DateTime.Now 随着时间的推移是否不一致？

Question

我的应用程序通过 UART 从总线记录电报。对于每封电报，我都会在接待处添加带有 DateTime.Now 的时间戳。现在我有这样的现象，有时下一个电报时间戳比之前的要低 100 毫秒。这太令人困惑了。

这是怎么发生的？我该如何预防？

这是我的代码：

private SerialPort port;

public void RegisterReceive()
        {
            ...
            port.DiscardOutBuffer();
            port.DiscardInBuffer();
            port.DataReceived += OnReceive;
            ....
        }

public static Mutex mutexReceivingCom = new Mutex();
        void OnReceive(object sender, SerialDataReceivedEventArgs args)
        {
            SerialPort port = sender as SerialPort;

            mutexReceivingCom.WaitOne();   // Wait until it is safe to enter. 

            if (data.AppIsRunning)
            {
                Byte by;
                try
                {
                    while (port.BytesToRead > 0)
                    {
                        by = (Byte)port.ReadByte();
                        mainWindow.Dispatcher.Invoke(() =>
                        {
                            General_HandleTelegram.Add_HandleTeleData_ByteToUartInBuffer(by);
                        });
                    }


                }
                catch (Exception ex)
                {
                    System.Windows.MessageBox.Show("SerialPort OnReceive Exception: " + ex.ToString());
                    //put other, more interesting error handling here.
                }
            }

            mutexReceivingCom.ReleaseMutex();    // Release the Mutex.

            ThreadPool.QueueUserWorkItem(handleReceivedBytes);
        }

private void handleReceivedBytes(object state)
        {
            mutexReceivingCom.WaitOne();   // Wait until it is safe to enter. 

            if (data.AppIsRunning)
            {
                try
                {
                    BusAnswerOrCyclic_Handling tempPack = null;

                    if (port.IsOpen)
                    {
                        tempPack = ReceiveTelegram(LastRecTelegramm, this);

                        while (tempPack != null)
                        {
                            mainWindow.Dispatcher.Invoke(() =>
                            {
                                if (tempPack != null)
                                    tempPack.ProcessBusTelegram();
                            });

                            if (tempPack != null)
                            {
                                LastRecTelegramm = tempPack;
                            }

                            if (port.IsOpen)
                            {
                                tempPack = ReceiveTelegram(LastRecTelegramm, this);
                            }
                            else
                                break;
                        }

                    }

                    CheckIfBufferCanBeReset();
                }
                catch (Exception ex)
                {
                    System.Windows.MessageBox.Show("Error ComPort.cs handleReceivedBytes: " + ex.Message);
                }

            }

            mutexReceivingCom.ReleaseMutex();    // Release the Mutex.
        }

然后

public BusAnswerOrCyclic_Handling ReceiveTelegram(BusAnswerOrCyclic_Handling parLastSendBusTelegram, ComPort comPort)
        {
...
pack= new BusAnswerOrCyclic_Handling(recState, CmdToAssignToReceivedTele, LastSendBusTelegram, fetchedByteList.ToArray(), Generic_HandleTelegrams.mainWindow, comPort, -1, ucTelTyp == enTelTyp.SynLine, true);
....

return pack;
        }


public BusAnswerOrCyclic_Handling(enRecStates recState, BusTelegram_Command command, BusAnswerOrCyclic_Handling LastBusTelegram, byte[] bytes, MainWindow mainWindow, 
            ComPort comPort, short iMasterByteCountWithCRC, bool isSynLine, bool isFullyReceived)
        {
            DateTime dt = DateTime.Now;
...
        }

同时

public void ProcessBusTelegram()
        {
           // adds it to the datalog

        }

我不明白下一个电报时间戳怎么会比上一个电报时间戳低？

查看我尝试过的代码

Answer 1

穿线。它总是线程。

你读到

DateTime.Now

已经很晚了，另一边却打电话给

ThreadPool.QueueUserWorkItem

。

ThreadPool.QueueUserWorkItem

不一定能保证被订购，无论如何你可能会遇到以下情况：

1. 您将消息 A 放入队列，然后将消息 B 放入队列
2. 线程 1 获取消息 A，然后被调度程序暂停
3. 线程 2 获取消息 B 并运行至完成（正在阅读

   DateTime.Now

   ）
4. 线程 1 恢复，并显示

   DateTime.Now

如果您关心接收字节的时间，请在执行任何类型的线程分派（

DateTime.Now

、

ThreadPool.QueueUserWorkItem

等）之前，在从串行端口读取字节时记录

mainWindow.Dispatcher.Invoke

.