我有一个 C# windows 窗体应用程序，它通过 COM 端口与 USB dongle 通信。我使用 .Net 2.0 中的 SerialPort 类进行通信，并且串行端口对象在应用程序的生命周期内处于打开状态。应用程序向设备发送命令，也可以从设备接收未经请求的数据。

我的问题发生在窗体关闭时 - 我在尝试关闭 COM 端口时(不幸的是随机地)得到一个 ObjectDisposedException。这是 Windows 堆栈跟踪:

System.ObjectDisposedException was unhandled


Message=Safe handle has been closed
  Source=System
  ObjectName=""
  StackTrace:
       at Microsoft.Win32.UnsafeNativeMethods.SetCommMask(SafeFileHandle hFile, Int32 dwEvtMask)
       at System.IO.Ports.SerialStream.Dispose(Boolean disposing)
       at System.IO.Ports.SerialStream.Finalize()
  InnerException: 

我找到了有类似问题的人的帖子，并尝试了[此处][1] 的解决方法

[1]: http://zachsaw.blogspot.com/2010/07/net-serialport-woes.html尽管这是针对 IOException 的，但并没有解决问题。

我的Close()代码如下:

        public void Close()
    {
        try
        {
            Console.WriteLine("******ComPort.Close - baseStream.Close*******");
            baseStream.Close();
        }
        catch (Exception ex)
        {
            Console.WriteLine("******ComPort.Close baseStream.Close raised exception: " + ex + "*******");
        }
        try
        {
            _onDataReceived = null;
            Console.WriteLine("******ComPort.Close - _serialPort.Close*******");
            _serialPort.Close();
        }
        catch (Exception ex)
        {
            Console.WriteLine("******ComPort.Close - _serialPort.Close raised exception: " + ex + "*******");
        }            
    }

我的日志记录表明，执行从来没有超越尝试关闭 SerialPort 的 BaseStream(这是在第一个 try block 中)，所以我尝试删除这一行，但仍然定期抛出异常 -登录第二个 try block 出现然后异常发生。两个 catch block 都没有捕获异常。

有什么想法吗？

更新 - 添加全类:

    namespace My.Utilities
{
    public interface ISerialPortObserver
    {
        void SerialPortWriteException();
    }

    internal class ComPort : ISerialPort
    {
        private readonly ISerialPortObserver _observer;
        readonly SerialPort _serialPort;

        private DataReceivedDelegate _onDataReceived;
        public event DataReceivedDelegate OnDataReceived
        {
            add { lock (_dataReceivedLocker) { _onDataReceived += value; } }
            remove { lock (_dataReceivedLocker) { _onDataReceived -= value; } }            
        }

        private readonly object _dataReceivedLocker = new object();
        private readonly object _locker = new object();

        internal ComPort()
        {         
            _serialPort = new SerialPort { ReadTimeout = 10, WriteTimeout = 100, DtrEnable = true };
            _serialPort.DataReceived += DataReceived;
        }

        internal ComPort(ISerialPortObserver observer) : this()
        {
            _observer = observer;         
        }

        private void DataReceived(object sender, SerialDataReceivedEventArgs e)
        {
            DataReceivedDelegate temp = null;

            lock (_locker)
            {
                lock (_dataReceivedLocker)
                {
                    temp = _onDataReceived;
                }

                string dataReceived = string.Empty;
                var sp = (SerialPort) sender;

                try
                {
                    dataReceived = sp.ReadExisting();
                }
                catch (Exception ex)
                {
                    Logger.Log(TraceLevel.Error, "ComPort.DataReceived raised exception: " + ex);
                }

                if (null != temp && string.Empty != dataReceived)
                {
                    try
                    {
                        temp(dataReceived, TickProvider.GetTickCount());
                    }
                    catch (Exception ex)
                    {
                        Logger.Log(TraceLevel.Error, "ComPort.DataReceived raised exception calling handler: " + ex);
                    }
                }
            }
        }

        public string Port
        {
            set
            {
                try
                {
                    _serialPort.PortName = value;
                }
                catch (Exception ex)
                {
                    Logger.Log(TraceLevel.Error, "ComPort.Port raised exception: " + ex);
                }
            }
        }

        private System.IO.Stream comPortStream = null;
        public bool Open()
        {
            SetupSerialPortWithWorkaround();
            try
            {
                _serialPort.Open();
                comPortStream = _serialPort.BaseStream;
                return true;
            }
            catch (Exception ex)
            {
                Logger.Log(TraceLevel.Warning, "ComPort.Open raised exception: " + ex);
                return false;
            }
        }

        public bool IsOpen
        {
            get
            {
                SetupSerialPortWithWorkaround();
                try
                {
                    return _serialPort.IsOpen;
                }
                catch(Exception ex)
                {
                    Logger.Log(TraceLevel.Error, "ComPort.IsOpen raised exception: " + ex);
                }

                return false;
            }
        }

        internal virtual void SetupSerialPortWithWorkaround()
        {
            try
            {
                //http://zachsaw.blogspot.com/2010/07/net-serialport-woes.html
                // This class is meant to fix the problem in .Net that is causing the ObjectDisposedException.
                SerialPortFixer.Execute(_serialPort.PortName);
            }
            catch (Exception e)
            {
                Logger.Log(TraceLevel.Info, "Work around for .Net SerialPort object disposed exception failed with : " + e + " Will still attempt open port as normal");
            }
        }

        public void Close()
        {
            try
            {
                comPortStream.Close();
            }
            catch (Exception ex)
            {
                Logger.Log(TraceLevel.Error, "ComPortStream.Close raised exception: " + ex);
            }
            try
            {
                _onDataReceived = null;
                _serialPort.Close();
            }
            catch (Exception ex)
            {
                Logger.Log(TraceLevel.Error, "ComPort.Close raised exception: " + ex);
            }            
        }

        public void WriteData(string aData, DataReceivedDelegate handler)
        {
            try
            {
                OnDataReceived += handler;
                _serialPort.Write(aData + "\r\n");
            }
            catch (Exception ex)
            {
                Logger.Log(TraceLevel.Error, "ComPort.WriteData raised exception: " + ex);                

                if (null != _observer)
                {
                    _observer.SerialPortWriteException();
                }
            }
        }
    }    
}

最佳答案

注意:目前的发现仅在 Windows 7 上的 .NET Framework 4.0 32 位上进行了测试，如果它在其他版本上有效，请随时发表评论。

编辑: 长话短说: 这是解决方法的关键。请参阅下面的解释。 不要忘记使用 SerialPortFixer打开 SerialPort 时也是如此。 ILog 来自 log4net。

static readonly ILog s_Log = LogManager.GetType("SerialWorkaroundLogger");

static void SafeDisconnect(SerialPort port, Stream internalSerialStream)
{
    GC.SuppressFinalize(port);
    GC.SuppressFinalize(internalSerialStream);

    ShutdownEventLoopHandler(internalSerialStream);

    try
    {
        s_Log.DebugFormat("Disposing internal serial stream");
        internalSerialStream.Close();
    }
    catch (Exception ex)
    {
        s_Log.DebugFormat(
            "Exception in serial stream shutdown of port {0}: {1}", port.PortName, ex);
    }

    try
    {
        s_Log.DebugFormat("Disposing serial port");
        port.Close();
    }
    catch (Exception ex)
    {
        s_Log.DebugFormat("Exception in port {0} shutdown: {1}", port.PortName, ex);
    }
}

static void ShutdownEventLoopHandler(Stream internalSerialStream)
{
    try
    {
        s_Log.DebugFormat("Working around .NET SerialPort class Dispose bug");

        FieldInfo eventRunnerField = internalSerialStream.GetType()
            .GetField("eventRunner", BindingFlags.NonPublic | BindingFlags.Instance);

        if (eventRunnerField == null)
        {
            s_Log.WarnFormat(
                "Unable to find EventLoopRunner field. "
                + "SerialPort workaround failure. Application may crash after "
                + "disposing SerialPort unless .NET 1.1 unhandled exception "
                + "policy is enabled from the application's config file.");
        }
        else
        {
            object eventRunner = eventRunnerField.GetValue(internalSerialStream);
            Type eventRunnerType = eventRunner.GetType();

            FieldInfo endEventLoopFieldInfo = eventRunnerType.GetField(
                "endEventLoop", BindingFlags.Instance | BindingFlags.NonPublic);

            FieldInfo eventLoopEndedSignalFieldInfo = eventRunnerType.GetField(
                "eventLoopEndedSignal", BindingFlags.Instance | BindingFlags.NonPublic);

            FieldInfo waitCommEventWaitHandleFieldInfo = eventRunnerType.GetField(
                "waitCommEventWaitHandle", BindingFlags.Instance | BindingFlags.NonPublic);

            if (endEventLoopFieldInfo == null
                || eventLoopEndedSignalFieldInfo == null
                || waitCommEventWaitHandleFieldInfo == null)
            {
                s_Log.WarnFormat(
                    "Unable to find the EventLoopRunner internal wait handle or loop signal fields. "
                    + "SerialPort workaround failure. Application may crash after "
                    + "disposing SerialPort unless .NET 1.1 unhandled exception "
                    + "policy is enabled from the application's config file.");
            }
            else
            {
                s_Log.DebugFormat(
                    "Waiting for the SerialPort internal EventLoopRunner thread to finish...");

                var eventLoopEndedWaitHandle =
                    (WaitHandle)eventLoopEndedSignalFieldInfo.GetValue(eventRunner);
                var waitCommEventWaitHandle =
                    (ManualResetEvent)waitCommEventWaitHandleFieldInfo.GetValue(eventRunner);

                endEventLoopFieldInfo.SetValue(eventRunner, true);

                // Sometimes the event loop handler resets the wait handle
                // before exiting the loop and hangs (in case of USB disconnect)
                // In case it takes too long, brute-force it out of its wait by
                // setting the handle again.
                do
                {
                    waitCommEventWaitHandle.Set();
                } while (!eventLoopEndedWaitHandle.WaitOne(2000));

                s_Log.DebugFormat("Wait completed. Now it is safe to continue disposal.");
            }
        }
    }
    catch (Exception ex)
    {
        s_Log.ErrorFormat(
            "SerialPort workaround failure. Application may crash after "
            + "disposing SerialPort unless .NET 1.1 unhandled exception "
            + "policy is enabled from the application's config file: {0}",
            ex);
    }
}

我在最近的一个项目中为此苦苦挣扎了几天。

.NET SerialPort 类有许多不同的错误(到目前为止我已经看到)导致网络上所有令人头疼的问题。

1. 此处缺少 DCB 结构标志:http://zachsaw.blogspot.com/2010/07/net-serialport-woes.html 这一个由 SerialPortFixer 类修复，该功劳归作者所有。

2. 当移除 USB 串行设备时，关闭 SerialPortStream 时，会要求 eventLoopRunner 停止并且 SerialPort.IsOpen 返回 false。在处置时检查此属性并跳过关闭内部串行流，从而使原始句柄无限期地保持打开状态(直到终结器运行导致下一个问题)。

   这个解决方案是手动关闭内部串行流。我们可以在异常发生前通过 SerialPort.BaseStream 或者通过反射获取它的引用 并获取“internalSerialStream”字段。

3. 当 USB 串行设备被移除时，关闭内部串行流会引发异常并关闭内部句柄而不等待其 eventLoopRunner 线程完成，从而导致稍后在后台事件循环运行器线程中出现无法捕获的 ObjectDisposedException流的终结器运行(这奇怪地避免了抛出异常但仍然无法等待 eventLoopRunner)。

   这里的症状:https://connect.microsoft.com/VisualStudio/feedback/details/140018/serialport-crashes-after-disconnect-of-usb-com-port

   解决方案是手动要求事件循环运行器停止(通过反射)并在关闭内部串行流之前等待它完成。

4. 由于 Dispose 会抛出异常，因此不会抑制终结器。这很容易解决:

   GC.SuppressFinalize(端口); GC.SuppressFinalize(port.BaseStream);

这是一个包装串行端口并修复所有这些问题的类: http://pastebin.com/KmKEVzR8

有了这个变通类，就不需要恢复到 .NET 1.1 未处理的异常行为，而且它具有出色的稳定性。

这是我的第一个贡献，如果我做的不对，请原谅。我希望它对某人有所帮助。

关于c# - 在 .Net 2.0 中关闭 SerialPort 时出现 ObjectDisposedException，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/8927410/