Re: won't work on MacOS X (JVM 1.6.0_05)

Owen Jacobson <>
Thu, 31 Jul 2008 09:54:30 -0700 (PDT)
On Jul 31, 12:01 pm, Sebastian Staudt <> wrote:


I have a problem with a call.
I'm using a DatagramChannel for server queries (i.e. client sends
request, server sends response).
After sending a request, I wait for the response with select(). The
DatagramChannel is registered with OP_READ.
Everything works fine on Linux and Windows, but on MacOS X select()
always returns 0. select() always times out or blocks infinetly
(depending on timeout argument). Wireshark shows that the request goes
out and the response is received successfully, but the Selector won't

Thanks for your help.

Without seeing the code, it's going to be very difficult to offer a
useful suggestion. A demo program, included below, does not
demonstrate the bug.

import java.nio.ByteBuffer;
import java.nio.channels.DatagramChannel;
import java.nio.channels.SelectableChannel;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.util.Iterator;
import java.util.Set;

public class DatagramSelectDemo {
    public static void main(String[] args) throws IOException {
        Selector s =;
        try {
            DatagramChannel dgc =;
            try {
                dgc.socket().bind(new InetSocketAddress(2600));
                dgc.register(s, SelectionKey.OP_READ);

                while (true) {

                    Set<SelectionKey> keys = s.selectedKeys();
                    for (Iterator<SelectionKey> i = keys.iterator();
i.hasNext();) {
                        SelectionKey key =;

                        if (key.isReadable()) {
                            SelectableChannel channel =;
                            if (channel == dgc) {
                                ByteBuffer buffer =
                                SocketAddress source =
                                        "Received %d bytes from %s\n",
                                        buffer.position(), source);

            } finally {
        } finally {

Sending messages to this with nc -u hostname 2600 triggers appropriate
"Received 16 bytes from /" messages.


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