What is non blocking IO?

I have heard that 1.4 supports non blocking IO, and that this is greath for servers. What is it, how does it work and why is it so good?

I could be wrong - but if they have not yet done so
a good optimization would be to rearrange the
select list - such that the sockets that have
an event appears at the top of the list.
This way - when the select completes - it tells
you that there are - say 2 - active events - you
would then just read the first two channels on
the select list.From the API javadoc:
The selected-key set is the set of keys such that each key's channel was detected to be ready for at least one of the operations identified in the key's interest set during a prior selection operation. This set is returned by the selectedKeys method. The selected-key set is always a subset of the key set.
ie- select and iterate. No polling involved.
They just completed the java EventListener model
for the GUI. It would have been simple and clean
to implement a similar model for io. You have
the io channel - you would just attach an event
listener to it much like you would do for a control.
When an io finishes on a channel, you would be
told immediately the channel that the io completed
and what event occured - read, write etc.
Now you could have a million sockets
( if ever unix could support that many file
discriptors )
and you when an io completes no need to poll
a bunch of idle sockets.Question: What thread would this run in?
* Does it run in the network layer? How many concurrent event notifications can the network layer at any one time? Is it likely it would be an EventQueue-esque single thread?
* Does it spawn a new thread for each event? This would certainly yield worse results than spawning a new thread for each socket, since each socket would generate a vast number of events.
* Does it have a thread pool to deal with the events? Then you would be using exactly the same model as java.nio's Selector.
FYI: The windows NT asynchronous IO model uses
an event model - IO completion ports. It is far more
modern, advanced and efficient that the select / poll
model used in unix.Do you have any links for more information?
Sun could have incorporated the most modern / best
features into java and make it competitive. Instead
they went for least common denominator.Sun's nio package was (somewhat) based on a community project, and was integrated into Java on JSR-051
http://www.cs.berkeley.edu/~mdw/proj/java-nbio/
If there were such an initiative for NT-style asynchronous IO, and this was proven to be more efficient, then I imagine it will be much more likely to be integrated with the language.
If it isn't, you could still use the community-based implementation, as you could with the nbio package before 1.4 was released.
Just because Sun doesn't do something, doesn't mean you can't!

Similar Messages

Non blocking IO in jdk1.2??

hi All,
I would like to know what all non blocking IO operations are available to me in jdk1.2.2 which I can use in URLConnection. Would really appreciate help from all you people :)
Thanks in advance,
Rishi

Fluffy is correct but there are work arounds.
There are two methods available() for InputStream and ready() for Reader
The first one returns you an integer - if 0, then there are no bytes to read.
The second returns a boolean - if false, there is nothing to read.
Ironluca

What is the difference between non-blocking and 1:1 oversubscribed?

Could someone tell me what the difference is between a non-blocked port and one with 1:1 oversubscription?

"non-blocking port" and "1:1 oversubscription" are the same. It's also the same when you are saying "line rate".

What is wrong with my non-blocking client?

I have two classes here, my abstract base class SingleSocketHandler, and its concrete subclass SingleSocketHandlerImpl. The subclass implements the protocol and parsing of my server.
For some reason, my server is not receiving the packet my client sends to it, and my client is getitng nothing in return (which makes sense, the server is supposed to respond to the logon packet). I make it non-blocking AFTER logon, so I knwo that this is not a problem. Can you see why my server is not receiving the packet my client writes to it? Did I not configure some setting with the SocketChannel that enables it to write? I am sort of unfamiliar with the java.nio.channels package, so the problem may be related to a setting in the SocketChannel or whatnot that I haven't configured.
NOTE: My chat server works fine with my blocking, multi-threaded test clients. Just not for my non-blocking client. The original problem for my blocking clients was that once the server stopped sending them data, they'd get caught in the in.read() loop and never get out of it. That's why I turned to non-blocking.
Just to remind you, my question is: why isn't my client sending the logon packet AND/OR my server receiving+responding to it?
public abstract class SingleSocketHandler extends Thread
     /* Subclasses must implement these methods
        /* Even though they're not a (public) interface */
     /** <------------------------------- */
          abstract void parse(int num);
          abstract void parseNext();
          abstract void doLogon();
     /** -------------------------------> */
     private SocketChannel sock;
     /* Queues for in and out buffers */
     private LinkedList <ByteBuffer> qIn;
     private LinkedList <ByteBuffer> qOut;
     /* Server info */
     private String hostname;
     private int port;
     /* Flags */
     protected int flags;
          protected final int LOGGED_ON = 0x01;
      * Default Constructor
     protected SingleSocketHandler()
          initQs();
      * Constructor that sets socket info
      * @param hostname
      * @param port
      * @param connect
     protected SingleSocketHandler(String hostname, int port, boolean connect)
          initQs();
          if (connect)
               connect(hostname, port);
          else
               setSocket(hostname, port);
      * Switches off between reading and writing
     protected void handleIO()
          try
               sock.configureBlocking(false);
          } catch (IOException e)
               // TODO
          readInBuffers(1);
          writeOutBuffers(1);
      * Read in specified number of buffers into in queue
      * Call for parsing
      * @param num
     protected void readInBuffers(int num)
          Reporter.println("READING BUFFER");
          for (int i = 0; i < num; i++)
               ByteBuffer header = ByteBuffer.allocate(ProtocolCheck.HEADER_LEN);
               try
                    Reporter.println("Reading header...");
                    sock.read(header);
                    Reporter.println("Read header.");
               } catch (IOException e)
                    // TODO
               /* Only add packet to in queue if it has a valid header */
               if (ProtocolCheck.validHeader(header.array()))
                    Reporter.println("valid header");
                    ByteBuffer packet = ByteBuffer.allocate(ProtocolCheck.findPacketLen(header.array()));
                    packet.put(header);
                    try
                         Reporter.println("Reading rest of packet...");
                         sock.read(packet);
                         Reporter.println("Read packet.");
                    } catch (IOException e)
                         // TODO
                    addInBuffer(packet);
      * Write out specified number of buffers from out queue
      * And remove from out queue
      * @param num
     protected void writeOutBuffers(int num)
          Reporter.println("WRITING BUFFER");
          int i = 0;
          while (qOut.size() > 0 && i < num)
               try
                    sock.write(nextOutBuffer());
                    Reporter.println("Wrote buffer.");
               } catch (IOException e)
                    // TODO
               i++;
      * Returns and removes next buffer from in queue
      * @return ByteBuffer
     protected ByteBuffer nextInBuffer()
          return qIn.remove();
      * Returns and removes next buffer from out queue
      * @return ByteBuffer
     protected ByteBuffer nextOutBuffer()
          return qOut.remove();
      * Sees if there is anohter in buffer
      * @return boolean
     protected boolean hasNextInBuffer()
          return qIn.size() > 0;
      * Sees if there is another out buffer
      * @return ByteBuffer
     protected boolean hasNextOutBuffer()
          return qOut.size() > 0;
      * Add a buffer to in queue
      * @param b
     public void addInBuffer(ByteBuffer b)
          qIn.add(b);
      * Add a buffer to in queue
      * @param b
     public void addInBuffer(Bufferable b)
          qIn.add(b.getByteBuffer());
      * Add a buffer to out queue
      * @param b
     public void addOutBuffer(ByteBuffer b)
          qOut.add(b);
      * Add a buffer to out queue
      * @param b
     public void addOutBuffer(Bufferable b)
          qOut.add(b.getByteBuffer());
      * Instantiate queues
     protected void initQs()
          qIn = new LinkedList <ByteBuffer> ();
          qOut = new LinkedList <ByteBuffer> ();
      * Set socket info then call connect()
      * @param hostname
      * @param port
     public void connect(String hostname, int port)
          setSocket(hostname, port);
          connect();
      * Connect to server
     public void connect()
          try
               sock = SocketChannel.open();
               sock.configureBlocking(true);
               sock.connect(new InetSocketAddress(hostname, port));
               while (!sock.finishConnect())
          } catch (IOException e)
               // TODO
      * Disconnect from server
     public void disconnect()
          try
               sock.close();
          } catch (IOException e)
               // TODO
      * Set socket info without connecting
      * @param hostname
      * @param port
     public void setSocket(String hostname, int port)
          this.hostname = hostname;
          this.port = port;
      * @return state of connection
     public boolean isConnected()
          return (sock != null && sock.isConnected());
      * @return state of being logged on
     public boolean isLoggedOn()
          return (sock != null && (flags & LOGGED_ON) == LOGGED_ON);
public final class SingleSocketHandlerImpl extends SingleSocketHandler
     private UserDatabase <User> users;
      * Constructor that does not set socket info
     public SingleSocketHandlerImpl(UserDatabase <User> users)
          super();
          this.users = users;
      * Constructor that does set socket info
      * @param hostname
      * @param port
      * @param connect
     public SingleSocketHandlerImpl(String hostname, int port, boolean connect, UserDatabase <User> users)
          super(hostname, port, connect);
          this.users = users;
      * Thread's run method (base class extends Thread)
     public void run()
          doLogon();
          while (isConnected() && isLoggedOn())
               handleIO();
      * Parses specified number of buffers from in queue
      * @param num
     /* (non-Javadoc)
      * @see client.SingleSocketHandler#parseNext()
     @Override
     protected void parse(int num)
          Reporter.println("Parse(int num) called.");
          int i = 0;
          while (hasNextInBuffer() && i < num)
               parseNext();
               i++;
     /* (non-Javadoc)
      * @see client.SingleSocketHandler#parseNext()
     @Override
     protected void parseNext()
          Reporter.println("Parsing!");
          if (!hasNextInBuffer())
               Reporter.println("NO IN BUFFER.");
               return;
          /* Get buffer to work with */
          ByteBuffer inBuffer = nextInBuffer();
          byte[] data = inBuffer.array();
          /* Decide what to do based on message ID */
          byte msgid = data[1];
          switch (msgid) {
          case 0x01:
               Reporter.println("0x01 packet.");
               /* Determine success of login */
               byte success = data[3];
               if (success == (byte) 1)
                    flags |= LOGGED_ON;
                    Reporter.println("Logged on!");
               else
                    flags &= ~LOGGED_ON;
                    Reporter.println(" <eChat> Unable to logon. Check the hostname and port settings.");
               break;
          case 0x02:
               /* Parse out text message */
               byte[] txtmsgbytes = new byte[data.length - 3];
               System.arraycopy(data, 3, txtmsgbytes, 0, txtmsgbytes.length);
               String txtmsg = new String(txtmsgbytes);
               Reporter.println(txtmsg);
               break;
          case 0x03:
               System.out.println("Packet ID not yet handled.");
               break;
          case 0x04:
               System.out.println("Packet ID not yet handled.");
               break;
          default:
               System.out.println("validID() method is buggy.");
         * I make it non-blocking after logon sequences
     /* (non-Javadoc)
      * @see client.SingleSocketHandler#doLogon()
     @Override
     protected void doLogon()
          Reporter.println("DOING LOGON!");
          User myUser = users.getCurr();
          addOutBuffer(new ScpLogon(myUser.getUsername(), myUser.getPassword()));
          writeOutBuffers(1);
          readInBuffers(1);
          parseNext();
}

Oh, if this helps, this is what gets output to my GUI. I did a lot of outputs for debugging purposes.
[3:29:27 PM]: Connecting...
[3:29:27 PM]: Connected!
[3:29:27 PM]: Logging on...
[3:29:27 PM]: DOING LOGON!
[3:29:27 PM]: WRITING BUFFER
[3:29:27 PM]: Wrote buffer.
[3:29:27 PM]: READING BUFFER
[3:29:27 PM]: Reading header...

ORA-03118 two-task error while doing a non blocking OCI call

Hi,
I have an application that runs on Linux and uses OCI API (version 8.1.6).
If I do the following in non blocking mode after polling about
70 times I get the error:
ORA-03118: two-task coroutine has invalid state
do {
call_cnt++;
rtc = OCIStmtFetch(stmtptr->stmt, oracle_err, 1, OCI_FETCH_NEXT,
OCI_DEFAULT);
} while (rtc == OCI_STILL_EXECUTING);
This doesn't happen all the time but it happens most often on big selects.
Does anyone have any idea what is happening here?
I have searched for related information but have come up dry. If anyone
knows anything or maybe a better place to ask this question please tell me.
Thanks,
Barry
null

Ask your basis guys to increase the table space...
check this thread...
[Error : DBIF_RSQL_SQL_ERROR;
--- Thanks...

Implementing non-blocking read

Hi all
I have some doubts about implementing non-blocking io in my application.
I am using Jsch library (an ssh implementation) to open an ssh connection with a host. The API only provides me with methods to open a connection and retreive the input & output streams. I want to make my read on inputstream non-blocking.In such a case is it possible to use nio for the purpose?
If it's not possible then I am planning to use threading to make read() non-blocking. Here also i need some clarifications. I am planning to use a ThreadPoolExecutor to create a thread pool for reading data. SO whenever i have a read i'll assign this task to the pool which will use one of the free threads to execute the inputStresm.read().
Now the question is if one of the threads in this pool blocks forever during a read since it didn't get any response from the other side, is there a way to stop that read and make that thread free again to execute more tasks? or will the thread block forever till the application is closed?
In my case i cannot afford to have too many such blocked threads, since this application will not be restarted very often. Once it is started it can go on for may be days or months.
Please suggest what would be best in my case taking into account performance as most important factor.
Thanks in advance.
Anu

endasil wrote:
First of all, let me state that I agree with the others in saying that I don't fully agree with your premises.
That said, I believe that this does a non-blocking read based on the contract of InputStream.available() and .read(byte[], int, int):
private int nonBlockingRead(InputStream in, byte[] buffer) throws IOException {
return in.read(buffer, 0, Math.min(in.available(), buffer.length));
If the InputStream is obtained from a JSSE socket then it is my understanding that available() always returns zero. This is allowed under the InputStream.available() contract as defined in the Javadoc - http://java.sun.com/javase/6/docs/api/java/io/InputStream.html#available() . If I am right then your code will never read anything from a JSSE socket InputStream and I would suspect that Jsch is using JSSE sockets.

Application Builder: Can you create non-blocking, return-immediately functions in a dll?

I need to include a procedure in a dll that is non-blocking, i.e. it should return immediately after the procedure has been called, and not return after its processes are completed.
The procedure is a LabView 7.0 VI, and the dll is being created using the Application Builder. Currently the procedure completes its desired task and then returns, but I would like the function to return immediately. Thanks for your help!

Rischaard,
I don't know if that will work in a dll, however as an idea:
use the vi-server functions:
Your dll-procedure opens a OwnTreat.vi(wich will do the work) with vi-server, and run it without waiting for completion.
First thing OwnTreat.vi should do is opening (with vi-server) a reference to itself (So your caller dll can close without stopping the OwnTreat.vi)
Then OwnTreat.vi con do what YOU want. When finished close the self-reference
Maybe you need a short wait or a feedback to make sure that OwnTreat has opened his own reverence before your dll stops.
Greetings from Germany
Henrik
LV since v3.1
“ground” is a convenient fantasy
'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'

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'
System.out.println(" * Received: "+new String(receiveBuf.array())); // writes: ' * Received: <system cmd="knock"/>'
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 worker servlet ?

Hi friends,
I have an issue to implement. We implemented a web application and now I want to separate some parts of this application. I can express the action shorter and simple below.
if a user requests x-y ticket {
��try {
��check db if x-y is available
��if true send available
��else not
��}catch (NonExistentData) {
��addJob2Queue(x-y)
��send available
��}
class AvailabilityHelper extends Thread{
��run(){
��while(true){
��checkQueue
��if there is job, updateDBfor(org,dest)
��}
��}
* updateDBfor(org,dest) includes other ejb references to request data and insert it into db
This web aplication runs with JSP 1.2 EL support on WAS 5.1
the check for db and the thread implementation was in a seperate package and were used in actions of web application. Now they also want to use these checks for other (non web) applications. So i think there should be a session bean in ejb and should process these requests and I used JMS (Message-Driven Bean) with WebSphere MQ to undertake the thread and queue mechanism.
Now it works like this :
class exampleSessionBean{
��getAvalibability(org, dest){
��try {
��check db if x-y is available
��if true send available
��else not
��}catch (NonExistentData) {
��queueSender.sendMessage(update x-y)
��send available;
��}
��}
class queueMDB{
��onMessage(){
��updateDBfor(org,dest)
��}
The purpose of this applications was, not to block the user for db update process, if there is data in db select and show to the user. the update process of db includes other ejb references and takes so much time. It is nonsense to make the user wait such time. And the info is not a big deal, because of this when i put a request for update, without blocking i send it as available...
So what is the problem ? :) Deployment team don't want to pay for websphere MQ and hire a admin for that. Also they don't want to use Embedded Messaging server client (JMS Server) of WAS. So I am asking you: is there a way to implement a non blocking servlet so that i will just make a request and don't wait for response, or a servlet will take the request and release the connection but will continue to process the request ?
thanks for all...

I tried to implement a web application and add a ServletContextListener as stevejluke suggests. But on contextInitialized function when creating new JobConsumer it gets following errors on server.
6/27/06 12:51:36:391 CEST] 33238138 WebContainer A SRVE0169I: Loading Web Module: non-blocking.
[6/27/06 12:51:36:438 CEST] 33238138 SystemOut O OlaListener initializing...
[6/27/06 12:51:36:516 CEST] 33238138 SystemOut O OlaListener - Queue added
[6/27/06 12:51:36:516 CEST] 33238138 SystemOut O OlaListener - keepWorking
[6/27/06 12:51:36:672 CEST] 33238138 WebApp E SRVE0015E: Failure to initialize Web application non-blocking
[6/27/06 12:51:36:844 CEST] 33238138 WebGroup E SRVE0054E: An error occurred while loading Web application
public class OlaListener implements ServletContextListener {
     * @see javax.servlet.ServletContextListener#void (javax.servlet.ServletContextEvent)
     public void contextDestroyed(ServletContextEvent event) {
             ServletContext context = event.getServletContext();
             context.setAttribute("keepWorking", Boolean.FALSE);
     * @see javax.servlet.ServletContextListener#void (javax.servlet.ServletContextEvent)
     public void contextInitialized(ServletContextEvent event) {
             System.out.println("OlaListener initializing...");
             ServletContext context = event.getServletContext();
             WorkQueue newJobs = new WorkQueue();
             context.setAttribute("newJobs", newJobs);
             System.out.println("OlaListener - Queue added");
             context.setAttribute("keepWorking", Boolean.TRUE);
             System.out.println("OlaListener - keepWorking");
             JobConsumer jc = new JobConsumer();
             System.out.println("OlaListener - Job Consumer created");
             jc.setContext(context);
             System.out.println("OlaListener - context set");
             Thread t = new Thread(jc);
             t.start();
public class JobConsumer implements Runnable{
     /*log4j*/     private static final Logger logger = Logger.getLogger(JobConsumer.class);
     private ServletContext context = null;
     public void run(){
             System.out.println("JobConsumer - run Start");
             processQueue(context);
             System.out.println("JobConsumer - run End");
}

Broken Pipe with Non-blocking Socket

Hello,
I write a Unix Agent who connect on a Windows Server with socket...
Working well on Linux but on Solaris my problem is:
-When my agent is running before server at connection all seems OK: Connect, Select and Getsockopt but when I try to send data I have always EPIPE Signal but I can receive datas from server !
- When my agent is strarting after the server all it's Ok
I don't unserstand this appears on Solaris SPARC 8 and Solaris 9 Intel ...
Please Help is there something special with non-blocking sockets on Solaris ?
Thanks

Can't help you much but what I would recommend is that you
insure that your pipes are opened for both read/write, even
though you are only going to read or write from it. This insures
that the pipe does not close down when you hit EOF.

Non-blocking J2EE calls

We wish to connect fat clients (in our case Powerbuilder) to a J2EE environment (Weblogic). We also need to make some of the calls from the fat client non-blocking (asynchronous). With many clients, JMS was rejected as a mechanism.
Our first solution, which works as a prototype, was to package a Java bean as an OLE object and deploy it to the client. This bean could make the calls non-blocking. However there are registry issues (the packaging implies a pre-defined directory structure), we need a JRE on every client and 15Mb of weblogic jars (aaargh), so it only really works as a prototype.
The next (current) solution is a C dll that can be called from Powerbuilder and uses a socket to talk to a Java J2EE Gateway on the server. This Gateway makes the system non-blocking and calls the EJBs. This is clearly easier in terms of configuring the client.
Ideally we would like to drop the Gateway by finding a non-blocking way to get into J2EE from the C dll but the only methods we have thought of:
- simulating an HTTP servlet call
- SOAP
are synchronous (or appear to be, my knowledge of SOAP is limited).
Has anyone come across other ways of getting non-blocking communications with J2EE?

CORBA, this is what it was designed to do, but it is not not a light weight solution.

Non-blocking ServerSocketChannel.accept()

This may be a dumb question, but what would the motivation be behind utilizing a non-blocking call to the accept method of the ServerSocketChannel? I'm just having a hard time thinking of any, although I'm sure there are good reasons for doing it.
Thanks,
Ken

it does seem pretty strange

Read Timeout on non-blocking sockets

Hi,
I was wondering if there is a way to specify a read timeout (like setSoTimeout for synchronous sockets) when using a non-blocking socket.
I'd like to have the select() method return is a sockets timeout expires, puting in the selected key set the timedout socket and have it's read operation return -1, something like what happens when a socket is closed by the other side.
The thing is I need this to be a timeout specific to each socket, thus the select(millis) isn't apropriate.
Anyone knows of something like this?
Thanks....

Yeah, select() is the only thing built in for that, and you have to do the bookkeeping yourself. You would start something like forming the disjunction of the ready keys and the registered keys after each select, to get the unready keys, and then looking at their history to see how long they have been unready via a Map{key,Long(time)).

Non-blocking file behaviour for Reader

Hi!
It will be really nice if Reader will not block files for writing. Assume someone is using TeX to create PDF and he need to
a) examine the results;
b) edit the source.
It becomes a nightmare with Reader. Compile TeX, open Reader, examine results, close Reader. And then from the beginning.
Auto reloading of a PDF file is also a nice feature!
So far I can see only one solution: one should use another viewer to get non-blocking behaviour.
Thanks!

OK, let us see. I use Windows XP Professional SP3, Reader version is 9.3.0. I made a simple test: openned a file in Reader, then openned this file in my favourite text editor and tried to change "%PDF-1.4" to "%PDF-1.3" and save. I received a "File sharing violation error". I can also try to do it in Ubuntu.
As for the open source viewers. That is what I am currently doing: I use additional viewer to view the files I create and I use Adobe Reader to view all other files. One can leave with such solution, but it is not the best.

Non-Blocking Multicast Sockets in JDK 1.4?

Hi,
I've been trying to create non-blocking multicast sockets in JDK1.4, which essentially seems (at this stage) to boil down to the simpler problem of creating a DatagramChannel that uses MulticastSockets, or at least DatagramSockets that can join a Multicast group. Not having found any obvious way to do it, I created this extraordinary hack:
package java.net; // Wicked, wicked!
import java.io.*;
public class MyDatagramSocket {
public static void join(java.net.DatagramSocket socket, InetAddress addr)
throws IOExceptio DatagramSocket ds = new DatagramSocket(port);
ds.setReuseAddress(true);
MyDatagramSocket.join(ds, InetAddress.getByName("224.0.0.104"));
DatagramPacket dp = new DatagramPacket(array, 5000);
ds.receive(dp);          /* READS FINE */
n
socket.impl.join(addr); // Uses knowledge of DatagramSocket culled from examining source to access DatagramSocketImpl
Now I compile this, and drop the class file into my rt.jar files (in the JDK and the JRE), so that I can use MyDatagramSocket.join (DatagramSocket, InetAddress), which looks like it should work from code like this:
try {
int port = 58501;
DatagramChannel dc = DatagramChannel.open();
dc.socket().setReuseAddress(true);
dc.socket().bind(new InetSocketAddress(port));
MyDatagramSocket.join(dc.socket(), InetAddress.getByName("224.0.0.104"));
byte [] array = new byte[5000];
ByteBuffer bb = ByteBuffer.wrap(array);
dc.receive(bb);
System.out.println("Read from dc");
} catch (Exception x) {
x.printStackTrace();
But it doesn't work - it just doesn't read. A simpler example is this:
DatagramSocket ds = new DatagramSocket(port);
ds.setReuseAddress(true);
MyDatagramSocket.join(ds, InetAddress.getByName("224.0.0.104"));
DatagramPacket dp = new DatagramPacket(array, 5000);
ds.receive(dp);          /* READS FINE */
So I know that my hack is working, but this fails:
DatagramChannel dc = DatagramChannel.open();
dc.socket().bind(new InetSocketAddress(port));
dc.socket().setReuseAddress(true);
MyDatagramSocket.join(dc.socket(), InetAddress.getByName("224.0.0.104"));
DatagramPacket dp = new DatagramPacket(array, 5000);
dc.socket().receive(dp);     /* NEVER READS */
I've reduced the problem to one of the difference between a java.net.DatagramSocket - the standard DatagramSocket, and a sun.nio.ch.DatagramSocketAdaptor, which is what DatagramChannels seem to use.
My questions are:
a) Is there a proper way to do this, without my adding my own classes to java.net?
b) If NO is the answer to a), any ideas what I'm doing wrong in my code?
Many thanks for any assistance,
Craig

I've encountered the same problem in my code. The datagramChannel never receives incoming data. Doesn't matter the rate at which you send it or anything else. I don't see any way around this problem at the moment. If i find something i'll post it. Interesting enough, my friend who programs with C++ got non-blocking I/O with datagrams to work in windows. So this might just be java.

What is non blocking IO?

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