（3）Asp.Net Core 服务生命周期

1.前言

在configureservices方法中的容器注册每个应用程序的服务，asp.core都可以为每个应用程序提供三种服务生命周期：
●transient（暂时）：每次请求都会创建一个新的实例。这种生命周期最适合轻量级，无状态服务。
●scoped（作用域）：在同一个作用域内只初始化一个实例 ，可以理解为每一个请求只创建一个实例，同一个请求会在一个作用域内。
●singleton（单例）：整个应用程序生命周期以内只创建一个实例，后续每个请求都使用相同的实例。如果应用程序需要单例行为，建议让服务容器管理服务的生命周期，而不是在自己的类中实现单例模式。

2.服务生命周期与注册选项案例演示

为了演示生命周期和注册选项之间的差异，请考虑以下接口，将任务表示为具有唯一标识符 operationid 的操作。根据以下接口配置操作服务的生命周期的方式，容器在类请求时提供相同或不同的服务实例：

public interface ioperation
{
    guid operationid { get; }
}
public interface ioperationtransient : ioperation
{
}
public interface ioperationscoped : ioperation
{
}
public interface ioperationsingleton : ioperation
{
}
public interface ioperationsingletoninstance : ioperation
{
}

上面四种服务接口在 operation 类中实现。调用operation类时将自动生成一个guid，下面是operation类的实现：

public class operation : ioperationtransient, ioperationscoped, ioperationsingleton, ioperationsingletoninstance
{
    public operation() : this(guid.newguid())
    {
    }
    public operation(guid id)
    {
        operationid = id;
    }
    public guid operationid { get; private set; }
}

再注册一个operationservice服务实例，当通过依赖关系注入请求 operationservice 实例时，它将接收每个服务的新实例或基于从属服务（operation）的生命周期的现有实例。operationservice 服务作用就是第二次调用 operation类，查看operation类实例的作用域变化。

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()服务容器中注册各个生命周期的实例：

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模块里面调用onget方法输出，观察ioperation与operationservice类属性operationid 值的变化：

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("暂时:" + _transientoperation.operationid.tostring());
        console.writeline("作用域:" + _scopedoperation.operationid.tostring());
        console.writeline("单例:" + _singletonoperation.operationid.tostring());
        console.writeline("实例:" + _singletoninstanceoperation.operationid.tostring());
        console.writeline("operationservice操作:");
        console.writeline("暂时:" + _operationservice._transientoperation.operationid.tostring());
        console.writeline("作用域:" + _operationservice._scopedoperation.operationid.tostring());
        console.writeline("单例:" + _operationservice._singletonoperation.operationid.tostring());
        console.writeline("实例:" + _operationservice._singletoninstanceoperation.operationid.tostring());
    }
}

执行indexmodel 类输出结果：

由图总结如下：
2.1 transient（暂时）：每次调用服务的时候都会创建一个新的实例。即在indexmodel类的局部方法或属性中（这里是onget方法）实例化一个依赖对象operation类，伪代码是：

public class indexmodel: pagemodel
{
    public void onget()
    {
          //调用indexmodel类时，实例化了两次operation类
　　　　  //第一次
          operationservice operationservice=new operationservice();
　　　　　//第二次
　　　　　ioperationtransient transientoperation=new operation();
    }
}

2.2 scoped（作用域）：一次请求（action）内对象实例是相同的，但每次请求会产生一个新实例。相当于在indexmodel类的全局中实例化一次依赖对象operation类，伪代码是：

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（单例）：首次请求初始化同一个实例，后续每次请求都使用同一个实例。相当于在整个应用application中只实例化一次实例，常见的单例模式。

参考文献：
在asp.net core依赖注入