C#异步操作样本1

OVERLAPPED overlapped;
overlapped.hEvent = CreateEvent(NULL, FALSE, FALSE, NULL);
fns.NotifyStateChange(&overlapped);
WaitForSingleObject(overlapped.hEvent, INFINITE);
// ...query for the new state or whatever...

[DllImport("myfuncs.dll")]
unsafe public static extern int NotifyStateChange(NativeOverlapped* lpOverlapped);

static private ManualResetEvent m_stateChangeEvent = new ManualResetEvent(false);

public static DeviceState WaitForStateChange()
{
unsafe
{
Overlapped overlapped = new Overlapped(0, 0,
m_stateChangeEvent.SafeWaitHandle.DangerousGetHandle(), null);
IOCompletionCallback callback = StateChangeCallback;
byte[] userData = new byte[100];
NativeOverlapped* nativeOverlapped = overlapped.Pack(callback, userData);
NotifyStateChange(nativeOverlapped);
m_stateChangeEvent.WaitOne();
Overlapped.Unpack(nativeOverlapped);
Overlapped.Free(nativeOverlapped);
}
return GetCurrentState();
}

[ComVisibleAttribute(true)]
unsafe static public void StateChangeCallback (
uint errorCode,
uint bytesTransferred,
NativeOverlapped* overlapped)
{
m_stateChangeEvent.Set();
}