RFR: 6507038: Memory Leak in JTree / BasicTreeUI

[Prasanta Sadhukhan]

On Fri, 19 Jan 2024 22:16:46 GMT, Phil Race <prr at openjdk.org> wrote:

>> When using a TreeCellRenterer which creates new components in getTreeCellRendererComponent() in a JTree that is not visible, changes to the nodes cause a memory leak.
>> When a node is changed, the Method getNodeDimensions() is called to calculate the new dimensions for the node. In this method, getTreeCellRendererComponent() is called to obtain the renderer component (what else...) and [this component is added to rendererPane](https://github.com/openjdk/jdk/blob/36f4b34f1953af736706ec67192204727808bc6c/src/java.desktop/share/classes/javax/swing/plaf/basic/BasicTreeUI.java#L3283-L3284). It is not removed from the rendererPane afterwards. 
>> Only when the tree is painted, the paint() method does a removeAll on the rendererPane [in this code](https://github.com/openjdk/jdk/blob/36f4b34f1953af736706ec67192204727808bc6c/src/java.desktop/share/classes/javax/swing/plaf/basic/BasicTreeUI.java#L1500)
>> 
>> FIx is added to remove the components from rendererPane when the JTree UI is changed/uninstalled only when tree is not visible since they are already removed when tree is painted in paint() method..
>
> src/java.desktop/share/classes/javax/swing/plaf/basic/BasicTreeUI.java line 1338:
> 
>> 1336:         if(rendererPane != null) {
>> 1337:             if (!tree.isVisible()) {
>> 1338:                 rendererPane.removeAll();
> 
> if( -> if (
> 
> Is it actually necessary to check visibility ? 
> 
> But more importantly, in the case of the test in the bug, how and when does this uninstallComponents() method get called ? It isn't clear to me how it changes the reported behaviour of that test.
> 
> I thought uninstallComponents() is just part of uninstallUI() like when tearing down and freeing the tree, or at least switching L&F .. whereas the submitter seems to be implying nodeChanged() is the problem

Yes, the submitter mentioned during nodeChanged() but I mentioned it before [in this comment](https://github.com/openjdk/jdk/pull/17458#issuecomment-1897684665)
that the comment present, implied it's not an issue, if the component is not removed if UI is not changed (as it is in the case when tree is not visible)...I am not sure why it was added and when but should we ignore that comment and try to remove the component even if tree is not visible (and UI is not changing)? 

I went with the thought that the coder meant what he said and I freed the components at the end (as you told during tearing down) so that there is no leak..

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PR Review Comment: https://git.openjdk.org/jdk/pull/17458#discussion_r1461398341