Csharp 为什么任务需要在内部使用ManualResetEventSlim

根据Task https://source.dot.net/#System.Private.CoreLib/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/Task.cs,1483的源代码

因此Task在内部使用ManualResetEventSlim内核同步 struct

internal ManualResetEventSlim CompletedEvent
{
    get
    {
        ContingentProperties contingentProps = EnsureContingentPropertiesInitialized();
        if (contingentProps.m_completionEvent == null)
        {
            bool wasCompleted = IsCompleted;
            ManualResetEventSlim newMre = new ManualResetEventSlim(wasCompleted);  // <----------------
            if (Interlocked.CompareExchange(ref contingentProps.m_completionEvent, newMre, null) != null)
            {
                // Someone else already set the value, so we will just close the event right away.
                newMre.Dispose();
            }
            else if (!wasCompleted && IsCompleted)
            {
                // We published the event as unset, but the task has subsequently completed.
                // Set the event's state properly so that callers don't deadlock.
                ContingentProperties.SetEvent(newMre);
            }
        }

        return contingentProps.m_completionEvent;
    }
}

但是，运行任务难道不意味着线程池将"工作项"(在高级中表示为任务)放到全局/本地队列中，然后它将被工作线程拾取来运行吗？是否需要使用任何内核线程同步构造？我的意思是它与谁同步？这里使用内核构造的目的是什么？