具有非阻塞套接字的多线程

Question

I am trying to implement a TCP Server in Java using nio. Its simply using the Selector's select method to get the ready keys. And then processing those keys if they are acceptable, readable and so. Server is working just fine till im using a single thread. But when im trying to use more threads to process the keys, the server's response gets slowed and eventually stops responding, say after 4-5 requests. This is all what im doing:(Pseudo)

Iterator<SelectionKey> keyIterator =  selector.selectedKeys().iterator();
while (keyIterator.hasNext()) {
                SelectionKey readyKey = keyIterator.next();
                if (readyKey.isAcceptable()) {
                    //A new connection attempt, registering socket channel with selector

                } else {
                    Worker.add( readyKey );
                }

Worker is the thread class that performs Input/Output from the channel. This is the code of my Worker class:

private static List<SelectionKey> keyPool = Collections.synchronizedList(new LinkedList());

public static void add(SelectionKey key) {
    synchronized (keyPool) {
        keyPool.add(key);
        keyPool.notifyAll();
    }
}


public void run() {
    while ( true ) {

        SelectionKey myKey = null;
        synchronized (keyPool) {
            try {
                while (keyPool.isEmpty()) {
                    keyPool.wait();
                }
            } catch (InterruptedException ex) {                    
            }
            myKey = keyPool.remove(0);
            keyPool.notifyAll();
        }

        if (myKey != null && myKey.isValid() ) {

            if (myKey.isReadable()) {
                //Performing reading
            } else if (myKey.isWritable()) {
                //performing writing
                myKey.cancel();  
            }
        }
    }

My basic idea is to add the key to the keyPool from which various threads can get a key, one at a time. My BaseServer class itself is running as a thread. It is creating 10 Worker threads before the event loop to begin. I also tried to increase the priority of BaseServer thread, so that it gets more chance to accept the acceptable keys. Still, to it stops responding after approx 8 requests. Please help, were I am going wrong. Thanks in advance. :)

Answer 1

Third, you aren't removing anything from the selected-key set. You must do that every time around the loop, eg by calling keyIterator.remove() after you call next().

You need to read the NIO Tutorials.

Answer 2

Try using xsocket library. It saved me a lot of time reading on forums.

Download: http://xsocket.org/

Tutorial: http://xsocket.sourceforge.net/core/tutorial/V2/TutorialCore.htm

Server Code:

import org.xsocket.connection.*;

/**
 *
 * @author wsserver
 */
public class XServer {

    protected static IServer server;

    public static void main(String[] args) {
        try {
            server = new Server(9905, new XServerHandler());
            server.start();
        } catch (Exception ex) {
            System.out.println(ex.getMessage());
        }
    }
     protected static void shutdownServer(){
        try{
            server.close();
        }catch(Exception ex){
            System.out.println(ex.getMessage());
        }        
    }
}

Server Handler:

import java.io.IOException;
import java.nio.BufferUnderflowException;
import java.nio.ByteBuffer;
import java.nio.channels.ClosedChannelException;
import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
import java.nio.charset.CharsetEncoder;
import java.util.*;
import org.xsocket.*;
import org.xsocket.connection.*;

public class XServerHandler implements IConnectHandler, IDisconnectHandler, IDataHandler {

    private Set<ConnectedClients> sessions = Collections.synchronizedSet(new HashSet<ConnectedClients>());

    Charset charset = Charset.forName("ISO-8859-1");
    CharsetEncoder encoder = charset.newEncoder();
    CharsetDecoder decoder = charset.newDecoder();
    ByteBuffer buffer = ByteBuffer.allocate(1024);

    @Override
    public boolean onConnect(INonBlockingConnection inbc) throws IOException, BufferUnderflowException, MaxReadSizeExceededException {
        try {
            synchronized (sessions) {
                sessions.add(new ConnectedClients(inbc, inbc.getRemoteAddress()));
            }
            System.out.println("onConnect"+" IP:"+inbc.getRemoteAddress().getHostAddress()+" Port:"+inbc.getRemotePort());
        } catch (Exception ex) {
            System.out.println("onConnect: " + ex.getMessage());
        }
        return true;
    }

    @Override
    public boolean onDisconnect(INonBlockingConnection inbc) throws IOException {
        try {
            synchronized (sessions) {
                sessions.remove(inbc);
            }
            System.out.println("onDisconnect");
        } catch (Exception ex) {
            System.out.println("onDisconnect: " + ex.getMessage());
        }
        return true;
    }

    @Override
    public boolean onData(INonBlockingConnection inbc) throws IOException, BufferUnderflowException, ClosedChannelException, MaxReadSizeExceededException {
        inbc.read(buffer);
        buffer.flip();
        String request = decoder.decode(buffer).toString();
        System.out.println("request:"+request);
        buffer.clear();
        return true;
    }
}

Connected Clients:

import java.net.InetAddress;
import org.xsocket.connection.INonBlockingConnection;

/**
 *
 * @author wsserver
 */
public class ConnectedClients {

    private INonBlockingConnection inbc;
    private InetAddress address;

    //CONSTRUCTOR
    public ConnectedClients(INonBlockingConnection inbc, InetAddress address) {
        this.inbc = inbc;
        this.address = address;
    }

    //GETERS AND SETTERS
    public INonBlockingConnection getInbc() {
        return inbc;
    }

    public void setInbc(INonBlockingConnection inbc) {
        this.inbc = inbc;
    }

    public InetAddress getAddress() {
        return address;
    }

    public void setAddress(InetAddress address) {
        this.address = address;
    }
}

Client Code:

import java.net.InetAddress;
import org.xsocket.connection.INonBlockingConnection;
import org.xsocket.connection.NonBlockingConnection;

/**
 *
 * @author wsserver
 */
public class XClient {

    protected static INonBlockingConnection inbc;
    public static void main(String[] args) {
        try {
            inbc = new NonBlockingConnection(InetAddress.getByName("localhost"), 9905, new XClientHandler());

            while(true){

            }
        } catch (Exception ex) {
            System.out.println(ex.getMessage());
        }
    }
}

Client Handler:

import java.io.IOException;
import java.nio.BufferUnderflowException;
import java.nio.ByteBuffer;
import java.nio.channels.ClosedChannelException;
import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
import java.nio.charset.CharsetEncoder;
import org.xsocket.MaxReadSizeExceededException;
import org.xsocket.connection.IConnectExceptionHandler;
import org.xsocket.connection.IConnectHandler;
import org.xsocket.connection.IDataHandler;
import org.xsocket.connection.IDisconnectHandler;
import org.xsocket.connection.INonBlockingConnection;

/**
 *
 * @author wsserver
 */
public class XClientHandler implements IConnectHandler, IDataHandler,IDisconnectHandler, IConnectExceptionHandler {

    Charset charset = Charset.forName("ISO-8859-1");
    CharsetEncoder encoder = charset.newEncoder();
    CharsetDecoder decoder = charset.newDecoder();
    ByteBuffer buffer = ByteBuffer.allocate(1024);

    @Override
    public boolean onConnect(INonBlockingConnection nbc) throws IOException {
        System.out.println("Connected to server");
        nbc.write("hello server\r\n");
        return true;
    }

    @Override
    public boolean onConnectException(INonBlockingConnection nbc, IOException ioe) throws IOException {

        System.out.println("On connect exception:"+ioe.getMessage());
        return true;
    }

    @Override
    public boolean onDisconnect(INonBlockingConnection nbc) throws IOException {

        System.out.println("Dissconected from server");
        return true;
    }

    @Override
    public boolean onData(INonBlockingConnection inbc) throws IOException, BufferUnderflowException, ClosedChannelException, MaxReadSizeExceededException {

        inbc.read(buffer);
        buffer.flip();
        String request = decoder.decode(buffer).toString();
        System.out.println(request);
        buffer.clear();
        return true;
    }
}

I spent a lot of time reading on forums about this, i hope i can help u with my code.

Answer 3

First of all, you should not really be using wait() and notify() calls anymore since there exist good Standard Java (1.5+) wrapper classes in java.util.concurrent, such as BlockingQueue .

Second, it's suggested to do IO in the selecting thread itself, not in the worker threads. The worker threads should just queue up reads/and writes to the selector thread(s).

This page explains it pretty good and even provides working code samples of a simple TCP/IP server: http://rox-xmlrpc.sourceforge.net/niotut/

Sorry, I don't yet have time to look at your specific example.