Implementing a ReadFile with a timeout inducing too much CPU ussage

问题

I use kernel32.dll ReadFile to read the HID output of a connected device. I wanted to create a timeout because this call is a blocking method and if it hangs for any reason the main loop in my application also hangs.

    [DllImport("kernel32.dll", SetLastError = true)]
    static internal extern bool ReadFile(IntPtr hFile, [Out] byte[] lpBuffer, uint nNumberOfBytesToRead, out uint lpNumberOfBytesRead, IntPtr lpOverlapped);

    public static HidLibrary.HidDeviceData.ReadStatus FastReadWithTimeout(this HidLibrary.HidDevice device, byte[] inputBuffer, int timeout)
    {
        return FastReadWithTimeoutWorker(device, inputBuffer, timeout).GetAwaiter().GetResult();
    }

    private static async Task<HidLibrary.HidDeviceData.ReadStatus> FastReadWithTimeoutWorker(HidLibrary.HidDevice device, byte[] inputBuffer, int timeout)
    {
        var task = Task.Run(async () => {
            try
            {
                uint bytesRead;
                if (NativeMethods.ReadFile(device.Handle, inputBuffer, (uint)inputBuffer.Length, out bytesRead, IntPtr.Zero))
                {
                    return HidLibrary.HidDeviceData.ReadStatus.Success;
                }
                else
                {
                    return HidLibrary.HidDeviceData.ReadStatus.NoDataRead;
                }
            }
            catch (Exception)
            {
                return HidLibrary.HidDeviceData.ReadStatus.ReadError;
            }
        });
        if (await Task.WhenAny(task, Task.Delay(timeout)) == task)
        {
            return task.Result;
        }
        else
        {
            device.CancelIO();
            return HidLibrary.HidDeviceData.ReadStatus.WaitTimedOut;
        }
    }

The issue is my current method of doing this causing more CPU overhead than I can allow. Is there something wrong with the way I am doing this or is there a better way to implement a timeout in a native method?

I also just discovered SetCommTimeouts(), but am having trouble finding a working example of it, documentation is spotty.

来源：https://stackoverflow.com/questions/53362883/implementing-a-readfile-with-a-timeout-inducing-too-much-cpu-ussage

标签

readfile