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Async下处理多个异常
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???? Task Parallel Library (TPL) 中，當(dāng)你使用async/await? 語(yǔ)法關(guān)鍵字時(shí)，你可能遇到以下異常處理的情況: Catch 塊只會(huì)處理第一個(gè)異常而忽略其它的異常。來(lái)看下面代碼塊:
1: private static async
void TestCatchExceptionWithTPL()
2: {
3: try 4: {
5: await Task.Factory.StartNew(() =>
6: {
7: Task.Factory.StartNew(() =>
8: {
throw new NullReferenceException(); },
9: TaskCreationOptions.AttachedToParent);
10: Task.Factory.StartNew(() =>
11: {
throw new ArgumentException(); },
12: TaskCreationOptions.AttachedToParent);
13: });
14: }
15: catch (AggregateException aex)
16: {
17: // this catch will never be target 18: }
19: catch (Exception ex)
20: {
21: Console.WriteLine(
"## {0} ##" , ex.GetType().Name);
22: }
23: } 執(zhí)行上面的代碼，有注意8,11行分別有兩個(gè)Exception,而這時(shí)到第一個(gè)Catch塊中AggregateException只會(huì)捕捉第一個(gè)NullReferenceException異常，這是By Design的問(wèn)題。有個(gè)解決方案是這樣的:
1: try 2: {
3: Task t = Task.Factory.StartNew(() =>
4: {
5: Task.Factory.StartNew(() =>
6: {
throw new NullReferenceException(); },
7: TaskCreationOptions.AttachedToParent);
8: Task.Factory.StartNew(() =>
9: {
throw new ArgumentException(); },
10: TaskCreationOptions.AttachedToParent);
11: });
12: await t.ContinueWith(tsk => {
if (tsk.Exception !=
null )
throw tsk.Exception; });
13: }
14: catch (AggregateException ex)
15: {
16: foreach (var exc
in ex.Flatten().InnerExceptions)
17: {
18: Console.WriteLine(exc.GetType().Name);
19: }
20: }
?
注意上面12行代碼，使用了CoutinueWith方法，為了讓代碼更加簡(jiǎn)潔了，我們可以寫一個(gè)擴(kuò)展方法：
/// <summary> /// ThrowMultiple /// </summary> /// <param name="t">Task</param> /// <returns>Task type</returns> public static Task ThrowMultiple(
this Task t) {
return t.ContinueWith(tsk => {
if (tsk.Exception !=
null )
throw tsk.Exception; }); } ?
/// <summary> /// ThrowMultiple /// </summary> /// <typeparam name="T">Task this</typeparam> /// <param name="t">Task t</param> /// <returns>Task generic</returns> public static Task<T> ThrowMultiple<T>(
this Task<T> t) {
return t.ContinueWith(tsk => {
if (tsk.Exception !=
null )
throw tsk.Exception;
return tsk.Result; }); }
1: try 2: {
3: await Task.Factory.StartNew(() =>
4: {
5: Task.Factory.StartNew(() =>
6: {
throw new NullReferenceException(); },
7: TaskCreationOptions.AttachedToParent);
8: Task.Factory.StartNew(() =>
9: {
throw new ArgumentException(); },
10: TaskCreationOptions.AttachedToParent);
11: }).ThrowMultiple();
12: }
13: catch (AggregateException aex)
14: {
15: // this catch will never be target 16: }
17: catch (Exception ex)
18: {
19: Console.WriteLine(
"## {0} ##" , ex.GetType().Name);
20: }
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