Re: FireFox II setTimeout() Go Back and Applets

From:

"Richard Maher" <maher_rj@hotspamnotmail.com>

Newsgroups:

comp.lang.java.programmer,comp.lang.javascript

Date:

Fri, 15 May 2009 15:26:07 +0800

Message-ID:

<guj5c3$8oo$1@news-01.bur.connect.com.au>

"Richard Maher" <maher_rj@hotspamnotmail.com> wrote in message
news:guj2o0$6s1$1@news-01.bur.connect.com.au...

Hi,

I hope to come up with a small reproducer shortly but here's the gist of

in the hope that someone recognizes the foot print and may be able to

offer

advice or a work-around: -

1) The page contains an Applet with method send()
2) In the example setTimeout("witeIt()",10000); to fire writeIT() every 10
secs which will in turn call applet.send()
3) User navigates away from Applet-hosting page to a new page
4) When they hit the Go Back /Previous Page button: -
5) The page reloads
6) The old Applets destroy() method is called and should go away please
7) New version of the Applet is in the process of being init()ed
8) The "old" timer from the previous instantiation of the page seems to

take

up where it left off
9) The timer fires and writeIt() calls the SEND() from the previous

version

of the Applet
10) "synchronized" methods don't help as it looks to be a new instance of
the Applet
11) Historical send() gets called and trashes my latest initialization

This *only* appears to happen on "Go Back" button; "Refresh" is fine.

Also,

IE is fine in both cases.

Am I seeing timer and Applet ghosts on FF or just seeing things in general
:-)

Cheers Richard Maher

Ok, below its a tiny example.

You need to have the java console on and then you notice that (after you
load the page navigate away and then use the Back button with FF2) that the
instance variables behave like static class variables, and if it isn't a new
instance of the Applet then why are the synchronized methods not
synchronizing? Do I really have to put additional synchronization blocks in
to handle these phantoms?

Does anyone use FF2 anymore? Anyway to say "Nah I really mean destroy() or
reload()!"?

PS. Do a "refresh" to compare and contrast.

Sleeper.java
============

import java.applet.Applet;
import java.lang.InterruptedException;

public class Sleeper extends Applet {
     private int myNum = 0;

     public synchronized void init() {
         super.init();

         System.out.println("Before sleep call");
         try {
             Thread.sleep(5000);
         }
         catch (InterruptedException e){
             e.printStackTrace();
         }
         System.out.println("After sleep call");
         myNum = 33;
     }

     public synchronized int getNum(){
         int i = myNum++;
         System.out.println("in getNum " + myNum);
         return i;
     }

    public synchronized void destroy ()
    {
        System.out.println("Checked - out");
        super.destroy();
    }
}

sleeper.html
=============

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

<html>

  <meta name="author" content="Richard Maher"/>
  <meta name="description" content="JS Function and Applet Test"/>

  <head>

    <style>

    body
    {
    margin: 0px;
    background-color: white;
    color: Black;
    font-family: times;
    font-size: 16px;
    border: medium ridge;
    }

    </style>

    <script type="text/javascript">

    var timerCnt = 0;
    var chan;

    function load() {
        var lclNum;
        document.display.next.value = timerCnt;
        try {
            chan = document.getElementById("Sleeper");
            lclNum = chan.getNum();
            setTimeout("writeIt()",0);
        }
        catch (err) {
            alert("In catch " + err.description);
        }
        if (chan == null) alert("chan is null");
    }

    function writeIt(){
        timerCnt++;
        document.display.next.value = timerCnt;
        chan.getNum();
        setTimeout("writeIt()",1000);
    }

    </script>

  </head>

  <body onload="load();">

    <br /><h2>Test it</h2><hr /><br />

    <form name="display" style="margin-left: 100px;">

       <input
          type="text"
          style="text-align: Left;"
          name="next"
          size=10
       />
    </form>

    <script type="text/javascript">

    var myDef;
    if (navigator.appName == "Microsoft Internet Explorer")
       myDef =
          '<object classid="clsid:8AD9C840-044E-11D1-B3E9-00805F499D93" ' +
                   'width= "0" height= "0" id="Sleeper">'
+
                            '<param name="code" value="Sleeper">'
+
                            '<param name="mayscript" value="true">' +
                            '<param name="scriptable" value="true">' +
          '</object>'
    else
       myDef =
          '<object classid="java:Sleeper.class" '
+
                   'type="application/x-java-applet" ' +
                   'width= "0" height= "0" id="Sleeper">'
+
                            '<param name="code" value="Sleeper">'
+
                            '<param name="mayscript" value="true">' +
                            '<param name="scriptable" value="true">' +
          '</object>'

    document.write(myDef);
    </script>

  </body>

</html>