Custom Perspective Switcher Toolbar: How can I dynamically update it? - eclipse-rcp

Question

I'm trying to implement a custom perspective switcher toolbar to replace eclipse's built-in one. I couldn't get the toolbar to display, and it was shown to me that due to a bug with the dynamic element in a menu contribution, I have to use a control element instead, as described in the workaround to the dynamic bug.
I have a toolbar displaying following that approach, but I cannot figure out how to update it dynamically. The workaround instruction is to call ContributionItem#fill(CoolBar, int) from my WorkbenchControlContributionItem's update method instead of doing the fill in the createControl method.
I don't know who is supposed to call update, but it never gets invoked no matter what I do. I have a perspective listener which knows when to update the toolbar, so from that listener's callback I call fill(CoolBar, int). But I wasn't sure how to get the CoolBar to pass to that method, so I created one on the current shell.
The end result of all this is that the toolbar displays the correct number of items initially, but when I need to add an item, it has no effect. I call fill(CoolBar, int) and it adds the new item to the toolbar, but everything I've tried to make the CoolBar and ToolBarupdate does not work. When I re-launch the app, the toolbar has the added item.
I'm sure I'm doing this wrong, but I can't figure out the right way. Here's an elided representation of my code (omitting methods, layout code, etc not related to the update problem).
public class PerspectiveSwitcherToolbar extends WorkbenchWindowControlContribution implements IPerspectiveListener {
...
#Override
protected Control createControl(Composite parent) {
this.parent = parent;
IWorkbenchPage page = PlatformUI.getWorkbench().getActiveWorkbenchWindow().getActivePage();
page.getWorkbenchWindow().addPerspectiveListener(this);
toolBarManager = (ToolBarManager)parent.getParent().getData();
fTopControl = new Composite(parent, SWT.BORDER);
fill(new CoolBar(page.getWorkbenchWindow().getShell(), SWT.HORIZONTAL), -1);
return fTopControl;
}
#Override
public void fill(CoolBar coolbar, int index) {
IPerspectiveDescriptor[] openPerspectives = page.getOpenPerspectives();
String activePerspective = getPerspectiveId();
ToolBar toolbar = new ToolBar(fTopControl, SWT.NONE);
for(IPerspectiveDescriptor descriptor : openPerspectives) {
ToolItem item = new ToolItem(toolbar, SWT.RADIO);
//overkill here, trying to find some way to upate the toolbar
toolbar.update();
parent.update();
parent.layout(true);
parent.getParent().update();
parent.getParent().layout(true);
coolbar.layout(true);
}
//PerspectiveListener callback
#Override
public void perspectiveActivated(IWorkbenchPage page, IPerspectiveDescriptor perspective) {
fill(new CoolBar(page.getWorkbenchWindow().getShell(), SWT.HORIZONTAL), -1);
if (page.getWorkbenchWindow() instanceof WorkbenchWindow){
//this non-API call doesn't help either
((WorkbenchWindow) page.getWorkbenchWindow()).updateActionBars();
}
}
...
}