ASP.NET Core服務(wù)生命周期
1.前言
在ConfigureServices方法中的容器注冊(cè)每個(gè)應(yīng)用程序的服務(wù),Asp.Core都可以為每個(gè)應(yīng)用程序提供三種服務(wù)生命周期:
- Transient(暫時(shí)):每次請(qǐng)求都會(huì)創(chuàng)建一個(gè)新的實(shí)例。這種生命周期最適合輕量級(jí),無狀態(tài)服務(wù)。
- Scoped(作用域):在同一個(gè)作用域內(nèi)只初始化一個(gè)實(shí)例 ,可以理解為每一個(gè)請(qǐng)求只創(chuàng)建一個(gè)實(shí)例,同一個(gè)請(qǐng)求會(huì)在一個(gè)作用域內(nèi)。
- Singleton(單例):整個(gè)應(yīng)用程序生命周期以內(nèi)只創(chuàng)建一個(gè)實(shí)例,后續(xù)每個(gè)請(qǐng)求都使用相同的實(shí)例。如果應(yīng)用程序需要單例行為,建議讓服務(wù)容器管理服務(wù)的生命周期,而不是在自己的類中實(shí)現(xiàn)單例模式。
2.服務(wù)生命周期與注冊(cè)選項(xiàng)案例演示
為了演示生命周期和注冊(cè)選項(xiàng)之間的差異,請(qǐng)考慮以下接口,將任務(wù)表示為具有唯一標(biāo)識(shí)符 OperationId 的操作。根據(jù)以下接口配置操作服務(wù)的生命周期的方式,容器在類請(qǐng)求時(shí)提供相同或不同的服務(wù)實(shí)例:
public interface IOperation { Guid OperationId { get; } } public interface IOperationTransient : IOperation { } public interface IOperationScoped : IOperation { } public interface IOperationSingleton : IOperation { } public interface IOperationSingletonInstance : IOperation { }
上面四種服務(wù)接口在 Operation 類中實(shí)現(xiàn)。調(diào)用Operation類時(shí)將自動(dòng)生成一個(gè)GUID,下面是Operation類的實(shí)現(xiàn):
public class Operation : IOperationTransient, IOperationScoped, IOperationSingleton, IOperationSingletonInstance { public Operation() : this(Guid.NewGuid()) { } public Operation(Guid id) { OperationId = id; } public Guid OperationId { get; private set; } }
再注冊(cè)一個(gè)OperationService服務(wù)實(shí)例,當(dāng)通過依賴關(guān)系注入請(qǐng)求 OperationService 實(shí)例時(shí),它將接收每個(gè)服務(wù)的新實(shí)例或基于從屬服務(wù)(Operation)的生命周期的現(xiàn)有實(shí)例。OperationService 服務(wù)作用就是第二次調(diào)用 Operation類,查看Operation類實(shí)例的作用域變化。
public class OperationService { public OperationService( IOperationTransient transientOperation, IOperationScoped scopedOperation, IOperationSingleton singletonOperation, IOperationSingletonInstance instanceOperation) { _transientOperation = transientOperation; _scopedOperation = scopedOperation; _singletonOperation = singletonOperation; _singletonInstanceOperation = instanceOperation; } public IOperationTransient _transientOperation { get; } public IOperationScoped _scopedOperation { get; } public IOperationSingleton _singletonOperation { get; } public IOperationSingletonInstance _singletonInstanceOperation { get; } }
然后在Startup.ConfigureServices()服務(wù)容器中注冊(cè)各個(gè)生命周期的實(shí)例:
public void ConfigureServices(IServiceCollection services) { services.AddTransient<IOperationTransient, Operation>(); services.AddScoped<IOperationScoped, Operation>(); services.AddSingleton<IOperationSingleton, Operation>(); services.AddSingleton<IOperationSingletonInstance>(new Operation(Guid.Empty)); // OperationService depends on each of the other Operation types. services.AddTransient<OperationService, OperationService>(); }
再在IndexModel模塊里面調(diào)用OnGet方法輸出,觀察IOperation與OperationService類屬性O(shè)perationId 值的變化:
public class IndexModel : PageModel { public OperationService _operationService { get; } public IOperationTransient _transientOperation { get; } public IOperationScoped _scopedOperation { get; } public IOperationSingleton _singletonOperation { get; } public IOperationSingletonInstance _singletonInstanceOperation { get; } public IndexModel( OperationService operationService, IOperationTransient transientOperation, IOperationScoped scopedOperation, IOperationSingleton singletonOperation, IOperationSingletonInstance singletonInstanceOperation) { _operationService = operationService; _transientOperation = transientOperation; _scopedOperation = scopedOperation; _singletonOperation = singletonOperation; _singletonInstanceOperation = singletonInstanceOperation; } public void OnGet() { Console.WriteLine("IOperation操作:"); Console.WriteLine("暫時(shí):" + _transientOperation.OperationId.ToString()); Console.WriteLine("作用域:" + _scopedOperation.OperationId.ToString()); Console.WriteLine("單例:" + _singletonOperation.OperationId.ToString()); Console.WriteLine("實(shí)例:" + _singletonInstanceOperation.OperationId.ToString()); Console.WriteLine("OperationService操作:"); Console.WriteLine("暫時(shí):" + _operationService._transientOperation.OperationId.ToString()); Console.WriteLine("作用域:" + _operationService._scopedOperation.OperationId.ToString()); Console.WriteLine("單例:" + _operationService._singletonOperation.OperationId.ToString()); Console.WriteLine("實(shí)例:" + _operationService._singletonInstanceOperation.OperationId.ToString()); } }
執(zhí)行IndexModel 類輸出結(jié)果:
由圖總結(jié)如下:
2.1 Transient(暫時(shí)):每次調(diào)用服務(wù)的時(shí)候都會(huì)創(chuàng)建一個(gè)新的實(shí)例。即在IndexModel類的局部方法或?qū)傩灾校ㄟ@里是OnGet方法)實(shí)例化一個(gè)依賴對(duì)象Operation類,偽代碼是:
public class IndexModel: PageModel { public void OnGet() { //調(diào)用IndexModel類時(shí),實(shí)例化了兩次Operation類 //第一次 OperationService operationService=new OperationService(); //第二次 IOperationTransient TransientOperation=new Operation(); } }
2.2 Scoped(作用域):一次請(qǐng)求(Action)內(nèi)對(duì)象實(shí)例是相同的,但每次請(qǐng)求會(huì)產(chǎn)生一個(gè)新實(shí)例。相當(dāng)于在IndexModel類的全局中實(shí)例化一次依賴對(duì)象Operation類,偽代碼是:
OperationService operationService = null; public IndexModel() { operationService = new OperationService(); operationService._scopedOperation = new Operation(); } public void OnGet() { operationService._scopedOperation.OperationId; IOperationScoped operationScoped = operationService._scopedOperation; operationScoped.OperationId }
2.3 Singleton(單例):首次請(qǐng)求初始化同一個(gè)實(shí)例,后續(xù)每次請(qǐng)求都使用同一個(gè)實(shí)例。相當(dāng)于在整個(gè)應(yīng)用Application中只實(shí)例化一次實(shí)例,常見的單例模式。
生命周期流程圖如下:
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