LibUsbDotNet:关闭了退出WPF应用程序安全句柄的错误

Question

在WPF应用程序中使用USB设备，我可以成功地连接和发送命令到设备。设备只接收命令，没有回复，所以我所需要的只是一个EndpointWriter来与它通信。

MyUsbFinder = new UsbDeviceFinder(vid, pid);
MyUsbDevice = UsbDevice.OpenUsbDevice(MyUsbFinder);
wholeUsbDevice = MyUsbDevice as IUsbDevice;
if (!ReferenceEquals(wholeUsbDevice, null))
{
    wholeUsbDevice.SetConfiguration(1);
    wholeUsbDevice.ClaimInterface(0);
}

writer = MyUsbDevice.OpenEndpointWriter(WriteEndpointID.Ep01);

然后是写入设备的过程：

byte[] update = { some bytes };
int bytesWritten;

if (MyUsbDevice != null)
{
     ec = writer.Write(update, 2000, out bytesWritten);
}

所有工作都很好，包括关闭应用程序，除非在工作过程中USB设备断开，然后重新连接。应用程序成功地处理此场景并重新连接到设备，并继续成功地向其发送命令：

public bool reconnect()
{
    //clear the info so far
    if (MyUsbDevice != null)
    {
        writer.Dispose();
        wholeUsbDevice.ReleaseInterface(0);
        wholeUsbDevice.Close();
        MyUsbDevice.Close();
        UsbDevice.Exit();
    }

    //now start over
    MyUsbFinder = new UsbDeviceFinder(vid, pid);
    MyUsbDevice = UsbDevice.OpenUsbDevice(MyUsbFinder);

..。以此类推。

在发生这种断开/重新连接之后，当我关闭应用程序时会发生问题。虽然该程序成功地工作并与设备进行了相当长时间的通信，但在退出时我得到了以下例外情况：

System.ObjectDisposedException was unhandled
  Message="Safe handle has been closed"
  Source="mscorlib"
  ObjectName=""
  StackTrace:
       at System.StubHelpers.StubHelpers.SafeHandleC2NHelper(Object pThis, IntPtr pCleanupWorkList)
       at LibUsbDotNet.Internal.Kernel32.GetOverlappedResult(SafeHandle hDevice, IntPtr lpOverlapped, Int32& lpNumberOfBytesTransferred, Boolean bWait)
       at LibUsbDotNet.Internal.LibUsb.LibUsbAPI.GetOverlappedResult(SafeHandle interfaceHandle, IntPtr pOverlapped, Int32& numberOfBytesTransferred, Boolean wait)
       at LibUsbDotNet.Internal.OverlappedTransferContext.Wait(Int32& transferredCount, Boolean cancel)
       at LibUsbDotNet.Main.UsbTransfer.Wait(Int32& transferredCount)
       at LibUsbDotNet.Main.UsbTransfer.Dispose()
       at LibUsbDotNet.Main.UsbTransfer.Finalize()
  InnerException: 

我在usb设备上尝试了许多不同的配置和退出方式，也就是端点程序，但到目前为止还没有成功。我假设一些东西在断开之前仍然是开放的，所以我得到了这个错误，但是我不知道它是什么，以及如何摆脱它。

因为只有在关闭应用程序时才会发生这种情况，我甚至不介意以某种方式忽略异常并让应用程序分片死亡，但我不知道如何捕获该异常，因为Window_Closing事件成功返回，然后异常发生，因此我无法捕获它……

任何小费都要感谢，谢谢！

Answer 1

在关闭我的WPF应用程序时，我也遇到了类似的问题：“安全句柄已关闭”ObjectDisposedException正在发生。

我的堆栈有点不同：

System.ObjectDisposedException was unhandled  
  HResult=-2146232798  
  Message=Safe handle has been closed  
  Source=mscorlib  
  ObjectName=""  
  StackTrace:  
       at System.Threading.WaitHandle.WaitOneNative(SafeHandle waitableSafeHandle, UInt32 millisecondsTimeout, Boolean hasThreadAffinity, Boolean exitContext)  
       at System.Threading.WaitHandle.InternalWaitOne(SafeHandle waitableSafeHandle, Int64 millisecondsTimeout, Boolean hasThreadAffinity, Boolean exitContext)  
       at System.Threading.WaitHandle.WaitOne(Int32 millisecondsTimeout, Boolean exitContext)  
       at LibUsbDotNet.Main.UsbTransfer.get_IsCancelled()  
       at LibUsbDotNet.Main.UsbTransfer.Dispose()  
       at LibUsbDotNet.Main.UsbTransfer.Finalize()  
  InnerException:

但是，通过在我的发送和接收函数中添加以下代码，我成功地修复了它。

using (UsbEndpointWriter writer = device.OpenEndpointWriter(WriteEndpoint))
{
    UsbTransfer usbTransfer = null;

    try
    {
        // Code to do transfer here .. not shown as not pertinent here..
    }
    finally
    {
        if (usbTransfer != null)
        {
            // **** Start of code added to fix ObjectDisposedException
            if (!usbTransfer.IsCancelled || !usbTransfer.IsCompleted)
            {
                usbTransfer.Cancel();
            }
            // **** End of code added to fix ObjectDisposedException
            usbTransfer.Dispose();
        }
    }
}

希望这个片段可以帮助其他人在解决问题的同时发现这个问题。

Answer 2

我在Windows服务中也收到了类似的异常。我的调用堆栈如下：

Exception Info: System.ObjectDisposedException
Stack:
   at System.Runtime.InteropServices.SafeHandle.DangerousAddRef(Boolean ByRef)
   at System.StubHelpers.StubHelpers.SafeHandleAddRef(System.Runtime.InteropServices.SafeHandle, Boolean ByRef)
   at LibUsbDotNet.Internal.Kernel32.GetOverlappedResult(System.Runtime.InteropServices.SafeHandle, IntPtr, Int32 ByRef, Boolean)
   at LibUsbDotNet.Internal.LibUsb.LibUsbAPI.GetOverlappedResult(System.Runtime.InteropServices.SafeHandle, IntPtr, Int32 ByRef, Boolean)
   at LibUsbDotNet.Internal.OverlappedTransferContext.Wait(Int32 ByRef, Boolean)
   at LibUsbDotNet.Main.UsbTransfer.Dispose()
   at LibUsbDotNet.Main.UsbTransfer.Finalize()

为了解决这个问题，我通过添加对LibUsbDotNet.Internal.LibUsb.LibUsbAPI.GetOverlappedResult()的检查来修正interfaceHandle.IsClosed方法。现在，该方法看起来如下：

public override bool GetOverlappedResult(SafeHandle interfaceHandle, IntPtr pOverlapped, out int numberOfBytesTransferred, bool wait)
{
    // To prevent ObjectDisposedException check if SafeHandle's been closed
    if (!interfaceHandle.IsClosed)
        return Kernel32.GetOverlappedResult(interfaceHandle, pOverlapped, out numberOfBytesTransferred, wait);
    else
    {
        numberOfBytesTransferred = 0;
        return true;
    }
}

希望能帮上忙。