<Swing Dev> Input needed: JDK-8161664: Memory leak in com.apple.laf.AquaProgressBarUI: removed progress bar still referenced

[Alexandr Scherbatiy]

On 7/19/2016 12:27 PM, Robin Stevens wrote:
> Hello,
>
> I wanted to discuss my approach for issue JDK-8161664 
> (https://bugs.openjdk.java.net/browse/JDK-8161664) before I started 
> working on this issue.
>
> In certain scenarios (see the JIRA issue for an example), the Timer in 
> the Animator inner class of the AquaProgressBarUI class remains 
> running, even when the JProgressBar has already been removed from the 
> UI. This causes a memory leak, as that running Timer avoids that the 
> JProgressBar can be GC-ed. As long as the Timer is running, the 
> JProgressBar is referenced through
>
> Timer -> ActionListener (=Animator inner class) -> AquaProgressBarUI 
> outer class -> JProgressBar field
>
>
>
> I see two possible approaches to fix this:
>
> 1) I carefully investigate the particular scenario I found, and try to 
> figure out why the Timer is not stopped and fix this particular 
> scenario. This offers of course no guarantees that there are no other 
> scenarios which keep the Timer running.
>
> 2) I replace one of the hard references with a weak reference, hence 
> avoiding the memory leak in all cases.
> If I do not attach the Animator inner class directly as listener to 
> the timer, but use another ActionListener which only has a 
> WeakReference to the Animator class, the memory leak is solved.
> The ActionListener could then stop the timer when the timer is fired 
> and the WeakReference#get returns null.
>
>
>
> I prefer the second approach. By cutting the hard reference between 
> the Timer and the Animator + stopping the Timer when the Animator is 
> GC-ed, I ensure that the Timer cannot cause a memory leak anymore. 
> This avoids overlooking certain scenarios.
>
> Any input on this ? Any preferences for a certain approach, or 
> proposal for another approach.
    Does other L&Fs (for example Metal) have the same memory leak with 
the JProgressBar? If no, it would be interesting to know what is the 
difference between them and the AquaProgressBarUI.

   Thanks,
   Alexandr.
>
>
> Robin