"""Base classes to manage the interaction with a running kernel. TODO * Create logger to handle debugging and console messages. """ #----------------------------------------------------------------------------- # 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 #----------------------------------------------------------------------------- # Standard library imports. import atexit import errno import json from subprocess import Popen import os import signal import sys from threading import Thread import time # System library imports. import zmq # import ZMQError in top-level namespace, to avoid ugly attribute-error messages # during garbage collection of threads at exit: from zmq import ZMQError from zmq.eventloop import ioloop, zmqstream # Local imports. from IPython.config.loader import Config from IPython.utils.localinterfaces import LOCALHOST, LOCAL_IPS from IPython.utils.traitlets import ( HasTraits, Any, Instance, Type, Unicode, Integer, Bool, CaselessStrEnum ) from IPython.utils.py3compat import str_to_bytes from IPython.zmq.entry_point import write_connection_file from session import Session #----------------------------------------------------------------------------- # Constants and exceptions #----------------------------------------------------------------------------- class InvalidPortNumber(Exception): pass #----------------------------------------------------------------------------- # Utility functions #----------------------------------------------------------------------------- # some utilities to validate message structure, these might get moved elsewhere # if they prove to have more generic utility def validate_string_list(lst): """Validate that the input is a list of strings. Raises ValueError if not.""" if not isinstance(lst, list): raise ValueError('input %r must be a list' % lst) for x in lst: if not isinstance(x, basestring): raise ValueError('element %r in list must be a string' % x) def validate_string_dict(dct): """Validate that the input is a dict with string keys and values. Raises ValueError if not.""" for k,v in dct.iteritems(): if not isinstance(k, basestring): raise ValueError('key %r in dict must be a string' % k) if not isinstance(v, basestring): raise ValueError('value %r in dict must be a string' % v) #----------------------------------------------------------------------------- # ZMQ Socket Channel classes #----------------------------------------------------------------------------- class ZMQSocketChannel(Thread): """The base class for the channels that use ZMQ sockets. """ context = None session = None socket = None ioloop = None stream = None _address = None _exiting = False def __init__(self, context, session, address): """Create a channel Parameters ---------- context : :class:`zmq.Context` The ZMQ context to use. session : :class:`session.Session` The session to use. address : zmq url Standard (ip, port) tuple that the kernel is listening on. """ super(ZMQSocketChannel, self).__init__() self.daemon = True self.context = context self.session = session if isinstance(address, tuple): if address[1] == 0: message = 'The port number for a channel cannot be 0.' raise InvalidPortNumber(message) address = "tcp://%s:%i" % address self._address = address atexit.register(self._notice_exit) def _notice_exit(self): self._exiting = True def _run_loop(self): """Run my loop, ignoring EINTR events in the poller""" while True: try: self.ioloop.start() except ZMQError as e: if e.errno == errno.EINTR: continue else: raise except Exception: if self._exiting: break else: raise else: break def stop(self): """Stop the channel's activity. This calls :method:`Thread.join` and returns when the thread terminates. :class:`RuntimeError` will be raised if :method:`self.start` is called again. """ self.join() @property def address(self): """Get the channel's address as a zmq url string ('tcp://127.0.0.1:5555'). """ return self._address def _queue_send(self, msg): """Queue a message to be sent from the IOLoop's thread. Parameters ---------- msg : message to send This is threadsafe, as it uses IOLoop.add_callback to give the loop's thread control of the action. """ def thread_send(): self.session.send(self.stream, msg) self.ioloop.add_callback(thread_send) def _handle_recv(self, msg): """callback for stream.on_recv unpacks message, and calls handlers with it. """ ident,smsg = self.session.feed_identities(msg) self.call_handlers(self.session.unserialize(smsg)) class ShellSocketChannel(ZMQSocketChannel): """The DEALER channel for issues request/replies to the kernel. """ command_queue = None # flag for whether execute requests should be allowed to call raw_input: allow_stdin = True def __init__(self, context, session, address): super(ShellSocketChannel, self).__init__(context, session, address) self.ioloop = ioloop.IOLoop() def run(self): """The thread's main activity. Call start() instead.""" self.socket = self.context.socket(zmq.DEALER) self.socket.setsockopt(zmq.IDENTITY, self.session.bsession) self.socket.connect(self.address) self.stream = zmqstream.ZMQStream(self.socket, self.ioloop) self.stream.on_recv(self._handle_recv) self._run_loop() try: self.socket.close() except: pass def stop(self): self.ioloop.stop() super(ShellSocketChannel, self).stop() def call_handlers(self, msg): """This method is called in the ioloop thread when a message arrives. Subclasses should override this method to handle incoming messages. It is important to remember that this method is called in the thread so that some logic must be done to ensure that the application leve handlers are called in the application thread. """ raise NotImplementedError('call_handlers must be defined in a subclass.') def execute(self, code, silent=False, store_history=True, user_variables=None, user_expressions=None, allow_stdin=None): """Execute code in the kernel. Parameters ---------- code : str A string of Python code. silent : bool, optional (default False) If set, the kernel will execute the code as quietly possible, and will force store_history to be False. store_history : bool, optional (default True) If set, the kernel will store command history. This is forced to be False if silent is True. user_variables : list, optional A list of variable names to pull from the user's namespace. They will come back as a dict with these names as keys and their :func:`repr` as values. user_expressions : dict, optional A dict mapping names to expressions to be evaluated in the user's dict. The expression values are returned as strings formatted using :func:`repr`. allow_stdin : bool, optional (default self.allow_stdin) Flag for whether the kernel can send stdin requests to frontends. Some frontends (e.g. the Notebook) do not support stdin requests. If raw_input is called from code executed from such a frontend, a StdinNotImplementedError will be raised. Returns ------- The msg_id of the message sent. """ if user_variables is None: user_variables = [] if user_expressions is None: user_expressions = {} if allow_stdin is None: allow_stdin = self.allow_stdin # Don't waste network traffic if inputs are invalid if not isinstance(code, basestring): raise ValueError('code %r must be a string' % code) validate_string_list(user_variables) validate_string_dict(user_expressions) # Create class for content/msg creation. Related to, but possibly # not in Session. content = dict(code=code, silent=silent, store_history=store_history, user_variables=user_variables, user_expressions=user_expressions, allow_stdin=allow_stdin, ) msg = self.session.msg('execute_request', content) self._queue_send(msg) return msg['header']['msg_id'] def complete(self, text, line, cursor_pos, block=None): """Tab complete text in the kernel's namespace. Parameters ---------- text : str The text to complete. line : str The full line of text that is the surrounding context for the text to complete. cursor_pos : int The position of the cursor in the line where the completion was requested. block : str, optional The full block of code in which the completion is being requested. Returns ------- The msg_id of the message sent. """ content = dict(text=text, line=line, block=block, cursor_pos=cursor_pos) msg = self.session.msg('complete_request', content) self._queue_send(msg) return msg['header']['msg_id'] def object_info(self, oname, detail_level=0): """Get metadata information about an object. Parameters ---------- oname : str A string specifying the object name. detail_level : int, optional The level of detail for the introspection (0-2) Returns ------- The msg_id of the message sent. """ content = dict(oname=oname, detail_level=detail_level) msg = self.session.msg('object_info_request', content) self._queue_send(msg) return msg['header']['msg_id'] def history(self, raw=True, output=False, hist_access_type='range', **kwargs): """Get entries from the history list. Parameters ---------- raw : bool If True, return the raw input. output : bool If True, then return the output as well. hist_access_type : str 'range' (fill in session, start and stop params), 'tail' (fill in n) or 'search' (fill in pattern param). session : int For a range request, the session from which to get lines. Session numbers are positive integers; negative ones count back from the current session. start : int The first line number of a history range. stop : int The final (excluded) line number of a history range. n : int The number of lines of history to get for a tail request. pattern : str The glob-syntax pattern for a search request. Returns ------- The msg_id of the message sent. """ content = dict(raw=raw, output=output, hist_access_type=hist_access_type, **kwargs) msg = self.session.msg('history_request', content) self._queue_send(msg) return msg['header']['msg_id'] def shutdown(self, restart=False): """Request an immediate kernel shutdown. Upon receipt of the (empty) reply, client code can safely assume that the kernel has shut down and it's safe to forcefully terminate it if it's still alive. The kernel will send the reply via a function registered with Python's atexit module, ensuring it's truly done as the kernel is done with all normal operation. """ # Send quit message to kernel. Once we implement kernel-side setattr, # this should probably be done that way, but for now this will do. msg = self.session.msg('shutdown_request', {'restart':restart}) self._queue_send(msg) return msg['header']['msg_id'] class SubSocketChannel(ZMQSocketChannel): """The SUB channel which listens for messages that the kernel publishes. """ def __init__(self, context, session, address): super(SubSocketChannel, self).__init__(context, session, address) self.ioloop = ioloop.IOLoop() def run(self): """The thread's main activity. Call start() instead.""" self.socket = self.context.socket(zmq.SUB) self.socket.setsockopt(zmq.SUBSCRIBE,b'') self.socket.setsockopt(zmq.IDENTITY, self.session.bsession) self.socket.connect(self.address) self.stream = zmqstream.ZMQStream(self.socket, self.ioloop) self.stream.on_recv(self._handle_recv) self._run_loop() try: self.socket.close() except: pass def stop(self): self.ioloop.stop() super(SubSocketChannel, self).stop() def call_handlers(self, msg): """This method is called in the ioloop thread when a message arrives. Subclasses should override this method to handle incoming messages. It is important to remember that this method is called in the thread so that some logic must be done to ensure that the application leve handlers are called in the application thread. """ raise NotImplementedError('call_handlers must be defined in a subclass.') def flush(self, timeout=1.0): """Immediately processes all pending messages on the SUB channel. Callers should use this method to ensure that :method:`call_handlers` has been called for all messages that have been received on the 0MQ SUB socket of this channel. This method is thread safe. Parameters ---------- timeout : float, optional The maximum amount of time to spend flushing, in seconds. The default is one second. """ # We do the IOLoop callback process twice to ensure that the IOLoop # gets to perform at least one full poll. stop_time = time.time() + timeout for i in xrange(2): self._flushed = False self.ioloop.add_callback(self._flush) while not self._flushed and time.time() < stop_time: time.sleep(0.01) def _flush(self): """Callback for :method:`self.flush`.""" self.stream.flush() self._flushed = True class StdInSocketChannel(ZMQSocketChannel): """A reply channel to handle raw_input requests that the kernel makes.""" msg_queue = None def __init__(self, context, session, address): super(StdInSocketChannel, self).__init__(context, session, address) self.ioloop = ioloop.IOLoop() def run(self): """The thread's main activity. Call start() instead.""" self.socket = self.context.socket(zmq.DEALER) self.socket.setsockopt(zmq.IDENTITY, self.session.bsession) self.socket.connect(self.address) self.stream = zmqstream.ZMQStream(self.socket, self.ioloop) self.stream.on_recv(self._handle_recv) self._run_loop() try: self.socket.close() except: pass def stop(self): self.ioloop.stop() super(StdInSocketChannel, self).stop() def call_handlers(self, msg): """This method is called in the ioloop thread when a message arrives. Subclasses should override this method to handle incoming messages. It is important to remember that this method is called in the thread so that some logic must be done to ensure that the application leve handlers are called in the application thread. """ raise NotImplementedError('call_handlers must be defined in a subclass.') def input(self, string): """Send a string of raw input to the kernel.""" content = dict(value=string) msg = self.session.msg('input_reply', content) self._queue_send(msg) class HBSocketChannel(ZMQSocketChannel): """The heartbeat channel which monitors the kernel heartbeat. Note that the heartbeat channel is paused by default. As long as you start this channel, the kernel manager will ensure that it is paused and un-paused as appropriate. """ time_to_dead = 3.0 socket = None poller = None _running = None _pause = None _beating = None def __init__(self, context, session, address): super(HBSocketChannel, self).__init__(context, session, address) self._running = False self._pause =True self.poller = zmq.Poller() def _create_socket(self): if self.socket is not None: # close previous socket, before opening a new one self.poller.unregister(self.socket) self.socket.close() self.socket = self.context.socket(zmq.REQ) self.socket.setsockopt(zmq.LINGER, 0) self.socket.connect(self.address) self.poller.register(self.socket, zmq.POLLIN) def _poll(self, start_time): """poll for heartbeat replies until we reach self.time_to_dead Ignores interrupts, and returns the result of poll(), which will be an empty list if no messages arrived before the timeout, or the event tuple if there is a message to receive. """ until_dead = self.time_to_dead - (time.time() - start_time) # ensure poll at least once until_dead = max(until_dead, 1e-3) events = [] while True: try: events = self.poller.poll(1000 * until_dead) except ZMQError as e: if e.errno == errno.EINTR: # ignore interrupts during heartbeat # this may never actually happen until_dead = self.time_to_dead - (time.time() - start_time) until_dead = max(until_dead, 1e-3) pass else: raise except Exception: if self._exiting: break else: raise else: break return events def run(self): """The thread's main activity. Call start() instead.""" self._create_socket() self._running = True self._beating = True while self._running: if self._pause: # just sleep, and skip the rest of the loop time.sleep(self.time_to_dead) continue since_last_heartbeat = 0.0 # io.rprint('Ping from HB channel') # dbg # no need to catch EFSM here, because the previous event was # either a recv or connect, which cannot be followed by EFSM self.socket.send(b'ping') request_time = time.time() ready = self._poll(request_time) if ready: self._beating = True # the poll above guarantees we have something to recv self.socket.recv() # sleep the remainder of the cycle remainder = self.time_to_dead - (time.time() - request_time) if remainder > 0: time.sleep(remainder) continue else: # nothing was received within the time limit, signal heart failure self._beating = False since_last_heartbeat = time.time() - request_time self.call_handlers(since_last_heartbeat) # and close/reopen the socket, because the REQ/REP cycle has been broken self._create_socket() continue try: self.socket.close() except: pass def pause(self): """Pause the heartbeat.""" self._pause = True def unpause(self): """Unpause the heartbeat.""" self._pause = False def is_beating(self): """Is the heartbeat running and responsive (and not paused).""" if self.is_alive() and not self._pause and self._beating: return True else: return False def stop(self): self._running = False super(HBSocketChannel, self).stop() def call_handlers(self, since_last_heartbeat): """This method is called in the ioloop thread when a message arrives. Subclasses should override this method to handle incoming messages. It is important to remember that this method is called in the thread so that some logic must be done to ensure that the application level handlers are called in the application thread. """ raise NotImplementedError('call_handlers must be defined in a subclass.') #----------------------------------------------------------------------------- # Main kernel manager class #----------------------------------------------------------------------------- class KernelManager(HasTraits): """ Manages a kernel for a frontend. The SUB channel is for the frontend to receive messages published by the kernel. The REQ channel is for the frontend to make requests of the kernel. The REP channel is for the kernel to request stdin (raw_input) from the frontend. """ # config object for passing to child configurables config = Instance(Config) # The PyZMQ Context to use for communication with the kernel. context = Instance(zmq.Context) def _context_default(self): return zmq.Context.instance() # The Session to use for communication with the kernel. session = Instance(Session) # The kernel process with which the KernelManager is communicating. kernel = Instance(Popen) # The addresses for the communication channels. connection_file = Unicode('') transport = CaselessStrEnum(['tcp', 'ipc'], default_value='tcp') ip = Unicode(LOCALHOST) def _ip_changed(self, name, old, new): if new == '*': self.ip = '0.0.0.0' shell_port = Integer(0) iopub_port = Integer(0) stdin_port = Integer(0) hb_port = Integer(0) # The classes to use for the various channels. shell_channel_class = Type(ShellSocketChannel) sub_channel_class = Type(SubSocketChannel) stdin_channel_class = Type(StdInSocketChannel) hb_channel_class = Type(HBSocketChannel) # Protected traits. _launch_args = Any _shell_channel = Any _sub_channel = Any _stdin_channel = Any _hb_channel = Any _connection_file_written=Bool(False) def __init__(self, **kwargs): super(KernelManager, self).__init__(**kwargs) if self.session is None: self.session = Session(config=self.config) def __del__(self): self.cleanup_connection_file() #-------------------------------------------------------------------------- # Channel management methods: #-------------------------------------------------------------------------- def start_channels(self, shell=True, sub=True, stdin=True, hb=True): """Starts the channels for this kernel. This will create the channels if they do not exist and then start them. If port numbers of 0 are being used (random ports) then you must first call :method:`start_kernel`. If the channels have been stopped and you call this, :class:`RuntimeError` will be raised. """ if shell: self.shell_channel.start() if sub: self.sub_channel.start() if stdin: self.stdin_channel.start() self.shell_channel.allow_stdin = True else: self.shell_channel.allow_stdin = False if hb: self.hb_channel.start() def stop_channels(self): """Stops all the running channels for this kernel. """ if self.shell_channel.is_alive(): self.shell_channel.stop() if self.sub_channel.is_alive(): self.sub_channel.stop() if self.stdin_channel.is_alive(): self.stdin_channel.stop() if self.hb_channel.is_alive(): self.hb_channel.stop() @property def channels_running(self): """Are any of the channels created and running?""" return (self.shell_channel.is_alive() or self.sub_channel.is_alive() or self.stdin_channel.is_alive() or self.hb_channel.is_alive()) #-------------------------------------------------------------------------- # Kernel process management methods: #-------------------------------------------------------------------------- def cleanup_connection_file(self): """cleanup connection file *if we wrote it* Will not raise if the connection file was already removed somehow. """ if self._connection_file_written: # cleanup connection files on full shutdown of kernel we started self._connection_file_written = False try: os.remove(self.connection_file) except (IOError, OSError): pass self._cleanup_ipc_files() def _cleanup_ipc_files(self): """cleanup ipc files if we wrote them""" if self.transport != 'ipc': return for port in (self.shell_port, self.iopub_port, self.stdin_port, self.hb_port): ipcfile = "%s-%i" % (self.ip, port) try: os.remove(ipcfile) except (IOError, OSError): pass def load_connection_file(self): """load connection info from JSON dict in self.connection_file""" with open(self.connection_file) as f: cfg = json.loads(f.read()) from pprint import pprint pprint(cfg) self.transport = cfg.get('transport', 'tcp') self.ip = cfg['ip'] self.shell_port = cfg['shell_port'] self.stdin_port = cfg['stdin_port'] self.iopub_port = cfg['iopub_port'] self.hb_port = cfg['hb_port'] self.session.key = str_to_bytes(cfg['key']) def write_connection_file(self): """write connection info to JSON dict in self.connection_file""" if self._connection_file_written: return self.connection_file,cfg = write_connection_file(self.connection_file, transport=self.transport, ip=self.ip, key=self.session.key, stdin_port=self.stdin_port, iopub_port=self.iopub_port, shell_port=self.shell_port, hb_port=self.hb_port) # write_connection_file also sets default ports: self.shell_port = cfg['shell_port'] self.stdin_port = cfg['stdin_port'] self.iopub_port = cfg['iopub_port'] self.hb_port = cfg['hb_port'] self._connection_file_written = True def start_kernel(self, **kw): """Starts a kernel process and configures the manager to use it. If random ports (port=0) are being used, this method must be called before the channels are created. Parameters: ----------- launcher : callable, optional (default None) A custom function for launching the kernel process (generally a wrapper around ``entry_point.base_launch_kernel``). In most cases, it should not be necessary to use this parameter. **kw : optional See respective options for IPython and Python kernels. """ if self.transport == 'tcp' and self.ip not in LOCAL_IPS: raise RuntimeError("Can only launch a kernel on a local interface. " "Make sure that the '*_address' attributes are " "configured properly. " "Currently valid addresses are: %s"%LOCAL_IPS ) # write connection file / get default ports self.write_connection_file() self._launch_args = kw.copy() launch_kernel = kw.pop('launcher', None) if launch_kernel is None: from ipkernel import launch_kernel self.kernel = launch_kernel(fname=self.connection_file, **kw) def shutdown_kernel(self, restart=False): """ Attempts to the stop the kernel process cleanly. If the kernel cannot be stopped and the kernel is local, it is killed. """ # FIXME: Shutdown does not work on Windows due to ZMQ errors! if sys.platform == 'win32': self.kill_kernel() return # Pause the heart beat channel if it exists. if self._hb_channel is not None: self._hb_channel.pause() # Don't send any additional kernel kill messages immediately, to give # the kernel a chance to properly execute shutdown actions. Wait for at # most 1s, checking every 0.1s. self.shell_channel.shutdown(restart=restart) for i in range(10): if self.is_alive: time.sleep(0.1) else: break else: # OK, we've waited long enough. if self.has_kernel: self.kill_kernel() if not restart and self._connection_file_written: # cleanup connection files on full shutdown of kernel we started self._connection_file_written = False try: os.remove(self.connection_file) except IOError: pass def restart_kernel(self, now=False, **kw): """Restarts a kernel with the arguments that were used to launch it. If the old kernel was launched with random ports, the same ports will be used for the new kernel. Parameters ---------- now : bool, optional If True, the kernel is forcefully restarted *immediately*, without having a chance to do any cleanup action. Otherwise the kernel is given 1s to clean up before a forceful restart is issued. In all cases the kernel is restarted, the only difference is whether it is given a chance to perform a clean shutdown or not. **kw : optional Any options specified here will replace those used to launch the kernel. """ if self._launch_args is None: raise RuntimeError("Cannot restart the kernel. " "No previous call to 'start_kernel'.") else: # Stop currently running kernel. if self.has_kernel: if now: self.kill_kernel() else: self.shutdown_kernel(restart=True) # Start new kernel. self._launch_args.update(kw) self.start_kernel(**self._launch_args) # FIXME: Messages get dropped in Windows due to probable ZMQ bug # unless there is some delay here. if sys.platform == 'win32': time.sleep(0.2) @property def has_kernel(self): """Returns whether a kernel process has been specified for the kernel manager. """ return self.kernel is not None def kill_kernel(self): """ Kill the running kernel. This method blocks until the kernel process has terminated. """ if self.has_kernel: # Pause the heart beat channel if it exists. if self._hb_channel is not None: self._hb_channel.pause() # Signal the kernel to terminate (sends SIGKILL on Unix and calls # TerminateProcess() on Win32). try: self.kernel.kill() except OSError as e: # In Windows, we will get an Access Denied error if the process # has already terminated. Ignore it. if sys.platform == 'win32': if e.winerror != 5: raise # On Unix, we may get an ESRCH error if the process has already # terminated. Ignore it. else: from errno import ESRCH if e.errno != ESRCH: raise # Block until the kernel terminates. self.kernel.wait() self.kernel = None else: raise RuntimeError("Cannot kill kernel. No kernel is running!") def interrupt_kernel(self): """ Interrupts the kernel. Unlike ``signal_kernel``, this operation is well supported on all platforms. """ if self.has_kernel: if sys.platform == 'win32': from parentpoller import ParentPollerWindows as Poller Poller.send_interrupt(self.kernel.win32_interrupt_event) else: self.kernel.send_signal(signal.SIGINT) else: raise RuntimeError("Cannot interrupt kernel. No kernel is running!") def signal_kernel(self, signum): """ Sends a signal to the kernel. Note that since only SIGTERM is supported on Windows, this function is only useful on Unix systems. """ if self.has_kernel: self.kernel.send_signal(signum) else: raise RuntimeError("Cannot signal kernel. No kernel is running!") @property def is_alive(self): """Is the kernel process still running?""" if self.has_kernel: if self.kernel.poll() is None: return True else: return False elif self._hb_channel is not None: # We didn't start the kernel with this KernelManager so we # use the heartbeat. return self._hb_channel.is_beating() else: # no heartbeat and not local, we can't tell if it's running, # so naively return True return True #-------------------------------------------------------------------------- # Channels used for communication with the kernel: #-------------------------------------------------------------------------- def _make_url(self, port): """make a zmq url with a port""" if self.transport == 'tcp': return "tcp://%s:%i" % (self.ip, port) else: return "%s://%s-%s" % (self.transport, self.ip, port) @property def shell_channel(self): """Get the REQ socket channel object to make requests of the kernel.""" if self._shell_channel is None: self._shell_channel = self.shell_channel_class(self.context, self.session, self._make_url(self.shell_port), ) return self._shell_channel @property def sub_channel(self): """Get the SUB socket channel object.""" if self._sub_channel is None: self._sub_channel = self.sub_channel_class(self.context, self.session, self._make_url(self.iopub_port), ) return self._sub_channel @property def stdin_channel(self): """Get the REP socket channel object to handle stdin (raw_input).""" if self._stdin_channel is None: self._stdin_channel = self.stdin_channel_class(self.context, self.session, self._make_url(self.stdin_port), ) return self._stdin_channel @property def hb_channel(self): """Get the heartbeat socket channel object to check that the kernel is alive.""" if self._hb_channel is None: self._hb_channel = self.hb_channel_class(self.context, self.session, self._make_url(self.hb_port), ) return self._hb_channel