Fix periodic async callbacks (#6053)

* Do not resolve references on PeriodicCallback

* Add tests

panel/io/callbacks.py

@@ -13,7 +13,7 @@
 
 from ..util import edit_readonly, function_name
 from .logging import LOG_PERIODIC_END, LOG_PERIODIC_START
-from .state import curdoc_locked, state
+from .state import curdoc_locked, set_curdoc, state
 
 log = logging.getLogger('panel.callbacks')
 _periodic_logger = logging.getLogger(f'{__name__}.PeriodicCallback')
@@ -29,7 +29,7 @@ class PeriodicCallback(param.Parameterized):
     the running parameter to True or False respectively.
     """
 
-    callback = param.Callable(doc="""
+    callback = param.Callable(allow_refs=False, doc="""
         The callback to execute periodically.""")
 
     counter = param.Integer(default=0, doc="""
@@ -79,7 +79,6 @@ def _update_period(self):
             self.start()
 
     def _exec_callback(self, post=False):
-        from .state import set_curdoc
         try:
             with set_curdoc(self._doc):
                 if self.running:
@@ -129,7 +128,11 @@ async def _periodic_callback(self):
         try:
             cb = self._exec_callback()
             if inspect.isawaitable(cb):
-                await cb
+                if self._doc:
+                    with set_curdoc(self._doc):
+                        await cb
+                else:
+                    await cb
         except Exception:
             log.exception('Periodic callback failed.')
             raise

panel/tests/test_server.py

@@ -282,6 +282,23 @@ def test_server_session_info():
     assert state.session_info['live'] == 0
 
 
+def test_server_periodic_async_callback(threads, port):
+    counts = []
+
+    async def cb(count=[0]):
+        counts.append(count[0])
+        count[0] += 1
+
+    def app():
+        button = Button(name='Click')
+        state.add_periodic_callback(cb, 100)
+        return button
+
+    serve_and_request(app)
+
+    wait_until(lambda: len(counts) >= 5 and counts == list(range(len(counts))))
+
+
 def test_server_schedule_repeat():
     state.cache['count'] = 0
     def periodic_cb():