[win] Slow Tree expand

[jukzi]

For example when showing the quick-type hierarchy of java.lang.Object multiple seconds are spend in SWT expanding the tree.
most time is spend in CallWindwProc that follows each TreeItem.setExpanded()'s OS.SendMessage (hwnd, OS.TVM_EXPAND.
I don't get why it is that slow since org.eclipse.jface.viewers.AbstractTreeViewer.inputChanged(Object, Object) sets tree.setRedraw(false); before that.
Help wanted.
Screenshot from Sampling:

[vogella]

See also #882

[SyntevoAlex]

If you make a snippet, I could profile it with native profiler.
I remember that Tree likes to calculate scrollbars even with tree.setRedraw(false).
It's likely that the problem will go away if you expand items while parent is collapsed, and in the very end expand parent.

[jukzi]

It's likely that the problem will go away if you expand items while parent is collapsed, and in the very end expand parent.

I don't have a snippet, but when i move setExpanded() after expanding the children, performance problem is gone. :-) And i don't see a visual difference. Thanks.

[laeubi]

It's likely that the problem will go away if you expand items while parent is collapsed, and in the very end expand parent.

Could this be made somehow in the JFace impl to perform it in such a way by default?

[jukzi]

Could this be made somehow in the JFace impl to perform it in such a way by default?

Absolutely. See my proposed PR. @SyntevoAlex After doing so the next hotspot (2seconds )is in CallWindwProc inside org.eclipse.swt.widgets.Tree.createItem() is there a trick against that too? It also happens while the tree's redraw is disabled.

[SyntevoAlex]

You might want to read code comments here

eclipse.platform.swt/bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/widgets/TreeItem.java

Lines 93 to 99 in 02c8a22

	* The fastest way to insert many items is:
	* <ol>
	* <li>Use {@link Tree#setRedraw} to disable drawing during bulk insert</li>
	* <li>Insert every item at index 0 (insert them in reverse to get the same result)</li>
	* <li>Collapse the parent item before inserting (gives massive improvement on Windows)</li>
	* </ol>
	*

and here

eclipse.platform.swt/bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/widgets/TreeItem.java

Lines 1694 to 1698 in 02c8a22

	* The fastest way to insert many items is:
	* <ol>
	* <li>Use {@link Tree#setRedraw} to disable drawing during bulk insert</li>
	* <li>Collapse the parent item before inserting (gives massive improvement on Windows)</li>
	* </ol>

[vogella]

cc @basilevs