Merge pull request #1312 from minrk/hb

two small heartbeat changes:

* flush outgoing heartbeats (notebook and parallel):
  - Prevents mismatch between heartbeat timer and actual heartbeat send/recv events.

* relax default heartbeat period in IPython.parallel to 3s from 1s
  - Matches heartbeats elsewhere.  3s should be extremely conservative, as most heartbeat responses are O(1ms) unless there's a bug in our code (like the above flush and previously-discovered GIL issues).

closes  #1304

IPython/frontend/html/notebook/handlers.py

@@ -1,676 +1,678 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 AuthenticatedFileHandler(AuthenticatedHandler, web.StaticFileHandler):
     """static files should only be accessible when logged in"""
 
     @authenticate_unless_readonly
     def get(self, path):
         return web.StaticFileHandler.get(self, path)
 
 
 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,
         )
 
 
 class PrintNotebookHandler(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(
             'printnotebook.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')
+                    # flush stream to force immediate socket send
+                    self.hb_stream.flush()
                 else:
                     try:
                         callback()
                     except:
                         pass
                     finally:
                         self.stop_hb()
 
             def beat_received(msg):
                 self._kernel_alive = True
 
             self.hb_stream.on_recv(beat_received)
             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._really_start_hb)
             self._beating= True
     
     def _really_start_hb(self):
         """callback for delayed heartbeat start
         
         Only start the hb loop if we haven't been closed during the wait.
         """
         if self._beating and not self.hb_stream.closed():
             self._hb_periodic_callback.start()
 
     def stop_hb(self):
         """Stop the heartbeating and cancel all related callbacks."""
         if self._beating:
             self._beating = False
             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.application.log.error("Kernel %s failed to respond to heartbeat", 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()
 
 
 class NotebookCopyHandler(AuthenticatedHandler):
 
     @web.authenticated
     def get(self, notebook_id):
         nbm = self.application.notebook_manager
         project = nbm.notebook_dir
         notebook_id = nbm.copy_notebook(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=False,
             logged_in=self.logged_in,
             login_available=self.login_available,
             mathjax_url=self.application.ipython_app.mathjax_url,
         )
 
 #-----------------------------------------------------------------------------
 # 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/parallel/controller/heartmonitor.py

@@ -1,178 +1,180 b''
 #!/usr/bin/env python
 """
 A multi-heart Heartbeat system using PUB and XREP sockets. pings are sent out on the PUB,
 and hearts are tracked based on their XREQ identities.
 
 Authors:
 
 * Min RK
 """
 #-----------------------------------------------------------------------------
 #  Copyright (C) 2010-2011  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.
 #-----------------------------------------------------------------------------
 
 from __future__ import print_function
 import time
 import uuid
 
 import zmq
 from zmq.devices import ThreadDevice
 from zmq.eventloop import ioloop, zmqstream
 
 from IPython.config.configurable import LoggingConfigurable
 from IPython.utils.traitlets import Set, Instance, CFloat, Integer
 
 from IPython.parallel.util import asbytes
 
 class Heart(object):
     """A basic heart object for responding to a HeartMonitor.
     This is a simple wrapper with defaults for the most common
     Device model for responding to heartbeats.
 
     It simply builds a threadsafe zmq.FORWARDER Device, defaulting to using
     SUB/XREQ for in/out.
 
     You can specify the XREQ's IDENTITY via the optional heart_id argument."""
     device=None
     id=None
     def __init__(self, in_addr, out_addr, in_type=zmq.SUB, out_type=zmq.DEALER, heart_id=None):
         self.device = ThreadDevice(zmq.FORWARDER, in_type, out_type)
         # do not allow the device to share global Context.instance,
         # which is the default behavior in pyzmq > 2.1.10
         self.device.context_factory = zmq.Context
         
         self.device.daemon=True
         self.device.connect_in(in_addr)
         self.device.connect_out(out_addr)
         if in_type == zmq.SUB:
             self.device.setsockopt_in(zmq.SUBSCRIBE, b"")
         if heart_id is None:
             heart_id = uuid.uuid4().bytes
         self.device.setsockopt_out(zmq.IDENTITY, heart_id)
         self.id = heart_id
 
     def start(self):
         return self.device.start()
 
 
 class HeartMonitor(LoggingConfigurable):
     """A basic HeartMonitor class
     pingstream: a PUB stream
     pongstream: an XREP stream
     period: the period of the heartbeat in milliseconds"""
 
-    period = Integer(1000, config=True,
+    period = Integer(3000, config=True,
         help='The frequency at which the Hub pings the engines for heartbeats '
         '(in ms)',
     )
 
     pingstream=Instance('zmq.eventloop.zmqstream.ZMQStream')
     pongstream=Instance('zmq.eventloop.zmqstream.ZMQStream')
     loop = Instance('zmq.eventloop.ioloop.IOLoop')
     def _loop_default(self):
         return ioloop.IOLoop.instance()
 
     # not settable:
     hearts=Set()
     responses=Set()
     on_probation=Set()
     last_ping=CFloat(0)
     _new_handlers = Set()
     _failure_handlers = Set()
     lifetime = CFloat(0)
     tic = CFloat(0)
 
     def __init__(self, **kwargs):
         super(HeartMonitor, self).__init__(**kwargs)
 
         self.pongstream.on_recv(self.handle_pong)
 
     def start(self):
         self.tic = time.time()
         self.caller = ioloop.PeriodicCallback(self.beat, self.period, self.loop)
         self.caller.start()
 
     def add_new_heart_handler(self, handler):
         """add a new handler for new hearts"""
         self.log.debug("heartbeat::new_heart_handler: %s", handler)
         self._new_handlers.add(handler)
 
     def add_heart_failure_handler(self, handler):
         """add a new handler for heart failure"""
         self.log.debug("heartbeat::new heart failure handler: %s", handler)
         self._failure_handlers.add(handler)
 
     def beat(self):
         self.pongstream.flush()
         self.last_ping = self.lifetime
 
         toc = time.time()
         self.lifetime += toc-self.tic
         self.tic = toc
         self.log.debug("heartbeat::sending %s", self.lifetime)
         goodhearts = self.hearts.intersection(self.responses)
         missed_beats = self.hearts.difference(goodhearts)
         heartfailures = self.on_probation.intersection(missed_beats)
         newhearts = self.responses.difference(goodhearts)
         map(self.handle_new_heart, newhearts)
         map(self.handle_heart_failure, heartfailures)
         self.on_probation = missed_beats.intersection(self.hearts)
         self.responses = set()
         # print self.on_probation, self.hearts
         # self.log.debug("heartbeat::beat %.3f, %i beating hearts", self.lifetime, len(self.hearts))
         self.pingstream.send(asbytes(str(self.lifetime)))
+        # flush stream to force immediate socket send
+        self.pingstream.flush()
 
     def handle_new_heart(self, heart):
         if self._new_handlers:
             for handler in self._new_handlers:
                 handler(heart)
         else:
             self.log.info("heartbeat::yay, got new heart %s!", heart)
         self.hearts.add(heart)
 
     def handle_heart_failure(self, heart):
         if self._failure_handlers:
             for handler in self._failure_handlers:
                 try:
                     handler(heart)
                 except Exception as e:
                     self.log.error("heartbeat::Bad Handler! %s", handler, exc_info=True)
                     pass
         else:
             self.log.info("heartbeat::Heart %s failed :(", heart)
         self.hearts.remove(heart)
 
 
     def handle_pong(self, msg):
         "a heart just beat"
         current = asbytes(str(self.lifetime))
         last = asbytes(str(self.last_ping))
         if msg[1] == current:
             delta = time.time()-self.tic
             # self.log.debug("heartbeat::heart %r took %.2f ms to respond"%(msg[0], 1000*delta))
             self.responses.add(msg[0])
         elif msg[1] == last:
             delta = time.time()-self.tic + (self.lifetime-self.last_ping)
             self.log.warn("heartbeat::heart %r missed a beat, and took %.2f ms to respond", msg[0], 1000*delta)
             self.responses.add(msg[0])
         else:
             self.log.warn("heartbeat::got bad heartbeat (possibly old?): %s (current=%.3f)", msg[1], self.lifetime)
 
 
 if __name__ == '__main__':
     loop = ioloop.IOLoop.instance()
     context = zmq.Context()
     pub = context.socket(zmq.PUB)
     pub.bind('tcp://127.0.0.1:5555')
     xrep = context.socket(zmq.ROUTER)
     xrep.bind('tcp://127.0.0.1:5556')
 
     outstream = zmqstream.ZMQStream(pub, loop)
     instream = zmqstream.ZMQStream(xrep, loop)
 
     hb = HeartMonitor(loop, outstream, instream)
 
     loop.start()