在日常的電腦使用過程中，估計最難以忍受的就是軟件界面“卡住”“無響應(yīng)”,在我有限的開發(fā)生涯中一直都是在挑戰(zhàn)
它。在WPF中，主線程即UI線程，當(dāng)我們在UI線程中執(zhí)行一個很耗時的操作，以至于UI線程沒能繼續(xù)繪制窗體，這時給人
的感覺就是“卡住”了。
很耗時的操作分為2種
復(fù)雜計算
I/O操作
為了有一個良好的用戶操作體驗，我們都會使用異步方法，在另外一個線程中處理耗時的操作，當(dāng)操作結(jié)束時，僅僅使用
UI線程更新結(jié)果到界面。.Net中的異步模型也有很多種，園子里有很多，不過用起來很舒服的還是async/await。
async/await 的引入讓我們編寫異步方法更加容易，它的目的就是使得我們像同步方法一樣編寫異步方法。上面鋪墊稍微
啰嗦了點。馬上進入正題，當(dāng)我們在await一個方法時，如果這個方法它是支持超時的，那么當(dāng)超時時是以異常的形式來
通知我們的，這樣await以下的方法就沒有辦法執(zhí)行了。
注意：這里補充下，一個Task超時了，并不意味著這個Task就結(jié)束了，它還是會運行，直到結(jié)束或是發(fā)生異常，一個超 時的Task返回的結(jié)果不應(yīng)該被繼續(xù)使用，應(yīng)該丟棄
提供了超時設(shè)置還好，但是如果這個方法沒有超時設(shè)置，那豈不就是一直在這里傻等？那肯定不，只有自己實現(xiàn)超時，一個
線程是沒有辦法做超時功能的。一般都是一個線程執(zhí)行耗時操作，一個線程來計算超時，并且超時了要以異常的形式通知出來，所以
代碼應(yīng)該是這樣的：
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); } 如此看來，已經(jīng)滿足我們的需求了，但是作為一個上進的程序員，這么寫真累啊，能不能提出一個簡單易用的方法出來，
于是上Bing（這兩天有點厭惡百度）搜索，看到這么一篇好像有點意思，自己琢磨著改進了一下，所以有了如下版本：
/// <summary>/// 無返回值 可超時，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 靜態(tài)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 構(gòu)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> /// 運行 /// </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> /// 執(zhí)行Action /// </summary> private void ExecuteAction() { Task.Factory.StartNew(() => { _action.Invoke(); OnAsyncCompleteEvent(null); }); } /// <summary> /// 異步完成事件處理 /// </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> /// 觸發(fā)異步完成事件 /// </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，可超時，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 靜態(tài)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 構(gòu)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> /// 運行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> /// 執(zhí)行 /// </summary> private void ExecuteFunc() { ThreadPool.QueueUserWorkItem(s => { var result = _func.Invoke(); OnAsyncCompleteEvent(result); }); } /// <summary> /// 異步完成事件處理 /// </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> /// 觸發(fā)異步完成事件 /// </summary> /// <param name="userState"></param> private void OnAsyncCompleteEvent(object userState) { if (_asyncCompletedEvent != null) { _asyncCompletedEvent(this, new AsyncCompletedEventArgs(error: null, cancelled: false, userState: userState)); } } #endregion}使用起來也很方便
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"; } 其中有一些很少見的CancellationTokenSource CancellationToken TaskCompletionSource AsyncCompletedEventHandler AsyncCompletedEventArgs
不要怕，MSDN上一會就弄懂了。記錄一下，算是這兩天的研究成果。
