add first_beat delay to notebook heartbeats

Heartbeats start immediately, causing false heart failures on slow systems that can take a while to start kernel subprocesses.

Also adds a 'flush' to the heartbeat callback (just like in IPython.parallel), to protect against server load being detected as heart failures.

IPython/frontend/html/notebook/handlers.py

@@ -1,614 +1,618 b''
 """Tornado handlers for the notebook.
 
 Authors:
 
 * Brian Granger
 """
 
 #-----------------------------------------------------------------------------
 #  Copyright (C) 2008-2011  The IPython Development Team
 #
 #  Distributed under the terms of the BSD License.  The full license is in
 #  the file COPYING, distributed as part of this software.
 #-----------------------------------------------------------------------------
 
 #-----------------------------------------------------------------------------
 # Imports
 #-----------------------------------------------------------------------------
 
 import logging
 import Cookie
+import time
 import uuid
 
 from tornado import web
 from tornado import websocket
 
 from zmq.eventloop import ioloop
 from zmq.utils import jsonapi
 
 from IPython.external.decorator import decorator
 from IPython.zmq.session import Session
 from IPython.lib.security import passwd_check
 
 try:
     from docutils.core import publish_string
 except ImportError:
     publish_string = None
 
 #-----------------------------------------------------------------------------
 # Monkeypatch for Tornado <= 2.1.1 - Remove when no longer necessary!
 #-----------------------------------------------------------------------------
 
 # Google Chrome, as of release 16, changed its websocket protocol number.  The
 # parts tornado cares about haven't really changed, so it's OK to continue
 # accepting Chrome connections, but as of Tornado 2.1.1 (the currently released
 # version as of Oct 30/2011) the version check fails, see the issue report:
 
 # https://github.com/facebook/tornado/issues/385
 
 # This issue has been fixed in Tornado post 2.1.1:
 
 # https://github.com/facebook/tornado/commit/84d7b458f956727c3b0d6710
 
 # Here we manually apply the same patch as above so that users of IPython can
 # continue to work with an officially released Tornado.  We make the
 # monkeypatch version check as narrow as possible to limit its effects; once
 # Tornado 2.1.1 is no longer found in the wild we'll delete this code.
 
 import tornado
 
 if tornado.version_info <= (2,1,1):
 
     def _execute(self, transforms, *args, **kwargs):
         from tornado.websocket import WebSocketProtocol8, WebSocketProtocol76
         
         self.open_args = args
         self.open_kwargs = kwargs
 
         # The difference between version 8 and 13 is that in 8 the
         # client sends a "Sec-Websocket-Origin" header and in 13 it's
         # simply "Origin".
         if self.request.headers.get("Sec-WebSocket-Version") in ("7", "8", "13"):
             self.ws_connection = WebSocketProtocol8(self)
             self.ws_connection.accept_connection()
             
         elif self.request.headers.get("Sec-WebSocket-Version"):
             self.stream.write(tornado.escape.utf8(
                 "HTTP/1.1 426 Upgrade Required\r\n"
                 "Sec-WebSocket-Version: 8\r\n\r\n"))
             self.stream.close()
             
         else:
             self.ws_connection = WebSocketProtocol76(self)
             self.ws_connection.accept_connection()
 
     websocket.WebSocketHandler._execute = _execute
     del _execute
     
 #-----------------------------------------------------------------------------
 # Decorator for disabling read-only handlers
 #-----------------------------------------------------------------------------
 
 @decorator
 def not_if_readonly(f, self, *args, **kwargs):
     if self.application.read_only:
         raise web.HTTPError(403, "Notebook server is read-only")
     else:
         return f(self, *args, **kwargs)
 
 @decorator
 def authenticate_unless_readonly(f, self, *args, **kwargs):
     """authenticate this page *unless* readonly view is active.
     
     In read-only mode, the notebook list and print view should
     be accessible without authentication.
     """
     
     @web.authenticated
     def auth_f(self, *args, **kwargs):
         return f(self, *args, **kwargs)
     if self.application.read_only:
         return f(self, *args, **kwargs)
     else:
         return auth_f(self, *args, **kwargs)
 
 #-----------------------------------------------------------------------------
 # Top-level handlers
 #-----------------------------------------------------------------------------
 
 class RequestHandler(web.RequestHandler):
     """RequestHandler with default variable setting."""
 
     def render(*args, **kwargs):
         kwargs.setdefault('message', '')
         return web.RequestHandler.render(*args, **kwargs)
 
 class AuthenticatedHandler(RequestHandler):
     """A RequestHandler with an authenticated user."""
 
     def get_current_user(self):
         user_id = self.get_secure_cookie("username")
         # For now the user_id should not return empty, but it could eventually
         if user_id == '':
             user_id = 'anonymous'
         if user_id is None:
             # prevent extra Invalid cookie sig warnings:
             self.clear_cookie('username')
             if not self.application.password and not self.application.read_only:
                 user_id = 'anonymous'
         return user_id
 
     @property
     def logged_in(self):
         """Is a user currently logged in?
 
         """
         user = self.get_current_user()
         return (user and not user == 'anonymous')
 
     @property
     def login_available(self):
         """May a user proceed to log in?
 
         This returns True if login capability is available, irrespective of
         whether the user is already logged in or not.
 
         """
         return bool(self.application.password)
 
     @property
     def read_only(self):
         """Is the notebook read-only?
 
         """
         return self.application.read_only
 
     @property
     def ws_url(self):
         """websocket url matching the current request
         
         turns http[s]://host[:port] into
                 ws[s]://host[:port]
         """
         proto = self.request.protocol.replace('http', 'ws')
         return "%s://%s" % (proto, self.request.host)
 
 
 class ProjectDashboardHandler(AuthenticatedHandler):
 
     @authenticate_unless_readonly
     def get(self):
         nbm = self.application.notebook_manager
         project = nbm.notebook_dir
         self.render(
             'projectdashboard.html', project=project,
             base_project_url=u'/', base_kernel_url=u'/',
             read_only=self.read_only,
             logged_in=self.logged_in,
             login_available=self.login_available
         )
 
 
 class LoginHandler(AuthenticatedHandler):
 
     def _render(self, message=None):
         self.render('login.html',
                 next=self.get_argument('next', default='/'),
                 read_only=self.read_only,
                 logged_in=self.logged_in,
                 login_available=self.login_available,
                 message=message
         )
 
     def get(self):
         if self.current_user:
             self.redirect(self.get_argument('next', default='/'))
         else:
             self._render()
 
     def post(self):
         pwd = self.get_argument('password', default=u'')
         if self.application.password:
             if passwd_check(self.application.password, pwd):
                 self.set_secure_cookie('username', str(uuid.uuid4()))
             else:
                 self._render(message={'error': 'Invalid password'})
                 return
 
         self.redirect(self.get_argument('next', default='/'))
 
 
 class LogoutHandler(AuthenticatedHandler):
 
     def get(self):
         self.clear_cookie('username')
         if self.login_available:
             message = {'info': 'Successfully logged out.'}
         else:
             message = {'warning': 'Cannot log out.  Notebook authentication '
                        'is disabled.'}
 
         self.render('logout.html',
                     read_only=self.read_only,
                     logged_in=self.logged_in,
                     login_available=self.login_available,
                     message=message)
 
 
 class NewHandler(AuthenticatedHandler):
 
     @web.authenticated
     def get(self):
         nbm = self.application.notebook_manager
         project = nbm.notebook_dir
         notebook_id = nbm.new_notebook()
         self.render(
             'notebook.html', project=project,
             notebook_id=notebook_id,
             base_project_url=u'/', base_kernel_url=u'/',
             kill_kernel=False,
             read_only=False,
             logged_in=self.logged_in,
             login_available=self.login_available,
             mathjax_url=self.application.ipython_app.mathjax_url,
         )
 
 
 class NamedNotebookHandler(AuthenticatedHandler):
 
     @authenticate_unless_readonly
     def get(self, notebook_id):
         nbm = self.application.notebook_manager
         project = nbm.notebook_dir
         if not nbm.notebook_exists(notebook_id):
             raise web.HTTPError(404, u'Notebook does not exist: %s' % notebook_id)
         
         self.render(
             'notebook.html', project=project,
             notebook_id=notebook_id,
             base_project_url=u'/', base_kernel_url=u'/',
             kill_kernel=False,
             read_only=self.read_only,
             logged_in=self.logged_in,
             login_available=self.login_available,
             mathjax_url=self.application.ipython_app.mathjax_url,
         )
 
 
 #-----------------------------------------------------------------------------
 # Kernel handlers
 #-----------------------------------------------------------------------------
 
 
 class MainKernelHandler(AuthenticatedHandler):
 
     @web.authenticated
     def get(self):
         km = self.application.kernel_manager
         self.finish(jsonapi.dumps(km.kernel_ids))
 
     @web.authenticated
     def post(self):
         km = self.application.kernel_manager
         notebook_id = self.get_argument('notebook', default=None)
         kernel_id = km.start_kernel(notebook_id)
         data = {'ws_url':self.ws_url,'kernel_id':kernel_id}
         self.set_header('Location', '/'+kernel_id)
         self.finish(jsonapi.dumps(data))
 
 
 class KernelHandler(AuthenticatedHandler):
 
     SUPPORTED_METHODS = ('DELETE')
 
     @web.authenticated
     def delete(self, kernel_id):
         km = self.application.kernel_manager
         km.kill_kernel(kernel_id)
         self.set_status(204)
         self.finish()
 
 
 class KernelActionHandler(AuthenticatedHandler):
 
     @web.authenticated
     def post(self, kernel_id, action):
         km = self.application.kernel_manager
         if action == 'interrupt':
             km.interrupt_kernel(kernel_id)
             self.set_status(204)
         if action == 'restart':
             new_kernel_id = km.restart_kernel(kernel_id)
             data = {'ws_url':self.ws_url,'kernel_id':new_kernel_id}
             self.set_header('Location', '/'+new_kernel_id)
             self.write(jsonapi.dumps(data))
         self.finish()
 
 
 class ZMQStreamHandler(websocket.WebSocketHandler):
 
     def _reserialize_reply(self, msg_list):
         """Reserialize a reply message using JSON.
 
         This takes the msg list from the ZMQ socket, unserializes it using
         self.session and then serializes the result using JSON. This method
         should be used by self._on_zmq_reply to build messages that can
         be sent back to the browser.
         """
         idents, msg_list = self.session.feed_identities(msg_list)
         msg = self.session.unserialize(msg_list)
         try:
             msg['header'].pop('date')
         except KeyError:
             pass
         try:
             msg['parent_header'].pop('date')
         except KeyError:
             pass
         msg.pop('buffers')
         return jsonapi.dumps(msg)
 
     def _on_zmq_reply(self, msg_list):
         try:
             msg = self._reserialize_reply(msg_list)
         except:
             self.application.log.critical("Malformed message: %r" % msg_list)
         else:
             self.write_message(msg)
 
 
 class AuthenticatedZMQStreamHandler(ZMQStreamHandler):
 
     def open(self, kernel_id):
         self.kernel_id = kernel_id.decode('ascii')
         try:
             cfg = self.application.ipython_app.config
         except AttributeError:
             # protect from the case where this is run from something other than
             # the notebook app:
             cfg = None
         self.session = Session(config=cfg)
         self.save_on_message = self.on_message
         self.on_message = self.on_first_message
 
     def get_current_user(self):
         user_id = self.get_secure_cookie("username")
         if user_id == '' or (user_id is None and not self.application.password):
             user_id = 'anonymous'
         return user_id
 
     def _inject_cookie_message(self, msg):
         """Inject the first message, which is the document cookie,
         for authentication."""
         if isinstance(msg, unicode):
             # Cookie can't constructor doesn't accept unicode strings for some reason
             msg = msg.encode('utf8', 'replace')
         try:
             self.request._cookies = Cookie.SimpleCookie(msg)
         except:
             logging.warn("couldn't parse cookie string: %s",msg, exc_info=True)
 
     def on_first_message(self, msg):
         self._inject_cookie_message(msg)
         if self.get_current_user() is None:
             logging.warn("Couldn't authenticate WebSocket connection")
             raise web.HTTPError(403)
         self.on_message = self.save_on_message
 
 
 class IOPubHandler(AuthenticatedZMQStreamHandler):
 
     def initialize(self, *args, **kwargs):
         self._kernel_alive = True
         self._beating = False
         self.iopub_stream = None
         self.hb_stream = None
 
     def on_first_message(self, msg):
         try:
             super(IOPubHandler, self).on_first_message(msg)
         except web.HTTPError:
             self.close()
             return
         km = self.application.kernel_manager
         self.time_to_dead = km.time_to_dead
+        self.first_beat = km.first_beat
         kernel_id = self.kernel_id
         try:
             self.iopub_stream = km.create_iopub_stream(kernel_id)
             self.hb_stream = km.create_hb_stream(kernel_id)
         except web.HTTPError:
             # WebSockets don't response to traditional error codes so we
             # close the connection.
             if not self.stream.closed():
                 self.stream.close()
             self.close()
         else:
             self.iopub_stream.on_recv(self._on_zmq_reply)
             self.start_hb(self.kernel_died)
 
     def on_message(self, msg):
         pass
 
     def on_close(self):
         # This method can be called twice, once by self.kernel_died and once
         # from the WebSocket close event. If the WebSocket connection is
         # closed before the ZMQ streams are setup, they could be None.
         self.stop_hb()
         if self.iopub_stream is not None and not self.iopub_stream.closed():
             self.iopub_stream.on_recv(None)
             self.iopub_stream.close()
         if self.hb_stream is not None and not self.hb_stream.closed():
             self.hb_stream.close()
 
     def start_hb(self, callback):
         """Start the heartbeating and call the callback if the kernel dies."""
         if not self._beating:
             self._kernel_alive = True
 
             def ping_or_dead():
+                self.hb_stream.flush()
                 if self._kernel_alive:
                     self._kernel_alive = False
                     self.hb_stream.send(b'ping')
                 else:
                     try:
                         callback()
                     except:
                         pass
                     finally:
                         self._hb_periodic_callback.stop()
 
             def beat_received(msg):
                 self._kernel_alive = True
 
             self.hb_stream.on_recv(beat_received)
-            self._hb_periodic_callback = ioloop.PeriodicCallback(ping_or_dead, self.time_to_dead*1000)
-            self._hb_periodic_callback.start()
+            loop = ioloop.IOLoop.instance()
+            self._hb_periodic_callback = ioloop.PeriodicCallback(ping_or_dead, self.time_to_dead*1000, loop)
+            loop.add_timeout(time.time()+self.first_beat, self._hb_periodic_callback.start)
             self._beating= True
 
     def stop_hb(self):
         """Stop the heartbeating and cancel all related callbacks."""
         if self._beating:
             self._hb_periodic_callback.stop()
             if not self.hb_stream.closed():
                 self.hb_stream.on_recv(None)
 
     def kernel_died(self):
         self.application.kernel_manager.delete_mapping_for_kernel(self.kernel_id)
         self.write_message(
             {'header': {'msg_type': 'status'},
              'parent_header': {},
              'content': {'execution_state':'dead'}
             }
         )
         self.on_close()
 
 
 class ShellHandler(AuthenticatedZMQStreamHandler):
 
     def initialize(self, *args, **kwargs):
         self.shell_stream = None
 
     def on_first_message(self, msg):
         try:
             super(ShellHandler, self).on_first_message(msg)
         except web.HTTPError:
             self.close()
             return
         km = self.application.kernel_manager
         self.max_msg_size = km.max_msg_size
         kernel_id = self.kernel_id
         try:
             self.shell_stream = km.create_shell_stream(kernel_id)
         except web.HTTPError:
             # WebSockets don't response to traditional error codes so we
             # close the connection.
             if not self.stream.closed():
                 self.stream.close()
             self.close()
         else:
             self.shell_stream.on_recv(self._on_zmq_reply)
 
     def on_message(self, msg):
         if len(msg) < self.max_msg_size:
             msg = jsonapi.loads(msg)
             self.session.send(self.shell_stream, msg)
 
     def on_close(self):
         # Make sure the stream exists and is not already closed.
         if self.shell_stream is not None and not self.shell_stream.closed():
             self.shell_stream.close()
 
 
 #-----------------------------------------------------------------------------
 # Notebook web service handlers
 #-----------------------------------------------------------------------------
 
 class NotebookRootHandler(AuthenticatedHandler):
 
     @authenticate_unless_readonly
     def get(self):
         
         nbm = self.application.notebook_manager
         files = nbm.list_notebooks()
         self.finish(jsonapi.dumps(files))
 
     @web.authenticated
     def post(self):
         nbm = self.application.notebook_manager
         body = self.request.body.strip()
         format = self.get_argument('format', default='json')
         name = self.get_argument('name', default=None)
         if body:
             notebook_id = nbm.save_new_notebook(body, name=name, format=format)
         else:
             notebook_id = nbm.new_notebook()
         self.set_header('Location', '/'+notebook_id)
         self.finish(jsonapi.dumps(notebook_id))
 
 
 class NotebookHandler(AuthenticatedHandler):
 
     SUPPORTED_METHODS = ('GET', 'PUT', 'DELETE')
 
     @authenticate_unless_readonly
     def get(self, notebook_id):
         nbm = self.application.notebook_manager
         format = self.get_argument('format', default='json')
         last_mod, name, data = nbm.get_notebook(notebook_id, format)
         
         if format == u'json':
             self.set_header('Content-Type', 'application/json')
             self.set_header('Content-Disposition','attachment; filename="%s.ipynb"' % name)
         elif format == u'py':
             self.set_header('Content-Type', 'application/x-python')
             self.set_header('Content-Disposition','attachment; filename="%s.py"' % name)
         self.set_header('Last-Modified', last_mod)
         self.finish(data)
 
     @web.authenticated
     def put(self, notebook_id):
         nbm = self.application.notebook_manager
         format = self.get_argument('format', default='json')
         name = self.get_argument('name', default=None)
         nbm.save_notebook(notebook_id, self.request.body, name=name, format=format)
         self.set_status(204)
         self.finish()
 
     @web.authenticated
     def delete(self, notebook_id):
         nbm = self.application.notebook_manager
         nbm.delete_notebook(notebook_id)
         self.set_status(204)
         self.finish()
 
 #-----------------------------------------------------------------------------
 # RST web service handlers
 #-----------------------------------------------------------------------------
 
 
 class RSTHandler(AuthenticatedHandler):
 
     @web.authenticated
     def post(self):
         if publish_string is None:
             raise web.HTTPError(503, u'docutils not available')
         body = self.request.body.strip()
         source = body
         # template_path=os.path.join(os.path.dirname(__file__), u'templates', u'rst_template.html')
         defaults = {'file_insertion_enabled': 0,
                     'raw_enabled': 0,
                     '_disable_config': 1,
                     'stylesheet_path': 0
                     # 'template': template_path
         }
         try:
             html = publish_string(source, writer_name='html',
                                   settings_overrides=defaults
             )
         except:
             raise web.HTTPError(400, u'Invalid RST')
         print html
         self.set_header('Content-Type', 'text/html')
         self.finish(html)
 
 

IPython/frontend/html/notebook/kernelmanager.py

@@ -1,309 +1,312 b''
 """A kernel manager for multiple kernels.
 
 Authors:
 
 * Brian Granger
 """
 
 #-----------------------------------------------------------------------------
 #  Copyright (C) 2008-2011  The IPython Development Team
 #
 #  Distributed under the terms of the BSD License.  The full license is in
 #  the file COPYING, distributed as part of this software.
 #-----------------------------------------------------------------------------
 
 #-----------------------------------------------------------------------------
 # Imports
 #-----------------------------------------------------------------------------
 
 import os
 import signal
 import sys
 import uuid
 
 import zmq
 from zmq.eventloop.zmqstream import ZMQStream
 
 from tornado import web
 
 from IPython.config.configurable import LoggingConfigurable
 from IPython.zmq.ipkernel import launch_kernel
 from IPython.zmq.kernelmanager import KernelManager
 from IPython.utils.traitlets import Instance, Dict, List, Unicode, Float, Integer
 
 #-----------------------------------------------------------------------------
 # Classes
 #-----------------------------------------------------------------------------
 
 class DuplicateKernelError(Exception):
     pass
 
 
 class MultiKernelManager(LoggingConfigurable):
     """A class for managing multiple kernels."""
 
     context = Instance('zmq.Context')
     def _context_default(self):
         return zmq.Context.instance()
     
     connection_dir = Unicode('')
 
     _kernels = Dict()
 
     @property
     def kernel_ids(self):
         """Return a list of the kernel ids of the active kernels."""
         return self._kernels.keys()
 
     def __len__(self):
         """Return the number of running kernels."""
         return len(self.kernel_ids)
 
     def __contains__(self, kernel_id):
         if kernel_id in self.kernel_ids:
             return True
         else:
             return False
 
     def start_kernel(self, **kwargs):
         """Start a new kernel."""
         kernel_id = unicode(uuid.uuid4())
         # use base KernelManager for each Kernel
         km = KernelManager(connection_file=os.path.join(
                     self.connection_dir, "kernel-%s.json" % kernel_id),
                     config=self.config,
         )
         km.start_kernel(**kwargs)
         self._kernels[kernel_id] = km
         return kernel_id
 
     def kill_kernel(self, kernel_id):
         """Kill a kernel by its kernel uuid.
 
         Parameters
         ==========
         kernel_id : uuid
             The id of the kernel to kill.
         """
         self.get_kernel(kernel_id).kill_kernel()
         del self._kernels[kernel_id]
 
     def interrupt_kernel(self, kernel_id):
         """Interrupt (SIGINT) the kernel by its uuid.
 
         Parameters
         ==========
         kernel_id : uuid
             The id of the kernel to interrupt.
         """
         return self.get_kernel(kernel_id).interrupt_kernel()
 
     def signal_kernel(self, kernel_id, signum):
         """ Sends a signal to the kernel by its uuid.
 
         Note that since only SIGTERM is supported on Windows, this function
         is only useful on Unix systems.
 
         Parameters
         ==========
         kernel_id : uuid
             The id of the kernel to signal.
         """
         return self.get_kernel(kernel_id).signal_kernel(signum)
 
     def get_kernel(self, kernel_id):
         """Get the single KernelManager object for a kernel by its uuid.
 
         Parameters
         ==========
         kernel_id : uuid
             The id of the kernel.
         """
         km = self._kernels.get(kernel_id)
         if km is not None:
             return km
         else:
             raise KeyError("Kernel with id not found: %s" % kernel_id)
 
     def get_kernel_ports(self, kernel_id):
         """Return a dictionary of ports for a kernel.
 
         Parameters
         ==========
         kernel_id : uuid
             The id of the kernel.
 
         Returns
         =======
         port_dict : dict
             A dict of key, value pairs where the keys are the names
             (stdin_port,iopub_port,shell_port) and the values are the
             integer port numbers for those channels.
         """
         # this will raise a KeyError if not found:
         km = self.get_kernel(kernel_id)
         return dict(shell_port=km.shell_port,
                     iopub_port=km.iopub_port,
                     stdin_port=km.stdin_port,
                     hb_port=km.hb_port,
         )
 
     def get_kernel_ip(self, kernel_id):
         """Return ip address for a kernel.
 
         Parameters
         ==========
         kernel_id : uuid
             The id of the kernel.
 
         Returns
         =======
         ip : str
             The ip address of the kernel.
         """
         return self.get_kernel(kernel_id).ip
 
     def create_connected_stream(self, ip, port, socket_type):
         sock = self.context.socket(socket_type)
         addr = "tcp://%s:%i" % (ip, port)
         self.log.info("Connecting to: %s" % addr)
         sock.connect(addr)
         return ZMQStream(sock)
 
     def create_iopub_stream(self, kernel_id):
         ip = self.get_kernel_ip(kernel_id)
         ports = self.get_kernel_ports(kernel_id)
         iopub_stream = self.create_connected_stream(ip, ports['iopub_port'], zmq.SUB)
         iopub_stream.socket.setsockopt(zmq.SUBSCRIBE, b'')
         return iopub_stream
 
     def create_shell_stream(self, kernel_id):
         ip = self.get_kernel_ip(kernel_id)
         ports = self.get_kernel_ports(kernel_id)
         shell_stream = self.create_connected_stream(ip, ports['shell_port'], zmq.XREQ)
         return shell_stream
 
     def create_hb_stream(self, kernel_id):
         ip = self.get_kernel_ip(kernel_id)
         ports = self.get_kernel_ports(kernel_id)
         hb_stream = self.create_connected_stream(ip, ports['hb_port'], zmq.REQ)
         return hb_stream
 
 
 class MappingKernelManager(MultiKernelManager):
     """A KernelManager that handles notebok mapping and HTTP error handling"""
 
     kernel_argv = List(Unicode)
     kernel_manager = Instance(KernelManager)
+    
     time_to_dead = Float(3.0, config=True, help="""Kernel heartbeat interval in seconds.""")
+    first_beat = Float(5.0, config=True, help="Delay (in seconds) before sending first heartbeat.")
+    
     max_msg_size = Integer(65536, config=True, help="""
         The max raw message size accepted from the browser
         over a WebSocket connection.
     """)
 
     _notebook_mapping = Dict()
 
     #-------------------------------------------------------------------------
     # Methods for managing kernels and sessions
     #-------------------------------------------------------------------------
 
     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]
         else:
             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 for a notebok 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.
         """
         kernel_id = self.kernel_for_notebook(notebook_id)
         if kernel_id is None:
             kwargs = dict()
             kwargs['extra_arguments'] = self.kernel_argv
             kernel_id = super(MappingKernelManager, self).start_kernel(**kwargs)
             self.set_kernel_for_notebook(notebook_id, kernel_id)
             self.log.info("Kernel started: %s" % kernel_id)
             self.log.debug("Kernel args: %r" % kwargs)
         else:
             self.log.info("Using existing kernel: %s" % kernel_id)
         return kernel_id
 
     def kill_kernel(self, kernel_id):
         """Kill a kernel and remove its notebook association."""
         self._check_kernel_id(kernel_id)
         super(MappingKernelManager, self).kill_kernel(kernel_id)
         self.delete_mapping_for_kernel(kernel_id)
         self.log.info("Kernel killed: %s" % kernel_id)
 
     def interrupt_kernel(self, kernel_id):
         """Interrupt a kernel."""
         self._check_kernel_id(kernel_id)
         super(MappingKernelManager, self).interrupt_kernel(kernel_id)
         self.log.info("Kernel interrupted: %s" % kernel_id)
 
     def restart_kernel(self, kernel_id):
         """Restart a kernel while keeping clients connected."""
         self._check_kernel_id(kernel_id)
         km = self.get_kernel(kernel_id)
         km.restart_kernel(now=True)
         self.log.info("Kernel restarted: %s" % kernel_id)
         return kernel_id
         
         # the following remains, in case the KM restart machinery is
         # somehow unacceptable
         # Get the notebook_id to preserve the kernel/notebook association.
         notebook_id = self.notebook_for_kernel(kernel_id)
         # Create the new kernel first so we can move the clients over.
         new_kernel_id = self.start_kernel()
         # Now kill the old kernel.
         self.kill_kernel(kernel_id)
         # 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.set_kernel_for_notebook(notebook_id, new_kernel_id)
         self.log.info("Kernel restarted: %s" % new_kernel_id)
         return new_kernel_id
 
     def create_iopub_stream(self, kernel_id):
         """Create a new iopub stream."""
         self._check_kernel_id(kernel_id)
         return super(MappingKernelManager, self).create_iopub_stream(kernel_id)
 
     def create_shell_stream(self, kernel_id):
         """Create a new shell stream."""
         self._check_kernel_id(kernel_id)
         return super(MappingKernelManager, self).create_shell_stream(kernel_id)
 
     def create_hb_stream(self, kernel_id):
         """Create a new hb stream."""
         self._check_kernel_id(kernel_id)
         return super(MappingKernelManager, self).create_hb_stream(kernel_id)
 
     def _check_kernel_id(self, kernel_id):
         """Check a that a kernel_id exists and raise 404 if not."""
         if kernel_id not in self:
             raise web.HTTPError(404, u'Kernel does not exist: %s' % kernel_id)