LiveConnect Applet Architecture Bug with Thread utilization (with SSCCE!)


R

Richard Maher

Hi,

I make no claim to being either a Javascript or JAVA expert so,
before
logging a bug report with SUN/Oracle, I would appreciate those here
with
relevant skills casting a critical eye of my small reproducer to see
if the
anomalies can be explained as simple pilot error rather than a bug in
the
plugin code.

To reproduce the example locally, save the three text files below to
the
filenames and extensions specified. Then: -

javac -cp "c:\Program Files\Java\jdk1.6.0_22\jre\lib\plugin.jar"
OutThread.java

javac -cp ".;c:\Program Files\Java\jdk1.6.0_22\jre\lib\plugin.jar"
Sleeper.java

jar -cf Sleeper2.jar Sleeper.class OutThread.class

NB* The above specified the classpath so as to match my version and
Windows
location of the relevant bits from the SDK. Your OS, Java Version and
SDK
path may vary or may already be defined.

Note also there will be some minimal text wrapping to be corrected in
the
files.

Once you have compiled the two classes into the JAR, copy Sleeper2.jar
and
dyntest_embed.html to your web root directory. Pull up
http://127.0.0.1/dyntest_embed.html with your FireBug/DeveloperTools
Console
window enabled and your JAVA console enabled and watch what happens.
It can
take up to 30,000 iterations or as little as 100 but you will see the
"hang". (If you become impatient you can add further tabs with the
same page
(work the static vars) or load the browser instance and/or machine)

What I observe and accuse the plugin of doing is allocating the wrong
work
to the wrong thread. That is, unlike the documented behaviour that can
be
seen at: -
http://download.oracle.com/javase/6/docs/technotes/guides/jweb/applet/applet_exe
cution.html#threads
I believe that something makes the plugin lose track of the Thread
pool and
allocate the setBack()/notifyAll() call to the LiveConnect worker
thread
(when it should go to "Fred") and horror of horrors, my consumer
thread
"Fred" that should be exclusively processing jobs on the queue
sometimes is
allocated producer work (getNum()) which leads to an unavoidable
deadlock
:-(

Actual example output: -
[1]in getNum() 2490 caller [TO3] Thread Applet 1 LiveConnect Worker
ThreadThread[Applet 1 LiveConnect Worker
Thread,4,http://127.0.0.1/-threadGroup] hash 19c0bd6
[1]Queueing work
[1]Going for wait
**[2]in getNum() 2409 caller [TO2] Thread
FredThread[Fred,4,http://127.0.0.1/-threadGroup] hash 1827d1**
[2]Queueing work
[2]Going for wait


This can be observed with FF and/or IE8 (Chrome doesn't seem to fail
with
only one tab but with multiple dyntest_embed.html tabs the results can
be
reproduced).

Does it coincide with garbage collection? Is the code/logic
fundamentally
flawed? Is it a LiveConnect Thread management bug in desperate need
of
correction?

Cheers Richard Maher

OutThread.java
===========

/**
* Copyright (c) Richard Maher
* All rights reserved.
*/
import netscape.javascript.JSObject;
import java.util.ArrayList;
import java.util.concurrent.*;

class OutThread extends Thread {
ArrayList<JSObject> windows;
BlockingQueue<JSObject> queue;
JSObject item;

public OutThread(String name, ArrayList<JSObject> windows,
BlockingQueue<JSObject> queue) {
super(name);
System.out.println("Thread constructor");
this.setDaemon(true);
this.windows = windows;
this.queue = queue;
}

private boolean readNext(){
try {
System.out.println("before take");
item = queue.take();
System.out.println("after take");
} catch (InterruptedException e) {
return false;
}
return true;
}

public void run() {
while (readNext()) {
// try {
System.out.println("before call");
// sleep((int)(Math.random() * 1000));
try {
item.call("dispatcher", null);
} catch (Exception e){e.printStackTrace();}
System.out.println("after call");
// } catch (InterruptedException e) {break;}
}
System.out.println("DONE!");
}
}

Sleeper.java
========
/**
* Copyright (c) Richard Maher
* All rights reserved.
*/
import java.applet.Applet;
import netscape.javascript.JSObject;
//import netscape.javascript.JSException;
//import java.lang.InterruptedException;
import java.util.ArrayList;
import java.util.concurrent.*;

public class Sleeper extends Applet {
private int myNum = 0;
private int myInstance = 0;
private JSObject browser;
private final Object lock = new Object();
private boolean initFlag = false;
private boolean idle = true;

private static OutThread writer;
private volatile static int appletIndex = 0;
private volatile static ArrayList<JSObject> windows = new
ArrayList<JSObject>();
private static BlockingQueue<JSObject> queue = new
ArrayBlockingQueue<JSObject>(5);

public synchronized void init() {
super.init();
Thread curr = Thread.currentThread();
System.out.println(" In Init() " + curr.getName() +
curr + " hash " + Integer.toHexString(curr.hashCode()));

try {
browser = JSObject.getWindow(this); }
catch (netscape.javascript.JSException e) {
e.printStackTrace(); }
catch (Exception e) {
e.printStackTrace(); }

synchronized(windows){
appletIndex++;
myInstance = appletIndex;
windows.add(browser);
if (writer == null){
writer = new OutThread("Fred", windows, queue);
writer.start();
}
}
/**
System.out.println("Before sleep call");
try {
Thread.sleep(1000);
}
catch (InterruptedException e){
e.printStackTrace();
}
System.out.println("After sleep call");
*/
myNum = 33;
initFlag = true;
}

public synchronized boolean isDone() {
Thread curr = Thread.currentThread();
System.out.println(" In isDone() " + curr.getName() +
curr + " hash " + Integer.toHexString(curr.hashCode()));
return initFlag;
}

public synchronized int getNum(String caller, JSObject callback){
if (!idle){
System.out.println("******* boom *********");
}
idle = false;
int i = myNum++;
Thread curr = Thread.currentThread();
System.out.println("["+myInstance+"]"+"in getNum() " + myNum +
"
caller " +
caller + " Thread " + curr.getName() +
curr + " hash " + Integer.toHexString(curr.hashCode()));

try {
synchronized (lock){
System.out.println("["+myInstance+"]"+"Queueing work");
queue.put(callback);
System.out.println("["+myInstance+"]"+"Going for wait");
lock.wait();
// Thread.sleep(1000);
}
}
catch (InterruptedException e){
e.printStackTrace();
}

System.out.println("["+myInstance+"]"+"After wait call " + i);
idle = true;
return i;
}

public void setBack(String caller){
Thread curr = Thread.currentThread();
System.out.println("["+myInstance+"]"+"in setBack() " + myNum + "
caller " +
caller + " Thread " + curr.getName() +
curr + " hash " + Integer.toHexString(curr.hashCode()));

synchronized (lock){
lock.notifyAll();
}
System.out.println("["+myInstance+"]"+"After notify");
}

public synchronized void destroy ()
{
System.out.println("["+myInstance+"]"+"Shutting down");
if (writer != null){
writer.interrupt();
try {
writer.join();
}
catch (InterruptedException e){
e.printStackTrace();
}
writer = null;
}

System.out.println("["+myInstance+"]"+"Checked - out");
super.destroy();
}
}

dyntest_embed.html
==============

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">

<html>
<head>
<style>

body
{
background-color: aliceblue;
color: black;
font-family: Georgia;
font-size: 12px;
}

</style>

<script type="text/javascript">

var callNum = 0;
var chanG;
var activeTesters = [];
var ctrl;

function load()
{
var objectTag = "<object ";

if (/Internet Explorer/.test(navigator.appName)) {
objectTag = objectTag +
'classid="clsid:8AD9C840-044E-11D1-B3E9-00805F499D93" ';
} else {
objectTag = objectTag +
'type="application/x-java-applet" ' +
'archive="http://127.0.0.1/Sleeper2.jar" ';
}

objectTag = objectTag +
'width= "0" height= "0" id="TestApp">' +
'<param name="archive" value="Sleeper2.jar">' +
'<param name="codebase" value="http://127.0.0.1/">' +
'<param name="code" value="Sleeper">' +
'<param name="java_version" value="1.6+">' +
'<param name="mayscript" value="true">' +
'<param name="scriptable" value="true">' +
'<param name="codebase_lookup" value="false">' +
'</object>';

var appletDiv = document.createElement("div");
appletDiv.innerHTML = objectTag;

try {
document.body.appendChild(appletDiv);
chanG = document.getElementById("TestApp");
}
catch(err) {
alert("Tier3 unable to load applet: -\n" +
(err.description||err.message));
chanG = null;
};

if (chanG == null) {
throw new Error("Tier3 was unable to initialize the applet");
} else {
try {
if (!chanG.isDone())
alert("*******RACE******");
}
catch(err) {
chanG.setAttribute("id",null);
chanG = null;
throw new Error("Tier3 unable to load applet: -\n" +
(err.description||err.message));
}
}

ctrl = new blob();
var tester1 = new tester(1,1000);
var tester2 = new tester(2,300);
var tester3 = new tester(3,500);

}

function tester(myId,timer){
this.myId = myId;
this.timer = timer;
var sendIt = function(){ctrl.send("[TO"+myId+"]", fred);};
var fred = function() {
if (window.console) console.log("In callback");
callNum++;
document.mfForm.username.value=myId+"CB<:"+callNum;
this.rendezvous();
if (window.console) console.log("After setBack()");
document.mfForm.state.value=myId+"CB>:"+callNum;
setTimeout(sendIt,timer);
}
setTimeout(sendIt,0);
activeTesters.push(this);
return this;
}

function blob(){

this.chan = chanG;

return this;
}

blob.prototype = {

send:
function(msgBody, callback)
{
var chan = this.chan;
var responseCnt = 0;
var i = 0;

var msgCandidate =
{
msgSeqNum : -1,
chan : chan,
callback : callback,

dispatcher :
function()
{
this.responseCnt++;

try {
callback.apply(this);
}
catch (err) {
var errMsg = "Error calling callback
routine: -\n";
for (var prop in err) {
errMsg += " Property: " + prop + " Value:
" +
err[prop] + "\n";
}
errMsg += " toString() = " + err.toString()
+
"\n";

if (window.console) console.log("Client: "
+
errMsg);
// document.write("Client: " + errMsg);
throw new Error(errMsg);
}
},

getResponseCnt:
function() {
return this.responseCnt;
},

rendezvous :
function() {
if (window.console) console.log("In
rendezvous");
chan.setBack("CB");
}

};

if (window.console) console.log("Before SEND: " + msgBody);
return chan.getNum(msgBody, msgCandidate);
}
}
</script>
</head>

<body id="torso" onload="load()">
<form name="mfForm">
Something:
<input
name="username";
type="text";
size=20;
/>
Stuff:
<input
name="state";
type="text";
size=20;
/>
</form>
</body>
</html>
 
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L

Lew

Richard said:
I make no claim to being either a Javascript or JAVA expert so,
before
logging a bug report with SUN/Oracle, I would appreciate those here
with
relevant skills casting a critical eye of my small reproducer to see
if the
anomalies can be explained as simple pilot error rather than a bug in
the
plugin code.

This post looks very similar to the one you posted yesterday with the same
subject line.
 
R

Richard Maher

Lew said:
This post looks very similar to the one you posted yesterday with the same
subject line.

Yes, my appologies for those who see both posts. I checked for replies
this morning via Google groups and there was no trace of my original
post so I assumed it didn't get through.

Cheers Richard Maher
 
S

Screamin' Lord Byron

Yes, my appologies for those who see both posts. I checked for replies
this morning via Google groups and there was no trace of my original
post so I assumed it didn't get through.

I can confirm that as I don't see the original post on c.l.j.programmer.
 
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