Serialization + Non-blocking IO + Channels ?
Hi,
I use a lot of object serialization. The serialized objects can be big. I would like to transform my server to make it non-blocking so that I don't have to use one thread per connection.
Do I have to use channels if I want non-blocking IO?
If yes, how can I achieve object serialization?
The code below seems to work for small objects, but not for bigger ones (5 Kb, for example). I believe it is due to the fact that the whole object is not read at once by the channel. If so, how can I determine that an object is fully read before desializing it?
Should I take another appoach?
Thnaks.
byte[] byts = new byte[ buffer.remaining() ];
buffer.get( byts );
ByteArrayInputStream bais = new ByteArrayInputStream( byts );
ObjectInputStream ois = new ObjectInputStream( bais );
Object myObject = ois.readObject();
Hi,
It might be a good solution to zip the ObjectStream and the UnZip it when you read from the stream.
This will decrease the size of the objects alot.
/Richard
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Non-blocking Vectored read from SocketChannel fails
Hi.
Please look at the code example:
ByteBuffer tmp1 = ByteBuffer.allocate(500);
ByteBuffer tmp2 = ByteBuffer.allocate(500);
ByteBuffer[] tmp = {tmp1, tmp2};
while ((count = socketChannel.read(tmp)) > 0) {
+ "bytes.");
When I run this code, (using non-blocking socket channel), the first buffer is read ok, but on the second round of the while loop, I get an IOException, saying: "a non blocking socket operation could not be completed immediately".
If I put 'tmp1' instead of 'tmp' in the read(), (i.e - use a normal buffer), the read successfully finishes.
Why?
I found nothing in the documentation, and in the 'Java NIO' book (Ron Hitchens).
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About NIO non-blocking socket write method behavior
Hi all -
I hope anyone could help in this issue.
Assume you create a NIO socket and configure its channel in non blocking mode:
channel.configureBlocking(false);
then you write a byte buffer into it:
int sentBytesNum = channel.write(byteBuffer);
What are the possibilities of sentBytesNum value? I am sure of two possibilities, which are:
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RockaYes, case three can occur. The usual NIO write loop looks like this:
int count = 0;
while (buf.position() > 0)
buf.flip();
count = ch.write(buf);
buf.compact();
if (count == 0)
break;
}This will run until buf.position() == 0 or count == 0. If the partial write case happens it will loop one more time and probably get a 0 count.
At the end of the loop, if buf.position() > 0 there is still unwritten data and at this point you should register for OP_WRITE and return to the selector. Otherwise if there is no data unwritten you should deregister OP_WRITE as you have nothing to write and aren't interested in the event any longer.
If you are reading something and writing at the same time the logic goes like this:
while (inch.read(buf) >= 0 || buf.position() > 0)
// etc
}This will read until EOF occurs and either buf.position() is zero or a zero length write occurred. -
Dear all,
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And in which version?
If not, is there any work-around?
Thanks a lot.
best regards
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Serialization plays an important role in distributing interdependent objects, especially when master data is being distributed.
IDocs can be created, sent and posted in a specified order by distributing message types serially.
Errors can then be avoided when processing inbound IDocs.
Interdependent messages can be serially distributed in the following ways:
Serialization by Object Type
Serialization by Message Type
Serialization at IDoc Level
(not for IDocs from generated BAPI-ALE interfaces)
Serialization at IDoc Level
Use
Delays in transferring IDocs may result in an IDoc containing data belonging to a specific object arriving at its destination before an "older" IDoc that contains different data belonging to the same object. Applications can use the ALE Serialization API to specify the order IDocs of the same message type are processed in and to prevent old IDocs from being posted if processing is repeated.
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checks the time stamps in the serialization field of the IDoc header.
u2022 IDOC_SERIAL_POST
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Check the following link:
http://help.sap.com/saphelp_nw04s/helpdata/en/0b/2a66d6507d11d18ee90000e8366fc2/frameset.htm
http://help.sap.com/saphelp_nw04s/helpdata/en/78/2175a751ce11d189570000e829fbbd/frameset.htm
How to serialize IDoc XML messages fed into XI
cheers -
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 )
oItSelKeys = oSel.selectedKeys().iterator();
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*
this.getWriter().add(oSelKey); *// sending key to writing thread*
break;
case SelectionKey.OP_CONNECT :
default :
*// nothing to do*
catch ( IOException oExcept )
*// do some actions*
</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. -
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Hi,
I am developing a classic UDP-based server which serves hundreds of clients simultaneously. After receiving a simple request from a client, the server replies with a simple response (messages are no larger than 50 bytes).
What, if any non-blocking-related advantages would there be in using nio? Specifically, if I used select() without turning on non-blocking on the data channel, what do I lose?
The architecture consists of only one socket for responding to client requests. It uses receive() and send(), not read()/write()/connect().
Thanks in advance,
Dan.>>
What, if any non-blocking-related advantageswould
there be in using nio? Specifically, if I used
select() without turning on non-blocking on thedata
channel, what do I lose?You cannot do this. The runtime will throw an
IllegalBlockingModeException when you tried to
register it.
So in order to use select(), your registered channels must
be in non-blocking mode? Why? That's just the way it is?
So to conclude, using non-blocking mode provides no real advantage for
my application. It is only required or else I would not be able to use
select(), right? If so, what is so good about nio? Can you give an example that is similar to my application which would benefit from the non-blocking characteristic of nio?
Thanks for your help so far...
Daniel.
>>
The architecture consists of only one socket for
responding to client requests. It uses receive()and
send(), not read()/write()/connect().If you are only reading from one socket there are
theoretical advantages to servicing requests on more
than one thread, but you would not use non-blocking
mode to do this.
However I think some operating systems have
performance problems when doing this. Look at this
article under accept serialization:
http://httpd.apache.org/docs/misc/perf-tuning.html
The same problems may apply to multi-thread udp socket
readers. -
NIO: Strange problem when using ByteBuffer with non-blocking SocketChannel
Hi,
I have a server that uses multiplexed, non-blocking I/O with java.nio. When a client connects, the server waits for the message: <system cmd="knock"/>, returns a message and disconnects the client. The clients are shortly serviced in less than a second.
But the server newer receive anything from about 20% of the clients - even though it is sent. Or with other words: it is received and the data is contained in the ByteBuffer - SocketChannel.read(ByteBuffer) - but a call to ByteBuffer.remaing() returns 0 !!
ByteBuffer receiveBuf = ByteBuffer.allocate(65536);
receiveBuf.clear(); // the code is elsewhere used for longer living clients
int readBytes = channel.read(receiveBuf);
receiveBuf.flip();
StringBuffer sb = new StringBuffer();
System.out.println(" * Remaining: "+receiveBuf.remaining()); // writes: ' * Remaining: 0'
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while(receiveBuf.remaining() >= 2) {
byte b = receiveBuf.get();
sb.append((char)b);
System.out.println(" * sb content: "+sb.toString()); // writes: ' * sb content: 'The ByteBuffer clearly receives the correct data, but the ByteBuffer.remaining() returns 0 and therefore the StringBuffer will never have any content.
The problem seems to occur randomly and for about 20% of the clients (simulated from the same computer and therefore has the same bandwidth and so on).
Anyone knows what is going on, and how to solve the problem !?It's always possible in any read that the number of bytes read is less than the number of bytes requested. You need to keep reading until you have got everything you expected, and cope with every possible error condition on each iteration.
EJP -
Non-Blocking Writing and Strings
Hello.
My question is simple, is it possible to write strings using a non-blocking method?
I was praying that there was a method in the NIO API that allowed me to, yet i can't find one.
If the answer is blatantly obvious please forgive me, i'm tired and hungry :)
Thank you for looking at this topicStrings are written to files or sockets using a certain encoding. I usually use UTF-8, but your application might be different.
1. Get the SocketChannel from your non-blocking socket.
SocketChannel ch = mySocket.getChannel(); // mySocket is java.net.Socket2. Make a CharBuffer out of the String you want to send.
CharBuffer chars = CharBuffer.wrap(myString); // myString is your data3. Encode it so it becomes a ByteBuffer. I'll use the [UTF-8|http://www.joelonsoftware.com/articles/Unicode.html] Charset here.
ByteBuffer bytes = Charset.forName("UTF-8").encode(chars);4. Use the write(ByteBuffer) method in the SocketChannel from 1.
ch.write(bytes);Import declarations:
import java.nio.channels.SocketChannel;
import java.nio.CharBuffer;
import java.nio.ByteBuffer;
import java.nio.charset.Charset;s -
Does Java provide any way to implement a non-blocking accept()?
There is no 'more or less' about it, it can be done. See java.nio.channels.ServerSocketChannel.
You could also set a very short timeout on a ServerSocket if you don't want the entire NIO circus ... -
I'm trying to learn how to use non-blocking socket channles, but I haven't found much info (nor luck) so far.
To learn, I'm building a server and a client. The server accepts input from the clients and process it in only one thread. The clients should send Objects to the server, and the server process them and return the result also as an Object. For this, I'm trying to use ObjectOutputStream and ObjectInputStream.
The problem I don't know how to solve is that the SocketChannel is in non-bolcking mode, so I can't use their input/output streams (I get a IllegalBlockingModeException). In the server process loop I can reconfigure the SocketChannel to blocking mode to be able to read the Object, but I can't configure it to non-blocking mode again because I get a CancelledKeyException.
Does anyone know how to work with InputStreams and non-blocking channels? Or where to find more info about it?
Here are the relevant part of the server code:
Set ready = selector.selectedKeys();
Iterator i = ready.iterator();
while (i.hasNext()) {
try {
SelectionKey sk = i.next();
i.remove();
if (sk.isAcceptable()) {
ServerSocketChannel ssc = (ServerSocketChannel)sk.channel();
SocketChannel sc = ssc.accept();
sc.configureBlocking(false);
sc.register(selector, SelectionKey.OP_READ);
} else if (sk.isReadable()) {
SocketChannel sc = (SocketChannel)sk.channel();
// PROBLEM: If the channel is in non-blocking mode
// I cannot use InputStreams
sk.cancel();
sc.configureBlocking(true);
// Read the object sent by the client
ObjectInputStream in = new ObjectInputStream(Channels.newInputStream(sc));
Object o = in.readObject();
// PROBLEM: Can't put the channel back to non-blocking mode
sc.configureBlocking(false);
sc.register(selector, SelectionKey.OP_READ); // CancelledKeyException
} catch (...){
}In my client, this is working fine:
ObjectOutputStream oos = null;
ObjectInputStream ois = null;
for (int i = 0; i < 30000; i++) {
oos = new ObjectOutputStream(sc.socket().getOutputStream());
oos.writeObject(object);
oos.flush();
ois = new ObjectInputStream(sc.socket().getInputStream());
Object o = ois.readObject();
}But trying to do it like this throws a StreamCorruptedException at the server side.
ObjectOutputStream oos = new ObjectOutputStream(sc.socket().getOutputStream());
ObjectInputStream ois = new ObjectInputStream(sc.socket().getInputStream());
for (int i = 0; i < 30000; i++) {
oos.writeObject(object);
oos.flush();
Object o = ois.readObject();
}Do you know why? -
NIO Non-Blocking Server not Reading from Key
I have created a NIO non blocking server (below) and it will not pick up any input from the client.... My log doesnt even show that it enters the readKey() method, so it must be something before. Any help would be appreciated.
Scott
package jamb.server;
import java.io.IOException;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.channels.ClosedChannelException;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.nio.channels.spi.SelectorProvider;
import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
import java.util.Iterator;
import java.util.Set;
import java.util.logging.Logger;
import java.util.prefs.Preferences;
import jamb.server.client.Client;
public class Server {
private Selector selector;
private ServerSocketChannel serverChannel;
private static Logger logger = Logger.getLogger("jamb.server");
private static Preferences prefs = Preferences.systemRoot().node("/jamb/server");
public void init() {
logger.entering("jamb.server.Server", "init");
//Get a selector...
try {
selector = SelectorProvider.provider().openSelector();
//Open the SocketChannel and make it non-blocking...
serverChannel = ServerSocketChannel.open();
serverChannel.configureBlocking(false);
//Bind the server to the port....
int port = prefs.getInt("Port", 4000);
logger.config("Server configured on port " + port + " (default: 4000)");
InetSocketAddress isa = new InetSocketAddress(
InetAddress.getLocalHost(), port);
serverChannel.socket().bind(isa);
} catch (IOException ioe) {
logger.severe ("IOException during server initialization!");
logger.exiting("jamb.server.Server", "init");
public void run() {
logger.entering("jamb.server.Server", "run");
int bufferSize = prefs.getInt("BufferSize", 8);
logger.config("Buffer size set to " + bufferSize + " (default: 8)");
SelectionKey acceptKey = null;
try {
acceptKey = serverChannel.register(
selector, SelectionKey.OP_ACCEPT);
} catch (ClosedChannelException cce) {
try {
while (acceptKey.selector().select() > 0) {
Set readyKeys = selector.selectedKeys();
Iterator i = readyKeys.iterator();
while (i.hasNext()) {
//logger.finest("Processing keys...");
//Get the key from the set and remove it
SelectionKey currentKey = (SelectionKey) i.next();
i.remove();
if (currentKey.isAcceptable()) {
logger.finest("Accepting key...");
acceptKey(currentKey);
} else if (currentKey.isReadable()) {
logger.finest("Reading key...");
readKey(currentKey, bufferSize);
} else if (currentKey.isWritable()) {
//logger.finest("Writing key...");
writeKey(currentKey);
} catch (IOException ioe) {
logger.warning("IOException during key handling!");
logger.exiting("jamb.server.Server", "run");
public void flushClient (Client client) {
try {
ByteBuffer buf = ByteBuffer.wrap( client.getOutputBuffer().toString().getBytes());
client.getChannel().write(buf);
} catch (IOException ioe) {
System.out.println ("Error writing to player");
client.setOutputBuffer(new StringBuffer());
private void acceptKey (SelectionKey acceptKey) {
logger.entering("jamb.server.Server", "acceptKey");
//Retrieve a SocketChannel for the new client, and register a new selector with
//read/write interests, and then register
try {
SocketChannel channel = ((ServerSocketChannel) acceptKey.channel()).accept();
channel.configureBlocking(false);
SelectionKey readKey = channel.register(
selector, SelectionKey.OP_READ|SelectionKey.OP_WRITE );
readKey.attach(new Client(this, channel));
} catch (IOException ioe) {
System.out.println ("Error accepting key");
logger.exiting("jamb.server.Server", "acceptKey");
private void readKey (SelectionKey readKey, int bufSize) {
logger.entering("jamb.server.Server", "readKey");
Client client = (Client) readKey.attachment();
try {
ByteBuffer byteBuffer = ByteBuffer.allocate(bufSize);
int nbytes = client.getChannel().read( byteBuffer );
byteBuffer.flip();
Charset charset = Charset.forName( "us-ascii" );
CharsetDecoder decoder = charset.newDecoder();
CharBuffer charBuffer = decoder.decode(byteBuffer);
String text = charBuffer.toString();
client.getInputBuffer().append(text);
if ( text.indexOf( "\n" ) >= 0 )
client.input();
} catch (IOException ioe) {
logger.warning("Unexpected quit...");
client.disconnect();
logger.exiting("jamb.server.Server", "readKey");
private void writeKey (SelectionKey writeKey) {
//logger.entering("jamb.server.Server", "writeKey");
Client client = (Client) writeKey.attachment();
if (!client.isConnected()) {
client.connect();
//logger.exiting("jamb.server.Server", "writeKey");From my own expierence with the NIO (Under Windows XP/ jdk1.4.1_01); you can't seem to set READ and WRITE at the same time.
The program flow I usually end up with for a echo server is:
When the selector.isAcceptable(): accept a connection; register for READs
In the read event; write the incoming characters to a buffer; register for a WRITE and add the buffer as an attachment.
In the write event; write the data to the socket If all the data was written; register for a READ; otherwise register for another WRITE so that you can write the rest.
Not sure if that the "proper" way; but it works well for me.
- Chris -
Non-blocking connection on a SocketChannel?
I'm trying out the non-blocking connection of a SocketChannel. So I wrote the following test code and supply a list of IPs (both good and bad IPs). But disregard the IPs I always get the result of a channel being in connection pending state (even for some bogus IPs). Any help will be great.
public class ConnectTest
public static void main(String[] args) throws
Exception
List<SocketChannel> channels = new ArrayList<SocketChannel>();
for ( String s: args )
SocketChannel channel = SocketChannel.open();
channel.configureBlocking(false);
channels.add(channel);
InetSocketAddress remote = new InetSocketAddress(s, 80);
channel.connect(remote);
System.out.println("wait for timeout...");
Thread.sleep(10000);
for ( SocketChannel c : channels )
if ( c.isConnected() )
System.out.println(c.socket().getInetAddress() + " connected ");
else if ( c.isConnectionPending() )
System.out.println(c.socket().getInetAddress() + " connection pending ");
else
System.out.println(c.socket().getInetAddress() + " timeout ");
c.close();
}Forget the sleep: use a Selector, selecting on OP_CONNECT. When you get it, call SocketChannel.finishConnect() for the channel(s) selected. If that method returns 'true', the connection is complete. If it returns 'false', the connection is still pending (and in fact OP_CONNECT should not have fired); if it throws an exception, the connection attempt has failed.
If the connection is complete you must also deregister it for OP_CONNECT before registering it for OP_READ or OP_WRITE. -
Non-blocking socket concurrent limitation?
I have 2 socket program,one is server side used nio package with JDK1.4.1,the other is client used traditional socket,the client will initialize about 50
threads trying to connect with server when starting,but only about 15
can be accepted,these 2 program are runnning in the same computer which
OS is win2000 professional PC.
the followd is these code:
please make a probe with them ,and tell me what's going on?
server:
package nio_select_demo;
import java.io.*;
import java.net.*;
import java.nio.*;
import java.nio.channels.*;
import java.util.*;
import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
public class Server implements Runnable
// The port we will listen on
private int port;
// A pre-allocated buffer for processing data
private final ByteBuffer buffer = ByteBuffer.allocate( 16384 );
private ByteBuffer resBuf = ByteBuffer.allocate( 128 );
Selector selector;
AddInfo test ;
public Server( int port ) {
this.port = port;
// for (int i=0; i<threadnum; ++i) {
new Thread( this ).start();
test = new AddInfo();
test.start();
public void run() {
try {
// create a ServerSocketChannel
ServerSocketChannel ssc1 = ServerSocketChannel.open();
// ServerSocketChannel ssc2 = ServerSocketChannel.open();
// Set it to non-blocking
ssc1.configureBlocking( false );
// Get the Socket connected to this channel, and bind it
// to the listening port
ServerSocket ss = ssc1.socket();
InetSocketAddress isa = new InetSocketAddress( port );
ss.bind( isa , 60 );
// Create a new Selector for selecting
selector = Selector.open();
// Register the ServerSocketChannel, so we can
// listen for incoming connections
ssc1.register( selector, SelectionKey.OP_ACCEPT );
System.out.println( "Listening on port "+port );
int n = 0;
while (true) {
// See if we've had any activity -- either
// an incoming connection, or incoming data on an
// existing connection
int num = selector.select();
// If we don't have any activity, loop around and wait
// again
if (num == 0) {
continue;
// Get the keys corresponding to the activity
// that has been detected, and process them
// one by one
Set keys = selector.selectedKeys();
Iterator it = keys.iterator();
while (it.hasNext()) {
// Get a key representing one of bits of I/O
// activity
SelectionKey key = (SelectionKey)it.next();
// What kind of activity is it?
if ((key.readyOps() & SelectionKey.OP_ACCEPT) ==
SelectionKey.OP_ACCEPT) {
System.out.println( "accept request" );
// It's an incoming connection.
// Register this socket with the Selector
// so we can listen for input on it
SocketChannel sc = ((ServerSocketChannel)key.channel()).accept();
System.out.println( "Got connection from "+sc.socket());
// Make sure to make it non-blocking, so we can
// use a selector on it.
//SocketChannel sc = s.getChannel();
sc.configureBlocking( false );
// Register it with the selector, for reading
sc.register( selector, SelectionKey.OP_READ| SelectionKey.OP_WRITE);
} else if ((key.readyOps() & SelectionKey.OP_READ) ==
SelectionKey.OP_READ) {
//ssc.register(selector , SelectionKey.OP_READ);
SocketChannel sc = null;
try {
// It's incoming data on a connection, so
// process it
sc = (SocketChannel)key.channel();
Socket s1 = sc.socket();
s1.setTcpNoDelay(true);
System.out.println( "enter processing data" );
boolean ok = processInput( key );
synchronized (selector) {
key.interestOps(key.interestOps() & ~SelectionKey.OP_READ);
// If the connection is dead, then remove it
// from the selector and close it
if (!ok) {
key.cancel();
System.out.println("dead");
Socket s = null;
try {
s = sc.socket();
s.close();
} catch( IOException ie ) {
System.err.println( "Error closing socket "+s+": "+ie );
} catch( IOException ie ) {
ie.printStackTrace();
// On exception, remove this channel from the selector
key.cancel();
System.err.println( "Error raised in this socket");
try {
sc.close();
} catch( IOException ie2 ) { System.out.println( ie2 ); }
System.out.println( "Closed "+sc );
else if ((key.readyOps() & SelectionKey.OP_WRITE) ==
SelectionKey.OP_WRITE) {
System.out.println("Enter Writing");
String response = new String();
if((response=this.test.getInfo())!=null){
resBuf.clear();
SocketChannel sc = (SocketChannel)key.channel();
resBuf = ByteBuffer.wrap( response.getBytes("ISO-8859-1" ) );
sc.write( resBuf );
synchronized (selector) {
key.interestOps(key.interestOps() & ~SelectionKey.OP_WRITE);
// We remove the selected keys, because we've dealt
// with them.
keys.clear();
} catch( IOException ie ) {
System.err.println( ie );
private boolean processInput( SelectionKey key ) throws IOException {
buffer.clear();
SocketChannel sc = (SocketChannel)key.channel();
sc.read( buffer );
buffer.flip();
String response = new String("response ok");
// If no data, close the connection
if (buffer.limit()==0) {
return false;
Charset charset=Charset.forName("ISO-8859-1");
CharsetDecoder decoder = charset.newDecoder();
CharBuffer charBuffer = decoder.decode(buffer);
System.out.println(charBuffer.toString());
System.out.println( "Processed "+buffer.limit()+" from "+sc );
return true;
static public void main( String args[] ) throws Exception {
int port = Integer.parseInt( args[0] );
System.out.println(port);
new Server( port );
cilent:
import java.io.*;
import java.net.*;
import java.util.*;
public class Client implements Runnable
private String host;
private int port;
private int acport;
//the size of buffer on how much we write and read per cycle
private static final int maxWriteSize = 128;
public Client( String host, int port, int numThreads ) {
this.host = host;
this.port = port;
for(int i =0;i<50;i++){//initialize 50 client threads
new Thread(this).start();
public void run() {
byte buffer[] = new byte[maxWriteSize];
byte buffer2[] = new byte[maxWriteSize];
try {
Socket s = new Socket( );
InetSocketAddress sa = new InetSocketAddress(host,this.port);
s.connect(sa);
System.out.println(s);
s.setTcpNoDelay(true);
InputStream in = s.getInputStream();
OutputStream out = s.getOutputStream();
for (int i=0; i<maxWriteSize; ++i) {
buffer[i] = (byte)'a';
out.write( buffer, 0, maxWriteSize );
int pause = 500;
in.read( buffer , 0 , maxWriteSize );
System.out.println( Thread.currentThread()+" wrote "+maxWriteSize);
String res = new String ( buffer );
String res2 = new String ( buffer2 );
System.out.println( res );
try { Thread.sleep( pause ); } catch( InterruptedException ie ) {}
} catch( Exception ie ) {
ie.printStackTrace();
System.err.println(ie.getMessage());
static public void main( String args[] ) throws Exception {
String host = "127.0.0.1";
int port = Integer.parseInt( args[0] );
int numThreads = Integer.parseInt( args[1] );
new Client( host, port, numThreads );I have found the reason!!!
because of system resource limitation,windows can't afford to maintain
so many concurrent stream-IO,so some socket will be closed.
I modified the client side code,adding thes segments to client instantialize
such as :
public Client( String host, int port, int numThreads ) {
for(int i =0;i<1000;i++){
new Thread(this).start();
try {
Thread.currentThread().sleep(100);//give system some idle
} catch (InterruptedException e) {
/* ignore */
then the server can accept more than 1000 client request concurrently.
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