c# Task.Wait()与awaiat Task异常处理区别

Task异常处理

下面有两个例子代码，可以直接复制粘贴到.net core中运行。两个代码要实现的功能完全一样，但是内核却又很大差异。
先看下面用await的例子与输出：

using System;
using System.Threading;
using System.Threading.Tasks;

class Program
{
    static async Task Main()
    {
        System.Console.WriteLine($"Main Task ID:{Thread.CurrentThread.ManagedThreadId}");
        var task = Task.Run(() =>
        {
            System.Console.WriteLine($"In Task.Run(), Task ID:{Thread.CurrentThread.ManagedThreadId}");
            int[] vary=new int[5];
            while (true)
            {
               Thread.Sleep(3000);
               int d = vary[6];
            }
        });

        // Just continue on this thread, or await with try-catch:
        try
        {
            await task;
        }
        catch (IndexOutOfRangeException ex)
        {
            System.Console.WriteLine(ex.Message);
            System.Console.WriteLine($"After Wait(), Task ID:{Thread.CurrentThread.ManagedThreadId}");
        }
        catch(AggregateException ex)
        {
           System.Console.WriteLine(ex.Message);
           System.Console.WriteLine($"After Wait(), Task ID:{Thread.CurrentThread.ManagedThreadId}");
        }
        finally
        {
            //...
        }
        System.Console.WriteLine("Reach end.");
        Console.ReadKey();
    }
}
/*
Main Task ID:1
In Task.Run(), Task ID:4
Index was outside the bounds of the array.
Catch System.IndexOutOfRangeException
After Wait(), Task ID:4
Reach end.
*/

再看Task.Wait()方法下的异常处理与输出:

using System;
using System.Threading;
using System.Threading.Tasks;

class Program
{
    static void Main()
    {
        System.Console.WriteLine($"Main Task ID:{Thread.CurrentThread.ManagedThreadId}");
        var task = Task.Run(() =>
        {
            System.Console.WriteLine($"In Task.Run(), Task ID:{Thread.CurrentThread.ManagedThreadId}");
            int[] vary=new int[5];
            while (true)
            {
               Thread.Sleep(3000);
               int d = vary[6];
            }
        });

        // Just continue on this thread, or await with try-catch:
        try
        {
            task.Wait();
        }
        catch (IndexOutOfRangeException ex)
        {
            System.Console.WriteLine($"Catch {ex.GetType()}");
            System.Console.WriteLine($"After Wait(), Task ID:{Thread.CurrentThread.ManagedThreadId}");
        }
        catch(AggregateException ex)
        {
           System.Console.WriteLine($"Catch {ex.GetType()}");
           System.Console.WriteLine($"After Wait(), Task ID:{Thread.CurrentThread.ManagedThreadId}");
        }
        finally
        {
            //...
        }
        System.Console.WriteLine("Reach end.");
        Console.ReadKey();
    }
}
/*
Main Task ID:1
In Task.Run(), Task ID:4
Catch System.AggregateException
One or more errors occurred. (Index was outside the bounds of the array.)
After Wait(), Task ID:1
Reach end.
*/

从例子中可以看出，await之后的代码其实都是在新的线程(4线程)中执行，而Task.Wait()方法后的线程则是在主线程中执行。因此，await之后的代码完全以传统方式处理异常；而Task.Wait()抛出的异常则由于是从新线程往外部线程抛出，所以它是被重新封装为AggregateException异常抛出。