merge individual periodic callbacks (one for each plot) to one periodic callback

actor.py

@@ -57,7 +57,7 @@ class Actor:
     def __init__(self, pvname, cache_size=100):
         self.src, plt, self.cache, self._update = decide_src_plt_cache_update(pvname)
         self.plt = Frame(plt)
-        self.cb = self.container = None
+        self.container = None
 
     def update(self):
         self._update(self.plt, self.cache)

director.py

@@ -20,6 +20,14 @@ class Director:
         layout = column(ti_add_pv, plot_container)
         doc.add_root(layout)
 
+        self.updates = []
+        self.doc.add_periodic_callback(self.periodic_update, 1000)
+
+
+    def periodic_update(self):
+        for func in self.updates:
+            func()
+
 
     def on_add_pv(self, attr, old, new):
         if not new: return
@@ -55,16 +63,18 @@ class Director:
         fig = a.plt.fig
 #        a.container.children.append(fig)
         a.container.children.insert(0, fig)
-        assert a.cb is None #TODO
-        a.cb = self.doc.add_periodic_callback(a.update, 1000)
+#        assert a.cb is None #TODO
+#        a.cb = self.doc.add_periodic_callback(a.update, 1000)
+        self.updates.append(a.update)
 
 
     def remove_plot(self, a):
         print("Remove plot:", a)
         fig = a.plt.fig
         a.container.children.remove(fig) #TODO: remove container if emptied?
-        assert a.cb is not None #TODO
-        self.doc.remove_periodic_callback(a.cb)
+#        assert a.cb is not None #TODO
+#        self.doc.remove_periodic_callback(a.cb)
+        self.updates.remove(a.update)