每次对选项类进行读取的时候,都是先尝试从缓存读取,如果没有才创建。而由于 IOptionsSnapshot 被注册为请求域生命周期,所以单次请求内相应对象不会销毁,缓存不会清空,会一直保持一个。

点击查看代码 OptionsManager
public class OptionsManager<[DynamicallyAccessedMembers(Options.DynamicallyAccessedMembers)] TOptions> : 	IOptions<TOptions>, 	IOptionsSnapshot<TOptions> 	where TOptions : class { 	private readonly IOptionsFactory<TOptions> _factory; 	private readonly OptionsCache<TOptions> _cache = new OptionsCache<TOptions>(); // Note: this is a private cache  	/// <summary> 	/// Initializes a new instance with the specified options configurations. 	/// </summary> 	/// <param name="factory">The factory to use to create options.</param> 	public OptionsManager(IOptionsFactory<TOptions> factory) 	{ 		_factory = factory; 	}  	/// <summary> 	/// The default configured <typeparamref name="TOptions"/> instance, equivalent to Get(Options.DefaultName). 	/// </summary> 	public TOptions Value => Get(Options.DefaultName);  	/// <summary> 	/// Returns a configured <typeparamref name="TOptions"/> instance with the given <paramref name="name"/>. 	/// </summary> 	public virtual TOptions Get(string name) 	{ 		name = name ?? Options.DefaultName;  		if (!_cache.TryGetValue(name, out TOptions options)) 		{ 			// Store the options in our instance cache. Avoid closure on fast path by storing state into scoped locals. 			IOptionsFactory<TOptions> localFactory = _factory; 			string localName = name; 			options = _cache.GetOrAdd(name, () => localFactory.Create(localName)); 		}  		return options; 	} } 

IOptionsMonitor、OptionsMonitor

IOptionsMonitor 每次获取选项类都是最新的值,它实现类是 OptionsMonitor,实现类中使用了从容器中注入的单例缓存 IOptionsMonitorCache 来保存选项类,并且通过相应的 IOptionsChangeTokenSource 注册了选项类绑定内容的监听,例如上面讲到的 ConfigurationChangeTokenSource,在选项类配置内容改变的时候会触发事件,而在事件中会将缓存先情况并重新获取创建类,并且执行注册进来的额外的监听事件,可以看看下面的 InvokeChanged 方法。

点击查看代码 OptionsMonitor
public class OptionsMonitor<[DynamicallyAccessedMembers(Options.DynamicallyAccessedMembers)] TOptions> : 	IOptionsMonitor<TOptions>, 	IDisposable 	where TOptions : class { 	private readonly IOptionsMonitorCache<TOptions> _cache; 	private readonly IOptionsFactory<TOptions> _factory; 	private readonly List<IDisposable> _registrations = new List<IDisposable>(); 	internal event Action<TOptions, string> _onChange;  	/// <summary> 	/// Constructor. 	/// </summary> 	/// <param name="factory">The factory to use to create options.</param> 	/// <param name="sources">The sources used to listen for changes to the options instance.</param> 	/// <param name="cache">The cache used to store options.</param> 	public OptionsMonitor(IOptionsFactory<TOptions> factory, IEnumerable<IOptionsChangeTokenSource<TOptions>> sources, IOptionsMonitorCache<TOptions> cache) 	{ 		_factory = factory; 		_cache = cache;  		void RegisterSource(IOptionsChangeTokenSource<TOptions> source) 		{ 			IDisposable registration = ChangeToken.OnChange( 					  () => source.GetChangeToken(), 					  (name) => InvokeChanged(name), 					  source.Name);  			_registrations.Add(registration); 		}  		// The default DI container uses arrays under the covers. Take advantage of this knowledge 		// by checking for an array and enumerate over that, so we don't need to allocate an enumerator. 		if (sources is IOptionsChangeTokenSource<TOptions>[] sourcesArray) 		{ 			foreach (IOptionsChangeTokenSource<TOptions> source in sourcesArray) 			{ 				RegisterSource(source); 			} 		} 		else 		{ 			foreach (IOptionsChangeTokenSource<TOptions> source in sources) 			{ 				RegisterSource(source); 			} 		} 	}  	private void InvokeChanged(string name) 	{ 		name = name ?? Options.DefaultName; 		_cache.TryRemove(name); 		TOptions options = Get(name); 		if (_onChange != null) 		{ 			_onChange.Invoke(options, name); 		} 	}  	/// <summary> 	/// The present value of the options. 	/// </summary> 	public TOptions CurrentValue 	{ 		get => Get(Options.DefaultName); 	}  	/// <summary> 	/// Returns a configured <typeparamref name="TOptions"/> instance with the given <paramref name="name"/>. 	/// </summary> 	public virtual TOptions Get(string name) 	{ 		name = name ?? Options.DefaultName; 		return _cache.GetOrAdd(name, () => _factory.Create(name)); 	}  	/// <summary> 	/// Registers a listener to be called whenever <typeparamref name="TOptions"/> changes. 	/// </summary> 	/// <param name="listener">The action to be invoked when <typeparamref name="TOptions"/> has changed.</param> 	/// <returns>An <see cref="IDisposable"/> which should be disposed to stop listening for changes.</returns> 	public IDisposable OnChange(Action<TOptions, string> listener) 	{ 		var disposable = new ChangeTrackerDisposable(this, listener); 		_onChange += disposable.OnChange; 		return disposable; 	}  	/// <summary> 	/// Removes all change registration subscriptions. 	/// </summary> 	public void Dispose() 	{ 		// Remove all subscriptions to the change tokens 		foreach (IDisposable registration in _registrations) 		{ 			registration.Dispose(); 		}  		_registrations.Clear(); 	}  	internal sealed class ChangeTrackerDisposable : IDisposable 	{ 		private readonly Action<TOptions, string> _listener; 		private readonly OptionsMonitor<TOptions> _monitor;  		public ChangeTrackerDisposable(OptionsMonitor<TOptions> monitor, Action<TOptions, string> listener) 		{ 			_listener = listener; 			_monitor = monitor; 		}  		public void OnChange(TOptions options, string name) => _listener.Invoke(options, name);  		public void Dispose() => _monitor._onChange -= OnChange; 	} } 

OnChange 方法中传入的委托本来可以可以直接追加到事件中的,这里将其再包装多一层,是为了 OptionsMonitor 对象销毁的时候能够将相应的事件释放,如果不包装多一层的话,委托只在方法作用域中,对象释放的时候是获取不到的。

IOptionsMonitorCache、OptionsCache

OptionsCache 是 IOptionsMonitorCache 接口的的实现类,从上面可以看到 OptionsMonitor 和 OptionsSnapshot 都使用到了这个,OptionsSnapshot 通过内部创建的私有的缓存属性实现了请求域内选项类不变,而 OptionsMonitor 则通过它减少了每次都直接读取配置来源(如文件、数据库、配置中心api)的性能消耗,而是通过变更事件的方式进行更新。其实我们还可以在需要的时候注入IOptionsMonitorCache 服务自行对选项类进行更新。

OptionsCache 的具体实现比较简单,主要就是通过 ConcurrentDictionary<string, Lazy> 对象作为内存缓存,其中为了性能还再使用了 Lazy 方式。

IOptionsFactory、OptionsFactory

OptionsFactory 类实现 IOptionsFactory 接口,是选项类的实际创建配置之处,其实就是将之前注册到容器中与当前相关的各种配置、验证的行为配置类注入进来,再通过放射创建对象之后,将选项类对象传进去,逐一对相应的行为进行调用,最后得到一个成型的选项类。这里选项类的创建方式很简单,这也是要求选项类要有无参构造函数的原因。

点击查看代码 OptionsFactory
public class OptionsFactory<[DynamicallyAccessedMembers(Options.DynamicallyAccessedMembers)] TOptions> : 	IOptionsFactory<TOptions> 	where TOptions : class { 	private readonly IConfigureOptions<TOptions>[] _setups; 	private readonly IPostConfigureOptions<TOptions>[] _postConfigures; 	private readonly IValidateOptions<TOptions>[] _validations;  	/// <summary> 	/// Initializes a new instance with the specified options configurations. 	/// </summary> 	/// <param name="setups">The configuration actions to run.</param> 	/// <param name="postConfigures">The initialization actions to run.</param> 	public OptionsFactory(IEnumerable<IConfigureOptions<TOptions>> setups, IEnumerable<IPostConfigureOptions<TOptions>> postConfigures) : this(setups, postConfigures, validations: Array.Empty<IValidateOptions<TOptions>>()) 	{ }  	/// <summary> 	/// Initializes a new instance with the specified options configurations. 	/// </summary> 	/// <param name="setups">The configuration actions to run.</param> 	/// <param name="postConfigures">The initialization actions to run.</param> 	/// <param name="validations">The validations to run.</param> 	public OptionsFactory(IEnumerable<IConfigureOptions<TOptions>> setups, IEnumerable<IPostConfigureOptions<TOptions>> postConfigures, IEnumerable<IValidateOptions<TOptions>> validations) 	{ 		// The default DI container uses arrays under the covers. Take advantage of this knowledge 		// by checking for an array and enumerate over that, so we don't need to allocate an enumerator. 		// When it isn't already an array, convert it to one, but don't use System.Linq to avoid pulling Linq in to 		// small trimmed applications.  		_setups = setups as IConfigureOptions<TOptions>[] ?? new List<IConfigureOptions<TOptions>>(setups).ToArray(); 		_postConfigures = postConfigures as IPostConfigureOptions<TOptions>[] ?? new List<IPostConfigureOptions<TOptions>>(postConfigures).ToArray(); 		_validations = validations as IValidateOptions<TOptions>[] ?? new List<IValidateOptions<TOptions>>(validations).ToArray(); 	}  	/// <summary> 	/// Returns a configured <typeparamref name="TOptions"/> instance with the given <paramref name="name"/>. 	/// </summary> 	public TOptions Create(string name) 	{ 		TOptions options = CreateInstance(name); 		foreach (IConfigureOptions<TOptions> setup in _setups) 		{ 			if (setup is IConfigureNamedOptions<TOptions> namedSetup) 			{ 				namedSetup.Configure(name, options); 			} 			else if (name == Options.DefaultName) 			{ 				setup.Configure(options); 			} 		} 		foreach (IPostConfigureOptions<TOptions> post in _postConfigures) 		{ 			post.PostConfigure(name, options); 		}  		if (_validations != null) 		{ 			var failures = new List<string>(); 			foreach (IValidateOptions<TOptions> validate in _validations) 			{ 				ValidateOptionsResult result = validate.Validate(name, options); 				if (result is not null && result.Failed) 				{ 					failures.AddRange(result.Failures); 				} 			} 			if (failures.Count > 0) 			{ 				throw new OptionsValidationException(name, typeof(TOptions), failures); 			} 		}  		return options; 	}  	/// <summary> 	/// Creates a new instance of options type 	/// </summary> 	protected virtual TOptions CreateInstance(string name) 	{ 		return Activator.CreateInstance<TOptions>(); 	} } 

以上就是 .NET Core 下的选项系统,由于选项系统的源码不多,这里也就将大部分类都拿出来讲了一下,相当于把这个框架的流程思路都讲了一遍,不知不觉写得字数又很多了,希望有童鞋能够耐心地看到这里。

参考文章:
ASP.NET Core 中的选项模式 | Microsoft Learn
选项模式 - .NET | Microsoft Learn
面向 .NET 库创建者的选项模式指南 - .NET | Microsoft Learn
理解ASP.NET Core - 选项(Options)

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