TPL——等待Task

野性酷女 2022-07-17 03:25 35阅读 0赞

等待特定时间：

CancallationToken.WaitHandle.WaitOne()
    Thread.Sleep()
    Thread.SpinWait()

前两个函数将在等待的时候被投入睡眠，而Thread.SpinWait()却会使线程处于一个高强度的运行状态。

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等待线程的完成：

Waiting for a Single Task  
You can wait for a single **Task** to complete by calling the**Wait()** instance method. The calling method will not return until the**Task** instance has completed, been cancelled or thrown an exception.  
  
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using System;
    using System.Threading;
    using System.Threading.Tasks;
    namespace Listing_16 {
    class Listing_16 {
    static void Main(string[] args) {
    // create the cancellation token source
    CancellationTokenSource tokenSource = new CancellationTokenSource();
    // create the cancellation token
    CancellationToken token = tokenSource.Token;
    // create and start the first task, which we will let run fully
    Task task = createTask(token);
    task.Start();
    // wait for the task
    Console.WriteLine("Waiting for task to complete.");
    task.Wait();
    Console.WriteLine("Task Completed.");
    // create and start another task
    task = createTask(token);
    task.Start();
    Console.WriteLine("Waiting 2 secs for task to complete.");
    bool completed = task.Wait(2000);
    Console.WriteLine("Wait ended - task completed: {0}", completed);
    // create and start another task
    task = createTask(token);
    task.Start();
    Console.WriteLine("Waiting 2 secs for task to complete.");
    completed = task.Wait(2000, token);
    Console.WriteLine("Wait ended - task completed: {0} task cancelled {1}",
    completed, task.IsCanceled);
    // wait for input before exiting
    Console.WriteLine("Main method complete. Press enter to finish.");
    Console.ReadLine();
    }
    static Task createTask(CancellationToken token) {
    return new Task(() => {
    for (int i = 0; i < 5; i++) {
    // check for task cancellation
    token.ThrowIfCancellationRequested();
    // print out a message
    Console.WriteLine("Task - Int value {0}", i);
    // put the task to sleep for 1 second
    token.WaitHandle.WaitOne(1000);
    }
    }, token);
    }
    }
    }

Waiting for Several Tasks  
You can wait for a number of tasks to complete by using the static**Task.WaitAll()**method. This method will not return until all of the tasks passed as arguments have completed, been cancelled, or thrown an exception.   
 **Tip**When using this method, a**Task** is considered complete if it has finished its workload, been cancelled, or thrown an exception. If one or more of your tasks has thrown an exception, the**WaitAll()**method will throw an exception. See the “Handling Exceptions” section in this chapter for details.

using System;
    using System.Threading;
    using System.Threading.Tasks;
    namespace Listing_17 {
    class Listing_17 {
    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 < 5; i++) {
    // check for task cancellation
    token.ThrowIfCancellationRequested();
    // print out a message
    Console.WriteLine("Task 1 - Int value {0}", i);
    // put the task to sleep for 1 second
    token.WaitHandle.WaitOne(1000);
    }
    Console.WriteLine("Task 1 complete");
    }, token);
    Task task2 = new Task(() => {
    Console.WriteLine("Task 2 complete");
    }, token);
    // start the tasks
    task1.Start();
    task2.Start();
    // wait for the tasks
    Console.WriteLine("Waiting for tasks to complete.");
    Task.WaitAll(task1, task2);
    Console.WriteLine("Tasks Completed.");
    // wait for input before exiting
    Console.WriteLine("Main method complete. Press enter to finish.");
    Console.ReadLine();
    }
    }
    }

Waiting for One of Many Tasks  
The **Task.WaitAny()** method waits for one of a set of tasks to complete, and this method has a number of overloads, all of which take a**Task** array.   
 **Tip**When using this method, a**Task** is considered complete if it has finished its workload, been cancelled, or thrown an exception. If one or more of your tasks has thrown an exception, the**WaitAny()**method will throw an exception.

using System;
    using System.Threading;
    using System.Threading.Tasks;
    namespace Listing_18 {
    class Listing_18 {
    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 < 5; i++) {
    // check for task cancellation
    token.ThrowIfCancellationRequested();
    // print out a message
    Console.WriteLine("Task 1 - Int value {0}", i);
    // put the task to sleep for 1 second
    token.WaitHandle.WaitOne(1000);
    }
    Console.WriteLine("Task 1 complete");
    }, token);
    Task task2 = new Task(() => {
    Console.WriteLine("Task 2 complete");
    }, token);
    // start the tasks
    task1.Start();
    task2.Start();
    // wait for the tasks
    Console.WriteLine("Waiting for tasks to complete.");
    int taskIndex = Task.WaitAny(task1, task2);
    Console.WriteLine("Task Completed. Index: {0}", taskIndex);
    // wait for input before exiting
    Console.WriteLine("Main method complete. Press enter to finish.");
    Console.ReadLine();
    }
    }
    }

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[Image 1]: