Overlapped.AsyncResult 即使在操作成功完成后也不会改变

Question

为了与 HID 设备通信，我使用了 kernel32 中的一些函数。代码是从 Microchip MLA 自定义 HID 设备项目中借用的。它使用阻塞方法。

我发现我可以使这些方法异步。这是我尝试进行异步写入的方法：

//...

internal const uint FILE_FLAG_OVERLAPPED = 0x40000000;
//...

[DllImport("kernel32.dll", SetLastError = true, CharSet = CharSet.Unicode)]
private static extern bool ReadFile(
    SafeFileHandle hFile,
    IntPtr lpBuffer,
    uint nNumberOfBytesToRead,
    ref uint lpNumberOfBytesRead,
    Overlapped lpOverlapped);        // Formerly: IntPtr lpOverlapped);
//...

WriteHandleToUSBDevice = CreateFile(DevicePath, GENERIC_WRITE, FILE_SHARE_READ | FILE_SHARE_WRITE, IntPtr.Zero,
    OPEN_EXISTING, FILE_FLAG_OVERLAPPED, IntPtr.Zero);    // Formerly: 0 instead of FILE_FLAG_OVERLAPPED
//...

Overlapped OL = new Overlapped();
WriteFile(WriteHandleToUSBDevice, OUTBuffer, 65, ref BytesWritten, OL);    // Formerly: IntPtr.Zero instead of OL
//Some code to run while write operation is in progress asynchronously...
while (OL.AsyncResult == null) ;    // Wait until write is completed; waits forever.

您可以在 Microchip MLA 自定义 HID 设备项目中找到完整代码。
OL.AsyncResult 虽然写入成功完成，但仍然为空；我敢肯定，因为设备可以正确接收数据和响应。我的代码有什么问题？

Answer 1

感谢 Gserg 的评论，我找到了比使用 kernel32 C++ 样式函数更好的解决方案：

SafeFileHandle HandleToUSBDevice = CreateFile(DevicePath, GENERIC_READ | GENERIC_WRITE,
        FILE_SHARE_READ | FILE_SHARE_WRITE, IntPtr.Zero, OPEN_EXISTING, FILE_FLAG_OVERLAPPED,
        IntPtr.Zero);

FileStream HID = new FileStream(HandleToUSBDevice, FileAccess.ReadWrite, (int)(PacketSize + 1), true);


Task WriteTask = Task.Factory.StartNew(() => HID.Write(OUTBuffer, 0, 65));
//Some Code
if (!WriteTask.Wait(2500)) throw new TimeoutException("Failed to send data within 2.5s timeout.");

如果您的 .Net 框架目标高于 4.5，您可以使用 async/await 和 WriteAsync。

我可以使用 ReadFile 而不是 HID.Write，但关闭句柄会更难。此外，使用托管 C# 方法优于导入和使用非托管 C++ 函数。

编辑： 我还为 BeginRead 添加了一个代码：

IAsyncResult result = HID.BeginRead(INBuffer, 0, 65, null, null);
while (FavoriteCondition)
{
    MethodWhichShouldBeCalledRepeatedly();
    if (result.IsCompleted)
    {
        ProcessData(INBuffer);
    }
}

Overlapped.AsyncResult 即使在操作成功完成后也不会改变

Overlapped.AsyncResult doesn't change even after operation completed successfully

c#

kernel32

overlapped-io