Java NIO and sockets in 1.4.1FCS

Hi,
I have built a client server system using the new 1.4 java.nio packages. In 1.4 everything worked fine, yet in 1.4.1 FCS it definitely does not. The process is as follows.
Everything work in non-blocking mode:
- Server receives connection and accepts it, the new SocketChannel is put in non-blocking mode and registered with the same selector as the server.
- New SocketChannel waits for data from the client so it waits for OP_READ from the selector. All it gets is OP_WRITE, OP_CONNECT. With 1.4 it received OP_READ, OP_WRITE.
I tried adding a call to finishConnect, but that didn't help.
Anyone have any thoughts about this?
Thanks,
Mike.

The code in the bug report is incorrect. The key will of course always be writable if you do not write anything to the socket! And since it is writable the readable part of the code will never be executed (its in an else-statement). When you are not interested in the OP_WRITE, change the ops on the selection key.

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Help "ascending" to Java NIO

Hello there.
I've been using Java for quite some time, but the few really networked client/server applications I have used, have used java.io and java.net. Now, even I have heard the rumours about Java NIO, and I am curious. I have tried reading up and down the API on java.nio.* , but I must say I am still kind of confused.
Basically, I am looking for some example code, or a thorough explanation of how all the classes and components come together to form efficient asynchronous non-blocking I/O.
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Take a look at my thread Taming the NIO Circus. It starts with simple examples of a single thread echo server and a swing client.

Announcement: Java NIO Framework

Hi all,
After reading Ron Hitchen's book "Java NIO" and watching his presentation "How to Build a Scalable Multiplexed Server With NIO" at the 2006 JavaOne Conference, I implemented a framework based on his ideas.
Here is the website: http://nioframework.sourceforge.net/
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Finally I found the time to write some benchmark programs for the NIO Framework and take a look at the MINA API.
If you download the latest NIO Framework release you can run the plaintext benchmark as follows:
Start the benchmark server (this is just the echo server without any session debugging output or logging) with the following command:
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And now to MINA:
I used the very simple echo server example from the MINA project and just removed the logger from the chain. You may download this package from here (it includes all relevant source code):
http://nioframework.sourceforge.net/mina_echo_server.jar
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java -jar mina_echo_server.jar
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Troubles with timeout using java.nio.channels and non-blocking sockets

Hello.
I have a server application that employs java.nio.channels with non-blocking sockets.
The server waits for connections. The client should connect and be first in sending data.
Timeouts are significant! If client exceeds the allowed time to send data, the server should break the connection.
The huge trouble I've discovered that I cannot control the timeout when client connects but remains silent.
My code looks as follows:
<pre>
Selector oSel;
SocketChannel oSockChan;
Socket oSock;
SelectionKey oSelKey;
Iterator<SelectionKey> oItSelKeys;
int iCurrState, iMask, iCount;
iCurrState = INT_SERVER_WORKING;
iMask = SelectionKey.OP_ACCEPT | SelectionKey.OP_CONNECT | SelectionKey.OP_READ | SelectionKey.OP_WRITE;
while ( iCurrState == INT_SERVER_WORKING )
try
*// retrieving next action*
iCount = oSel.select();
if ( iCount > 0 )
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while ( oItSelKeys.hasNext() )
oSelKey = oItSelKeys.next();
oItSelKeys.remove();
if ( oSelKey.isValid() )
switch ( oSelKey.readyOps() & iMask ) {
case SelectionKey.OP_ACCEPT :
oSockChan = oSSockChan.accept();
oSockChan.configureBlocking(false);
oSock = oSockChan.socket();
oSock.setKeepAlive(true);
oSockChan.register(oSel,SelectionKey.OP_READ,new MyPacket(oSock.getInetAddress(),oSock.getPort()));
break;
case SelectionKey.OP_READ :
oSelKey.interestOps(0);
((MyPacket) oSelKey.attachment()).inRequest(); *// preparing request*
this.getReader().add(oSelKey); *// sending key to reading thread*
break;
case SelectionKey.OP_WRITE :
oSelKey.interestOps(0);
((MyRequest) oSelKey.attachment()).inResponse(); *// preparing response*
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*// nothing to do*
catch ( IOException oExcept )
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</pre>
Timeouts are easily controlled by reading and writing threads (see OP_READ and OP_WRITE ).
But when a client just connects without consequent data send, the state of this connection remains as OP_ACCEPT. The connection remains open for arbitrarily large time and I cannot control it!
Please help with idea how can I terminate such connections!

How can I process the keys that weren't selected at the bottom of the loop? Should I use the method keys() ?Yes. Form a new set from keys() and removeAll(selectedKeys()). Do that before you process selectedKeys().
And the second moment: as I understood a single key may contain several operations simultaneously? Thus I should use several if's (but not if/else 'cause it's the equivalent of switch ... case ).If there is anything unclear about 'your switch statement is invalid. You need an if/else chain' I fail to see what it is. Try reading it again. And if several ifs were really the equivalent of "switch ... case", there wouldn't be a problem in the first place. They're not, and there is.

Socket seems too slow...maybe java.nio?

Hello
In our system I have to receive Multicast Packets repeats very quick(1-5 ms). I have to link them one after an other in the order they sent. And if I miss a packet, something will go wrong...
I have to listen to different IPs and I use different threads for different IPs. If I use only one thread (and listens to only one IP) everything seems ok.
But if I starts listening to an other ip too, I miss 2 packets in a row, or only one if I turn off parsing the message (XML).
Here is the code I use in the Threads:
try{
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               if(nInterface!=null)socket.setNetworkInterface(nInterface);
               socket.joinGroup(inetAddress);
          catch(IOException ioe){
               logger.error(ioe.getMessage(), ioe);
return;
          try{
               while (!interrupted()) {
                    try{
                         byte[] buffer = new byte[1480];
                         packet = new DatagramPacket(buffer, buffer.length);
                         socket.receive(packet);
parse(buffer);
                    }catch(SocketTimeoutException stoe){
                         //     DO NOTHING
                    }catch(IOException ioe){
                         logger.error(ioe.getMessage(), ioe);
          }finally{
               try {
                    if(socket!=null){
                         socket.leaveGroup(inetAddress);
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Every Thread has its own parsing object.
Any tips, what is wrong?
Maybe java.nio could solve the problem somehow. There is a sample server in [Java Home]/sample/nio/server and it suggest that there are quicker methods to receive messages from different IPs (maybe Blocking/Pooled-Thread Server). But I can't understand the API and the Sample while I was reading it (20-30 minutes).
Could it be quicker? Does it worth toying with the idea?
Thanks:
Bence

In our system I have to receive Multicast Packets
repeats very quick(1-5 ms). I have to link them one
after an other in the order they sent. And if I miss
a packet, something will go wrong...There is no guarantee anywhere in the system that you won't miss a datagram. UDP doesn't make such guarantees. If you need all the packets you will have to build ACK or NACK into your protocol.
You can alleviate the problem by running a very large socket receive buffer. But you can't eliminate it. Rethink this.
NIO is not significantly quicker for applications like this, it is more scalable.

Java NIO, ByteBuffers and Linksys router

I have a client server app/game that uses NIO for communication sending ByteBuffers. On a LAN with 5-8 users it runs great. On the internet, through a Linksys router, with one user, it has a blip. I get all my data transmissions except for one buffer. Whenever I chat the buffer contains a size, an int typeID and the encoded string for chat. This particular buffer never makes it to the client on the outside of the router. I have a port forwarded and regular tcp/ip java io sockets stuff works fine. As does al lof the other NIO buffer traffic for locational data, login in and out, etc... ANy thoughts??

But not sure what would be the performance of those clients?? when compared to Java NIO performance....Telnet isn't a high-performance protocol anyway. Don't worry about it. Use existing code. Get it working. Measure. If you have a performance issue, then worry, while at least you have something you can deploy. It won't be a problem. The router is there to route, not to talk high-speed telnet.

Socket disconnection event not being reveived java.nio

Hi All
My question is as below
i am using java.nio package + win 2K + jdk1.4.1_02
I have a Server accepting socket connection and is configured
in Nonblocking mode.
-The server receives (selector) events (accept event)
when a client requests for a connection .
-The server is getting read and write events when
client wants to read and write
-The server gets a read event when the client disconnects
My only problem is that the Server is not getting any events
when the client disconnect due to network break down
for EX when the network connection breaks the client disconnects
but the server selector is not getting any events
I am storing the client Socket objects in a Hash Table and
if i execute the .isConnected() method it returns true
even though the the client is down
The only work around is to try to read and write on the socket
i get an IO exception and am able to make out that the
client is disconnected
But this is not desirable for my client
as client modification to give any kind of echo is not possible and
a read /write event will cause problem.
Can any one tell how to detect client side disconnection
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Regards
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int ct = read.selectNow();
if (ct > 0)
Set readyKeys = read.selectedKeys();
Iterator i = readyKeys.iterator();
while (i.hasNext())
SelectionKey key = (SelectionKey) i.next();
i.remove();
if (key.isReadable())
SelectableChannel nextReady = (SelectableChannel) key.channel();
SocketChannel sc = (SocketChannel) key.channel();
int rd = sc.read(buffer);
// Link is dead
if (rd == -1)
key.cancel();
key.attach(null);
nextReady.close();
continue;
// Process your data
catch (Exception e)
e.printStackTrace();

NIO and traditional sockets

I have a little server that I was porting from traditional thread per socket programming to NIO. The first thing I ported was the Listen-Accept loop. This worked well but the resulting sockets obtained from
SocketChannel.socket()
have very strange behaviour with respect to flush. I send the data by
out.write(data);
out.flush();
where out is the BufferedOutputStream. The data doesn't get sent until the next input arrives on the Socket. If I change to using just old style I/O or completely NIO the problem goes away.
I found several bug reports on NIO and flush, but they all seem to be considered Feechures by SUN.

Thanks for posting the link to your NIO code. I downloaded the src-raining-1.2pre1 source and took a look. I noticed that you still have some doubts about how OP_WRITE works. This piece of code will definitely have problems.
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        //RK modified on 20031008 23:19:39 - NOOO
                //registerChannel(selector, channel(), SelectionKey.OP_WRITE);
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        SelectionKey sk = sc.keyFor(selector);
        int ops = sk.interestOps();
        sk.interestOps( ops | SelectionKey.OP_WRITE);
        selector.wakeup(); // is this required or not ???
    }The sk.interestOps will block if there is an active select. If there isn't an active select you don't need the wakeup. The only way to make this work properly in 1.4.2 is to build a queue of runnables that set interestOps and execute them just before or after the select. Also the setting of OP_WRITE in that code won't handle the case where the network exerts flow control on the channel. The correct setting of OP_WRITE is
- set interest in OP_WRITE when the socket is connected
- remove interest as soon as you successfully write all the data in a buffer
- add interest only when you write less bytes than requested.
My post Taming the NIO Circus provides an example of this in the swing based client. I posted this in response to Java.nio. SelectionKey interestOps(int) method blocks

Need help with java.nio.socket program.

Can someone please help me here? I am trying to create a class that listens on a socket for an incoming connection, but I am getting the following error on compile:
SocketIn.java:48: incompatible types
found : java.nio.channels.SocketChannel
required: java.net.Socket
Socket requestSocket = requestChannel.accept();
Here is my code:
package NETC;
import java.net.*;
import java.util.*;
import java.io.*;
import java.nio.*;
import java.nio.charset.*;
import java.nio.channels.*;
import java.nio.channels.spi.*;
public class SocketIn{
     // Buffer for any incoming data.
     private static ByteBuffer inBuffer = ByteBuffer.allocateDirect(1024);
     CharBuffer charBuffer = null;
     public SocketIn(int intPort)throws Exception{
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          serverChannel.configureBlocking(false);
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          InetAddress inetAddress = InetAddress.getLocalHost();
          InetSocketAddress socketAddress = new InetSocketAddress(inetAddress, intPort);
          serverChannel.socket().bind(socketAddress);
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          Selector requestSelector = SelectorProvider.provider().openSelector();
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          serverChannel.register(requestSelector, SelectionKey.OP_ACCEPT);
          while(requestSelector.select() > 0){
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               Set requestKeys = requestSelector.selectedKeys();
               Iterator iterator = requestKeys.iterator();
               while(iterator.hasNext()){
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                    ServerSocketChannel requestChannel = (ServerSocketChannel)requestKey.channel();
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                    inBuffer.clear();
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                    Charset charset = Charset.forName("ISO-8859-1");
                    CharsetDecoder decoder = charset.newDecoder();
                    charBuffer = decoder.decode(inBuffer);
                    iterator.remove();
}

Well its been about a month and a half so I guess you have your answer. In case you don't...
// This shouldn't block.
Socket requestSocket = requestChannel.accept();
The problem is quite simple. The ServerSocketChannel.accept() returns a SocketChannel. (Channel -> Channel).
You can get access to the socket using the SocketChannel.
SocketChannel requestSocketChannel = requestChannel.accept();
Socket requestSocket = requestSocketChannel.socket();
But you don't need the socket to read and write.

Selecting between java.io and java.nio

Hi,
I'm a bit confused between java.io and java.nio. What sre the major differences between these two?
In areas are these best applicable?

The java.nio package improves on the basic Java I/O that was available prior to JDK 1.4.
It is designed to interoperate more natively with the underlying file handles (sockets, open files etc) to achieve better performance.
The improvements include true non-blocking I/O, better buffer management, character-set support, channels (similar to Occam's channels) and selectors, and some other ancillery stuff. Most of these classes are designed to be inherently threadsafe.
There are some examples here:
http://java.sun.com/j2se/1.4.2/docs/guide/nio/example/index.html
However, if you are still a beginner with file or network I/O, its better if you start with the simple I/O first. You'll appreciate the NIO improvements better afterwards.

Java NIO and sockets in 1.4.1FCS

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