grc: fixes crash when using function probe with bokehgui

blocks/variable_function_probe.block.yml

@@ -31,12 +31,22 @@ templates:
         import time
         import threading
     var_make: self.${id} = ${id} = ${value}
-    make: "\ndef _${id}_probe():\n    while True:\n        <% obj = 'self' + ('.'\
-        \ + block_id if block_id else '') %>\n        val = ${obj}.${function_name}(${function_args})\n\
-        \        try:\n            self.set_${id}(val)\n        except AttributeError:\n\
-        \            pass\n        time.sleep(1.0 / (${poll_rate}))\n_${id}_thread\
-        \ = threading.Thread(target=_${id}_probe)\n_${id}_thread.daemon = True\n_${id}_thread.start()\n\
-        \    "
+    make: |+
+        def _${id}_probe():
+          while True:
+            <% obj = 'self' + ('.' + block_id if block_id else '') %>
+            val = ${obj}.${function_name}(${function_args})
+            try:
+              try:
+                self.doc.add_next_tick_callback(functools.partial(self.set_${id},val))
+              except AttributeError:
+                self.set_${id}(val)
+            except AttributeError:
+              pass
+            time.sleep(1.0 / (${poll_rate}))
+        _${id}_thread = threading.Thread(target=_${id}_probe)
+        _${id}_thread.daemon = True
+        _${id}_thread.start()
     callbacks:
     - self.set_${id}(${value})