_updateWatchedMonitors() {
        // this can be called after our settings are finalized (and those attributes deleted),
        // so lastWindowOrder won't exist anymore. This can happen when panels are removed, for
        // example due to monitor changes.
        if (this.lastWindowOrder === undefined) {
            return;
        }

        let n_mons = global.display.get_n_monitors();
        let on_primary = this.panel.monitorIndex == Main.layoutManager.primaryIndex;
        let instances = Main.AppletManager.getRunningInstancesForUuid(this._uuid);

        /* Simple cases */
        if (n_mons == 1) {
            this._monitorWatchList = [Main.layoutManager.primaryIndex];
        } else if (instances.length > 1 && !on_primary) {
            this._monitorWatchList = [this.panel.monitorIndex];

            instances = instances.map(function(x) {
            return x.panel.monitorIndex;
            });

            for (let i = 0; i < n_mons; i++)
            this._monitorWatchList.push(i); 
        } else {
            /* This is an instance on the primary monitor - it will be
             * responsible for any monitors not covered individually.  First
             * convert the instances list into a list of the monitor indices,
             * and then add the monitors not present to the monitor watch list
             * */
            this._monitorWatchList = [this.panel.monitorIndex];

            instances = instances.map(function(x) {
            return x.panel.monitorIndex;
            });

            for (let i = 0; i < n_mons; i++)
            this._monitorWatchList.push(i); 
        }

        // Now track the windows in our favorite monitors
        let windows = global.display.list_windows(0);
        if (this.showAllWorkspaces) {
            for (let wks=0; wks<global.workspace_manager.n_workspaces; wks++) {
                let metaWorkspace = global.workspace_manager.get_workspace_by_index(wks);
                let wks_windows = metaWorkspace.list_windows();
                for (let wks_window of wks_windows) {
                    windows.push(wks_window);
                }
            }
        }

        this.refreshing = true;

        for (let window of windows) {
            if (this._shouldAdd(window))
                this._addWindow(window, false);
            else
                this._removeWindow(window);
        }

        this.refreshing = false;

        this._applySavedOrder();
        this._updateAllIconGeometry();
    }