Question on NIO

How Repeater arechitecture in NIO detect a new client has come for the request?

What's a "repeater architecture" in this context? (ie: what's it got to do with Java networking?)
Are you looking for information on how to use the NIO API, or are you trying to figure out how the NIO API works?
This is where I'd start for learning to use the API:
http://java.sun.com/j2se/1.5.0/docs/guide/nio/
The examples are of particular interest.

Similar Messages

JRockit & java.nio

Hello
I have a question regarding .nio API in JRokit SDK. Is it implemented there at
all? We are trying to test a connector application on top of WLS 8.1 and with
SUN 1.4.1 SDK it works fine, but when we try to use JRocket SDK it gives an error
during the Selector.open() method call (creation of a selector with a default
system provider).
So is the question is: is this feature supported or not? Can it be due to configuration
settings (and which ones)?
BR
VA

Thats funny back in Nov
Redhat was in touting RH AS 3.0 and Weblogic 8.1 being certified by BEA.
As the reps said
"The new POSIX threading gives a tremendous increase in performance for the JDK"
Staffan Larsen <[email protected]> wrote:
JRockit 8.1 is not supported on RHEL 3.0. If you want to try running
it
you have to set LD_ASSUME_KERNEL=2.4.1
/Staffan
Valeri Atamaniouk wrote:
Hello again
Well, we have tried. But before that we have upgraded the system toRed Hat Enterprise
Linux 3.0 AS edition. Now JRockit just gives core dumps. Right whenthe NodeManager
is started.
Files are submitted to [email protected] Hopefully there will be a positive
response
If nothing helps we will try to set install RH EL 2.1 back. Unfortunatelythere
are also some problems with the application server itself, but thatgoes to different
topic.
BR
VA
BR
VA
"Sathish Santhanam" <[email protected]> wrote:
Can you please try JRockit 81SP1? I remember one similar which has
been
fixed in this release.
http://commerce.bea.com/showallversions.jsp?family=WLJR
Sathish Santhanam
Developer Relations Engineer
BEA Support
"Valeri Atamaniouk" <[email protected]> wrote in message
news:3f99284e$[email protected]..
An update to the question above.
The implementation works fine on Windows NT, but the problem ariseswith
Linux
version. We are currently using Red Hat Advanced Server 2.1.
If we try to start up a standalone J2SE application over JRockit,
then
we
get
a message: "/dev/poll unavailable". Probably that would help.
BR
VA

SSLSocket on client & NIO w/ SSLEngine on server

Hi, I have a question about NIO & SSL...
Does it make sense to use SSLSocket on the client-side to connect to a server, which uses NIO w/ SSLEngine?
In my current code the server side is set up to be non-blocking. The handshaking part on the client side seems to work fine with the server's NIO & SSLEngine code, but after that it behaves oddly on the first read for application data (on the server-side). My SSLEngineResult from the unwrap of the first read has zero bytes for both produced and consumed. Not sure why...any thoughts?

Thanks for the replies.
I'm using the sample code that comes with the Java 5.0 SE. Although, I modified it a bit (the example is set up for an HTTP server).
The read method looks like this:
int read() throws IOException
        SSLEngineResult result;
        if (!initialHSComplete)
            throw new IllegalStateException();
        int pos = requestBB.position();
        if (sc.read(inNetBB) == -1)
            sslEngine.closeInbound(); // probably throws exception
            return -1;
        do
            resizeRequestBB();    // guarantees enough room for unwrap
            inNetBB.flip();
            result = sslEngine.unwrap(inNetBB, requestBB);
            inNetBB.compact();
            * Could check here for a renegotation, but we're only
            * doing a simple read/write, and won't have enough state
            * transitions to do a complete handshake, so ignore that
            * possibility.
            switch (result.getStatus())
                case BUFFER_UNDERFLOW:
                case OK:
                    if (result.getHandshakeStatus() == HandshakeStatus.NEED_TASK)
                        doTasks();
                    break;
                default:
                    throw new IOException("sslEngine error during data read: " +
                            result.getStatus());
        } while ((inNetBB.position() != 0) &&
                result.getStatus() != Status.BUFFER_UNDERFLOW);
        return (requestBB.position() - pos);
    }It returns from that method with the Status.BUFFER_UNDERFLOW.

Easy way to non-blocked sockets

Use JSSE and NIO for a quick way to implement non-blocking communications
October 22, 2003
Although SSL blocking operations -- in which the socket is blocked from access while data is being read from or written to -- provide better I/O-error notification than the non-blocking counterpart, non-blocking operations allow the calling thread to continue. In this article, the author will cover both the client and server side as he describes how to create non-blocking secure connections using the Java Secure Socket Extensions (JSSE) and the Java NIO (new I/O) library, and he will explain the traditional approach to creating a non-blocking socket, as well as an alternative (and necessary) method if you want to use JSSE with NIO.
http://www-106.ibm.com/developerworks/java/library/j-sslnb.html?ca=dgr-jw03j-sslnb

MORE IBM SPAM Previous discussion
I find it interesting spam, but thats a matter of taste. If the OP was truly interested in "trying to get new information out there" he would answer the mulitple questions about NIO and especially NIO mixed with traditional Sockets and NIO vs Secure Sockets. These are all on ALT, NIO is of no interest to New to Java folk.
Given their budget I think IBM could do a better job of publishing their research.

Java.nio read/write question

Hello,
I just started to learn the java.nio package so I decided to make a simple Echo server. I made a client which reads a line from the keyboard, sends it to the server and the server returns it. It all works except one little detail. Here's little code from the server:
                             int n = client.read(buffer);
                             if ( n > 0)
                                 buffer.flip();
                                 client.write(buffer);
                                 Charset charset = Charset.forName("ISO-8859-1");
                                 CharsetDecoder decoder = charset.newDecoder();
                                 charBuffer = decoder.decode(buffer);
                                 System.out.println(charBuffer.toString());
                                 buffer.clear();
                              }So that works, I send the data and then I receive it back. But only for the client. I also wanted the server to print the line which is the reason for the charset and the decoder. The above code however prints only a blank line. Thus I tried this:
                             int n = client.read(buffer);
                             if ( n > 0)
                                 buffer.flip();
                                 Charset charset = Charset.forName("ISO-8859-1");
                                 CharsetDecoder decoder = charset.newDecoder();
                                 charBuffer = decoder.decode(buffer);
                                 System.out.println(charBuffer.toString());
                                 client.write(buffer);
                                 buffer.clear();
                              }Or in other words I just moved the write() part downwards. So far so good, now the server was actually printing the lines that the client was sending but nothing was sent back to the client.
The question is how to make both, the send back line and the print line on the server side to work as intended. Also a little explanation why the events described above are happening is going to be more than welcome :)
Thanks in advance!

Strike notice
A number of the regular posters here are striking in protest at the poor
management of these forums. Although it is our unpaid efforts which make the
forums function, the Sun employees responsible for them seem to regard us as
contemptible. We hope that this strike will enable them to see the value
which we provide to Sun. Apologies to unsuspecting innocents caught up in
the cross-fire.

NIO design question

Hi,
I'm looking for advice on how to implement the following architecture in a scalable way. Can NIO be used for this?
- My application exposes a bunch of servlets. Multiple clients invoke those servlets simultaneously.
- I want to limit the number of connections across the application (all servlets) and have a separate limit on the number of connections per specific servlet.
- When a servlet is invoked, I want to push a Callable onto a worker thread (which imposes the above limits) and have the servlet thread recycled back into the web server without closing the underlying connection.
- The worker thread would eventually service the client, but a single worker thread would service potentially thousands of waiting clients.
Why do I want to these limits? Because some servlets are very expensive (cpu and memory) and are likely to cause database update collisions.
The problem is that I don't know how to return from the servlet body without closing the underlying connection. I believe the web container closes it automatically.
Any ideas?
Thanks,
Gili

Peter__Lawrey wrote:
cowwoc wrote:
1) It's container-specific as you mentioned.How many containers are you planning to use?I plan on using Tomcat or GlassFish. I'm not sure which yet.
2) MaxThreads limits across the entire container instead of on a per-servlet basis.The maximum is per application. You can put each servlet in separate applications (in the same container)
What is the motivation for having a purely per servlet limit?Some servlets are very computationally expensive and/or are liable to cause frequent database update collisions (using optimistic locking) if I allow too many simultaneous connections.

Java NIO question...

Hey, I've just start reading and programming a client/server using NIO and got to a point where i need to keep a list of connected clients to send them messages as the server processes information it received... How could i handle this selection of clients that i want to send a specific message and how should I store those clients after they connect (I mean, when a client connects, a channel is started, but how can i identify later that a channel is related to THAT client?)
Thanks in advance
Message was edited by:
Lemmerich

Generally you will associate some kind of client session object with the channel via the attachment. This will also contain the input buffer and whatever you need in your application to identify the client.

Very simple question on J NIO

This will be the easiest to answer i guess.
I have a SocketChannel and i want to read two characters from it and store then in two char variables.
I dont wanna use the socket().getInputStream().read() function as it is blocking
and also i want to avail the non-blocking read option using configureBlocking Function.
thanks for reading the post

NIO is a lot of work, but there are examples, take a look at Taming the NIO Circus for an example and some pointers about problems.
The simplest approach is to use threads and streams. It all depends on what your application structure is, whether blocking is a problem. You can also limit the time the read blocks for by using Socket.setSoTimeout.
You will need to eventually block before you can use the data that you have read. If your application uses Swing, you can use SwingUtilities.invokeLater to post an event to the GUI when the data arrives.

Question on use of NIO with je

I saw the FAQ entry about NIO: http://www.oracle.com/technology/products/berkeley-db/faq/je_faq.html#24
Could you clarify the problems with NIO and situations it shouldn't be used? Currently we are using it with 3.2 and haven't run into any issues but I don't know if we are just getting lucky.
-Nick

What I recall is that the NIO JVM bugs were related to GC. Direct memory is not managed like ordinary heap memory, so a separate (and buggy) mechanism is used in the JVM. The symptoms were very slow GC and OOME. It's possible that Sun has fixed these problems since then, but as Charles said there is no measurable performance benefit for direct memory in JE, so it is no longer used in JE. As Charles says, ByteBuffers are still used, but this is not a use of direct memory.
--mark

Java.nio selector non-blocking IO question

Hi,
I am designing an interactive server where multiple clients can log on and communicate with the server. I designed a protocol that the client/server use to talk to each other. My server runs a Selector to monitor a ServerSocket, accepting connections and reading continuously from clients.
Now my question is, since read() on ServerChannel are non-blocking using selector, how can I be sure that my entire protocol message will be read each time selector wakes up? For example, a slow client sends me a 5kb message, in one write() command, can I be sure that I will be able to read the entire message in one non-blocking read() command as well? If not, then the design becomes much more complicated, as I have to pipe each client's input into a handler thread that performs blocking i/o to read a protocol message one at a time. If I do that, then I might as well not use select() at all.
I did some preliminary tests, and it seems that for my purpose (message of size <= 50kb), a read() command will always be able to read the entire message. But I can't find any documentation on this subject. My guess is that I cannot trust non-blocking I/O as well, which means it does not fit my purpose.
Any help will be much appreciated.
Thanks,
Frank

You can't be sure a read() will read in all the data from a client in one call.
For example, say your message from the client to the server is of the following format. <start>message here<end>, where <start> indicates the start of a message and <end> the end of the message. In one read() call you might get "<start>message he". Your server would recognize this is partially correct but it needs the rest of the message. The server would store this and on the second read() you might get "re<end>" for the complete message.
The purpose of non-blocking I/O is so you don't have to wait around for the second part of the message, you can process other client messages while the first client finishes sending their message. This way other clients aren't waiting around while you(the server) sit and wait for client 1 to finish sending it's data.
So basically there is no gaurantee you will get a whole message intact. Your protocol will have to deal with partial messages, recognize them, store the partial message in a buffer, and on subsequent reads get the rest of the message.
Nick

Questions about jdk nio charset

During load test, work threads all wait for reading charset classes from Classloader. Why not keep the stable result in cache? Thanks a lot!
"ExecuteThread: '25' for queue: 'weblogic.kernel.Default'" daemon prio=1 tid=0x5c941800 nid=0x38ee waiting for monitor entry [5d697000..5d6988c8]
     at sun.net.www.protocol.jar.JarFileFactory.get(JarFileFactory.java:49)
     - waiting to lock <0x5113ebe0> (a sun.net.www.protocol.jar.JarFileFactory)
     at sun.net.www.protocol.jar.JarURLConnection.connect(JarURLConnection.java:85)
     at sun.net.www.protocol.jar.JarURLConnection.getInputStream(JarURLConnection.java:107)
     at java.net.URL.openStream(URL.java:913)
     at sun.misc.Service.parse(Service.java:203)
     at sun.misc.Service.access$100(Service.java:111)
     at sun.misc.Service$LazyIterator.hasNext(Service.java:257)
     at java.nio.charset.Charset$1.getNext(Charset.java:303)
     at java.nio.charset.Charset$1.hasNext(Charset.java:318)
     at java.nio.charset.Charset$2.run(Charset.java:361)
     at java.security.AccessController.doPrivileged(Native Method)
     at java.nio.charset.Charset.lookupViaProviders(Charset.java:358)
     at java.nio.charset.Charset.lookup(Charset.java:385)
     at java.nio.charset.Charset.isSupported(Charset.java:407)
     at java.lang.StringCoding.lookupCharset(StringCoding.java:82)
     at java.lang.StringCoding.encode(StringCoding.java:363)
     at java.lang.StringCoding.encode(StringCoding.java:380)
     at java.lang.String.getBytes(String.java:590)

who can tell me how to avoid this? Thanks a lot!

A NIO question

I want to use NIO to improve our servlet program,
but I found that there are only File and socket operation source in the WWW
I had to use a Channels.newChannel(OutputStream o ) to convert a outputStream to a WritableByteChannel ,
however this mehtod only redirect the IO operation to stream. It does not improve the performence after I writing the code below:
// this one use IO method
     public void doGet(HttpServletRequest req, HttpServletResponse res)
     throws ServletException, IOException{
          byte[] bt = new byte[4096*512];
          for(int i = 0; i < 4096*512; i++)
          bt[i] = (byte)i;
          long startTime2 = System.currentTimeMillis();
          ServletOutputStream sos = res.getOutputStream();
          sos.write(bt);
          sos.flush();
          sos.close();
          long endTime2 = System.currentTimeMillis();
          System.out.println("IO outPut spend " + (endTime2 - startTime2));
// this one use NIO method
     protected void doGet(HttpServletRequest req, HttpServletResponse res)
          throws ServletException, IOException {
byte[] nb = new byte[4096 * 512];
          for (int i = 0; i < 4096 * 512; i++)
               nb[i] = (byte) i;
     long startTime2 = System.currentTimeMillis();
          WritableByteChannel wbc = Channels.newChannel(res.getOutputStream());
          wbc.write(ByteBuffer.wrap(nb));
          wbc.close();
          long endTime2 = System.currentTimeMillis();
          System.out.println("NIO outPut use " + (endTime2 - startTime2));
how could I use NIO to improve the HttpServlet writing speed?
Thanks u.

If you have only a single connection, and especially if you have multiple threads, NIO will not help. Its most effective when multiple connections can be processed by a single thread.

Two NIO questions

Hi,
I'm very intrigued by some of the possible performance enchancements my application can use with NIO. I've got 2 situations that I want to ask the NIO experts about:
1. In one scenario, I do my own "broadcasts" over TCP (instead of UDP) by populating an OutputStream that is backed by a ByteArrayOutputStream. Then I convert my ByteArrayOutputSTream to a byte[] using toByteArray, and for each one of my OutputStream's I need to broadcast to (these are OutputStreams going thru Sockets), I write the entire byte[] into it. Is there a more efficient way to handle this with NIO? It seems like there is lots of extra bytes being copied in the JVM since the same byte[] is being sent to multiple OutputStreams. Would using a direct ByteBuffer help? Is there a performance penalty for using a ByteBuffer instead of a byte[] if I'm only sending it to one OutputStream?
2. In another scenario, I'm reading an InputStream. After a certain point of reading the stream, I need to redirect the remaining bytes in the stream to an OutputStream. Currently I'm populating the remaining bytes of the InputStream into a ByteArrayOutputStream, convert it to a byte[] usinng toByteArray(), and then send that out to my designated OutputStream. Once again, it seems like I'm doing unnecessary copying of bytes and the NIO package should have something to directly transfer the bytes from my InputStream to my OutputStream.
Thank you in advance for any help.
Mark

Well here is some pseudo-code for my first scenario.. It's basically restating what I explained earlier but I hope this helps:
import java.io.*;
public class Asdf{
private ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
public ObjectOutputStream getOutputStream(){
     this.byteArrayOutputStream.reset();
     return new ObjectOutputStream(this.byteArrayOutputStream);
public void broadcastMessage(ObjectOutputStream oos){
     oos.close();
     Iterator broadcastOutputStreamIter = getBroadcastOutputStreamIter();
     while (broadcastOutputStreamIter.hasNext()){
     ObjectOutputStream curOos = (ObjectOutputStream)broadcastOutputStreamIter.next();
     this.byteArrayOutputStream.writeTo(curOos);
     curOos.flush();
private Iterator getBroadcastOutputStreamIter(){
     //left out for clarity
public static void main(String[] args){
     Asdf asdf = new Asdf();
     ObjectOutputStream oos = asdf.getOutputStream();
     oos.writeObject("asdflkj");
     oos.writeBoolean(true);
     broadcastMessage();
To use NIO, I assume instead of using a ByteArrayOutputStream, I need to use a ByteBuffer, right? How would I tie in my usage of my ObjectOutputStream with the ByteBuffer? Or would I have to just create a new ByteBuffer on my ByteArrayOutputStream within broadcastMessage() and send that out over my Socket's Channel?
I actually haven't written code for #2 yet b/c I'm trying to figure this out. Basically I want to create an ObjectInputStream from a socket, and after reading an undetermined number of objects from the stream, I want to send the remaining bytes of that stream to another Socket's OutputStream.
Thanks,
Mark

A few general java.nio.* questions

Hi,
I've been reading up on selectors and channels for networking programming. During my reading I came across this website, http://www.javaworld.com/javaworld/jw-09-2001/jw-0907-merlin.html
It's kind of dated (3 years ago) but the example they provide on non-blocking I/O still compiles.
Further in the article (http://www.javaworld.com/javaworld/jw-09-2001/jw-0907-merlin-p4.html) they mention a few "gotcha's" with using selectors. One in particular that caught my attention was "a selector can have only 63 channels registered, which is probably not a big deal."
So only 63 channels max can be registered to a selector ? I searched around the web and the java API looking to confirm this. Does anyone know this to be true or if the max 63 registered channels was dropped before java 1.4 beta became the stable release of java 1.4? The article was written when java 1.4 was in beta.
Lastly, do selectors weed out dropped socket connections? For example. Say I have 500 socket (TCP/IP) connections to a server of mine. Of those 500 , 100 are now closed by the client by the time the server comes around to send them data. As the server loops through the 500 connections using a selector, will there be a delay because 100 connections are dropped and the server must wait for a timeout before proceeding to send the data to the next connection or does the selector detect these 100 dropped connections and only use the 400 still connected?
I hope this last question makes sense.
Thanks in advance,
Nick

Hi,
I've been reading up on selectors and channels for
networking programming. During my reading I came
across this website,
http://www.javaworld.com/javaworld/jw-09-2001/jw-0907-m
rlin.html
It's kind of dated (3 years ago) but the example they
provide on non-blocking I/O still compiles.
Further in the article
(http://www.javaworld.com/javaworld/jw-09-2001/jw-0907-
erlin-p4.html) they mention a few "gotcha's" with
using selectors. One in particular that caught my
attention was "a selector can have only 63 channels
registered, which is probably not a big deal."
So only 63 channels max can be registered to a
selector ? I searched around the web and the java API
looking to confirm this. Does anyone know this to be
true or if the max 63 registered channels was dropped
before java 1.4 beta became the stable release of java
1.4? The article was written when java 1.4 was in
beta.I don't know if that limit of 63 is still there, but it probably makes sense to use a pool of threads each supporting a Selector if the number of connections gets that high.
Lastly, do selectors weed out dropped socket
connections? For example. Say I have 500 socket
(TCP/IP) connections to a server of mine. Of those 500
, 100 are now closed by the client by the time the
server comes around to send them data. As the server
loops through the 500 connections using a selector,
will there be a delay because 100 connections are
dropped and the server must wait for a timeout before
proceeding to send the data to the next connection or
does the selector detect these 100 dropped connections
and only use the 400 still connected?closed channels are removed by the select statement. When using non-blocking IO, nothing waits anyway.
I hope this last question makes sense.
Thanks in advance,
Nick

NIO question...

saw this sample code on a webpage...
while (it.hasNext()) {
      SelectionKey sk = (SelectionKey)it.next();
      it.remove();
      int readyOps = sk.readyOps();
      // Disable the interest for the operation
      // that is ready. This prevents the same
      // event from being raised multiple times.
      sk.interestOps(sk.interestOps() & ~readyOps);
...is the setting of interestOps for the selection key necessary? i've not done this in my program and it seems to be working fine.

is the setting of interestOps for the selection key
necessary? i've not done this in my program and it
seems to be working fine.That is something which you should do if e.g the read is handled by another (service) thread. You don't want to get readiness notifications while you are processing.
Kaj

Question on NIO

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