在哪里处理 Task 抛出的异常

Question

我正在单独的任务中执行一些轮询 IO 循环。这些循环可能会遇到异常。如果遇到异常，我想提醒调用者以便它可以：

1. 记录下来
2. 杀死所有IO线程
3. 重置连接
4. 重启 IO 线程

用户界面必须保持响应。处理这种情况的首选方法是什么？我在下面包含了一个说明性程序。

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

namespace TaskExceptionCatching
{
    class Program
    {
        static void Main(string[] args)
        {
            startLoops();

            System.Console.WriteLine("Type 'Exit' when you're ready to stop.");
            while (System.Console.ReadLine() != "Exit")
            {
                System.Console.WriteLine("Seriously, just type 'Exit' when you're ready to stop.");
            }
        }

        static private void startLoops()
        {
            System.Console.WriteLine("Starting fizzLoop.");
            var fizzTask = Task.Factory.StartNew(new Action(fizzLoop));

            System.Console.WriteLine("Starting buzzLoop.");
            var buzzTask = Task.Factory.StartNew(new Action(buzzLoop));
        }

        static private void fizzLoop()
        {
            while (true)
            {
                //simulate something error prone, like some risky IO
                System.Threading.Thread.Sleep(200);
                bool isErr = (new Random().Next(1, 100) == 10);
                if (isErr)
                    throw new Exception("Fizz got an exception.");
            }
        }

        static private void buzzLoop()
        {
            while (true)
            {
                //simulate something error prone, like some risky IO
                System.Threading.Thread.Sleep(200);
                bool isErr = (new Random().Next(1, 100) == 10);
                if (isErr)
                    throw new Exception("Buzz got an exception.");
            }
        }
    }
}

Answer 1

这可能是async void 方法很方便的少数情况之一：

static async void StartAndMonitorAsync(Func<Task> taskFunc)
{
    while (true)
    {
        var task = taskFunc();
        try
        {
            await task;
            // process the result if needed
            return;
        }
        catch (Exception ex)
        {
            // log the error
            System.Console.WriteLine("Error: {0}, restarting...", ex.Message);
        }
        // do other stuff before restarting (if any)
    }
}

static private void startLoops()
{
    System.Console.WriteLine("Starting fizzLoop.");
    StartAndMonitorAsync(() => Task.Factory.StartNew(new Action(fizzLoop)));

    System.Console.WriteLine("Starting buzzLoop.");
    StartAndMonitorAsync(() => Task.Factory.StartNew(new Action(buzzLoop)));
}

如果不能使用async/await，可以使用Task.ContinueWith实现类似的逻辑。

如果startLoops 可以被多次调用（而任务已经“进行中”），您需要使用CancelltionToken 将取消逻辑添加到StartAndMonitorAsync 和它所启动的任务中（更多详细信息见"A pattern for self-cancelling and restarting task")。

Answer 2

来自 MSDN “Task 基础结构将它们包装在一个 AggregateException 实例中。AggregateException 具有一个 InnerExceptions 属性，可以枚举该属性以检查所有引发的原始异常，并单独处理（或不处理）每个异常。即使只抛出一个异常，它仍然包含在 AggregateException 中。” 更多信息您可以check this

try
{
System.Console.WriteLine("Starting fizzLoop.");
            var fizzTask = Task.Factory.StartNew(new Action(fizzLoop));

            System.Console.WriteLine("Starting buzzLoop.");
            var buzzTask = Task.Factory.StartNew(new Action(buzzLoop));

}
catch (AggregateException ae)
{
    // Assume we know what's going on with this particular exception. 
    // Rethrow anything else. AggregateException.Handle provides 
    // another way to express this. See later example. 
    foreach (var e in ae.InnerExceptions)
    {
        if (e is MyCustomException)
        {
            Console.WriteLine(e.Message);
        }
        else
        {
            throw;
        }
    }

}