Apply changes per review

Add comments and rename self.super to self.pinned_superclass to
clarify intent.

Add run_sync() util method to clean up shutdown_all() invocation.

notebook/notebookapp.py

@@ -107,7 +107,7 @@
 from notebook._sysinfo import get_sys_info
 
 from ._tz import utcnow, utcfromtimestamp
-from .utils import url_path_join, check_pid, url_escape, urljoin, pathname2url
+from .utils import url_path_join, check_pid, url_escape, urljoin, pathname2url, run_sync
 
 # Check if we can use async kernel management
 try:
@@ -1801,11 +1801,7 @@ def cleanup_kernels(self):
         n_kernels = len(self.kernel_manager.list_kernel_ids())
         kernel_msg = trans.ngettext('Shutting down %d kernel', 'Shutting down %d kernels', n_kernels)
         self.log.info(kernel_msg % n_kernels)
-        # If we're using async kernel management, we need to invoke the async method via the event loop.
-        if isinstance(self.kernel_manager, AsyncMappingKernelManager):
-            asyncio.get_event_loop().run_until_complete(self.kernel_manager.shutdown_all())
-        else:
-            self.kernel_manager.shutdown_all()
+        run_sync(self.kernel_manager.shutdown_all())
 
     def notebook_info(self, kernel_count=True):
         "Return the current working directory and the server url information"

notebook/services/kernels/kernelmanager.py

@@ -122,10 +122,6 @@ def _default_kernel_buffers(self):
     last_kernel_activity = Instance(datetime,
         help="The last activity on any kernel, including shutting down a kernel")
 
-    def __init__(self, **kwargs):
-        super().__init__(**kwargs)
-        self.last_kernel_activity = utcnow()
-
     allowed_message_types = List(trait=Unicode(), config=True,
         help="""White list of allowed kernel message types.
         When the list is empty, all message types are allowed.
@@ -137,8 +133,11 @@ def __init__(self, **kwargs):
     #-------------------------------------------------------------------------
 
     def __init__(self, **kwargs):
-        self.super = MultiKernelManager
-        self.super.__init__(self, **kwargs)
+        # Pin the superclass to better control the MRO.  This is needed by
+        # AsyncMappingKernelManager so that it can give priority to methods
+        # on AsyncMultiKernelManager over this superclass.
+        self.pinned_superclass = MultiKernelManager
+        self.pinned_superclass.__init__(self, **kwargs)
         self.last_kernel_activity = utcnow()
 
     def _handle_kernel_died(self, kernel_id):
@@ -173,7 +172,7 @@ async def start_kernel(self, kernel_id=None, path=None, **kwargs):
         if kernel_id is None:
             if path is not None:
                 kwargs['cwd'] = self.cwd_for_path(path)
-            kernel_id = await maybe_future(self.super.start_kernel(self, **kwargs))
+            kernel_id = await maybe_future(self.pinned_superclass.start_kernel(self, **kwargs))
             self._kernel_connections[kernel_id] = 0
             self.start_watching_activity(kernel_id)
             self.log.info("Kernel started: %s" % kernel_id)
@@ -302,12 +301,12 @@ def shutdown_kernel(self, kernel_id, now=False, restart=False):
             type=self._kernels[kernel_id].kernel_name
         ).dec()
 
-        return self.super.shutdown_kernel(self, kernel_id, now=now, restart=restart)
+        return self.pinned_superclass.shutdown_kernel(self, kernel_id, now=now, restart=restart)
 
     async def restart_kernel(self, kernel_id, now=False):
         """Restart a kernel by kernel_id"""
         self._check_kernel_id(kernel_id)
-        await maybe_future(self.super.restart_kernel(self, kernel_id, now=now))
+        await maybe_future(self.pinned_superclass.restart_kernel(self, kernel_id, now=now))
         kernel = self.get_kernel(kernel_id)
         # return a Future that will resolve when the kernel has successfully restarted
         channel = kernel.connect_shell()
@@ -374,7 +373,7 @@ def kernel_model(self, kernel_id):
     def list_kernels(self):
         """Returns a list of kernel_id's of kernels running."""
         kernels = []
-        kernel_ids = self.super.list_kernel_ids(self)
+        kernel_ids = self.pinned_superclass.list_kernel_ids(self)
         for kernel_id in kernel_ids:
             model = self.kernel_model(kernel_id)
             kernels.append(model)
@@ -485,8 +484,9 @@ def _default_kernel_manager_class(self):
         return "jupyter_client.ioloop.AsyncIOLoopKernelManager"
 
     def __init__(self, **kwargs):
-        self.super = AsyncMultiKernelManager
-        self.super.__init__(self, **kwargs)
+        # Pin the superclass to better control the MRO.
+        self.pinned_superclass = AsyncMultiKernelManager
+        self.pinned_superclass.__init__(self, **kwargs)
         self.last_kernel_activity = utcnow()
 
     async def shutdown_kernel(self, kernel_id, now=False, restart=False):
@@ -505,4 +505,4 @@ async def shutdown_kernel(self, kernel_id, now=False, restart=False):
             type=self._kernels[kernel_id].kernel_name
         ).dec()
 
-        return await self.super.shutdown_kernel(self, kernel_id, now=now, restart=restart)
+        return await self.pinned_superclass.shutdown_kernel(self, kernel_id, now=now, restart=restart)

notebook/utils.py

@@ -327,3 +327,43 @@ def maybe_future(obj):
         f.set_result(obj)
         return f
 
+
+def run_sync(maybe_async):
+    """If async, runs maybe_async and blocks until it has executed,
+    possibly creating an event loop.
+    If not async, just returns maybe_async as it is the result of something
+    that has already executed.
+    Parameters
+    ----------
+    maybe_async : async or non-async object
+        The object to be executed, if it is async.
+    Returns
+    -------
+    result :
+        Whatever the async object returns, or the object itself.
+    """
+    if not inspect.isawaitable(maybe_async):
+        # that was not something async, just return it
+        return maybe_async
+    # it is async, we need to run it in an event loop
+
+    def wrapped():
+        create_new_event_loop = False
+        try:
+            loop = asyncio.get_event_loop()
+        except RuntimeError:
+            create_new_event_loop = True
+        else:
+            if loop.is_closed():
+                create_new_event_loop = True
+        if create_new_event_loop:
+            loop = asyncio.new_event_loop()
+            asyncio.set_event_loop(loop)
+        try:
+            result = loop.run_until_complete(maybe_async)
+        except RuntimeError as e:
+            if str(e) == 'This event loop is already running':
+                # just return a Future, hoping that it will be awaited
+                result = asyncio.ensure_future(maybe_async)
+        return result
+    return wrapped()