NET8中增加的簡單適用的DI擴展庫Microsoft.Extensions.DependencyInjection.AutoActivation

這個庫提供了在啟動期間實例化已註冊的單例，而不是在首次使用它時實例化。

單例通常在首次使用時創建，這可能會導致響應傳入請求的延遲高於平時。在註冊時創建實例有助於防止第一次Request請求的SLA

以往我們要在註冊的時候實例單例可能會這樣寫:

//註冊:
services.AddSingleton<FileChangeNotifier>();
//初始化
using var scope = services.BuildServiceProvider().CreateScope();
scope.ServiceProvider.GetRequiredService<FileChangeNotifier>();

但是藉助Microsoft.Extensions.DependencyInjection.AutoActivation 我們的寫法就特別的簡單了:

//註冊服務,並直接實例化
services.AddActivatedSingleton<FileChangeNotifier>();

AutoActivation擴展庫其實相當簡單,內部實現了一個AutoActivationHostedService的 HostedService,當系統啟動的時候就從IServiceProvider中取到所有註冊為AutoActivation的單例,下麵是他的源碼:

internal sealed class AutoActivationHostedService : IHostedService
{
    private readonly AutoActivatorOptions _options;
    private readonly IServiceProvider _provider;

    public AutoActivationHostedService(IServiceProvider provider, IOptions<AutoActivatorOptions> options)
    {
        _provider = provider;
        _options = Throw.IfMemberNull(options, options.Value);
    }

    public Task StartAsync(CancellationToken cancellationToken)
    {
        foreach (var singleton in _options.AutoActivators)
        {
            _ = _provider.GetRequiredService(singleton);
        }

        foreach (var (serviceType, serviceKey) in _options.KeyedAutoActivators)
        {
            _ = _provider.GetRequiredKeyedService(serviceType, serviceKey);
        }

        return Task.CompletedTask;
    }

    public Task StopAsync(CancellationToken cancellationToken) => Task.CompletedTask;
}

當然提供的擴展不限於AddActivatedSingleton<T>一個,還有如下的擴展方法:

public static IServiceCollection ActivateSingleton<TService>(this IServiceCollection services)
public static IServiceCollection ActivateSingleton(this IServiceCollection services, Type serviceType)
public static IServiceCollection AddActivatedSingleton<TService, TImplementation>(this IServiceCollection services, Func<IServiceProvider, TImplementation> implementationFactory)
public static IServiceCollection AddActivatedSingleton<TService, TImplementation>(this IServiceCollection services)
public static IServiceCollection AddActivatedSingleton<TService>(this IServiceCollection services, Func<IServiceProvider, TService> implementationFactory)
public static IServiceCollection AddActivatedSingleton<TService>(this IServiceCollection services)
public static IServiceCollection AddActivatedSingleton(this IServiceCollection services, Type serviceType)
public static IServiceCollection AddActivatedSingleton(this IServiceCollection services, Type serviceType, Func<IServiceProvider, object> implementationFactory)
public static IServiceCollection AddActivatedSingleton(this IServiceCollection services, Type serviceType, Type implementationType)
public static void TryAddActivatedSingleton(this IServiceCollection services, Type serviceType)
public static void TryAddActivatedSingleton(this IServiceCollection services, Type serviceType, Type implementationType)
public static void TryAddActivatedSingleton(this IServiceCollection services, Type serviceType, Func<IServiceProvider, object> implementationFactory)
public static void TryAddActivatedSingleton<TService>(this IServiceCollection services)
public static void TryAddActivatedSingleton<TService, TImplementation>(this IServiceCollection services)
public static void TryAddActivatedSingleton<TService>(this IServiceCollection services, Func<IServiceProvider, TService> implementationFactory)
 
public static IServiceCollection ActivateKeyedSingleton<TService>(this IServiceCollection services, object? serviceKey)
public static IServiceCollection ActivateKeyedSingleton(this IServiceCollection services, Type serviceType, object? serviceKey)
public static IServiceCollection AddActivatedKeyedSingleton<TService, TImplementation>(this IServiceCollection services, object? serviceKey, Func<IServiceProvider, object?, TImplementation> implementationFactory)
public static IServiceCollection AddActivatedKeyedSingleton<TService, TImplementation>(this IServiceCollection services, object? serviceKey)
public static IServiceCollection AddActivatedKeyedSingleton<TService>(this IServiceCollection services, object? serviceKey, Func<IServiceProvider, object?, TService> implementationFactory)
public static IServiceCollection AddActivatedKeyedSingleton<TService>(this IServiceCollection services, object? serviceKey)
public static IServiceCollection AddActivatedKeyedSingleton(this IServiceCollection services, Type serviceType, object? serviceKey)
public static IServiceCollection AddActivatedKeyedSingleton(this IServiceCollection services, Type serviceType, object? serviceKey, Func<IServiceProvider, object?, object> implementationFactory)
public static IServiceCollection AddActivatedKeyedSingleton(this IServiceCollection services, Type serviceType, object? serviceKey, Type implementationType)
public static void TryAddActivatedKeyedSingleton(this IServiceCollection services, Type serviceType, object? serviceKey)
public static void TryAddActivatedKeyedSingleton(this IServiceCollection services, Type serviceType, object? serviceKey, Type implementationType)
public static void TryAddActivatedKeyedSingleton(this IServiceCollection services, Type serviceType, object? serviceKey, Func<IServiceProvider, object?, object> implementationFactory)
public static void TryAddActivatedKeyedSingleton<TService>(this IServiceCollection services, object? serviceKey)
public static void TryAddActivatedKeyedSingleton<TService, TImplementation>(this IServiceCollection services, object? serviceKey)
public static void TryAddActivatedKeyedSingleton<TService>(this IServiceCollection services, object? serviceKey, Func<IServiceProvider, object?, TService> implementationFactory)

最近我在Biwen.Settings添加了對JSON配置監聽的功能,有這方面的需求,最初是有一個Start方法,也就是啟動系統的時候獲取服務然後調用Start方法,如果使用了AutoActivation 那Start的方法體可以直接使用構造函數替代,這個也是除了開頭解決SLA以外的一個用例吧

有任何不足的地方歡迎小伙伴們留言指正