NIO SocketChannel non-blocking read

Question

Hello.
I'm not sure a resembling message has already been posted in a forum. In such a case, thanks for redirecting to it.
Goals :
A selector is used by a main server thread to make accept and read operations non-blocking.
When a connection is accepted, the newly created socket channel is configured as non-blocking, and a key is added to the selector with the OP_READ flag.
When data are available on sockets, a new task (runnable) is created and submitted to a thread pool.
When a thread is ready to process the request, a pre-allocated bytebuffer is used to read arriving data.
The problem :
When the bytebuffer capacity is less than the received bytes count, the read method on the socket channel interrupts the selector on the same selection key. In response to this event, a new task is initiated, interferring with the previous one.
As expected according to my concurrency policy (ie. with a pool of threads), several requests are processed by parallel threads. To avoid unsafe accesses, i added a synchronized statement on the channel blocking lock, and it seems to works fine. But a better way should exist...
Questions :
Is this the expected behavior ?
Is there any other way to read received data with a small buffer ?
The full copy of the source code :
import java.io.*;
import java.nio.*;
import java.nio.channels.*;
import java.nio.channels.spi.*;
import java.nio.charset.*;
import java.net.*;
import java.util.*;
import net.moon.threads.*;
public class Nio1 {
     static class Request {
          boolean isCompleted = false;
          int inputs = 0;
          Set workers = new HashSet();
          ByteArrayOutputStream baos = new ByteArrayOutputStream();
          byte p = 0;
          boolean isCompleted() {
               return isCompleted;
          void countInput() {
               inputs++;
          void append(final ByteBuffer byteBuffer) {
               if (isCompleted)
                    throw new IllegalStateException("Request is already completed");
               workers.add(Thread.currentThread());
               while (byteBuffer.hasRemaining()) {
                    byte b = byteBuffer.get();
                    baos.write(b);
                    if ((b == '\r') && (p == '\n'))
                         isCompleted = true;
                    p = b;
          int inputs() {
               return inputs;
          Thread[] workers() {
               return (Thread[]) workers.toArray(new Thread[0]);
          int size() {
               return baos.size();
          byte[] getData() {
               return baos.toByteArray();
          void reset() {
               isCompleted = false;
               inputs = 0;
               baos.reset();
               workers.clear();
     static private class RequestTask implements Runnable {
     private final static Charset charset = Charset.forName("US-ASCII");
          private final Server server;
          private final SelectionKey selectionKey;
          RequestTask(final Server server, final SelectionKey selectionKey) {
               this.server = server;
               this.selectionKey = selectionKey;
          public void run() {
               log("*** Processing input...");
               try {
                    SocketChannel channel = (SocketChannel) selectionKey.channel();
synchronized(channel.blockingLock()) {
                    Request request = (Request) selectionKey.attachment();
                    request.countInput();
                    State state = getState();
                    log("Reading first...");
                    int c = channel.read(state.byteBuffer);
                    log("... Read first : " + c);
                    if (c > 0) {
                         for(;;) {
                              state.byteBuffer.flip();
                         request.append(state.byteBuffer);
                              state.byteBuffer.clear();
                              if (c < state.byteBuffer.capacity()) break;
                              log("Reading next...");
                              c = channel.read(state.byteBuffer);
                              log("... Read next : " + c);
                              if (c <= 0) break;
                         if (request.isCompleted()) {
                              log("Request completed : " + request.inputs());
                              StringBuffer bodyBuffer = new StringBuffer();
                              bodyBuffer.append("-----------------------------\r\n");
                              bodyBuffer.append("Request processed in " + request.inputs() + " inputs\r\n");
                              bodyBuffer.append("Request size is " + request.size() + " bytes\r\n");
                              bodyBuffer.append("Participating workers :\r\n");
                              Thread[] workers = request.workers();
                              for (int i = 0; i < workers.length; i++)
                                   bodyBuffer.append(" * " + workers[i] + "\r\n");
                              bodyBuffer.append("-----------------------------\r\n");
                              StringBuffer headerBuffer = new StringBuffer();
                              headerBuffer.append("HTTP/1.1 200 OK\r\n");
                              headerBuffer.append("Server: NIO Server 1\r\n");
                              headerBuffer.append("Content-Type: text/plain\r\n");
                              headerBuffer.append("Content-Length: ").append(request.size() + bodyBuffer.length()).append("\r\n");
                              headerBuffer.append("\r\n");
                         CharsetEncoder encoder = charset.newEncoder();
                              channel.write(encoder.encode(CharBuffer.wrap(headerBuffer)));
                              channel.write(encoder.encode(CharBuffer.wrap(bodyBuffer)));
                              channel.write(ByteBuffer.wrap(request.getData()));
                              request.reset();
                    if (c < 0) {
                         selectionKey.attach(null);
                         selectionKey.cancel();
                         log("!!! Connection terminated for channel " + channel);
               catch(final Exception x) {
                    x.printStackTrace();
               log("*** Request processed...");
          private State getState() {
               State state = (State) server.taskManager.getCurrentWorkerState();
               if (state == null) {
                    state = new State();
                    server.taskManager.setCurrentWorkerState(state);
               else {
                    state.byteBuffer.clear();
               return state;
          private void log(final String text) {
               System.out.println(Thread.currentThread() + " : " + text);
          static class State {
               ByteBuffer byteBuffer = ByteBuffer.allocateDirect(32);
     static private class Server implements Runnable {
          private final int port;
          private Thread worker;
          private FIFOTaskManager taskManager;
          Server(final int port) {
               this.port = port;
               worker = null;
          synchronized void start() throws Exception {
               if (worker == null) {
                    log("Starting the server...");
                    taskManager = new FIFOTaskManager("Nio1Workers", 24);
                    worker = new Thread(this);
                    worker.start();
                    synchronized(worker) {
                         try {
                              worker.wait();
                         catch(InterruptedException x) {
                    log("Server started !");
          public void run() {
               try {
                    log("Server is starting...");
                    Selector selector = SelectorProvider.provider().openSelector();
                    log("Creating listener on port " + port);
                    ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
                    serverSocketChannel.configureBlocking(false);
                    InetSocketAddress inetSocketAddress = new InetSocketAddress(port);
                    serverSocketChannel.socket().bind(inetSocketAddress);
                    SelectionKey selectionKey = serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
                    synchronized(worker) {
                         worker.notify();
                    while (selector.select() >= 0) {
                         Set readyKeys = selector.selectedKeys();
                         log("Keys are ready : " + readyKeys.size());
                         for (Iterator i = readyKeys.iterator(); i.hasNext(); ) {
                              SelectionKey selectedKey = (SelectionKey) i.next();
                              if (selectedKey.isAcceptable()) {
                                   ServerSocketChannel ssc = (ServerSocketChannel) selectedKey.channel();
                                   SocketChannel sc = ssc.accept();
                                   sc.configureBlocking(false);
                                   SelectionKey sk = sc.register(selector, SelectionKey.OP_READ);
                                   sk.attach(new Request());
                                   log("Connection accepted for channel " + sc);
                              else if (selectedKey.isReadable()) {
                                   log("Key ready for input : " + selectedKey);
                                   taskManager.execute(new RequestTask(this, selectedKey));
                              i.remove();
                         readyKeys = null;
                    log("Server loop interrupted !");
               catch(Exception x) {
                    x.printStackTrace();
          private void log(final String text) {
               System.out.println("SERVER: " + text);
     public static void main(final String[] args) throws Exception {
          Server server = new Server(9001);
          server.start();

Answer 1

Thanks for the trick. I hope the code will be more readable than my sockets !
import java.io.*;
import java.nio.*;
import java.nio.channels.*;
import java.nio.channels.spi.*;
import java.nio.charset.*;
import java.net.*;
import java.util.*;
import net.moon.threads.*;
public class Nio1 {
     static class Request {
          boolean isCompleted = false;
          int inputs = 0;
          Set workers = new HashSet();
          ByteArrayOutputStream baos = new ByteArrayOutputStream();
          byte p = 0;
          boolean isCompleted() {
               return isCompleted;
          void countInput() {
               inputs++;
          void append(final ByteBuffer byteBuffer) {
               if (isCompleted)
                    throw new IllegalStateException("Request is already completed");
               workers.add(Thread.currentThread());
               while (byteBuffer.hasRemaining()) {
                    byte b = byteBuffer.get();
                    baos.write(b);
                    if ((b == '\r') && (p == '\n'))
                         isCompleted = true;
                    p = b;
          int inputs() {
               return inputs;
          Thread[] workers() {
               return (Thread[]) workers.toArray(new Thread[0]);
          int size() {
               return baos.size();
          byte[] getData() {
               return baos.toByteArray();
          void reset() {
               isCompleted = false;
               inputs = 0;
               baos.reset();
               workers.clear();
     static private class RequestTask implements Runnable {
         private final static Charset charset = Charset.forName("US-ASCII");
          private final Server server;
          private final SelectionKey selectionKey;
          RequestTask(final Server server, final SelectionKey selectionKey) {
               this.server = server;
               this.selectionKey = selectionKey;
          public void run() {
               log("*** Processing input...");
               try {
                    SocketChannel channel = (SocketChannel) selectionKey.channel();
synchronized(channel.blockingLock()) {
                    Request request = (Request) selectionKey.attachment();
                    request.countInput();
                    State state = getState();
                    log("Reading first...");
                    int c = channel.read(state.byteBuffer);
                    log("... Read first : " + c);
                    if (c > 0) {
                         for(;;) {
                              state.byteBuffer.flip();
                             request.append(state.byteBuffer);
                              state.byteBuffer.clear();
                              if (c < state.byteBuffer.capacity()) break;
                              log("Reading next...");
                              c = channel.read(state.byteBuffer);
                              log("... Read next : " + c);
                              if (c <= 0) break;
                         if (request.isCompleted()) {
                              log("Request completed : " + request.inputs());
                              StringBuffer bodyBuffer = new StringBuffer();
                              bodyBuffer.append("-----------------------------\r\n");
                              bodyBuffer.append("Request processed in " + request.inputs() + " inputs\r\n");
                              bodyBuffer.append("Request size is " + request.size() + " bytes\r\n");
                              bodyBuffer.append("Participating workers :\r\n");
                              Thread[] workers = request.workers();
                              for (int i = 0; i < workers.length; i++)
                                   bodyBuffer.append(" * " + workers[i] + "\r\n");
                              bodyBuffer.append("-----------------------------\r\n");
                              StringBuffer headerBuffer = new StringBuffer();
                              headerBuffer.append("HTTP/1.1 200 OK\r\n");
                              headerBuffer.append("Server: NIO Server 1\r\n");
                              headerBuffer.append("Content-Type: text/plain\r\n");
                              headerBuffer.append("Content-Length: ").append(request.size() + bodyBuffer.length()).append("\r\n");
                              headerBuffer.append("\r\n");
                             CharsetEncoder encoder = charset.newEncoder();
                              channel.write(encoder.encode(CharBuffer.wrap(headerBuffer)));
                              channel.write(encoder.encode(CharBuffer.wrap(bodyBuffer)));
                              channel.write(ByteBuffer.wrap(request.getData()));
                              request.reset();
                    if (c < 0) {
                         selectionKey.attach(null);
                         selectionKey.cancel();
                         log("!!! Connection terminated for channel " + channel);
               catch(final Exception x) {
                    x.printStackTrace();
               log("*** Request processed...");
          private State getState() {
               State state = (State) server.taskManager.getCurrentWorkerState();
               if (state == null) {
                    state = new State();
                    server.taskManager.setCurrentWorkerState(state);
               else {
                    state.byteBuffer.clear();
               return state;
          private void log(final String text) {
               System.out.println(Thread.currentThread() + " : " + text);
          static class State {
               ByteBuffer byteBuffer = ByteBuffer.allocateDirect(32);
     static private class Server implements Runnable {
          private final int port;
          private Thread worker;
          private FIFOTaskManager taskManager;
          Server(final int port) {
               this.port = port;
               worker = null;
          synchronized void start() throws Exception {
               if (worker == null) {
                    log("Starting the server...");
                    taskManager = new FIFOTaskManager("Nio1Workers", 24);
                    worker = new Thread(this);
                    worker.start();
                    synchronized(worker) {
                         try {
                              worker.wait();
                         catch(InterruptedException x) {
                    log("Server started !");
          public void run() {
               try {
                    log("Server is starting...");
                    Selector selector = SelectorProvider.provider().openSelector();
                    log("Creating listener on port " + port);
                    ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
                    serverSocketChannel.configureBlocking(false);
                    InetSocketAddress inetSocketAddress = new InetSocketAddress(port);
                    serverSocketChannel.socket().bind(inetSocketAddress);
                    SelectionKey selectionKey = serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
                    synchronized(worker) {
                         worker.notify();
                    while (selector.select() >= 0) {
                         Set readyKeys = selector.selectedKeys();
                         log("Keys are ready : " + readyKeys.size());
                         for (Iterator i = readyKeys.iterator(); i.hasNext(); ) {
                              SelectionKey selectedKey = (SelectionKey) i.next();
                              if (selectedKey.isAcceptable()) {
                                   ServerSocketChannel ssc = (ServerSocketChannel) selectedKey.channel();
                                   SocketChannel sc = ssc.accept();
                                   sc.configureBlocking(false);
                                   SelectionKey sk = sc.register(selector, SelectionKey.OP_READ);
                                   sk.attach(new Request());
                                   log("Connection accepted for channel " + sc);
                              else if (selectedKey.isReadable()) {
                                   log("Key ready for input : " + selectedKey);
                                   taskManager.execute(new RequestTask(this, selectedKey));
                              i.remove();
                         readyKeys = null;
                    log("Server loop interrupted !");
               catch(Exception x) {
                    x.printStackTrace();
          private void log(final String text) {
               System.out.println("SERVER: " + text);
     public static void main(final String[] args) throws Exception {
          Server server = new Server(9001);
          server.start();
}