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我用 USB 编程了一个微控制器，并使用 WinUSB 将它连接到 PC。我能够在 c++ 和 VB.NET 中使用 pinvoke 与同步（阻塞，重叠 = NULL）调用与我的 uC 通信。我刚刚在 c++ 中进行了异步调用，但我不知道如何在 .NET 中对其进行编码，还有另一个我不确定的问题：

问题 1：在 c++ 中，我最初尝试使用 IO Completion Callback Objects 进行异步调用，但是当我调用 WinUSB 读取它时返回一个错误，即异步 IO 已在文件句柄（HANDLE hDevice）上进行，CreateThreadpoolIo 不会使用 WinUSB 句柄（ PWINUSB_INTERFACE_HANDLE hWinUsbHandle)。我的猜测是 WinUSB 将此文件句柄用于 IO，所以我不能。我最终使用等待回调对象让它工作。它现在正在工作，我只想澄清我所做的是正确的用法。

我有点困惑的部分是 CreateThreadpoolWait 调用。起初我认为这是像 MSDN 中的其他示例一样创建一个线程池，但是我认为现在它只是一个在默认线程池上运行的对象。此外，objConext 是用于将调用与其回调同步的变量，即回调中的 PVOID Context 指向 objConext。

这是c代码片段：

// Receive data asynchronously
void BeginReceiveData(UCHAR bytPipeId, UCHAR *bytData, ULONG intLength, PTP_WAIT_CALLBACK cbCallback)
{
    // Create the event
    HANDLE hEventCallback = CreateEvent(NULL, FALSE, FALSE, NULL);

    // Check for an error
    if (!hEventCallback)
    {
        // Set the error
        printf(strError, "Error creating callback event: %d.", GetLastError());
    }

    // Create the thread pool wait object
    tpWait = CreateThreadpoolWait(cbCallback, &objConext, NULL);

    // Check for an error
    if (!tpWait)
    {
        // Set the error
        printf(strError, "Error creating thread pool: %d.", GetLastError());
    }

    // Place the wait object in the thread pool
    SetThreadpoolWait(tpWait, hEventCallback, NULL);

    // Clear the callback
    ZeroMemory(&oCallback, sizeof(oCallback));

    // Set the event
    oCallback.hEvent = hEventCallback;

    // Read
    BOOL bResult = WinUsb_ReadPipe(*hWinUsbHandle, bytPipeId, bytData, intLength, NULL, &oCallback);

    // Check for an error
    if (!bResult)
    {
        if (GetLastError() != ERROR_IO_PENDING)
        {
            // Set the error
            printf(strError, "Error reading pipe: %d.", GetLastError());
        }
    }
}

// Receive data callback
void CALLBACK UsbCallback(PTP_CALLBACK_INSTANCE Instance, PVOID Context, PTP_WAIT Wait, TP_WAIT_RESULT WaitResult)
{
}

问题2：如何将上述转换为.NET？到目前为止，这是我的猜测：

    Dim wait As New WaitCallback(AddressOf UsbCallback)

    ' Create the event
    Dim eEventCallback As New AutoResetEvent(False)

    ThreadPool.QueueUserWorkItem(wait, Nothing)

    Dim oCallback As New Overlapped(0, 0, eEventCallback.SafeWaitHandle.DangerousGetHandle, Nothing)

    'Dim oCallback As New NativeOverlapped

    oCallback.EventHandleIntPtr = eEventCallback.SafeWaitHandle.DangerousGetHandle

    ' Read
    Dim bResult As Boolean = WinUsb_ReadPipe(hWinUsbHandle, bytPipeId, bytData, intLength, intLength, oCallback.EventHandleIntPtr)

<DllImport("winusb.dll", SetLastError:=True, CharSet:=CharSet.Auto)>
        Public Function WinUsb_ReadPipe(InterfaceHandle As IntPtr, PipeID As Byte, Buffer() As Byte, BufferLength As UInteger, ByRef LengthTransferred As UInteger, Overlapped As IntPtr) As Boolean
        End Function

编辑：我打算发布作为答案，但我没有足够的街头信誉

好吧，我有办法将代码转换为 .NET。我设法将所有 API 函数转换为 PInvoke，然后替换了 .NET 中内置的那些，除了一对。代码可以工作，但必须注意变量的声明位置，因为 GC 会在进行回调之前清理它们。此外，必须仔细分配和销毁上下文。例如，如果没有分配正确大小的内存，则可能会清理上下文结构中的数组，这很容易理解。

由于这些原因，将句柄引用保留在 USB 中每个管道的对象中并重用它们可能更有益，因为在前一个管道完成之前无法对同一个管道进行多次调用。如果这样做了，那么您可以对上下文执行相同的操作，并避免为上下文分配和销毁内存。例如，可以在回调中的等待指针上使用字典：

Dim dicHandlesAndContext As Dictionary(Of IntPtr, HandlesAndContext)

虽然我还没有真正找到问题 1 的答案：无论这是否是“正确”的做法，但它似乎表现得相当不错。以下是主要代码片段：

' Receive data asynchronously
    Private Sub BeginReceiveData(bytPipeId As Byte, bytData() As Byte, intLength As UInteger)
        ' Allocate memory for the callback
        ptrContext = Marshal.AllocHGlobal(Marshal.SizeOf(GetType(TestContext)))

        ' Copy the structure to memory
        Marshal.StructureToPtr(objConext, ptrContext, True)


        ' Create the callback
        cbCallback = New UsbCallbackDelegate(AddressOf UsbCallback)


        ' Create the event
        Dim areEvent As New AutoResetEvent(False)

        ' Set the event
        hEventCallback = areEvent.SafeWaitHandle.DangerousGetHandle

        ' Create the thread pool wait object
        tpWait = CreateThreadpoolWait(Marshal.GetFunctionPointerForDelegate(cbCallback), ptrContext, IntPtr.Zero)

        ' Place the wait object in the thread pool
        SetThreadpoolWait(tpWait, hEventCallback, IntPtr.Zero)

        ' Set the event
        oCallback.EventHandle = hEventCallback

        ' Read
        Dim bResult As Boolean = WinUsb_ReadPipe(hWinUsbHandle, bytPipeId, bytData, intLength, intLength, oCallback)

        If Not bResult Then
            If Not Marshal.GetLastWin32Error = 997 Then
                ' Get the error
                Dim intError As Integer = Marshal.GetLastWin32Error

                Throw New Win32Exception(intError, "Error getting device information.")
            End If
        End If
    End Sub

    ' Delegate for USB callbacks
    Private Delegate Sub UsbCallbackDelegate(Instance As IntPtr, Context As IntPtr, Wait As IntPtr, WaitResult As UInteger)

    ' Callback
    Private Sub UsbCallback(Instance As IntPtr, Context As IntPtr, Wait As IntPtr, WaitResult As UInteger)
        ' Number of bytes transferred
        Dim intTransferred As UInteger

        ' Get the number of bytes transferred
        WinUsb_GetOverlappedResult(hWinUsbHandle, oCallback, intTransferred, False)

        ' Get the context from memory
        Dim objConext As TestContext = Marshal.PtrToStructure(Context, GetType(TestContext))

        ' Free the memory
        Marshal.FreeHGlobal(Context)


        ' Do some work on the data


End Sub

主要 API DLL 导入

<DllImport("winusb.dll", SetLastError:=True, CharSet:=CharSet.Auto)>
        Public Function WinUsb_GetOverlappedResult(InterfaceHandle As IntPtr, ByRef lpOverlapped As Threading.NativeOverlapped, ByRef lpNumberOfBytesTransferred As UInteger, bWait As Boolean) As IntPtr
        End Function

        <DllImport("kernel32.dll", SetLastError:=True, CharSet:=CharSet.Auto)>
        Public Function CreateThreadpoolWait(pfnwa As IntPtr, pv As IntPtr, pcbe As IntPtr) As IntPtr
        End Function

        <DllImport("kernel32.dll", SetLastError:=True, CharSet:=CharSet.Auto)>
        Public Function SetThreadpoolWait(pwa As IntPtr, h As IntPtr, pftTimeout As IntPtr) As IntPtr
        End Function

        <DllImport("kernel32.dll", SetLastError:=True, CharSet:=CharSet.Auto)>
        Public Function CloseThreadpoolWait(pwa As IntPtr) As IntPtr
        End Function

我通过连续接收数据并同时运行GC来测试这些功能的GC保护，如果收集到东西，程序会崩溃。

' Receive data asynchronously on endpoint 1
    BeginReceiveData(129, bytData, 8)

    While True
    ' Garbage collection
        GC.Collect()
        GC.WaitForFullGCComplete()
    End While


    ' Callback
    Private Sub UsbCallback(Instance As IntPtr, Context As IntPtr, Wait As IntPtr, WaitResult As UInteger)
        ' ...
        ' Once data is received, receive more
        BeginReceiveData(129, bytData, 8)
        '...
    End Sub

警告：这里没有很多清理代码，请查看 MSDN 中的 c 代码以了解如何正确执行此操作。我认为面向对象的方法可能最好让句柄保持活动状态并实现 IDIsposable 以在完成后进行清理。

有人对开源 DLL 感兴趣吗？:P

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