.NET Framework 提供了以下兩種標(biāo)準(zhǔn)模式，用于執(zhí)行 I/O 密集型和計(jì)算密集型異步操作：

• 異步編程模型 (APM)，其中異步操作由一對(duì) Begin/End 方法（如?FileStream.BeginRead?和Stream.EndRead）表示。

• 基于事件的異步模式 (EAP)，其中異步操作由 OperationName Async 和 OperationName Completed 方法/事件對(duì)（如?WebClient.DownloadStringAsync?和?WebClient.DownloadStringCompleted）表示。?（EAP 是在 .NET Framework 2.0 版本中引入的。）

任務(wù)并行庫(kù) (TPL) 可采用各種方法與任一異步模式協(xié)同使用。?可將 APM 和 EAP 操作作為任務(wù)向庫(kù)使用者公開，也可以公開 APM 模式但用 Task 對(duì)象在內(nèi)部實(shí)現(xiàn)它們。?在這兩種情況下，可通過(guò)使用 Task 對(duì)象簡(jiǎn)化代碼和利用以下有用的功能：

• 在任務(wù)開始后隨時(shí)以任務(wù)延續(xù)形式注冊(cè)回調(diào)。

• 通過(guò)使用?ContinueWhenAll?和?ContinueWhenAny?方法，或者?WaitAll?方法或?WaitAny?方法并列為響應(yīng)?Begin_?方法而執(zhí)行的多個(gè)操作。

• 封裝同一 Task 對(duì)象中的異步 I/O 密集型和計(jì)算密集型操作。

• 監(jiān)視 Task 對(duì)象的狀態(tài)。

• 使用?TaskCompletionSource<TResult>?將操作狀態(tài)封送處理至 Task 對(duì)象。

在任務(wù)中包裝 APM 操作

System.Threading.Tasks.TaskFactory?和?System.Threading.Tasks.TaskFactory<TResult>?類都提供了幾個(gè)?TaskFactory.FromAsync?和?TaskFactory<TResult>.FromAsync?方法的重載，可以將 APM Begin/End 方法對(duì)封裝在?Task?或?Task<TResult>?實(shí)例中。?各種重載都可容納任何具有零至三個(gè)輸入?yún)?shù)的 Begin/End 方法對(duì)。

對(duì)于具有返回值（在 Visual Basic 中為?Function）的?End?方法的對(duì)，使用?TaskFactory<TResult>?中創(chuàng)建?Task<TResult>?的方法。?對(duì)于具有返回 void（在 Visual Basic 中為?Sub）的?End?方法，使用?TaskFactory?中創(chuàng)建?Task?的方法。

在極少情況下，如果?Begin?方法具有三個(gè)以上參數(shù)或包含?ref?或?out?參數(shù)，則提供僅封裝?End?方法的其他?FromAsync?重載。

下面的示例顯示了匹配?FileStream.BeginRead?和?FileStream.EndRead?方法的?FromAsync?重載的簽名。?此重載采用三個(gè)輸入?yún)?shù)，如下所示。

public Task<TResult> FromAsync<TArg1, TArg2, TArg3>(Func<TArg1, TArg2, TArg3, AsyncCallback, object, IAsyncResult> beginMethod, //BeginReadFunc<IAsyncResult, TResult> endMethod, //EndReadTArg1 arg1, // the byte[] bufferTArg2 arg2, // the offset in arg1 at which to start writing dataTArg3 arg3, // the maximum number of bytes to readobject state // optional state information) Public Function FromAsync(Of TArg1, TArg2, TArg3)(ByVal beginMethod As Func(Of TArg1, TArg2, TArg3, AsyncCallback, Object, IAsyncResult),ByVal endMethod As Func(Of IAsyncResult, TResult),ByVal dataBuffer As TArg1,ByVal byteOffsetToStartAt As TArg2,ByVal maxBytesToRead As TArg3,ByVal stateInfo As Object)

第一個(gè)參數(shù)是匹配?FileStream.BeginRead?方法簽名的?Func<T1,T2,T3,T4,T5,TResult>?委托。?第二個(gè)參數(shù)使用?IAsyncResult?并返回?TResult?的?Func<T,TResult>?委托。?由于?EndRead?返回一個(gè)整數(shù)，因此編譯器會(huì)將?TResult?類型推斷為?Int32?并將任務(wù)類型推斷為?Task。?最后第四個(gè)參數(shù)與?FileStream.BeginRead?方法中的參數(shù)相同：

• 存儲(chǔ)文件數(shù)據(jù)的緩沖區(qū)。

• 開始寫入數(shù)據(jù)的緩沖區(qū)的偏移量。

• 要從文件中讀取的最大數(shù)據(jù)量。

• 存儲(chǔ)要傳遞至回調(diào)的用戶定義狀態(tài)數(shù)據(jù)的可選對(duì)象。

使用 ContinueWith 執(zhí)行回調(diào)功能

如果需要訪問(wèn)文件中的數(shù)據(jù)，而不僅僅訪問(wèn)字節(jié)數(shù)，則?FromAsync?方法不能滿足此操作。?請(qǐng)改用?Task，其?Result?屬性包含文件數(shù)據(jù)。?可以通過(guò)向原始任務(wù)添加延續(xù)來(lái)實(shí)現(xiàn)這種操作。?延續(xù)執(zhí)行通常由?AsyncCallback?委托執(zhí)行的任務(wù)。?先前任務(wù)完成且填充了數(shù)據(jù)緩沖區(qū)后調(diào)用此操作。?（FileStream?對(duì)象應(yīng)在返回前關(guān)閉。）

下面的示例演示如何返回封裝?FileStream?類的 BeginRead/EndRead 對(duì)的?Task。

const int MAX_FILE_SIZE = 14000000; public static Task<string> GetFileStringAsync(string path) {FileInfo fi = new FileInfo(path);byte[] data = null;data = new byte[fi.Length];FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, true);//Task<int> returns the number of bytes readTask<int> task = Task<int>.Factory.FromAsync(fs.BeginRead, fs.EndRead, data, 0, data.Length, null);// It is possible to do other work here while waiting// for the antecedent task to complete.// ...// Add the continuation, which returns a Task<string>. return task.ContinueWith((antecedent) =>{fs.Close();// Result = "number of bytes read" (if we need it.)if (antecedent.Result < 100){return "Data is too small to bother with.";}else{// If we did not receive the entire file, the end of the// data buffer will contain garbage.if (antecedent.Result < data.Length)Array.Resize(ref data, antecedent.Result);// Will be returned in the Result property of the Task<string>// at some future point after the asynchronous file I/O operation completes.return new UTF8Encoding().GetString(data);}}); } Const MAX_FILE_SIZE As Integer = 14000000 Shared Function GetFileStringAsync(ByVal path As String) As Task(Of String)Dim fi As New FileInfo(path)Dim data(fi.Length) As ByteDim fs As FileStream = New FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, True)' Task(Of Integer) returns the number of bytes readDim myTask As Task(Of Integer) = Task(Of Integer).Factory.FromAsync(AddressOf fs.BeginRead, AddressOf fs.EndRead, data, 0, data.Length, Nothing)' It is possible to do other work here while waiting' for the antecedent task to complete.' ...' Add the continuation, which returns a Task<string>. Return myTask.ContinueWith(Function(antecedent)fs.Close()If (antecedent.Result < 100) ThenReturn "Data is too small to bother with."End If' If we did not receive the entire file, the end of the' data buffer will contain garbage.If (antecedent.Result < data.Length) ThenArray.Resize(data, antecedent.Result)End If' Will be returned in the Result property of the Task<string>' at some future point after the asynchronous file I/O operation completes.Return New UTF8Encoding().GetString(data)End Function)End Function

然后可調(diào)用此方法，如下所示。

Task<string> t = GetFileStringAsync(path); // Do some other work:// ...try{Console.WriteLine(t.Result.Substring(0, 500));}catch (AggregateException ae){Console.WriteLine(ae.InnerException.Message);} Dim myTask As Task(Of String) = GetFileStringAsync(path)' Do some other work ' ...TryConsole.WriteLine(myTask.Result.Substring(0, 500)) Catch ex As AggregateExceptionConsole.WriteLine(ex.InnerException.Message) End Try

提供自定義狀態(tài)數(shù)據(jù)

在通常的?IAsyncResult?操作中，如果AsyncCallback?委托需要一些自定義狀態(tài)數(shù)據(jù)，則必須通過(guò)?Begin?方法中的最后一個(gè)參數(shù)將它傳入，以便可將數(shù)據(jù)打包到最終要傳遞至回調(diào)方法的?IAsyncResult?對(duì)象中。?當(dāng)使用?FromAsync?方法時(shí)，通常無(wú)需此操作。?如果延續(xù)知道自定義數(shù)據(jù)，可直接在延續(xù)委托中捕獲它。?下面的示例與以前的示例類似，但延續(xù)檢查此延續(xù)的用戶委托可直接訪問(wèn)的自定義狀態(tài)數(shù)據(jù)，而不是檢查歷史任務(wù)的?Result?屬性。

public Task<string> GetFileStringAsync2(string path) { FileInfo fi = new FileInfo(path);byte[] data = new byte[fi.Length]; MyCustomState state = GetCustomState();FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, true);// We still pass null for the last parameter because// the state variable is visible to the continuation delegate.Task<int> task = Task<int>.Factory.FromAsync(fs.BeginRead, fs.EndRead, data, 0, data.Length, null);return task.ContinueWith((antecedent) =>{// It is safe to close the filestream now.fs.Close();// Capture custom state data directly in the user delegate.// No need to pass it through the FromAsync method.if (state.StateData.Contains("New York, New York")){return "Start spreading the news!";}else{// If we did not receive the entire file, the end of the// data buffer will contain garbage.if (antecedent.Result < data.Length)Array.Resize(ref data, antecedent.Result);// Will be returned in the Result property of the Task<string>// at some future point after the asynchronous file I/O operation completes.return new UTF8Encoding().GetString(data);}}); } Public Function GetFileStringAsync2(ByVal path As String) As Task(Of String)Dim fi = New FileInfo(path)Dim data(fi.Length) As ByteDim state As New MyCustomState()Dim fs As New FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, True)' We still pass null for the last parameter because' the state variable is visible to the continuation delegate.Dim myTask As Task(Of Integer) = Task(Of Integer).Factory.FromAsync(AddressOf fs.BeginRead, AddressOf fs.EndRead, data, 0, data.Length, Nothing)Return myTask.ContinueWith(Function(antecedent)fs.Close()' Capture custom state data directly in the user delegate.' No need to pass it through the FromAsync method.If (state.StateData.Contains("New York, New York")) ThenReturn "Start spreading the news!"End If' If we did not receive the entire file, the end of the' data buffer will contain garbage.If (antecedent.Result < data.Length) ThenArray.Resize(data, antecedent.Result)End If'/ Will be returned in the Result property of the Task<string>'/ at some future point after the asynchronous file I/O operation completes.Return New UTF8Encoding().GetString(data)End Function)End Function

同步多個(gè) FromAsync 任務(wù)

當(dāng)結(jié)合使用?FromAsync?方法時(shí)，靜態(tài)?ContinueWhenAll?和?ContinueWhenAny?方法具有更大的靈活性。?下面的示例顯示如何啟動(dòng)多個(gè)異步 I/O 操作，然后等待所有這些操作都完成后再執(zhí)行延續(xù)。

public Task<string> GetMultiFileData(string[] filesToRead) {FileStream fs;Task<string>[] tasks = new Task<string>[filesToRead.Length];byte[] fileData = null;for (int i = 0; i < filesToRead.Length; i++){fileData = new byte[0x1000];fs = new FileStream(filesToRead[i], FileMode.Open, FileAccess.Read, FileShare.Read, fileData.Length, true);// By adding the continuation here, the // Result of each task will be a string.tasks[i] = Task<int>.Factory.FromAsync(fs.BeginRead, fs.EndRead, fileData, 0, fileData.Length, null).ContinueWith((antecedent) =>{fs.Close();// If we did not receive the entire file, the end of the// data buffer will contain garbage.if (antecedent.Result < fileData.Length)Array.Resize(ref fileData, antecedent.Result);// Will be returned in the Result property of the Task<string>// at some future point after the asynchronous file I/O operation completes.return new UTF8Encoding().GetString(fileData);});}// Wait for all tasks to complete. return Task<string>.Factory.ContinueWhenAll(tasks, (data) =>{// Propagate all exceptions and mark all faulted tasks as observed.Task.WaitAll(data);// Combine the results from all tasks.StringBuilder sb = new StringBuilder();foreach (var t in data){sb.Append(t.Result);}// Final result to be returned eventually on the calling thread.return sb.ToString();}); } Public Function GetMultiFileData(ByVal filesToRead As String()) As Task(Of String)Dim fs As FileStreamDim tasks(filesToRead.Length) As Task(Of String)Dim fileData() As Byte = NothingFor i As Integer = 0 To filesToRead.LengthfileData(&H1000) = New Byte()fs = New FileStream(filesToRead(i), FileMode.Open, FileAccess.Read, FileShare.Read, fileData.Length, True)' By adding the continuation here, the ' Result of each task will be a string.tasks(i) = Task(Of Integer).Factory.FromAsync(AddressOf fs.BeginRead,AddressOf fs.EndRead,fileData,0,fileData.Length,Nothing).ContinueWith(Function(antecedent)fs.Close()'If we did not receive the entire file, the end of the' data buffer will contain garbage.If (antecedent.Result < fileData.Length) ThenReDim Preserve fileData(antecedent.Result)End If'Will be returned in the Result property of the Task<string>' at some future point after the asynchronous file I/O operation completes.Return New UTF8Encoding().GetString(fileData)End Function)NextReturn Task(Of String).Factory.ContinueWhenAll(tasks, Function(data)' Propagate all exceptions and mark all faulted tasks as observed.Task.WaitAll(data)' Combine the results from all tasks.Dim sb As New StringBuilder()For Each t As Task(Of String) In datasb.Append(t.Result)Next' Final result to be returned eventually on the calling thread.Return sb.ToString()End Function) End Function

僅用于 End 方法的 FromAsync 任務(wù)

在極少情況下，如果?Begin?方法需要三個(gè)以上的輸入?yún)?shù)，或具有?ref?或?out?參數(shù)，可以使用僅表示?End?方法的?FromAsync?重載，例如，TaskFactory<TResult>.FromAsync(IAsyncResult, Func<IAsyncResult,TResult>)。?這些方法還可用于傳遞?IAsyncResult?并將其封裝到 Task 的任何方案中。

static Task<String> ReturnTaskFromAsyncResult() {IAsyncResult ar = DoSomethingAsynchronously();Task<String> t = Task<string>.Factory.FromAsync(ar, _ =>{return (string)ar.AsyncState;});return t; } Shared Function ReturnTaskFromAsyncResult() As Task(Of String)Dim ar As IAsyncResult = DoSomethingAsynchronously()Dim t As Task(Of String) = Task(Of String).Factory.FromAsync(ar, Function(res) CStr(res.AsyncState))Return t End Function

啟動(dòng)和取消 FromAsync 任務(wù)

FromAsync?方法返回的任務(wù)具有 WaitingForActivation 狀態(tài)，并在創(chuàng)建任務(wù)后在某個(gè)時(shí)刻由操作系統(tǒng)啟動(dòng)。?如果嘗試調(diào)用此類任務(wù)上的“啟動(dòng)”，將引發(fā)異常。

無(wú)法取消?FromAsync?任務(wù)，因?yàn)榛A(chǔ) .NET Framework API 目前不支持取消正在進(jìn)行中的文件或網(wǎng)絡(luò) I/O。?可以將取消功能添加到封裝?FromAsync?調(diào)用的方法中，但只能在調(diào)用?FromAsync?之前或在調(diào)用完成之后響應(yīng)取消（例如，在延續(xù)任務(wù)中）。

一些支持 EAP 的類（如?WebClient）不支持取消，但可以通過(guò)使用取消標(biāo)記集成該本機(jī)取消功能。

將復(fù)雜的 EAP 操作公開為任務(wù)

TPL 不提供任何專用于以?FromAsync?系列方法包裝?IAsyncResult?模式相同的方式封裝基于事件的異步操作的方法。?但是，TPL 會(huì)提供?System.Threading.Tasks.TaskCompletionSource<TResult>?類，此類可用于將任意一組操作表示為?Task<TResult>。?這些操作可能同步、可能異步，可能是 I/O 密集型、也可能是計(jì)算密集型，還可能兩者都是。

下面的示例顯示如何使用?TaskCompletionSource<TResult>?將一組異步?WebClient?操作作為基礎(chǔ)?Task<TResult>?向客戶端代碼公開。此方法允許輸入 Web URL 數(shù)組和術(shù)語(yǔ)或名稱來(lái)進(jìn)行搜索，然后返回每個(gè)站點(diǎn)搜索字詞出現(xiàn)的次數(shù)。

using System; using System.Collections.Generic; using System.Linq; using System.Net; using System.Threading; using System.Threading.Tasks;public class SimpleWebExample {public Task<string[]> GetWordCountsSimplified(string[] urls, string name,CancellationToken token){TaskCompletionSource<string[]> tcs = new TaskCompletionSource<string[]>();WebClient[] webClients = new WebClient[urls.Length];object m_lock = new object();int count = 0;List<string> results = new List<string>();// If the user cancels the CancellationToken, then we can use the// WebClient's ability to cancel its own async operations.token.Register(() =>{foreach (var wc in webClients){if (wc != null)wc.CancelAsync();}});for (int i = 0; i < urls.Length; i++){webClients[i] = new WebClient();#region callback// Specify the callback for the DownloadStringCompleted// event that will be raised by this WebClient instance.webClients[i].DownloadStringCompleted += (obj, args) =>{// Argument validation and exception handling omitted for brevity.// Split the string into an array of words,// then count the number of elements that match// the search term.string[] words = args.Result.Split(' ');string NAME = name.ToUpper();int nameCount = (from word in words.AsParallel()where word.ToUpper().Contains(NAME)select word).Count();// Associate the results with the url, and add new string to the array that// the underlying Task object will return in its Result property.lock (m_lock){results.Add(String.Format("{0} has {1} instances of {2}", args.UserState, nameCount, name));// If this is the last async operation to complete,// then set the Result property on the underlying Task.count++;if (count == urls.Length){tcs.TrySetResult(results.ToArray());}}};#endregion// Call DownloadStringAsync for each URL.Uri address = null;address = new Uri(urls[i]);webClients[i].DownloadStringAsync(address, address);} // end for// Return the underlying Task. The client code// waits on the Result property, and handles exceptions// in the try-catch block there.return tcs.Task;} } Imports System.Collections.Generic Imports System.Net Imports System.Threading Imports System.Threading.TasksPublic Class SimpleWebExampleDim tcs As New TaskCompletionSource(Of String())Dim token As CancellationTokenDim results As New List(Of String)Dim m_lock As New Object()Dim count As IntegerDim addresses() As StringDim nameToSearch As StringPublic Function GetWordCountsSimplified(ByVal urls() As String, ByVal str As String,ByVal token As CancellationToken) As Task(Of String())addresses = urlsnameToSearch = strDim webClients(urls.Length - 1) As WebClient' If the user cancels the CancellationToken, then we can use the' WebClient's ability to cancel its own async operations.token.Register(Sub()For Each wc As WebClient In webClientsIf wc IsNot Nothing Thenwc.CancelAsync()End IfNextEnd Sub)For i As Integer = 0 To urls.Length - 1webClients(i) = New WebClient()' Specify the callback for the DownloadStringCompleted' event that will be raised by this WebClient instance.AddHandler webClients(i).DownloadStringCompleted, AddressOf WebEventHandlerDim address As New Uri(urls(i))' Pass the address, and also use it for the userToken' to identify the page when the delegate is invoked.webClients(i).DownloadStringAsync(address, address)Next' Return the underlying Task. The client code' waits on the Result property, and handles exceptions' in the try-catch block there.Return tcs.TaskEnd FunctionPublic Sub WebEventHandler(ByVal sender As Object, ByVal args As DownloadStringCompletedEventArgs)If args.Cancelled = True Thentcs.TrySetCanceled()ReturnElseIf args.Error IsNot Nothing Thentcs.TrySetException(args.Error)ReturnElse' Split the string into an array of words,' then count the number of elements that match' the search term.Dim words() As String = args.Result.Split(" "c)Dim name As String = nameToSearch.ToUpper()Dim nameCount = (From word In words.AsParallel()Where word.ToUpper().Contains(name)Select word).Count()' Associate the results with the url, and add new string to the array that' the underlying Task object will return in its Result property.SyncLock (m_lock)results.Add(String.Format("{0} has {1} instances of {2}", args.UserState, nameCount, nameToSearch))count = count + 1If (count = addresses.Length) Thentcs.TrySetResult(results.ToArray())End IfEnd SyncLockEnd IfEnd Sub End Class

有關(guān)包括其他異常處理且展示了如何通過(guò)客戶端代碼調(diào)用方法的更完整示例，請(qǐng)參閱如何：在任務(wù)中包裝 EAP 模式。

請(qǐng)記住，通過(guò)?TaskCompletionSource<TResult>?創(chuàng)建的任何任務(wù)均由 TaskCompletionSource 啟動(dòng)，因此用戶代碼不應(yīng)在此任務(wù)中調(diào)用 Start 方法。

使用任務(wù)實(shí)現(xiàn) APM 模式

在某些情況下，可能需要通過(guò)使用 API 中 Begin/End 方法對(duì)直接公開?IAsyncResult?模式。?例如，可能想要與現(xiàn)有的 API 保持一致，或者可能具有需要這種模式的自動(dòng)化工具。?在這種情況下，可使用任務(wù)來(lái)簡(jiǎn)化在內(nèi)部實(shí)現(xiàn) APM 模式的方式。

下面的示例顯示如何使用任務(wù)實(shí)現(xiàn)長(zhǎng)時(shí)間運(yùn)行計(jì)算密集型方法的 APM Begin/End 方法對(duì)。

class Calculator {public IAsyncResult BeginCalculate(int decimalPlaces, AsyncCallback ac, object state){Console.WriteLine("Calling BeginCalculate on thread {0}", Thread.CurrentThread.ManagedThreadId);Task<string> f = Task<string>.Factory.StartNew(_ => Compute(decimalPlaces), state);if (ac != null) f.ContinueWith((res) => ac(f));return f;}public string Compute(int numPlaces){Console.WriteLine("Calling compute on thread {0}", Thread.CurrentThread.ManagedThreadId);// Simulating some heavy work.Thread.SpinWait(500000000);// Actual implemenation left as exercise for the reader.// Several examples are available on the Web.return "3.14159265358979323846264338327950288";}public string EndCalculate(IAsyncResult ar){Console.WriteLine("Calling EndCalculate on thread {0}", Thread.CurrentThread.ManagedThreadId);return ((Task<string>)ar).Result;} }public class CalculatorClient {static int decimalPlaces = 12;public static void Main(){Calculator calc = new Calculator();int places = 35;AsyncCallback callBack = new AsyncCallback(PrintResult);IAsyncResult ar = calc.BeginCalculate(places, callBack, calc);// Do some work on this thread while the calulator is busy.Console.WriteLine("Working...");Thread.SpinWait(500000);Console.ReadLine();}public static void PrintResult(IAsyncResult result){Calculator c = (Calculator)result.AsyncState;string piString = c.EndCalculate(result);Console.WriteLine("Calling PrintResult on thread {0}; result = {1}",Thread.CurrentThread.ManagedThreadId, piString);} } Class CalculatorPublic Function BeginCalculate(ByVal decimalPlaces As Integer, ByVal ac As AsyncCallback, ByVal state As Object) As IAsyncResultConsole.WriteLine("Calling BeginCalculate on thread {0}", Thread.CurrentThread.ManagedThreadId)Dim myTask = Task(Of String).Factory.StartNew(Function(obj) Compute(decimalPlaces), state)myTask.ContinueWith(Sub(antedecent) ac(myTask))End FunctionPrivate Function Compute(ByVal decimalPlaces As Integer)Console.WriteLine("Calling compute on thread {0}", Thread.CurrentThread.ManagedThreadId)' Simulating some heavy work.Thread.SpinWait(500000000)' Actual implemenation left as exercise for the reader.' Several examples are available on the Web.Return "3.14159265358979323846264338327950288"End FunctionPublic Function EndCalculate(ByVal ar As IAsyncResult) As StringConsole.WriteLine("Calling EndCalculate on thread {0}", Thread.CurrentThread.ManagedThreadId)Return CType(ar, Task(Of String)).ResultEnd Function End ClassClass CalculatorClientShared decimalPlaces As IntegerShared Sub Main()Dim calc As New CalculatorDim places As Integer = 35Dim callback As New AsyncCallback(AddressOf PrintResult)Dim ar As IAsyncResult = calc.BeginCalculate(places, callback, calc)' Do some work on this thread while the calulator is busy.Console.WriteLine("Working...")Thread.SpinWait(500000)Console.ReadLine()End SubPublic Shared Sub PrintResult(ByVal result As IAsyncResult)Dim c As Calculator = CType(result.AsyncState, Calculator)Dim piString As String = c.EndCalculate(result)Console.WriteLine("Calling PrintResult on thread {0}; result = {1}",Thread.CurrentThread.ManagedThreadId, piString)End SubEnd Class

使用 StreamExtensions 示例代碼

在使用 .NET Framework 4 的并行編程示例中，Streamextensions.cs 文件包含多個(gè)引用實(shí)現(xiàn)，以將 Task 對(duì)象用于異步文件和網(wǎng)絡(luò) I/O。

請(qǐng)參閱

• 任務(wù)并行庫(kù) (TPL)

總結(jié)

以上是生活随笔為你收集整理的TPL 和传统 .NET Framework 异步编程的全部?jī)?nèi)容，希望文章能夠幫你解決所遇到的問(wèn)題。

如果覺(jué)得生活随笔網(wǎng)站內(nèi)容還不錯(cuò)，歡迎將生活随笔推薦給好友。