Workaround for JDialog me

"Karl Mueller" <karl.mueller@THRWHITE.remove-dii-this>
Wed, 27 Apr 2011 15:36:27 GMT
I just submitted a bug report on a memory leak that I discovered in 1.6 (I
tested with 1.5 and there is no memory leak). What I am wondering is if
anyone has encountered this bug and if so if there is any better workaround
which I will describe shortly?

Basically one would first create a JFrame and then have a modal child dialog
(e.g,. PrimaryChildDialog) hanging off of it and then create another modal
child dialog (e.g., SecondardChildDialog) which hangs off the first modal
child dialog. Now one would close/dispose SecondaryChildDialog and then
close/dispose PrimaryChildDialog and then set PrimaryChildDialog to null.

Now if one repeats the above process n times one would see n
PrimaryChildDialog objects occupying memory (i.e.,
PrimaryChildDialog.finalize method never gets called and it is also returned
in the array of Window objects from the Windows.getWindows() method).

For example here is a code snippet for creating/showing and then disposing
public void openPrimaryChildDialog ()
 fPrimaryChildDialog = new PrimaryChildDialog(getFrame (),
   "Primary Child Dialog...", true);

 fPrimaryChildDialog.openDialog ();

 fPrimaryChildDialog.dispose ();

 fPrimaryChildDialog = null;

 // Note: there should be a better way of causing Java to IMMEDIATELY
 // release the fPrimaryChildDialog resource! ==> Ugh!
 getFrame ().dispose ();

 Runtime.getRuntime ().runFinalization ();

 getFrame ().setVisible (true);

In Java 1.5 PrimaryChildDialog's finalize method is correctly called each
time but in 1.6 there are n instances of PrimaryChildDialog and its finalize
method is never called. Oh yes, I got the following cool piece of code to
guarantee that the memory was indeed flushed which I called everytime I
disposed of PrimaryChildDialog:

private void flushMemory(PrintStream pPrintStream)
 pPrintStream.println ("\nFlush memory begin:");

 //Use a vector to hold the memory.
 Vector v = new Vector();
 int count = 0;
 //increment in megabyte chunks initially
 int size = 1048576;

 //Keep going until we would be requesting
 //chunks of 1 byte
 while(size > 1)
   for (; true ; count++)
    //request and hold onto more memory
    v.addElement( new byte[size] );
  //If we encounter an OutOfMemoryError, keep
  //trying to get more memory, but asking for
  //chunks half as big.
  catch (OutOfMemoryError bounded){size = size/2;}

 //Now release everything for GC
 v = null;
 //and ask for a new Vector as a new small object
 //to make sure garbage collection kicks in before
 //we exit the method.
 v = new Vector();

 // Let's run gc anyhow...
 Runtime.getRuntime ().gc ();

 pPrintStream.println ("\nFlush memory end.");

The only workaround that I could think of is to minimize the memory impact
by calling the JDialog's getContentPane().removeAll () method as well as any
hard references in the class which I extended so that at least those items
can be garbage collected.

Does anyone have any better workaround and has anyone encountered this

If anyone is interested I can send the small test case (4 small Java files)
that I just submitted to Sun.


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