|
在日常的電腦使用過(guò)程中，估計(jì)最難以忍受的就是軟件界面“卡住”“無(wú)響應(yīng)”,在我有限的開(kāi)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?cè)赨I線程中執(zhí)行一個(gè)很耗時(shí)的操作，以至于UI線程沒(méi)能繼續(xù)繪制窗體，這時(shí)給人
的感覺(jué)就是“卡住”了。
很耗時(shí)的操作分為2種
為了有一個(gè)良好的用戶操作體驗(yàn)，我們都會(huì)使用異步方法，在另外一個(gè)線程中處理耗時(shí)的操作，當(dāng)操作結(jié)束時(shí)，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(guò)用起來(lái)很舒服的還是async/await。
async/await 的引入讓我們編寫(xiě)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(xiě)異步方法。上面鋪墊稍微
啰嗦了點(diǎn)。馬上進(jìn)入正題，當(dāng)我們?cè)赼wait一個(gè)方法時(shí)，如果這個(gè)方法它是支持超時(shí)的，那么當(dāng)超時(shí)時(shí)是以異常的形式來(lái)
通知我們的，這樣await以下的方法就沒(méi)有辦法執(zhí)行了。
注意：這里補(bǔ)充下，一個(gè)Task超時(shí)了，并不意味著這個(gè)Task就結(jié)束了，它還是會(huì)運(yùn)行，直到結(jié)束或是發(fā)生異常，一個(gè)超 時(shí)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(shí)設(shè)置還好，但是如果這個(gè)方法沒(méi)有超時(shí)設(shè)置，那豈不就是一直在這里傻等？那肯定不，只有自己實(shí)現(xiàn)超時(shí)，一個(gè)
線程是沒(méi)有辦法做超時(shí)功能的。一般都是一個(gè)線程執(zhí)行耗時(shí)操作，一個(gè)線程來(lái)計(jì)算超時(shí)，并且超時(shí)了要以異常的形式通知出來(lái)，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(lái)，已經(jīng)滿足我們的需求了，但是作為一個(gè)上進(jìn)的程序員，這么寫(xiě)真累啊，能不能提出一個(gè)簡(jiǎn)單易用的方法出來(lái)，
于是上Bing（這兩天有點(diǎn)厭惡百度）搜索，看到這么一篇好像有點(diǎn)意思，自己琢磨著改進(jìn)了一下，所以有了如下版本：
/// <summary>
/// 無(wú)返回值 可超時(shí)，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(yùn)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(shí)，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(yùn)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(lái)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(jiàn)的CancellationTokenSource CancellationToken TaskCompletionSource AsyncCompletedEventHandler AsyncCompletedEventArgs
不要怕，MSDN上一會(huì)就弄懂了。記錄一下，算是這兩天的研究成果。
|
