Re: the best practise of udpchannel with selector??

From:
lightning <huang.lightning@gmail.com>
Newsgroups:
comp.lang.java.programmer
Date:
Tue, 19 Feb 2008 17:37:31 -0800 (PST)
Message-ID:
<d0da5351-756c-4183-8793-dd0aa65ea967@k2g2000hse.googlegroups.com>
Ok, I wrote the code like this:

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.DatagramChannel;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.util.Iterator;
import java.util.concurrent.ConcurrentLinkedQueue;

public class UDPSender implements Runnable {
    private Thread thread;

    private boolean run;

    private DatagramChannel channel;

    private Selector selector;
    private SelectionKey mykey;
    private ConcurrentLinkedQueue<String> queue = new
ConcurrentLinkedQueue<String>();

    private String ip = "192.168.43.158";

    private int port = 2222;

    public UDPSender() {
        run = true;
        try {
            channel = DatagramChannel.open();
            channel.configureBlocking(false);
            selector = Selector.open();
            mykey=channel.register(selector, SelectionKey.OP_READ|
SelectionKey.OP_WRITE);
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            throw new InstantiationError();
        }
    }

    public void start() {
        thread = new Thread(this);
        thread.start();
    }
    public void send(){
        queue.add("sadfasdf");
        selector.wakeup();
    }
    public void run() {
        // TODO Auto-generated method stub
        try {
            while (run) {
                if(!queue.isEmpty()){
                    mykey.interestOps(SelectionKey.OP_READ|SelectionKey.OP_WRITE);
                }
                selector.select();
                Iterator<SelectionKey> iter = selector.selectedKeys()
                        .iterator();
                while (iter.hasNext()) {
                    SelectionKey key = iter.next();
                    handle(key);
                    iter.remove();
                }

            }
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }

    private void handle(SelectionKey key) {
        if (key.isReadable()) {
            System.out.println("there are something to read");
            ByteBuffer k=ByteBuffer.allocate(1000);
            try {
                channel.receive(k);
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            System.out.println("received: --"+new String(k.array(),
0,k.position())+"--");
        }
        if (key.isWritable()) {
            ByteBuffer x = ByteBuffer.wrap("hello".getBytes());
            Iterator<String> iter = queue.iterator();
            while (iter.hasNext()) {
                System.out.println("I send!");
                String k=iter.next();
                try {
                    channel.send(x, new InetSocketAddress(ip, port));
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
            queue.clear();
            key.interestOps(SelectionKey.OP_READ);
        }
    }

    public void stop() {
        run = false;
        selector.wakeup();
    }

}

It seems the code works well, are there any more suggestions?? thx!

On 2=D4 19=C8=D5, =CF =CE=E73=CA=B113=B7=D6, EJP <esmond.not.p...@not.bi=
gpond.com> wrote:

lightning wrote:

It seems that udpchannel is always writable


Almost always, unless the socket send buffer is full. You shouldn't
normally register for OP_WRITE unless you've had a short write: in the
case of UPD, that would be a write() return of zero. If you get that,
queue the datagram, register for OP_WRITE, and when you get OP_WRITE,
unqueue the datagrams in the queue and try to send them all. If you
succeed, unregister OP_WRITE again.

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