TPL——取消一个Task

水深无声 2022-07-17 03:25 139阅读 0赞

取消一个Task

using System;
    using System.Threading;
    using System.Threading.Tasks;
    namespace Listing_07 {
    class Listing_07 {
    static void Main(string[] args) {
    // create the cancellation token source
    CancellationTokenSource tokenSource
    = new CancellationTokenSource();
    // create the cancellation token
    CancellationToken token = tokenSource.Token;
    // create the task
    Task task = new Task(() => {
    for (int i = 0; i < int.MaxValue; i++) {
    if (token.IsCancellationRequested) {
    Console.WriteLine("Task cancel detected");
    throw new OperationCanceledException(token);
    } else {
    Console.WriteLine("Int value {0}", i);
    }
    }
    }, token);
    // wait for input before we start the task
    Console.WriteLine("Press enter to start task");
    Console.WriteLine("Press enter again to cancel task");
    Console.ReadLine();
    // start the task
    task.Start();
    // read a line from the console.
    Console.ReadLine();
    // cancel the task
    Console.WriteLine("Cancelling task");
    tokenSource.Cancel();
    // wait for input before exiting
    Console.WriteLine("Main method complete. Press enter to finish.");
    Console.ReadLine();
    }
    }
    }

监控Task的取消1：使用委托

using System;
    using System.Threading;
    using System.Threading.Tasks;
    namespace Listing_08 {
    class Listing_08 {
    static void Main(string[] args) {
    // create the cancellation token source
    CancellationTokenSource tokenSource
    = new CancellationTokenSource();
    // create the cancellation token
    CancellationToken token = tokenSource.Token;
    // create the task
    Task task = new Task(() => {
    for (int i = 0; i < int.MaxValue; i++) {
    if (token.IsCancellationRequested) {
    Console.WriteLine("Task cancel detected");
    throw new OperationCanceledException(token);
    } else {
    Console.WriteLine("Int value {0}", i);
    }
    }
    }, token);
    // register a cancellation delegate
    token.Register(() => {
    Console.WriteLine(">>>>>> Delegate Invoked\n");
    });
    // wait for input before we start the task
    Console.WriteLine("Press enter to start task");
    Console.WriteLine("Press enter again to cancel task");
    Console.ReadLine();
    // start the task
    task.Start();
    // read a line from the console.
    Console.ReadLine();
    // cancel the task
    Console.WriteLine("Cancelling task");
    tokenSource.Cancel();
    // wait for input before exiting
    Console.WriteLine("Main method complete. Press enter to finish.");
    Console.ReadLine();
    }
    }
    }

监控Task的取消2：WaitOne()

using System;
    using System.Threading;
    using System.Threading.Tasks;
    namespace Listing_09 {
    class Listing_09 {
    static void Main(string[] args) {
    // create the cancellation token source
    CancellationTokenSource tokenSource
    = new CancellationTokenSource();
    // create the cancellation token
    CancellationToken token = tokenSource.Token;
    // create the task
    Task task1 = new Task(() => {
    for (int i = 0; i < int.MaxValue; i++) {
    if (token.IsCancellationRequested) {
    Console.WriteLine("Task cancel detected");
    throw new OperationCanceledException(token);
    } else {
    Console.WriteLine("Int value {0}", i);
    }
    }
    }, token);
    // create a second task that will use the wait handle
    Task task2 = new Task(() => {
    // wait on the handle
    token.WaitHandle.WaitOne();
    // write out a message
    Console.WriteLine(">>>>> Wait handle released");
    });
    // wait for input before we start the task
    Console.WriteLine("Press enter to start task");
    Console.WriteLine("Press enter again to cancel task");
    Console.ReadLine();
    // start the tasks
    task1.Start();
    task2.Start();
    // read a line from the console.
    Console.ReadLine();
    // cancel the task
    Console.WriteLine("Cancelling task");
    tokenSource.Cancel();
    // wait for input before exiting
    Console.WriteLine("Main method complete. Press enter to finish.");
    Console.ReadLine();
    }
    }
    }

取消几个Task

using System;
    using System.Threading;
    using System.Threading.Tasks;
    namespace Listing_10 {
    class Listing_10 {
    static void Main(string[] args) {
    // create the cancellation token source
    CancellationTokenSource tokenSource
    = new CancellationTokenSource();
    // create the cancellation token
    CancellationToken token = tokenSource.Token;
    // create the tasks
    Task task1 = new Task(() => {
    for (int i = 0; i < int.MaxValue; i++) {
    token.ThrowIfCancellationRequested();
    Console.WriteLine("Task 1 - Int value {0}", i);
    }
    }, token);
    Task task2 = new Task(() => {
    for (int i = 0; i < int.MaxValue; i++) {
    token.ThrowIfCancellationRequested();
    Console.WriteLine("Task 2 - Int value {0}", i);
    }
    }, token);
    // wait for input before we start the tasks
    Console.WriteLine("Press enter to start tasks");
    Console.WriteLine("Press enter again to cancel tasks");
    Console.ReadLine();
    // start the tasks
    task1.Start();
    task2.Start();
    // read a line from the console.
    Console.ReadLine();
    // cancel the task
    Console.WriteLine("Cancelling tasks");
    tokenSource.Cancel();
    // wait for input before exiting
    Console.WriteLine("Main method complete. Press enter to finish.");
    Console.ReadLine();
    }
    }
    }

复合Token

using System;
    using System.Threading;
    using System.Threading.Tasks;
    namespace Listing_11 {
    class Listing_11 {
    static void Main(string[] args) {
    // create the cancellation token sources
    CancellationTokenSource tokenSource1 = new CancellationTokenSource();
    CancellationTokenSource tokenSource2 = new CancellationTokenSource();
    CancellationTokenSource tokenSource3 = new CancellationTokenSource();
    // create a composite token source using multiple tokens
    CancellationTokenSource compositeSource =
    CancellationTokenSource.CreateLinkedTokenSource(
    tokenSource1.Token, tokenSource2.Token, tokenSource3.Token);
    // create a cancellable task using the composite token
    Task task = new Task(() => {
    // wait until the token has been cancelled
    compositeSource.Token.WaitHandle.WaitOne();
    // throw a cancellation exception
    throw new OperationCanceledException(compositeSource.Token);
    }, compositeSource.Token);
    // start the task
    task.Start();
    // cancel one of the original tokens
    tokenSource2.Cancel();
    // wait for input before exiting
    Console.WriteLine("Main method complete. Press enter to finish.");
    Console.ReadLine();
    }
    }
    }

一个Task是否已经被取消？

You can determine if a **Task**  has been cancelled by checking the **IsCancelled** property, which will return **true** if the **Task** was cancelled.

如果一个Task已经被取消，IsCancelled属性将返回true.