JTree display issues and thread safety

Question

I've recently ran into some issues with a JTree not displaying correctly. Infrequently, blank space will appear in the tree (big gaps between consecutive nodes), or the text of a node will be cut off ending with a "...". This happens when (but not yet proven a direct result of) one thread is expanding a node of the tree while another thread is inserting nodes into one of the expanding node's children through calls to DefaultTreeModel.insertNodeInto. (what I'm doing here is lazy loading the children's children when the parent is expanded, and the lazy loading is performed by a seperate thread so as not to delay the main thread.) It does not happen if the second thread simply adds child nodes without using the DefaultTreeModel's insertNodeInto method.
I think what might be happening here is that the DefaultTreeModel.insertNodeInto method is calling fireTreeNodesInserted which I think is in turn causing nodes in the tree to be re-rendered. This got me thinking that the problem may come down to the DefaultTreeCellRenderer being used by the two threads simultaneously. DefaultTreeCellRenderer extends JLabel and returns itself in the getTreeCellRendererComponent method. If two threads were causing nodes to be rendered at the same time, it would seem the rendered label could be occasionally in an inconsistent state.
Anyone ran into a situation like this before? The problem of text being cut off seems to be eliminated by having a custom renderer return a new component each time, rather than returning itself, but this results in degraded performance. It's almost as if each thread would need it's own renderer (or the renderer would need to return a different component for each thread), but I'm not sure how this would be done. And this doesn't solve the problem of gaps appearing in the tree.
As for the gaps, I think this might be solved by changing when the children's children are getting loaded in respect to the parent node expanding. At first I was using a TreeWillExpandListener that fired off loading the children's children. I think I might can solve the white space in the tree problem by changing that to a TreeExpansionListener that uses the treeExpanded method. So far this seems to be working...so that the parent node is done expanding before the second thread begins loading the children's children.
Any thoughts?

Answer 1

I actually found the thread3 article first... since there doesn't seem to be direct links between them, I thought I would add for anyone who reads this thread that there are several related articles. sabre150 linked the first; the others are the same base URL but with the number incremented for each. For example, the 2nd article is:
[http://java.sun.com/products/jfc/tsc/articles/threads/threads2.html]
And the 3rd article, which most directly applies to what I am doing, is:
[http://java.sun.com/products/jfc/tsc/articles/threads/threads3.html]
Edited by: Skotty on Mar 5, 2009 9:35 PM -- links turned into actual links
Edited by: Skotty on Mar 5, 2009 9:36 PM -- formatted for nicer display