Bug 253773 [Viewers] Collapsed expandable nodes in a TreeViewer are needlessly expensive
In the Expressions view, the debug platform TreeViewer needlessly causes the model to be queried for all children of collapsed expandable items. This can have serious performance repercussions. This can be easily seen in a CDT gdb debug session. Create a simple C project with the following main(). Launch a debug session and add 'arr1' and 'arr2' in the Expressions view. Don't expand them. Simple step through the loop. Every step takes about 3-4 seconds on a relatively fast machine. Close the Expressions view, stepping becomes instantaneous. int main() { int arr1[100]; int arr2[100]; while (1) { int i = 1; i++; } return arr1[0] + arr2[0]; }
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/TreeViewer.java
}
	protected Object[] getRawChildren(Object parent) {
		if (contentProviderIsLazy) {
			return new Object[0];
		}
		return super.getRawChildren(parent);
	}
	void preservingSelection(Runnable updateCode, boolean reveal) {
		if (preservingSelection){
			
			
			updateCode.run();
			return;
		}
		preservingSelection = true;
		try {
			super.preservingSelection(updateCode, reveal);
		} finally {
			preservingSelection = false;
		}
	}
	/**
	 * For a TreeViewer with a tree with the VIRTUAL style bit set, set the
	 * number of children of the given element or tree path. To set the number
	 * of children of the invisible root of the tree, you can pass the input
	 * object or an empty tree path.
	 *
	 * @param elementOrTreePath
	 *            the element, or tree path
	 * @param count