class FChange::Notifier

def read_events
  # can return WAIT_TIMEOUT  = 0x00000102
  dwWaitStatus = Native.WaitForMultipleObjects(@dwChangeHandles.count, 
    @lp_dwChangeHandles, 0, 500)
  events = []
  # this call blocks all threads completely.
  @dwChangeHandles.each_index do |index|
    if dwWaitStatus == WAIT_OBJECT_0 + index
      ev = Event.new(@watchers[@dwChangeHandles[index]])
      events << ev
    
      r = Native.FindNextChangeNotification(@dwChangeHandles[index]) 
      if r == 0 
          raise SystemCallError.new("Failed to watch", r) 
      end
    end
  end
  events
end