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。
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。
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。
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)。
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。
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/