public:
 static System::Threading::Tasks::Task ^ Run(Action ^ action);
public static System.Threading.Tasks.Task Run (Action action);
static member Run : Action -> System.Threading.Tasks.Task
Public Shared Function Run (action As Action) As Task

以下示例定义一个 ShowThreadInfo 显示 Thread.ManagedThreadId 当前线程的 的方法。 它直接从应用程序线程调用,并从传递给 Run(Action) 方法的 Action 委托中调用。

using System; using System.Threading; using System.Threading.Tasks; public class Example public static void Main() ShowThreadInfo("Application"); var t = Task.Run(() => ShowThreadInfo("Task") ); t.Wait(); static void ShowThreadInfo(String s) Console.WriteLine("{0} thread ID: {1}", s, Thread.CurrentThread.ManagedThreadId); // The example displays the following output: // Application thread ID: 1 // Task thread ID: 3 open System.Threading open System.Threading.Tasks let showThreadInfo s = printfn $"%s{s} thread ID: {Thread.CurrentThread.ManagedThreadId}" showThreadInfo "Application" let t = Task.Run(fun () -> showThreadInfo "Task") t.Wait() // The example displays the following output: // Application thread ID: 1 // Task thread ID: 3 Imports System.Threading Imports System.Threading.Tasks Module Example Public Sub Main() ShowThreadInfo("Application") Dim t As Task = Task.Run(Sub() ShowThreadInfo("Task") ) t.Wait() End Sub Private Sub ShowThreadInfo(s As String) Console.WriteLine("{0} Thread ID: {1}", s, Thread.CurrentThread.ManagedThreadId) End Sub End Module ' The example displays output like the following: ' Application thread ID: 1 ' Task thread ID: 3

以下示例类似于上一个示例,只不过它使用 lambda 表达式来定义任务要执行的代码。

using System; using System.Threading; using System.Threading.Tasks; public class Example public static void Main() Console.WriteLine("Application thread ID: {0}", Thread.CurrentThread.ManagedThreadId); var t = Task.Run(() => { Console.WriteLine("Task thread ID: {0}", Thread.CurrentThread.ManagedThreadId); t.Wait(); // The example displays the following output: // Application thread ID: 1 // Task thread ID: 3 open System.Threading open System.Threading.Tasks printfn $"Application thread ID: {Thread.CurrentThread.ManagedThreadId}" let t = Task.Run(fun () -> printfn $"Task thread ID: {Thread.CurrentThread.ManagedThreadId}") t.Wait() // The example displays the following output: // Application thread ID: 1 // Task thread ID: 3 Imports System.Threading Imports System.Threading.Tasks Module Example Public Sub Main() Console.WriteLine("Application thread ID: {0}", Thread.CurrentThread.ManagedThreadId) Dim t As Task = Task.Run(Sub() Console.WriteLine("Task thread ID: {0}", Thread.CurrentThread.ManagedThreadId) End Sub) t.Wait() End Sub End Module ' The example displays output like the following: ' Application thread ID: 1 ' Task thread ID: 3

这些示例显示异步任务在与main应用程序线程不同的线程上执行。

对 方法的 Wait 调用可确保任务在应用程序结束之前完成并显示其输出。 否则,方法可能在 Main 任务完成之前完成。

以下示例演示 了 Run(Action) 方法。 它定义目录名称数组,并启动单独的任务来检索每个目录中的文件名。 所有任务都会将文件名写入单个 ConcurrentBag<T> 对象。 然后,该示例调用 WaitAll(Task[]) 方法以确保所有任务都已完成,然后显示写入 ConcurrentBag<T> 对象的文件名总数的计数。

using System; using System.Collections.Concurrent; using System.Collections.Generic; using System.IO; using System.Threading.Tasks; public class Example public static void Main() var list = new ConcurrentBag<string>(); string[] dirNames = { ".", ".." }; List<Task> tasks = new List<Task>(); foreach (var dirName in dirNames) { Task t = Task.Run( () => { foreach(var path in Directory.GetFiles(dirName)) list.Add(path); } ); tasks.Add(t); Task.WaitAll(tasks.ToArray()); foreach (Task t in tasks) Console.WriteLine("Task {0} Status: {1}", t.Id, t.Status); Console.WriteLine("Number of files read: {0}", list.Count); // The example displays output like the following: // Task 1 Status: RanToCompletion // Task 2 Status: RanToCompletion // Number of files read: 23 open System.Collections.Concurrent open System.IO open System.Threading.Tasks let list = ConcurrentBag<string>() let dirNames = [ "."; ".." ] let tasks = ResizeArray() for dirName in dirNames do let t = Task.Run(fun () -> for path in Directory.GetFiles dirName do list.Add path) tasks.Add t tasks.ToArray() |> Task.WaitAll for t in tasks do printfn $"Task {t.Id} Status: {t.Status}" printfn $"Number of files read: {list.Count}" // The example displays output like the following: // Task 1 Status: RanToCompletion // Task 2 Status: RanToCompletion // Number of files read: 23 Imports System.Collections.Concurrent Imports System.Collections.Generic Imports System.IO Imports System.Threading.Tasks Module Example Public Sub Main() Dim list As New ConcurrentBag(Of String)() Dim dirNames() As String = { ".", ".." } Dim tasks As New List(Of Task)() For Each dirName In dirNames Dim t As Task = Task.Run( Sub() For Each path In Directory.GetFiles(dirName) list.Add(path) End Sub ) tasks.Add(t) Task.WaitAll(tasks.ToArray()) For Each t In tasks Console.WriteLine("Task {0} Status: {1}", t.Id, t.Status) Console.WriteLine("Number of files read: {0}", list.Count) End Sub End Module ' The example displays output like the following: ' Task 1 Status: RanToCompletion ' Task 2 Status: RanToCompletion ' Number of files read: 23

方法 Run 允许在单个方法调用中创建和执行任务,是方法的更简单的替代方法 StartNew 。 它创建具有以下默认值的任务:

  • 其取消标记为 CancellationToken.None

  • CreationOptions 属性值为 TaskCreationOptions.DenyChildAttach

  • 它使用默认的任务计划程序。

    有关处理任务操作引发的异常的信息,请参阅 异常处理

    public:
     static System::Threading::Tasks::Task ^ Run(Func<System::Threading::Tasks::Task ^> ^ function);
    public static System.Threading.Tasks.Task Run (Func<System.Threading.Tasks.Task> function);
    public static System.Threading.Tasks.Task Run (Func<System.Threading.Tasks.Task?> function);
    static member Run : Func<System.Threading.Tasks.Task> -> System.Threading.Tasks.Task
    Public Shared Function Run (function As Func(Of Task)) As Task
    public:
     static System::Threading::Tasks::Task ^ Run(Action ^ action, System::Threading::CancellationToken cancellationToken);
    public static System.Threading.Tasks.Task Run (Action action, System.Threading.CancellationToken cancellationToken);
    static member Run : Action * System.Threading.CancellationToken -> System.Threading.Tasks.Task
    Public Shared Function Run (action As Action, cancellationToken As CancellationToken) As Task

    以下示例调用 Run(Action, CancellationToken) 方法以创建一个任务,用于循环访问 C:\Windows\System32 目录中的文件。 lambda 表达式调用 Parallel.ForEach 方法,以将有关每个文件的信息添加到 List<T> 对象。 循环调用 Parallel.ForEach 的每个分离嵌套任务都会检查取消令牌的状态,如果请求取消,则调用 CancellationToken.ThrowIfCancellationRequested 方法。 当调用线程调用 Task.Wait 方法时,方法 CancellationToken.ThrowIfCancellationRequested 会引发 OperationCanceledException 在块中 catch 处理的异常。

    using System; using System.Collections.Generic; using System.IO; using System.Threading; using System.Threading.Tasks; public class Example public static async Task Main() var tokenSource = new CancellationTokenSource(); var token = tokenSource.Token; var files = new List<Tuple<string, string, long, DateTime>>(); var t = Task.Run( () => { string dir = "C:\\Windows\\System32\\"; object obj = new Object(); if (Directory.Exists(dir)) { Parallel.ForEach(Directory.GetFiles(dir), f => { if (token.IsCancellationRequested) token.ThrowIfCancellationRequested(); var fi = new FileInfo(f); lock(obj) { files.Add(Tuple.Create(fi.Name, fi.DirectoryName, fi.Length, fi.LastWriteTimeUtc)); , token); await Task.Yield(); tokenSource.Cancel(); try { await t; Console.WriteLine("Retrieved information for {0} files.", files.Count); catch (AggregateException e) { Console.WriteLine("Exception messages:"); foreach (var ie in e.InnerExceptions) Console.WriteLine(" {0}: {1}", ie.GetType().Name, ie.Message); Console.WriteLine("\nTask status: {0}", t.Status); finally { tokenSource.Dispose(); // The example displays the following output: // Exception messages: // TaskCanceledException: A task was canceled. // TaskCanceledException: A task was canceled. // ... // Task status: Canceled open System open System.IO open System.Threading open System.Threading.Tasks let main = task { use tokenSource = new CancellationTokenSource() let token = tokenSource.Token let files = ResizeArray() let t = Task.Run( (fun () -> let dir = "C:\\Windows\\System32\\" let obj = obj () if Directory.Exists dir then Parallel.ForEach( Directory.GetFiles dir, (fun f -> if token.IsCancellationRequested then token.ThrowIfCancellationRequested() let fi = FileInfo f lock obj (fun () -> files.Add(fi.Name, fi.DirectoryName, fi.Length, fi.LastWriteTimeUtc))) |> ignore), token do! Task.Yield() tokenSource.Cancel() do! t printfn $"Retrieved information for {files.Count} files." with :? AggregateException as e -> printfn "Exception messages:" for ie in e.InnerExceptions do printfn $" {ie.GetType().Name}: {ie.Message}" printfn $"Task status: {t.Status}" main.Wait() // The example displays the following output: // Exception messages: // TaskCanceledException: A task was canceled. // TaskCanceledException: A task was canceled. // ... // Task status: Canceled Imports System.Collections.Generic Imports System.IO Imports System.Threading Imports System.Threading.Tasks Module Example Public Sub Main() Dim tokenSource As New CancellationTokenSource() Dim token As CancellationToken = tokenSource.Token Dim files As New List(Of Tuple(Of String, String, Long, Date))() Dim t As Task = Task.Run( Sub() Dim dir As String = "C:\Windows\System32\" Dim obj As New Object() If Directory.Exists(dir)Then Parallel.ForEach(Directory.GetFiles(dir), Sub(f) If token.IsCancellationRequested Then token.ThrowIfCancellationRequested() End If Dim fi As New FileInfo(f) SyncLock(obj) files.Add(Tuple.Create(fi.Name, fi.DirectoryName, fi.Length, fi.LastWriteTimeUtc)) End SyncLock End Sub) End If End Sub, token) tokenSource.Cancel() t.Wait() Console.WriteLine("Retrieved information for {0} files.", files.Count) Catch e As AggregateException Console.WriteLine("Exception messages:") For Each ie As Exception In e.InnerExceptions Console.WriteLine(" {0}:{1}", ie.GetType().Name, ie.Message) Console.WriteLine() Console.WriteLine("Task status: {0}", t.Status) Finally tokenSource.Dispose() End Try End Sub End Module ' The example displays the following output: ' Exception messages: ' TaskCanceledException: A task was canceled. ' Task status: Canceled

    如果在任务开始执行之前请求取消,则任务不会执行。 相反,它设置为 状态 Canceled 并引发 TaskCanceledException 异常。

    方法 Run(Action, CancellationToken) 是 方法的一种更简单的 TaskFactory.StartNew(Action, CancellationToken) 替代方法。 它创建具有以下默认值的任务:

  • CreationOptions 属性值为 TaskCreationOptions.DenyChildAttach

  • 它使用默认的任务计划程序。

    有关处理任务操作引发的异常的信息,请参阅 异常处理

    public:
     static System::Threading::Tasks::Task ^ Run(Func<System::Threading::Tasks::Task ^> ^ function, System::Threading::CancellationToken cancellationToken);
    public static System.Threading.Tasks.Task Run (Func<System.Threading.Tasks.Task> function, System.Threading.CancellationToken cancellationToken);
    public static System.Threading.Tasks.Task Run (Func<System.Threading.Tasks.Task?> function, System.Threading.CancellationToken cancellationToken);
    static member Run : Func<System.Threading.Tasks.Task> * System.Threading.CancellationToken -> System.Threading.Tasks.Task
    Public Shared Function Run (function As Func(Of Task), cancellationToken As CancellationToken) As Task

    可用于取消工作(如果尚未启动)的取消标记。 Run(Func<Task>, CancellationToken) 不会将 cancellationToken 传递到 action

    public:
    generic <typename TResult>
     static System::Threading::Tasks::Task<TResult> ^ Run(Func<System::Threading::Tasks::Task<TResult> ^> ^ function);
    public static System.Threading.Tasks.Task<TResult> Run<TResult> (Func<System.Threading.Tasks.Task<TResult>> function);
    public static System.Threading.Tasks.Task<TResult> Run<TResult> (Func<System.Threading.Tasks.Task<TResult>?> function);
    static member Run : Func<System.Threading.Tasks.Task<'Result>> -> System.Threading.Tasks.Task<'Result>
    Public Shared Function Run(Of TResult) (function As Func(Of Task(Of TResult))) As Task(Of TResult)
    TResult
    public:
    generic <typename TResult>
     static System::Threading::Tasks::Task<TResult> ^ Run(Func<TResult> ^ function);
    public static System.Threading.Tasks.Task<TResult> Run<TResult> (Func<TResult> function);
    static member Run : Func<'Result> -> System.Threading.Tasks.Task<'Result>
    Public Shared Function Run(Of TResult) (function As Func(Of TResult)) As Task(Of TResult)
    TResult

    以下示例计算文本文件中表示已出版书籍的大致字数。 每个任务负责打开文件、异步读取其整个内容以及使用正则表达式计算字数计数。 WaitAll(Task[]) 调用 方法可确保在向控制台显示每本书的字数之前已完成所有任务。

    using System; using System.IO; using System.Text.RegularExpressions; using System.Threading.Tasks; public class Example public static void Main() string pattern = @"\p{P}*\s+"; string[] titles = { "Sister Carrie", "The Financier" }; Task<int>[] tasks = new Task<int>[titles.Length]; for (int ctr = 0; ctr < titles.Length; ctr++) { string s = titles[ctr]; tasks[ctr] = Task.Run( () => { // Number of words. int nWords = 0; // Create filename from title. string fn = s + ".txt"; if (File.Exists(fn)) { StreamReader sr = new StreamReader(fn); string input = sr.ReadToEndAsync().Result; nWords = Regex.Matches(input, pattern).Count; return nWords; Task.WaitAll(tasks); Console.WriteLine("Word Counts:\n"); for (int ctr = 0; ctr < titles.Length; ctr++) Console.WriteLine("{0}: {1,10:N0} words", titles[ctr], tasks[ctr].Result); // The example displays the following output: // Sister Carrie: 159,374 words // The Financier: 196,362 words open System open System.IO open System.Text.RegularExpressions open System.Threading.Tasks let pattern = @"\p{P}*\s+" let titles = [| "Sister Carrie"; "The Financier" |] let tasks = Array.map (fun title -> Task.Run(fun () -> // Create filename from title. let fn = title + ".txt" if File.Exists fn then use sr = new StreamReader(fn) let input = sr.ReadToEndAsync().Result Regex.Matches(input, pattern).Count 0)) titles tasks |> Seq.cast |> Array.ofSeq |> Task.WaitAll printfn "Word Counts:\n" for i = 0 to tasks.Length - 1 do printfn $"%s{titles.[i]}: %10d{tasks.[i].Result} words" // The example displays the following output: // Sister Carrie: 159,374 words // The Financier: 196,362 words Imports System.IO Imports System.Text.RegularExpressions Imports System.Threading.Tasks Module Example Public Sub Main() Dim pattern As String = "\p{P}*\s+" Dim titles() As String = { "Sister Carrie", "The Financier" } Dim tasks(titles.Length - 1) As Task(Of Integer) For ctr As Integer = 0 To titles.Length - 1 Dim s As String = titles(ctr) tasks(ctr) = Task.Run( Function() ' Number of words. Dim nWords As Integer = 0 ' Create filename from title. Dim fn As String = s + ".txt" If File.Exists(fn) Then Dim sr As New StreamReader(fn) Dim input As String = sr.ReadToEndAsync().Result nWords = Regex.Matches(input, pattern).Count End If Return nWords End Function) Task.WaitAll(tasks) Console.WriteLine("Word Counts:") Console.WriteLine() For ctr As Integer = 0 To titles.Length - 1 Console.WriteLine("{0}: {1,10:N0} words", titles(ctr), tasks(ctr).Result) End Sub End Module ' The example displays the following output: ' Sister Carrie: 159,374 words ' The Financier: 196,362 words

    正则表达式 \p{P}*\s+ 匹配零个、一个或多个标点字符,后跟一个或多个空格字符。 它假定匹配总数等于近似字数。

    方法 Run 是 方法的一种更简单的 TaskFactory.StartNew(Action) 替代方法。 它创建具有以下默认值的任务:

  • 其取消标记为 CancellationToken.None

  • CreationOptions 属性值为 TaskCreationOptions.DenyChildAttach

  • 它使用默认的任务计划程序。

    有关处理任务操作引发的异常的信息,请参阅 异常处理

    public:
    generic <typename TResult>
     static System::Threading::Tasks::Task<TResult> ^ Run(Func<System::Threading::Tasks::Task<TResult> ^> ^ function, System::Threading::CancellationToken cancellationToken);
    public static System.Threading.Tasks.Task<TResult> Run<TResult> (Func<System.Threading.Tasks.Task<TResult>> function, System.Threading.CancellationToken cancellationToken);
    public static System.Threading.Tasks.Task<TResult> Run<TResult> (Func<System.Threading.Tasks.Task<TResult>?> function, System.Threading.CancellationToken cancellationToken);
    static member Run : Func<System.Threading.Tasks.Task<'Result>> * System.Threading.CancellationToken -> System.Threading.Tasks.Task<'Result>
    Public Shared Function Run(Of TResult) (function As Func(Of Task(Of TResult)), cancellationToken As CancellationToken) As Task(Of TResult)
    TResult

    可用于取消工作(如果尚未启动)的取消标记。 Run<TResult>(Func<Task<TResult>>, CancellationToken) 不会将 cancellationToken 传递到 action

    public:
    generic <typename TResult>
     static System::Threading::Tasks::Task<TResult> ^ Run(Func<TResult> ^ function, System::Threading::CancellationToken cancellationToken);
    public static System.Threading.Tasks.Task<TResult> Run<TResult> (Func<TResult> function, System.Threading.CancellationToken cancellationToken);
    static member Run : Func<'Result> * System.Threading.CancellationToken -> System.Threading.Tasks.Task<'Result>
    Public Shared Function Run(Of TResult) (function As Func(Of TResult), cancellationToken As CancellationToken) As Task(Of TResult)
    TResult

    可用于取消工作(如果尚未启动)的取消标记。 Run<TResult>(Func<TResult>, CancellationToken) 不会将 cancellationToken 传递到 action

    以下示例创建 20 个任务,这些任务将循环执行,直到计数器递增为 200 万。 当前 10 个任务达到 200 万时,取消令牌将被取消,并且计数器未达到 200 万的任何任务将被取消。 该示例显示了可能的输出。

    using System; using System.Collections.Generic; using System.Threading; using System.Threading.Tasks; public class Example public static void Main() var tasks = new List<Task<int>>(); var source = new CancellationTokenSource(); var token = source.Token; int completedIterations = 0; for (int n = 0; n <= 19; n++) tasks.Add(Task.Run( () => { int iterations = 0; for (int ctr = 1; ctr <= 2000000; ctr++) { token.ThrowIfCancellationRequested(); iterations++; Interlocked.Increment(ref completedIterations); if (completedIterations >= 10) source.Cancel(); return iterations; }, token)); Console.WriteLine("Waiting for the first 10 tasks to complete...\n"); try { Task.WaitAll(tasks.ToArray()); catch (AggregateException) { Console.WriteLine("Status of tasks:\n"); Console.WriteLine("{0,10} {1,20} {2,14:N0}", "Task Id", "Status", "Iterations"); foreach (var t in tasks) Console.WriteLine("{0,10} {1,20} {2,14}", t.Id, t.Status, t.Status != TaskStatus.Canceled ? t.Result.ToString("N0") : "n/a"); // The example displays output like the following: // Waiting for the first 10 tasks to complete... // Status of tasks: // Task Id Status Iterations // 1 RanToCompletion 2,000,000 // 2 RanToCompletion 2,000,000 // 3 RanToCompletion 2,000,000 // 4 RanToCompletion 2,000,000 // 5 RanToCompletion 2,000,000 // 6 RanToCompletion 2,000,000 // 7 RanToCompletion 2,000,000 // 8 RanToCompletion 2,000,000 // 9 RanToCompletion 2,000,000 // 10 Canceled n/a // 11 Canceled n/a // 12 Canceled n/a // 13 Canceled n/a // 14 Canceled n/a // 15 Canceled n/a // 16 RanToCompletion 2,000,000 // 17 Canceled n/a // 18 Canceled n/a // 19 Canceled n/a // 20 Canceled n/a open System open System.Collections.Generic open System.Threading open System.Threading.Tasks let source = new CancellationTokenSource() let token = source.Token let mutable completedIterations = 0 let tasks = [| for _ = 0 to 19 do Task.Run( (fun () -> let mutable iterations = 0 for _ = 1 to 2000000 do token.ThrowIfCancellationRequested() iterations <- iterations + 1 Interlocked.Increment &completedIterations |> ignore if completedIterations >= 10 then source.Cancel() iterations), token printfn "Waiting for the first 10 tasks to complete...\n" tasks |> Seq.cast |> Array.ofSeq |> Task.WaitAll with :? AggregateException -> printfn "Status of tasks:\n" printfn "%10s %20s %14s" "Task Id" "Status" "Iterations" for t in tasks do if t.Status <> TaskStatus.Canceled then t.Result.ToString "N0" "n/a" |> printfn "%10i %20O %14s" t.Id t.Status // The example displays output like the following: // Waiting for the first 10 tasks to complete... // Status of tasks: // Task Id Status Iterations // 1 RanToCompletion 2,000,000 // 2 RanToCompletion 2,000,000 // 3 RanToCompletion 2,000,000 // 4 RanToCompletion 2,000,000 // 5 RanToCompletion 2,000,000 // 6 RanToCompletion 2,000,000 // 7 RanToCompletion 2,000,000 // 8 RanToCompletion 2,000,000 // 9 RanToCompletion 2,000,000 // 10 Canceled n/a // 11 Canceled n/a // 12 Canceled n/a // 13 Canceled n/a // 14 Canceled n/a // 15 Canceled n/a // 16 RanToCompletion 2,000,000 // 17 Canceled n/a // 18 Canceled n/a // 19 Canceled n/a // 20 Canceled n/a Imports System.Collections.Generic Imports System.Threading Imports System.Threading.Tasks Module Example Public Sub Main() Dim tasks As New List(Of Task(Of Integer))() Dim source As New CancellationTokenSource Dim token As CancellationToken = source.Token Dim completedIterations As Integer = 0 For n As Integer = 0 To 19 tasks.Add(Task.Run( Function() Dim iterations As Integer= 0 For ctr As Long = 1 To 2000000 token.ThrowIfCancellationRequested() iterations += 1 Interlocked.Increment(completedIterations) If completedIterations >= 10 Then source.Cancel() Return iterations End Function, token)) Console.WriteLine("Waiting for the first 10 tasks to complete... ") Task.WaitAll(tasks.ToArray()) Catch e As AggregateException Console.WriteLine("Status of tasks:") Console.WriteLine() Console.WriteLine("{0,10} {1,20} {2,14}", "Task Id", "Status", "Iterations") For Each t In tasks Console.WriteLine("{0,10} {1,20} {2,14}", t.Id, t.Status, If(t.Status <> TaskStatus.Canceled, t.Result.ToString("N0"), "n/a")) End Try End Sub End Module ' The example displays output like the following: ' Waiting for the first 10 tasks to complete... ' Status of tasks: ' Task Id Status Iterations ' 1 RanToCompletion 2,000,000 ' 2 RanToCompletion 2,000,000 ' 3 RanToCompletion 2,000,000 ' 4 RanToCompletion 2,000,000 ' 5 RanToCompletion 2,000,000 ' 6 RanToCompletion 2,000,000 ' 7 RanToCompletion 2,000,000 ' 8 RanToCompletion 2,000,000 ' 9 RanToCompletion 2,000,000 ' 10 Canceled n/a ' 11 Canceled n/a ' 12 Canceled n/a ' 13 Canceled n/a ' 14 Canceled n/a ' 15 Canceled n/a ' 16 RanToCompletion 2,000,000 ' 17 Canceled n/a ' 18 Canceled n/a ' 19 Canceled n/a ' 20 Canceled n/a

    该示例循环访问所有任务以确定哪些任务已成功完成,哪些任务已取消,而不是使用 InnerExceptions 属性来检查异常。 对于已完成的任务,它显示任务返回的值。

    由于取消是合作的,因此每个任务都可以决定如何响应取消。 以下示例与第一个示例类似,不同之处在于,取消令牌后,任务返回已完成的迭代次数,而不是引发异常。

    using System; using System.Collections.Generic; using System.Threading; using System.Threading.Tasks; public class Example public static void Main() var tasks = new List<Task<int>>(); var source = new CancellationTokenSource(); var token = source.Token; int completedIterations = 0; for (int n = 0; n <= 19; n++) tasks.Add(Task.Run( () => { int iterations = 0; for (int ctr = 1; ctr <= 2000000; ctr++) { if (token.IsCancellationRequested) return iterations; iterations++; Interlocked.Increment(ref completedIterations); if (completedIterations >= 10) source.Cancel(); return iterations; }, token)); Console.WriteLine("Waiting for the first 10 tasks to complete...\n"); try { Task.WaitAll(tasks.ToArray()); catch (AggregateException) { Console.WriteLine("Status of tasks:\n"); Console.WriteLine("{0,10} {1,20} {2,14:N0}", "Task Id", "Status", "Iterations"); foreach (var t in tasks) Console.WriteLine("{0,10} {1,20} {2,14}", t.Id, t.Status, t.Status != TaskStatus.Canceled ? t.Result.ToString("N0") : "n/a"); // The example displays output like the following: // Status of tasks: // Task Id Status Iterations // 1 RanToCompletion 2,000,000 // 2 RanToCompletion 2,000,000 // 3 RanToCompletion 2,000,000 // 4 RanToCompletion 2,000,000 // 5 RanToCompletion 2,000,000 // 6 RanToCompletion 2,000,000 // 7 RanToCompletion 2,000,000 // 8 RanToCompletion 2,000,000 // 9 RanToCompletion 2,000,000 // 10 RanToCompletion 1,658,326 // 11 RanToCompletion 1,988,506 // 12 RanToCompletion 2,000,000 // 13 RanToCompletion 1,942,246 // 14 RanToCompletion 950,108 // 15 RanToCompletion 1,837,832 // 16 RanToCompletion 1,687,182 // 17 RanToCompletion 194,548 // 18 Canceled Not Started // 19 Canceled Not Started // 20 Canceled Not Started open System open System.Collections.Generic open System.Threading open System.Threading.Tasks let source = new CancellationTokenSource() let token = source.Token let mutable completedIterations = 0 let tasks = [| for _ = 0 to 19 do Task.Run( (fun () -> let mutable iterations = 0 for _ = 1 to 2000000 do token.ThrowIfCancellationRequested() iterations <- iterations + 1 Interlocked.Increment &completedIterations |> ignore if completedIterations >= 10 then source.Cancel() iterations), token printfn "Waiting for the first 10 tasks to complete...\n" tasks |> Seq.cast |> Array.ofSeq |> Task.WaitAll with :? AggregateException -> printfn "Status of tasks:\n" printfn "%10s %20s %14s" "Task Id" "Status" "Iterations" for t in tasks do if t.Status <> TaskStatus.Canceled then t.Result.ToString "N0" "n/a" |> printfn "%10i %20O %14s" t.Id t.Status // The example displays output like the following: // Status of tasks: // Task Id Status Iterations // 1 RanToCompletion 2,000,000 // 2 RanToCompletion 2,000,000 // 3 RanToCompletion 2,000,000 // 4 RanToCompletion 2,000,000 // 5 RanToCompletion 2,000,000 // 6 RanToCompletion 2,000,000 // 7 RanToCompletion 2,000,000 // 8 RanToCompletion 2,000,000 // 9 RanToCompletion 2,000,000 // 10 RanToCompletion 1,658,326 // 11 RanToCompletion 1,988,506 // 12 RanToCompletion 2,000,000 // 13 RanToCompletion 1,942,246 // 14 RanToCompletion 950,108 // 15 RanToCompletion 1,837,832 // 16 RanToCompletion 1,687,182 // 17 RanToCompletion 194,548 // 18 Canceled Not Started // 19 Canceled Not Started // 20 Canceled Not Started Imports System.Collections.Generic Imports System.Threading Imports System.Threading.Tasks Module Example Public Sub Main() Dim tasks As New List(Of Task(Of Integer))() Dim source As New CancellationTokenSource Dim token As CancellationToken = source.Token Dim completedIterations As Integer = 0 For n As Integer = 0 To 19 tasks.Add(Task.Run( Function() Dim iterations As Integer= 0 For ctr As Long = 1 To 2000000 If token.IsCancellationRequested Then Return iterations End If iterations += 1 Interlocked.Increment(completedIterations) If completedIterations >= 10 Then source.Cancel() Return iterations End Function, token)) Task.WaitAll(tasks.ToArray()) Catch e As AggregateException Console.WriteLine("Status of tasks:") Console.WriteLine() Console.WriteLine("{0,10} {1,20} {2,14:N0}", "Task Id", "Status", "Iterations") For Each t In tasks Console.WriteLine("{0,10} {1,20} {2,14}", t.Id, t.Status, If(t.Status <> TaskStatus.Canceled, t.Result.ToString("N0"), "Not Started")) End Try End Sub End Module ' The example displays output like the following: ' Status of tasks: ' Task Id Status Iterations ' 1 RanToCompletion 2,000,000 ' 2 RanToCompletion 2,000,000 ' 3 RanToCompletion 2,000,000 ' 4 RanToCompletion 2,000,000 ' 5 RanToCompletion 2,000,000 ' 6 RanToCompletion 2,000,000 ' 7 RanToCompletion 2,000,000 ' 8 RanToCompletion 2,000,000 ' 9 RanToCompletion 2,000,000 ' 10 RanToCompletion 1,658,326 ' 11 RanToCompletion 1,988,506 ' 12 RanToCompletion 2,000,000 ' 13 RanToCompletion 1,942,246 ' 14 RanToCompletion 950,108 ' 15 RanToCompletion 1,837,832 ' 16 RanToCompletion 1,687,182 ' 17 RanToCompletion 194,548 ' 18 Canceled Not Started ' 19 Canceled Not Started ' 20 Canceled Not Started

    该示例仍必须处理异常 AggregateException ,因为请求取消时尚未启动的任何任务仍会引发异常。

    如果在任务开始执行之前请求取消,则任务不会执行。 相反,它设置为 状态 Canceled 并引发 TaskCanceledException 异常。

    方法 Run 是 方法的一种更简单的 StartNew 替代方法。 它创建具有以下默认值的任务:

  • CreationOptions 属性值为 TaskCreationOptions.DenyChildAttach

  • 它使用默认的任务计划程序。

    有关处理任务操作引发的异常的信息,请参阅 异常处理

  •