Fixed subtle bug in kernel restarting.

* Old routers were not being shutdown and removed.
* We were incorrectly associating the new kernel with the notebook
  (we were using the *old* kernel_id for this).
* General clean ups in the kernel manager.

IPython/frontend/html/notebook/handlers.py

@@ -90,14 +90,12 @@ class ZMQStreamHandler(websocket.WebSocketHandler):
         rkm = self.application.routing_kernel_manager
         self.router = rkm.get_router(kernel_id, self.stream_name)
         self.client_id = self.router.register_client(self)
-        logging.info("Connection open: %s, %s" % (kernel_id, self.client_id))
 
     def on_message(self, msg):
         self.router.forward_msg(self.client_id, msg)
 
     def on_close(self):
         self.router.unregister_client(self.client_id)
-        logging.info("Connection closed: %s" % self.client_id)
 
 
 #-----------------------------------------------------------------------------

IPython/frontend/html/notebook/kernelmanager.py

@@ -207,9 +207,20 @@ class RoutingKernelManager(LoggingConfigurable):
 
     @property
     def kernel_ids(self):
+        """List the kernel ids."""
         return self.kernel_manager.kernel_ids
 
+    def kernel_for_notebook(self, notebook_id):
+        """Return the kernel_id for a notebook_id or None."""
+        return self._notebook_mapping.get(notebook_id)
+
+    def set_kernel_for_notebook(self, notebook_id, kernel_id):
+        """Associate a notebook with a kernel."""
+        if notebook_id is not None:
+            self._notebook_mapping[notebook_id] = kernel_id
+
     def notebook_for_kernel(self, kernel_id):
+        """Return the notebook_id for a kernel_id or None."""
         notebook_ids = [k for k, v in self._notebook_mapping.iteritems() if v == kernel_id]
         if len(notebook_ids) == 1:
             return notebook_ids[0]
@@ -217,20 +228,29 @@ class RoutingKernelManager(LoggingConfigurable):
             return None
 
     def delete_mapping_for_kernel(self, kernel_id):
+        """Remove the kernel/notebook mapping for kernel_id."""
         notebook_id = self.notebook_for_kernel(kernel_id)
         if notebook_id is not None:
             del self._notebook_mapping[notebook_id]
 
     def start_kernel(self, notebook_id=None):
+        """Start a kernel an return its kernel_id.
+
+        Parameters
+        ----------
+        notebook_id : uuid
+            The uuid of the notebook to associate the new kernel with. If this
+            is not None, this kernel will be persistent whenever the notebook
+            requests a kernel.
+        """
         self.log.info
-        kernel_id = self._notebook_mapping.get(notebook_id)
+        kernel_id = self.kernel_for_notebook(notebook_id)
         if kernel_id is None:
             kwargs = dict()
             kwargs['extra_arguments'] = self.kernel_argv
             kernel_id = self.kernel_manager.start_kernel(**kwargs)
-            if notebook_id is not None:
-                self._notebook_mapping[notebook_id] = kernel_id
-            self.log.info("Kernel started for notebook %s: %s" % (notebook_id,kernel_id))
+            self.set_kernel_for_notebook(notebook_id, kernel_id)
+            self.log.info("Kernel started: %s" % kernel_id)
             self.log.debug("Kernel args: %r" % kwargs)
             self.start_session_manager(kernel_id)
         else:
@@ -238,6 +258,7 @@ class RoutingKernelManager(LoggingConfigurable):
         return kernel_id
 
     def start_session_manager(self, kernel_id):
+        """Start the ZMQ sockets (a "session") to connect to a kernel."""
         sm = self.kernel_manager.create_session_manager(kernel_id)
         self._session_dict[kernel_id] = sm
         iopub_stream = sm.get_iopub_stream()
@@ -248,10 +269,11 @@ class RoutingKernelManager(LoggingConfigurable):
         shell_router = ShellStreamRouter(
             zmq_stream=shell_stream, session=sm.session, config=self.config
         )
-        self._routers[(kernel_id, 'iopub')] = iopub_router
-        self._routers[(kernel_id, 'shell')] = shell_router
+        self.set_router(kernel_id, 'iopub', iopub_router)
+        self.set_router(kernel_id, 'shell', shell_router)
 
     def kill_kernel(self, kernel_id):
+        """Kill a kernel and remove its notebook association."""
         if kernel_id not in self.kernel_manager:
             raise web.HTTPError(404)
         try:
@@ -264,12 +286,14 @@ class RoutingKernelManager(LoggingConfigurable):
         self.log.info("Kernel killed: %s" % kernel_id)
 
     def interrupt_kernel(self, kernel_id):
+        """Interrupt a kernel."""
         if kernel_id not in self.kernel_manager:
             raise web.HTTPError(404)
         self.kernel_manager.interrupt_kernel(kernel_id)
         self.log.debug("Kernel interrupted: %s" % kernel_id)
 
     def restart_kernel(self, kernel_id):
+        """Restart a kernel while keeping clients connected."""
         if kernel_id not in self.kernel_manager:
             raise web.HTTPError(404)
 
@@ -286,6 +310,14 @@ class RoutingKernelManager(LoggingConfigurable):
         new_iopub_router.copy_clients(old_iopub_router)
         new_shell_router.copy_clients(old_shell_router)
 
+        # Shut down the old routers
+        old_shell_router.close()
+        old_iopub_router.close()
+        self.delete_router(kernel_id, 'shell')
+        self.delete_router(kernel_id, 'iopub')
+        del old_shell_router
+        del old_iopub_router
+
         # Now shutdown the old session and the kernel.
         # TODO: This causes a hard crash in ZMQStream.close, which sets
         # self.socket to None to hastily. We will need to fix this in PyZMQ
@@ -295,12 +327,24 @@ class RoutingKernelManager(LoggingConfigurable):
 
         # Now save the new kernel/notebook association. We have to save it
         # after the old kernel is killed as that will delete the mapping.
-        self._notebook_mapping[notebook_id] = kernel_id
+        self.set_kernel_for_notebook(notebook_id, new_kernel_id)
 
-        self.log.debug("Kernel restarted: %s -> %s" % (kernel_id, new_kernel_id))
+        self.log.debug("Kernel restarted: %s" % new_kernel_id)
         return new_kernel_id
 
     def get_router(self, kernel_id, stream_name):
+        """Return the router for a given kernel_id and stream name."""
         router = self._routers[(kernel_id, stream_name)]
         return router
 
+    def set_router(self, kernel_id, stream_name, router):
+        """Set the router for a given kernel_id and stream_name."""
+        self._routers[(kernel_id, stream_name)] = router
+
+    def delete_router(self, kernel_id, stream_name):
+        """Delete a router for a kernel_id and stream_name."""
+        try:
+            del self._routers[(kernel_id, stream_name)]
+        except KeyError:
+            pass
+