/// <summary>
/// Helper method to construct an asyncResult object and use it to
/// call NativeControl(). Called by BeginAsyncControl().
/// </summary>
private static DeviceAsyncResult <T> AsyncControl <T>(
SafeFileHandle device,
int controlCode,
T outBuffer,
AsyncCallback asyncCallback,
object state
)
{
SafePinnedObject outDeviceBuffer = null;
if (outBuffer != null)
{
outDeviceBuffer = new SafePinnedObject(outBuffer);
}
// Create the async result object
DeviceAsyncResult <T> asyncResult = new DeviceAsyncResult <T>(outDeviceBuffer,
asyncCallback,
state
);
unsafe
{
uint bytesReturned = 0;
NativeAsyncControl(device,
controlCode,
outDeviceBuffer,
ref bytesReturned,
asyncResult.GetNativeOverlapped()
);
}
return(asyncResult);
}
/// <summary>
/// Method to initiate an ASYNCHRONOUS device I/O control operation to
/// get a packet from the driver, whenever it may arrive.
///
/// The device handle MUST have been opened with the async option set
/// to TRUE prior to calling this method.
/// </summary>
/// <returns></returns>
public static IAsyncResult BeginGetPacketFromDriverAsync <TResult>(
SafeFileHandle device,
int controlCode,
Int32 maxElements,
AsyncCallback asyncCallback,
object state
)
{
// Error checking
if (device == null)
{
throw new InvalidEnumArgumentException("Device handle was null");
}
if (maxElements > 1280)
{
return(null);
}
// Construct the output buffer; that is, the packet. Shouldn't be
// more than 1280 bytes or the driver will reject the request.
byte[] packet = new byte[maxElements];
DeviceAsyncResult <byte[]> asyncResult = AsyncControl(device,
controlCode,
packet,
asyncCallback,
state
);
return(asyncResult);
}
/// <summary>
/// Ends asynchronous device I/O control operation to get a packet from
/// the driver.
///
/// The reciprocal of BeginGetPacketFromDriverAsync().
/// </summary>
/// <param name="result"></param>
public static byte[] EndGetPacketFromDriverAsync <TResult>(
IAsyncResult result
)
{
DeviceAsyncResult <byte[]> asyncResult = (DeviceAsyncResult <byte[]>)result;
byte[] packet = asyncResult.EndInvoke();
return(packet);
}
