[英]Is there a way to handle exceptions thrown by a task without the task freezing the UI?
[英]Where to handle exceptions thrown by Task
我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:
用户界面必须保持响应。 处理此方案的首选方法是什么? 我在下面列出了一个说明性的程序。
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.");
}
}
}
}
这可能是async void
方法可能很方便的极少数情况之一:
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)));
}
如果你不能使用async/await
,可以使用Task.ContinueWith
实现类似的逻辑。
如果可以多次调用startLoops
(当任务已经“在飞行中”时),则需要使用CancelltionToken
为StartAndMonitorAsync
及其启动的任务添加取消逻辑(更多细节见“自我取消和重启的模式”)任务“ )。
从MSDN“任务基础结构将它们包装在AggregateException实例中.AggregateException有一个InnerExceptions属性,可以枚举该属性以检查所有抛出的原始异常,并单独处理(或不处理)每个异常。即使只有一个例外是抛出,它仍然包含在AggregateException中。“ 有关详细信息,请查看此信息
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;
}
}
}
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