RFR: 6507038: Memory Leak in JTree / BasicTreeUI

[Prasanta Sadhukhan]

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..

As mentioned in the comment https://github.com/openjdk/jdk/blob/36f4b34f1953af736706ec67192204727808bc6c/src/java.desktop/share/classes/javax/swing/plaf/basic/BasicTreeUI.java#L3283-L3284
the components are to be removed when UI changes, so I guess it is expected to increase if UI is not changing (ie. in case tree is not visible) so I have removed at end when  component is uninstalled at which point it is a leak too, if not removed..
A testcase is hard to provide for this leak..it's all notional..

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PR Comment: https://git.openjdk.org/jdk/pull/17458#issuecomment-1897684665