private void childCompleted() {
            uncompletedChildren--;

            if (uncompletedChildren > 0) return;
            if (list.incoming().isComplete()) // i) if the parent had completed earlier, render it now, see ii)
                run();
        }
Called each time a direct child of this completed.
container-core/src/main/java/com/yahoo/processing/rendering/AsynchronousSectionedRenderer.java