wpf - 查询 Dispatcher 队列长度

Question

我正在尝试分析 UI 线程的使用情况。是否可以查询调度程序排队的项目数？

更新：克莱门斯的回答完美无缺，但是因为我想在 UI 启动后开始它，而且我只关心每秒对数据进行一次采样，所以我使用以下代码......

        int queueLength = 0;
        var currentDispatcher = Dispatcher.CurrentDispatcher;
        currentDispatcher.Hooks.OperationPosted += (s, e) => Interlocked.Increment(ref queueLength);
        currentDispatcher.Hooks.OperationCompleted += (s, e) => Interlocked.Decrement(ref queueLength);
        currentDispatcher.Hooks.OperationAborted += (s, e) => Interlocked.Decrement(ref queueLength);
        Observable
            .Interval(TimeSpan.FromSeconds(1))
            .Subscribe(x =>
                           {
                               int currentQueueLength = queueLength;
                               if (currentQueueLength < 0)
                               {
                                   Interlocked.Add(ref queueLength, currentQueueLength * -1);
                               }
                               UiQueueLength = queueLength;
                           });

Answer 1

Afaik 没有可以直接询问调度程序队列长度的属性或方法。但是，您可以将处理程序附加到Hooks属性提供的某些DispatcherHooks事件。

var queueLength = 0;
Dispatcher.Hooks.OperationPosted += (o, e) => Interlocked.Increment(ref queueLength);
Dispatcher.Hooks.OperationStarted += (o, e) => Interlocked.Decrement(ref queueLength);
Dispatcher.Hooks.OperationAborted += (o, e) => Interlocked.Decrement(ref queueLength);

---

如果您只对 Dispatcher 是否处于活动状态感兴趣，您可能只需将OperationPosted事件与DispatcherInactive一起处理。

Answer 2

l感谢以上，这里有一个类来完成这项工作：

/*
 This is for when you want to know the depth of the Dispatcher Queue an perhaps modifiy the behaviour of
 code to minimize impact like when data is comming into a TextBox faster that it can cope with.
  
 Usage:
 in MainWindow
 public DispatcherQueueLength dispatcherQueueLengthHelper;
 dispatcherQueueLengthHelper = new DispatcherQueueLength(App.Current.Dispatcher);
 dispatcherQueueLengthHelper.StartDispatcherHooks();
 in Loaded
 dispatcherQueueLengthHelper.StartUpdateTimer(new TimeSpan(0,0,0,1,0), DispatcherPriority.Send, () =>
    {
          App.mainVM.LblQueueCountContent = "UI Queue Count ~ " + dispatcherQueueLengthHelper.GetQueueLength.ToString("N0");
    });
 in Closing
 dispatcherQueueLengthHelper.EndDispatcherHooks();
 dispatcherQueueLengthHelper.EndUpdateTimer();
*/

public class DispatcherQueueLength
{
    private static int _queueLenth = 0;
    private Dispatcher _dispatcher = null;
    private DispatcherTimer _dispatcherTimer = null;

    /// <summary>
    /// Usually pass in App.Current.Dispatcher
    /// </summary>
    /// <param name="passedDispatcher"></param>
    public DispatcherQueueLength(Dispatcher passedDispatcher)
    {
        _dispatcher = passedDispatcher;

    }

    
    /// <summary>
    /// Call as needed. It is possible to have a negative number like when pending Dispatches exist
    /// when starting the class, they are zeroed out.
    /// </summary>
    public int GetQueueLength
    {
        get 
        {
            int currentQueueLength = _queueLenth;
            if (currentQueueLength < 0)
            {
                Interlocked.Add(ref _queueLenth, currentQueueLength * -1); //this zeros it
            }

            return currentQueueLength;
        }
    }


    /// <summary>
    /// Call directly after instantiating the class
    /// </summary>
    public void StartDispatcherHooks()
    {
        if (_dispatcher != null)
        {
            _dispatcher.Hooks.OperationPosted += (s, e) =>
            {
                Interlocked.Increment(ref _queueLenth);
                Debug.WriteLine("Queue Length: " + _queueLenth.ToString());
            };
            _dispatcher.Hooks.OperationCompleted += (s, e) =>
            {
                Interlocked.Decrement(ref _queueLenth);
            };
            _dispatcher.Hooks.OperationAborted += (s, e) =>
            {
                Interlocked.Decrement(ref _queueLenth);
            };
        }
    }

    /// <summary>
    /// You pass in the code you want run on each interval
    /// </summary>
    /// <param name="ts"></param>
    /// <param name="priority"></param>
    /// <param name="action"></param>
    public void StartUpdateTimer(TimeSpan ts, DispatcherPriority priority, Action action)
    {
        if(_dispatcherTimer == null)
        {
            _dispatcherTimer = new DispatcherTimer(priority);
            _dispatcherTimer.Tick += (s,e) => { action(); };
            _dispatcherTimer.Interval = ts;
            _dispatcherTimer.IsEnabled = true;
        }

    }

    /// <summary>
    /// Call in MainWindow Closing
    /// </summary>
    public void EndDispatcherHooks()
    {
        if(_dispatcher != null)
        {
            _dispatcher.Hooks.OperationPosted -= (s, e) => Interlocked.Increment(ref _queueLenth);
            _dispatcher.Hooks.OperationCompleted -= (s, e) => Interlocked.Decrement(ref _queueLenth);
            _dispatcher.Hooks.OperationAborted -= (s, e) => Interlocked.Decrement(ref _queueLenth);
        }
       
    }

    //Call in MainWindow Closing or if no longer needed
    public void EndUpdateTimer()
    {
        _dispatcherTimer.Stop();
        _dispatcher = null;

    }


}