This snippet is from the file _baseoverlappedasyncresult.cs in the SSCLI project (aka Rotor). This function is used in the Base Class Library of the .NET Framework.

private void InternalFree()
{
    m_Overlapped = null;
    m_PinnedObjects = null;

    if (m_NativeOverlapped != IntPtr.Zero)
    {
        unsafe
        {
            Overlapped.Free((NativeOverlapped*) m_NativeOverlapped);
        }
        m_NativeOverlapped = IntPtr.Zero;
    }
}

In this snippet is a bug that eluded Microsoft's many static analysis tools (RaceTrack, Spec#, etc). See if you can find it.