《通过C#学Proto.Actor模型》之Supervision

Supervision，字面意思是监督，是父Actor发现子Actor有异常发生后，对子Actor产用保种策略处理的机制，如果父Actor不处理，则往上传递。

 子Actor发生异常后处理的策略有：

Resume：立即恢复

Restart：恢复之前停止Actor并重新创建它

Stop：停止

Escalate：上报到父级 

Supervisor的通过Props.WithChildSupervisorStarategy()来实施的，这个方法第一个参数是接收异常和Actor的PID，以便按一定方式处理异常，第二个参数是重启的次数，第三个参数是两次重启的间隔（按照官方文档，两个连续重启时间大于间隔时间，次数会复位，但实则只按次数走，间隔不起作用）达到最大次数据，子Actor将重新生成。 

码友看代码：

using Proto;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace P006_Supervision
{
class Program
{
static void Main(string[] args)
{
//设置监督策略，指向SupervisiorMode方法，重启次数为3，两次之间间隔1s
var props = Actor.FromProducer(() => new ShopingCatActor()).WithChildSupervisorStrategy(new OneForOneStrategy(SupervisorMode.Decide, 3, TimeSpan.FromSeconds(1)));
var pid = Actor.Spawn(props);
var user = new User { UserName = "gsw" };

var sn = 1;
while (true)
{
Console.WriteLine($"{sn++}--------------------begin-----------------");
foreach (var goods in user.ShopingCat.Goodses)
{
Console.WriteLine(goods);
}
Console.WriteLine("---------------------end------------------");
Console.ReadLine();
pid.Request(user, pid);
}
}
}
/// <summary>
/// Supervisor 模式
/// </summary>
class SupervisorMode
{
/// <summary>
/// 用来处理异常发生的后续操作
/// </summary>
/// <param name="pid">PID</param>
/// <param name="reason">异常原因，Exception类型</param>
/// <returns></returns>
public static SupervisorDirective Decide(PID pid, Exception reason)
{
Console.WriteLine("   异常发生：" + reason.Message + "   " + pid);
switch (reason)
{
//重新开始的异常
case RecoverableException _:
return SupervisorDirective.Restart;
//停止异常
case FatalException _:
return SupervisorDirective.Stop;
//其他都上报
default:
return SupervisorDirective.Escalate;
}
}
}
/// <summary>
/// 购物车actor
/// </summary>
class ShopingCatActor : IActor
{
ShopingCat _shopingCat;
public ShopingCatActor()
{
_shopingCat = new ShopingCat();
Console.WriteLine("*******************actor ShopingCatActor************************");
}
public Task ReceiveAsync(IContext context)
{
PID childPid;
if (context.Children == null || context.Children.Count == 0)
{
var props = Actor.FromProducer(() => new GoodsActor());
childPid = context.Spawn(props);
}
else
{
childPid = context.Children.First();
}
switch (context.Message)
{
case User user:
childPid.Request(_shopingCat, childPid);
user.ShopingCat = _shopingCat;
break;
}
return Actor.Done;
}
}
/// <summary>
/// 商品actor
/// </summary>
class GoodsActor : IActor
{
public Task ReceiveAsync(IContext context)
{
switch (context.Message)
{
case ShopingCat shopingCat:

var goods = new Goods { Name = "红茶", Price = 3.0m, Describe = "统一" };
//用来随机产生异常
var random = new Random();
goods.Quantity = random.Next(1, 3) - 1;
if (goods.Quantity <= 0)
{
throw new RecoverableException("数量不能小于等于0");
}
else
{
shopingCat.Goodses.Add(goods);
Console.WriteLine($"添加 {goods} 到购物车里");
}
break;
}
return Actor.Done;
}
}
/// <summary>
/// 用户
/// </summary>
class User
{
public ShopingCat ShopingCat { get; set; } = new ShopingCat();
public string UserName { get; set; }
}
/// <summary>
/// 购物车
/// </summary>
class ShopingCat
{
public List<Goods> Goodses
{ get; set; } = new List<Goods>();
}
/// <summary>
/// 商品
/// </summary>
class Goods
{
public string Name { get; set; }

public int Quantity { get; set; }

public decimal Price { get; set; }

public string Describe { get; set; }
public override string ToString()
{
return $"Name={Name}，Quantity={Quantity}，Price={Price}，Describe={Describe}";
}
}

}

Demo中有三个实体类，用户类，购物车类，商品类，他们的关系一目了解，聚合关系。有两个Actor，购物车Actor（ShopingCatActor），商品Actor（GoodsActor），商品Actor是购物车Actor子Actor；ShopingCatActor下有监督策略，在

SupervisorMode下的Decide方法中，处理不同的异常，采用不同的Actor策略。GoodsActor中，添加商品时根据数量来决定是否产生异常。

看运行结果：

注意看ID $1/$2，是在发生四次异常后才生成$1/$3的（这个与文档说法有出入，也许是我理解有问题，是重启3次，不是启动3次）