RFR: 6507038: Memory Leak in JTree / BasicTreeUI

[Alexey Ivanov]

On Wed, 17 Jan 2024 07:19:21 GMT, Prasanta Sadhukhan <psadhukhan 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();

Wouldn't it be enough to remove `rendererPane` from and assign `null` to it?

It's done this way in `BasicTableUI` and `BasicListUI`:
https://github.com/openjdk/jdk/blob/0d8543d6773a516dad54038070dce507179d0709/src/java.desktop/share/classes/javax/swing/plaf/basic/BasicTableUI.java#L1656-L1658
and
https://github.com/openjdk/jdk/blob/0d8543d6773a516dad54038070dce507179d0709/src/java.desktop/share/classes/javax/swing/plaf/basic/BasicListUI.java#L986-L988

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PR Review Comment: https://git.openjdk.org/jdk/pull/17458#discussion_r1462246022