帶有已取消令牌的Task.Factory.StartNew的狀態為running

我認為不應計劃、運行使用已取消令牌的 Task.Factory.StartNew 初始化的任務，并且應以已取消狀態結束。但是在 .NET 5 上的 VS 2019 中，我很偶然地注意到，很少有任務處于運行狀態。

在這種情況下，任務內部的操作顯然沒有執行。因為在我的示例中 1 沒有輸出到控制臺。誰能解釋實際發生的事情？

問題。為什么這個示例中的任務有時會處于運行狀態，雖然它顯然不起作用？

升級版。在 .NET 6 上檢查了 VS 2022。同樣的事情。

using System;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            CancellationTokenSource cancellationTokenSource = new CancellationTokenSource(1);
            Thread.Sleep(100);

            Task t1 = new Task(() => { }, cancellationTokenSource.Token);
            Task t2 = new Task(() => { }, cancellationTokenSource.Token);
            Task t3 = new Task(() => { }, cancellationTokenSource.Token);
            Task t4 = new Task(() => { }, cancellationTokenSource.Token);
            Task t5 = new Task(() => { }, cancellationTokenSource.Token);           
           
            Console.WriteLine($"t1: {t1.Status}");
            Console.WriteLine($"t2: {t2.Status}");
            Console.WriteLine($"t3: {t3.Status}");
            Console.WriteLine($"t4: {t4.Status}");
            Console.WriteLine($"t5: {t5.Status}");

            Task t6 = Task.Factory.StartNew(() =>
            {
                while (true)
                {
                    Console.WriteLine(1);
                }

            }, cancellationTokenSource.Token);

            Console.WriteLine($"t6: {t6.Status}");
            Console.WriteLine($"t6: {t6.Status}");
            Console.WriteLine($"t6: {t6.Status}");
            Console.WriteLine($"t6: {t6.Status}");
        }
    }
}

uj5u.com熱心網友回復：

在我的機器上Running，無論是使用 Framework 4.7.2 還是使用 .NET 6（VS 2019），您的代碼都不會達到狀態。正如@JonasH 建議的那樣，我查看了代碼。以下是一種可能的解釋。

在下面的代碼中，在任務計劃運行后由（此處為）ExecuteEntryUnsafe呼叫。我嘗試了一個基本的自定義調度程式，在這種情況下，呼叫的方法帶有一些額外的安全性以防止雙重呼叫。但解釋仍然有效。免責宣告：我與斯蒂芬·克利里（Stephen Cleary）這樣的人的聲譽或知識相去甚遠，因此請謹慎回答。如果這不正確，我將洗掉它。TaskSchedulerThreadPoolTaskSchedulerExecuteEntry()

//---------
// Task.cs
//---------

internal void ExecuteEntryUnsafe(Thread? threadPoolThread)
{
    // [SOURCE comment] Remember that we started running the task delegate
    // This is what actually makes the status show as Running (see source):
    // ...
    // int sf = m_stateFlags;
    // 
    // if ((sf & TASK_STATE_FAULTED) != 0) rval = TaskStatus.Faulted;
    // else if ((sf & TASK_STATE_CANCELED) != 0) rval = TaskStatus.Canceled;
    // else if ((sf & TASK_STATE_RAN_TO_COMPLETION) != 0) rval = TaskStatus.RanToCompletion;
    // else if ((sf & TASK_STATE_WAITING_ON_CHILDREN) != 0) rval = TaskStatus.WaitingForChildrenToComplete;
    // else if ((sf & TASK_STATE_DELEGATE_INVOKED) != 0) rval = TaskStatus.Running; <-- here
    // ...

    m_stateFlags |= (int)TaskStateFlags.DelegateInvoked;

    // *** 
    // On your machine, execution probably switches back to main thread for a fraction of a second here.
    // Hence one of your WriteLines outputs "Running". But this means "delegate was invoked", not necessarily "code is executing".
    // On my machine this does not happen, so I do not see Running status.
    // *** 

    if (!IsCancellationRequested & !IsCanceled)
    {
        ExecuteWithThreadLocal(ref t_currentTask, threadPoolThread);
    }
    else
    {
        // As Cancellation is requested this will be executed, even if IsCancelled is false.
        ExecuteEntryCancellationRequestedOrCanceled(); 
    }
}

// ...

internal void ExecuteEntryCancellationRequestedOrCanceled()
{
    // If Task is cancelled; this is different that "is cancellation requested". So this block is executed.
    if (!IsCanceled) 
    {
        // Set Cancelled flag.
        int prevState = Interlocked.Exchange(ref m_stateFlags, m_stateFlags | (int)TaskStateFlags.Canceled);

        // If previous state was not yet Cancelled, perform some cleanup.
        if ((prevState & (int)TaskStateFlags.Canceled) == 0)
        {
            CancellationCleanupLogic();
        }
    }
}

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