即使在手术成功完成后，Overlapped.AsyncResult也不会改变

Question

为了与HID设备通信，我使用了来自kernel32的一些功能。代码是从微芯片MLA定制的HID设备项目中借来的。它使用阻塞方法。

我发现我可以使这些方法异步。下面是我尝试过的异步编写：

//...

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.

您可以在微芯片MLA定制HID设备项目中找到完整的代码。

OL.AsyncResult仍然是空的，尽管写已经成功完成；我确信，因为设备正确地接收数据和响应。我的代码有什么问题？

Answer 1

感谢Gserg的评论，我找到了一个比使用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async/await框架目标超过4.5，则可以使用.Net和WriteAsync。

我可以使用ReadFile而不是HID.Write，但是关闭句柄会更困难。此外，使用托管C#方法比导入和使用非托管C++函数更好。

编辑：我还为BeginRead添加了代码：

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