Hi Anil,
As per my understanding, the browser client is single threaded. How to
get the server to interrupt the browser client to say "stop"?
On the off-chance that you're not like every other xenophobic little-HTTPer
here, and you won't let any personal prejudices stop you from thinking
outside the Ajax-box for a moment, let me offer you a Java Applet
alternative. (If/when Flash or Silverlight get around to supporting UDP you
can probably do it with them as well.)
If you'd like to see an example of a threaded Java Applet that receives UDP
messages from an abitrary server(s), then please: -
1) Click on the following link and read the instructions:
http://manson.vistech.net/~tier3/tier3pager.html
2) Telnet to manson.vistech.net. (If you don't already have an account on
the Deathrow cluster then please use Username: DEMO Password: USER) and
then:
$set term/width=132
$run sys$users:[users.tier3.web]demo_udp_msg
3) Enter the IP address of your client node. Your "stock-monitor" from step
1 should now spring into life with random stock-prices generated at 2sec
intervals. (NATed clients will find this bit problematic :-)
4) Enter any adhoc messages that you wish to appear in the seperate Java
Frame on the client.
OPCOM messages to web-subscribers? CHAT conferences? Stock-Watching? Alarm
Monitoring? - It's all good!
The rationale here is not to use up a TCP/IP connection and a server
process/thread for ad-hoc, asynchronous, broadcasts, and most definitely do
use something other than a connectionless, context-devoid,
session-hijackable, pile of http-pooh as your middleware backbone.
Cheers Richard Maher
PS. The code for Tier3Pager.java aqnd DEMO_UDP_MSG.COB are below, but all
can be found at SYS$USERS:[USERS.TIER3.WEB]
PPS. If this is for the Intranet then you might wish to look at Broadcast or
even Multicast functionality as well, and eliminate the "subscribe" step
altogether.
Tier3Pager.java
===========
/**
* Copyight Tier3 Software. All rights reserved.
*
* Author: Richard Maher
*
**/
import java.applet.Applet;
import java.awt.*;
import java.net.*;
import java.io.IOException;
import netscape.javascript.JSObject;
import netscape.javascript.JSException;
public class Tier3Pager extends Applet
{
private String hostName;
private JSObject browser;
private static MessageThread socketThread;
private static Tier3Talk chat;
public class MessageThread extends Thread
{
private DatagramSocket socket;
private DatagramPacket packet;
private String threadData;
public MessageThread(String name, String txt) throws Exception
{
super(name);
byte[] buffer;
threadData = txt;
String port = getParameter("PORT");
String maxBuf = getParameter("MAXBUF");
try
{
if (port == null)
socket = new DatagramSocket();
else
socket = new DatagramSocket(Integer.parseInt(port));
if (maxBuf == null)
buffer = new byte[512];
else
buffer = new byte[Integer.parseInt(maxBuf)];
packet = new DatagramPacket(buffer, buffer.length);
}
catch (Exception e)
{
e.printStackTrace();
System.out.println("Unable to create UDP Socket");
throw new Exception("Message thread could not be created");
}
setDaemon(true);
start();
}
public void shutdown()
{
socket.close();
}
public int getLocalPort()
{
return socket.getLocalPort();
}
public void run()
{
System.out.println("Started Message thread. ThreadData = "
+threadData);
String args[] = {"Started Message Thread " + threadData};
browser.call("alert", args);
boolean stopThread = false;
readLoop:
while (!stopThread)
{
try
{
socket.receive(packet);
String received = new String(packet.getData(),
0,packet.getLength());
processMessage(received);
}
catch (SocketException e)
{
System.out.println("Shutting up shop");
stopThread = true;
continue readLoop;
}
catch (IOException e)
{
e.printStackTrace();
System.out.println("Unable to retrieve UDP message");
}
}
System.out.println("Thread run() unit terminating");
}
public void processMessage(String msgText)
{
int msgType = Integer.parseInt(msgText.substring(0,2));
switch (msgType){
case 1:
chat.append(msgText.substring(2));
break;
case 2:
String args[] = {msgText.substring(2)};
try {browser.call("priceUpdate", args);}
catch (JSException e)
{
System.out.println("Error when calling
JSpriceUpdate()");
}
break;
default:
System.out.println("Unknown rec type"+msgText);
}
}
}
public void init()
{
System.out.println("Initializing. . .");
hostName = getCodeBase().getHost();
chat = new Tier3Talk("Tier3 Messages");
requestFocus();
browser = JSObject.getWindow(this);
if (socketThread == null)
{
try
{
socketThread = new MessageThread("MsgDaemon", "SomeData");
}
catch (Exception e)
{
e.printStackTrace();
System.out.println("Could not init Tier3Pager");
}
}
}
public void alert(String alertText)
{
String args[] = {alertText};
browser.call("alert", args);
}
public void destroy()
{
if (chat != null)
chat.dispose();
boolean stillDying;
if (socketThread != null){
socketThread.shutdown();
do
{
stillDying = false;
System.out.println("Joining MessageThread");
try {socketThread.join();}
catch (InterruptedException e){
System.out.println("Interrupted Join");
stillDying = true;
}
} while (stillDying);
socketThread = null;
}
System.out.println("Tier3Pager Applet Rundown complete");
super.destroy();
}
}
"Anil" <an*******@gmail.comwrote in message
news:ff**********************************@a70g2000 hsh.googlegroups.com...
I have a Javascript program which runs in the browser and has
functions work(), and stop().
It listens to commands from the server to work() and can be
interrupted by the server to stop().
I am using XmlHttpRequest to talk to the server.
So I use http GET to send a command "ready" to the server, which
replies at some point in time by sending "work" which is invoked by
the callback.
As per my understanding, the browser client is single threaded. How to
get the server to interrupt the browser client to say "stop"?
I modified Flanagan's example code here:
var HTTP = {
// This is a list of XMLHttpRequest creation factory functions to try
_factories : [
function() { return new XMLHttpRequest(); },
function() { return new ActiveXObject("Msxml2.XMLHTTP"); },
function() { return new ActiveXObject("Microsoft.XMLHTTP"); }
],
// When we find a factory that works, store it here
_factory : null,
// Create and return a new XMLHttpRequest object.
//
// The first time we're called, try the list of factory functions
until
// we find one that returns a nonnull value and does not throw an
// exception. Once we find a working factory, remember it for later
use.
//
newRequest : function() {
if (HTTP._factory != null) return HTTP._factory();
for(var i = 0; i < HTTP._factories.length; i++) {
try {
var factory = HTTP._factories[i];
var request = factory();
if (request != null) {
HTTP._factory = factory;
return request;
}
}
catch(e) {
continue;
}
}
// If we get here, none of the factory candidates succeeded,
// so throw an exception now and for all future calls.
HTTP._factory = function() {
throw new Error("XMLHttpRequest not supported");
}
HTTP._factory(); // Throw an error
},
/**
* Use XMLHttpRequest to fetch the contents of the specified URL
using
* an HTTP GET request. When the response arrives, pass it (as plain
* text) to the specified callback function.
*
* This function does not block and has no return value.
*/
toServer : function(url) {
var request = HTTP.newRequest();
request.onreadystatechange = function() {
if (request.readyState == 4 && request.status == 200)
MyProxy.fromServer(request.responseText);
}
request.open("GET", url, true); // 3rd param implies asynchronous
console.log("sending " + url);
request.send(null);
},
};
.....
// MyProxy
...
fromServer: function(command) {
console.log("fromServer: " + command);
eval(command);
},
thanks,
Anil
