DatagramChannel.close() keeps port open on Windows

Question

I\'m implementing a Discover process that:

• Open a UDP socket to listen for broadcast response on a given port
• Send some requests (and expect later respons

Answer 1

Some parts of a channel close are deferred to the next select() if the channel is registered with a Selector. It is documented somewhere in the forest of Selector, AbstractSelector, SelectorSpi, SelectableChannel, AbstractSelectableChannel, where I can never find it when I need it. If you're within the select loop and thread when you close the channel, you can make it immediate by calling selectNow().

Answer 2

I did get some errors but the socket get closed properly... which is oki for my needs

No, in case you've got errors your channel is NOT closed properly.

You have to do close in the finally clause of your try block.

Selector selector = Selector.open();
try
{
  DatagramChannel channel = DatagramChannel.open();

  try
  {
    channel.configureBlocking(true);
    channel.socket().bind(
      new InetSocketAddress(InetAddress.getLocalHost(), 9005)
    );
    SelectionKey clientKey = channel.register(selector, SelectionKey.OP_READ);
    clientKey.cancel();
  }
  finally
  {
    channel.close();
  }
}
finally
{
  selector.close( )
}