async/await Task Timeout
在日常的电脑使用过程中，估计最难以忍受的就是软件界面“卡住”“无响应”,在我有限的开发生涯中一直都是在挑战
它。在WPF中，主线程即UI线程，当我们在UI线程中执行一个很耗时的操作，以至于UI线程没能继续绘制窗体，这时给人
的感觉就是“卡住”了。
很耗时的操作分为2种
复杂计算
I/O操作
为了有一个良好的用户操作体验，我们都会使用异步方法，在另外一个线程中处理耗时的操作，当操作结束时，仅仅使用
UI线程更新结果到界面。.Net中的异步模型也有很多种，园子里有很多，不过用起来很舒服的还是async/await。
async/await 的引入让我们编写异步方法更加容易，它的目的就是使得我们像同步方法一样编写异步方法。上面铺垫稍微
啰嗦了点。马上进入正题，当我们在await一个方法时，如果这个方法它是支持超时的，那么当超时时是以异常的形式来
通知我们的，这样await以下的方法就没有办法执行了。
注意：这里补充下，一个Task超时了，并不意味着这个Task就结束了，它还是会运行，直到结束或是发生异常，一个超 时的Task返回的结果不应该被继续使用，应该丢弃
提供了超时设置还好，但是如果这个方法没有超时设置，那岂不就是一直在这里傻等？那肯定不，只有自己实现超时，一个
线程是没有办法做超时功能的。一般都是一个线程执行耗时操作，一个线程来计算超时，并且超时了要以异常的形式通知出来，所以
代码应该是这样的：
private async void ButtonBase_OnClick(object sender, RoutedEventArgs e)
{
try
{
await CanTimeoutTask(LongTimeWork, 6000);
textBlock.Text = "XXD";
await CanTimeoutTask(LongTimeWork, 3000);
}
catch (Exception ex)
{
}
}
private async Task CanTimeoutTask(Action action, int timeout)
{
var task1 = Task.Run(action);
var task2 = Task.Delay(timeout);
var firstTask = await Task.WhenAny(task1, task2);
if (firstTask == task2)
{
throw new TimeoutException();
}
}
private void LongTimeWork()
{
Thread.Sleep(5000);
}
如此看来，已经满足我们的需求了，但是作为一个上进的程序员，这么写真累啊，能不能提出一个简单易用的方法出来，
于是上Bing（这两天有点厌恶百度）搜索，看到这么一篇好像有点意思，自己琢磨着改进了一下，所以有了如下版本：
/// <summary>
/// 无返回值 可超时，可取消的Task
/// </summary>
public class TimeoutTask
{
#region 字段
private Action _action;
private CancellationToken _token;
private event AsyncCompletedEventHandler _asyncCompletedEvent;
private TaskCompletionSource<AsyncCompletedEventArgs> _tcs;
#endregion
#region 静态方法
public static async Task<AsyncCompletedEventArgs> StartNewTask(Action action, CancellationToken token)
{
return await TimeoutTask.StartNewTask(action, token, Timeout.Infinite);
}
public static async Task<AsyncCompletedEventArgs> StartNewTask(Action action, int timeout)
{
return await TimeoutTask.StartNewTask(action, CancellationToken.None, timeout);
}
public static async Task<AsyncCompletedEventArgs> StartNewTask(Action action, CancellationToken token,
int timeout = Timeout.Infinite)
{
var task = new TimeoutTask(action, token, timeout);
return await task.Run();
}
#endregion
#region 构造
protected TimeoutTask(Action action, int timeout) : this(action, CancellationToken.None, timeout)
{
}
protected TimeoutTask(Action action, CancellationToken token) : this(action, token, Timeout.Infinite)
{
}
protected TimeoutTask(Action action, CancellationToken token, int timeout = Timeout.Infinite)
{
_action = action;
_tcs = new TaskCompletionSource<AsyncCompletedEventArgs>();
if (timeout != Timeout.Infinite)
{
var cts = CancellationTokenSource.CreateLinkedTokenSource(token);
cts.CancelAfter(timeout);
_token = cts.Token;
}
else
{
_token = token;
}
}
#endregion
#region 私有方法
/// <summary>
/// 运行
/// </summary>
/// <returns></returns>
private async Task<AsyncCompletedEventArgs> Run()
{
_asyncCompletedEvent += AsyncCompletedEventHandler;
try
{
using (_token.Register(() => _tcs.TrySetCanceled()))
{
ExecuteAction();
return await _tcs.Task.ConfigureAwait(false);
}
}
finally
{
_asyncCompletedEvent -= AsyncCompletedEventHandler;
}
}
/// <summary>
/// 执行Action
/// </summary>
private void ExecuteAction()
{
Task.Factory.StartNew(() =>
{
_action.Invoke();
OnAsyncCompleteEvent(null);
});
}
/// <summary>
/// 异步完成事件处理
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void AsyncCompletedEventHandler(object sender, AsyncCompletedEventArgs e)
{
if (e.Cancelled)
{
_tcs.TrySetCanceled();
}
else if (e.Error != null)
{
_tcs.TrySetException(e.Error);
}
else
{
_tcs.TrySetResult(e);
}
}
/// <summary>
/// 触发异步完成事件
/// </summary>
/// <param name="userState"></param>
private void OnAsyncCompleteEvent(object userState)
{
if (_asyncCompletedEvent != null)
{
_asyncCompletedEvent(this, new AsyncCompletedEventArgs(error: null, cancelled: false, userState: userState));
}
}
#endregion
}
/// <summary>
/// 有返回值，可超时，可取消的Task
/// </summary>
/// <typeparam name="T"></typeparam>
public class TimeoutTask<T>
{
#region 字段
private Func<T> _func;
private CancellationToken _token;
private event AsyncCompletedEventHandler _asyncCompletedEvent;
private TaskCompletionSource<AsyncCompletedEventArgs> _tcs;
#endregion
#region 静态方法
public static async Task<T> StartNewTask(Func<T> func, CancellationToken token,
int timeout = Timeout.Infinite)
{
var task = new TimeoutTask<T>(func, token, timeout);
return await task.Run();
}
public static async Task<T> StartNewTask(Func<T> func, int timeout)
{
return await TimeoutTask<T>.StartNewTask(func, CancellationToken.None, timeout);
}
public static async Task<T> StartNewTask(Func<T> func, CancellationToken token)
{
return await TimeoutTask<T>.StartNewTask(func, token, Timeout.Infinite);
}
#endregion
#region 构造
protected TimeoutTask(Func<T> func, CancellationToken token) : this(func, token, Timeout.Infinite)
{
}
protected TimeoutTask(Func<T> func, int timeout = Timeout.Infinite) : this(func, CancellationToken.None, timeout)
{
}
protected TimeoutTask(Func<T> func, CancellationToken token, int timeout = Timeout.Infinite)
{
_func = func;
_tcs = new TaskCompletionSource<AsyncCompletedEventArgs>();
if (timeout != Timeout.Infinite)
{
var cts = CancellationTokenSource.CreateLinkedTokenSource(token);
cts.CancelAfter(timeout);
_token = cts.Token;
}
else
{
_token = token;
}
}
#endregion
#region 私有方法
/// <summary>
/// 运行Task
/// </summary>
/// <returns></returns>
private async Task<T> Run()
{
_asyncCompletedEvent += AsyncCompletedEventHandler;
try
{
using (_token.Register(() => _tcs.TrySetCanceled()))
{
ExecuteFunc();
var args = await _tcs.Task.ConfigureAwait(false);
return (T)args.UserState;
}
}
finally
{
_asyncCompletedEvent -= AsyncCompletedEventHandler;
}
}
/// <summary>
/// 执行
/// </summary>
private void ExecuteFunc()
{
ThreadPool.QueueUserWorkItem(s =>
{
var result = _func.Invoke();
OnAsyncCompleteEvent(result);
});
}
/// <summary>
/// 异步完成事件处理
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void AsyncCompletedEventHandler(object sender, AsyncCompletedEventArgs e)
{
if (e.Cancelled)
{
_tcs.TrySetCanceled();
}
else if (e.Error != null)
{
_tcs.TrySetException(e.Error);
}
else
{
_tcs.TrySetResult(e);
}
}
/// <summary>
/// 触发异步完成事件
/// </summary>
/// <param name="userState"></param>
private void OnAsyncCompleteEvent(object userState)
{
if (_asyncCompletedEvent != null)
{
_asyncCompletedEvent(this, new AsyncCompletedEventArgs(error: null, cancelled: false, userState: userState));
}
}
#endregion
}
使用起来也很方便
private async void ButtonBase_OnClick(object sender, RoutedEventArgs e)
{
try
{
await TimeoutTask.StartNewTask(LongTimeWork, 6000);
var result = await TimeoutTask<string>.StartNewTask(LongTimeWork2, 2000);
textBlock.Text = result;
}
catch (Exception ex)
{
}
}
private void LongTimeWork()
{
Thread.Sleep(5000);
}
private string LongTimeWork2()
{
Thread.Sleep(5000);
return "XXD";
}
其中有一些很少见的CancellationTokenSource CancellationToken TaskCompletionSource AsyncCompletedEventHandler AsyncCompletedEventArgs
不要怕，MSDN上一会就弄懂了。记录一下，算是这两天的研究成果。