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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”,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
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，當操作結束時，僅僅使用
UI線程更新結果到界面。.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就結束了，它還是會運行，直到結束或是發(fā)生異常，一個超 時的Task返回的結果不應該被繼續(xù)使用，應該丟棄
提供了超時設置還好，但是如果這個方法沒有超時設置，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。
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