def create_consumer(self, topic, proxy, fanout=False):
        # Register with matchmaker.
        _get_matchmaker().register(topic, CONF.rpc_zmq_host)

        # Subscription scenarios
        if fanout:
            sock_type = zmq.SUB
            subscribe = ("", fanout)[type(fanout) == str]
            topic = "fanout~" + topic.split(".", 1)[0]
        else:
            sock_type = zmq.PULL
            subscribe = None
            topic = ".".join((topic.split(".", 1)[0], CONF.rpc_zmq_host))

        if topic in self.topics:
            LOG.info(_("Skipping topic registration. Already registered."))
            return

        # Receive messages from (local) proxy
        inaddr = "ipc://%s/zmq_topic_%s" % (CONF.rpc_zmq_ipc_dir, topic)

        LOG.debug(_("Consumer is a zmq.%s"), ["PULL", "SUB"][sock_type == zmq.SUB])

        self.reactor.register(proxy, inaddr, sock_type, subscribe=subscribe, in_bind=False)
        self.topics.append(topic)

def ssh_execute(ssh, cmd, process_input=None, addl_env=None, check_exit_code=True):
    LOG.debug(_("Running cmd (SSH): %s"), cmd)
    if addl_env:
        raise InvalidArgumentError(_("Environment not supported over SSH"))

    if process_input:
        # This is (probably) fixable if we need it...
        raise InvalidArgumentError(_("process_input not supported over SSH"))

    stdin_stream, stdout_stream, stderr_stream = ssh.exec_command(cmd)
    channel = stdout_stream.channel

    # NOTE(justinsb): This seems suspicious...
    # ...other SSH clients have buffering issues with this approach
    stdout = stdout_stream.read()
    stderr = stderr_stream.read()
    stdin_stream.close()

    exit_status = channel.recv_exit_status()

    # exit_status == -1 if no exit code was returned
    if exit_status != -1:
        LOG.debug(_("Result was %s") % exit_status)
        if check_exit_code and exit_status != 0:
            raise ProcessExecutionError(exit_code=exit_status, stdout=stdout, stderr=stderr, cmd=cmd)

    return (stdout, stderr)

    def run_periodic_tasks(self, context, raise_on_error=False):
        """Tasks to be run at a periodic interval."""
        idle_for = DEFAULT_INTERVAL
        for task_name, task in self._periodic_tasks:
            full_task_name = '.'.join([self.__class__.__name__, task_name])

            now = timeutils.utcnow()
            spacing = self._periodic_spacing[task_name]
            last_run = self._periodic_last_run[task_name]

            # If a periodic task is _nearly_ due, then we'll run it early
            if spacing is not None and last_run is not None:
                due = last_run + datetime.timedelta(seconds=spacing)
                if not timeutils.is_soon(due, 0.2):
                    idle_for = min(idle_for, timeutils.delta_seconds(now, due))
                    continue

            if spacing is not None:
                idle_for = min(idle_for, spacing)

            LOG.debug(_("Running periodic task %(full_task_name)s"),
                      {"full_task_name": full_task_name})
            self._periodic_last_run[task_name] = timeutils.utcnow()

            try:
                task(self, context)
            except Exception as e:
                if raise_on_error:
                    raise
                LOG.exception(_("Error during %(full_task_name)s: %(e)s"),
                              {"full_task_name": full_task_name, "e": e})
            time.sleep(0)

        return idle_for

    def _wait_for_exit_or_signal(self):
        status = None
        signo = 0

        LOG.debug(_('Full set of CONF:'))
        CONF.log_opt_values(LOG, std_logging.DEBUG)

        try:
            super(ServiceLauncher, self).wait()
        except SignalExit as exc:
            signame = _signo_to_signame(exc.signo)
            LOG.info(_('Caught %s, exiting'), signame)
            status = exc.code
            signo = exc.signo
        except SystemExit as exc:
            status = exc.code
        finally:
            self.stop()
            if rpc:
                try:
                    rpc.cleanup()
                except Exception:
                    # We're shutting down, so it doesn't matter at this point.
                    LOG.exception(_('Exception during rpc cleanup.'))

        return status, signo

    def __call__(self, message_data):
        """Consumer callback to call a method on a proxy object.

        Parses the message for validity and fires off a thread to call the
        proxy object method.

        Message data should be a dictionary with two keys:
            method: string representing the method to call
            args: dictionary of arg: value

        Example: {'method': 'echo', 'args': {'value': 42}}

        """
        # It is important to clear the context here, because at this point
        # the previous context is stored in local.store.context
        if hasattr(local.store, 'context'):
            del local.store.context
        rpc_common._safe_log(LOG.debug, _('received %s'), message_data)
        self.msg_id_cache.check_duplicate_message(message_data)
        ctxt = unpack_context(self.conf, message_data)
        method = message_data.get('method')
        args = message_data.get('args', {})
        version = message_data.get('version')
        namespace = message_data.get('namespace')
        if not method:
            LOG.warn(_('no method for message: %s') % message_data)
            ctxt.reply(_('No method for message: %s') % message_data,
                       connection_pool=self.connection_pool)
            return
        self.pool.spawn_n(self._process_data, ctxt, version, method,
                          namespace, args)

            def publisher(waiter):
                LOG.info(_("Creating proxy for topic: %s"), topic)

                try:
                    # The topic is received over the network,
                    # don't trust this input.
                    if self.badchars.search(topic) is not None:
                        emsg = _("Topic contained dangerous characters.")
                        LOG.warn(emsg)
                        raise RPCException(emsg)

                    out_sock = ZmqSocket("ipc://%s/zmq_topic_%s" % (ipc_dir, topic), sock_type, bind=True)
                except RPCException:
                    waiter.send_exception(*sys.exc_info())
                    return

                self.topic_proxy[topic] = eventlet.queue.LightQueue(CONF.rpc_zmq_topic_backlog)
                self.sockets.append(out_sock)

                # It takes some time for a pub socket to open,
                # before we can have any faith in doing a send() to it.
                if sock_type == zmq.PUB:
                    eventlet.sleep(0.5)

                waiter.send(True)

                while True:
                    data = self.topic_proxy[topic].get()
                    out_sock.send(data, copy=False)

    def consume(self, sock):
        # TODO(ewindisch): use zero-copy (i.e. references, not copying)
        data = sock.recv()
        LOG.debug(_("CONSUMER RECEIVED DATA: %s"), data)

        proxy = self.proxies[sock]

        if data[2] == "cast":  # Legacy protocol
            packenv = data[3]

            ctx, msg = _deserialize(packenv)
            request = rpc_common.deserialize_msg(msg)
            ctx = RpcContext.unmarshal(ctx)
        elif data[2] == "impl_zmq_v2":
            packenv = data[4:]

            msg = unflatten_envelope(packenv)
            request = rpc_common.deserialize_msg(msg)

            # Unmarshal only after verifying the message.
            ctx = RpcContext.unmarshal(data[3])
        else:
            LOG.error(_("ZMQ Envelope version unsupported or unknown."))
            return

        self.pool.spawn_n(self.process, proxy, ctx, request)

    def __init__(self, addr, zmq_type, bind=True, subscribe=None):
        self.sock = _get_ctxt().socket(zmq_type)
        self.addr = addr
        self.type = zmq_type
        self.subscriptions = []

        # Support failures on sending/receiving on wrong socket type.
        self.can_recv = zmq_type in (zmq.PULL, zmq.SUB)
        self.can_send = zmq_type in (zmq.PUSH, zmq.PUB)
        self.can_sub = zmq_type in (zmq.SUB,)

        # Support list, str, & None for subscribe arg (cast to list)
        do_sub = {list: subscribe, str: [subscribe], type(None): []}[type(subscribe)]

        for f in do_sub:
            self.subscribe(f)

        str_data = {"addr": addr, "type": self.socket_s(), "subscribe": subscribe, "bind": bind}

        LOG.debug(_("Connecting to %(addr)s with %(type)s"), str_data)
        LOG.debug(_("-> Subscribed to %(subscribe)s"), str_data)
        LOG.debug(_("-> bind: %(bind)s"), str_data)

        try:
            if bind:
                self.sock.bind(addr)
            else:
                self.sock.connect(addr)
        except Exception:
            raise RPCException(_("Could not open socket."))

    def _start_child(self, wrap):
        if len(wrap.forktimes) > wrap.workers:
            # Limit ourselves to one process a second (over the period of
            # number of workers * 1 second). This will allow workers to
            # start up quickly but ensure we don't fork off children that
            # die instantly too quickly.
            if time.time() - wrap.forktimes[0] < wrap.workers:
                LOG.info(_('Forking too fast, sleeping'))
                time.sleep(1)

            wrap.forktimes.pop(0)

        wrap.forktimes.append(time.time())

        pid = os.fork()
        if pid == 0:
            launcher = self._child_process(wrap.service)
            while True:
                self._child_process_handle_signal()
                status, signo = self._child_wait_for_exit_or_signal(launcher)
                if not _is_sighup(signo):
                    break
                launcher.restart()

            os._exit(status)

        LOG.info(_('Started child %d'), pid)

        wrap.children.add(pid)
        self.children[pid] = wrap

        return pid

    def wait(self):
        """Loop waiting on children to die and respawning as necessary."""

        LOG.debug(_('Full set of CONF:'))
        CONF.log_opt_values(LOG, std_logging.DEBUG)

        while True:
            self.handle_signal()
            self._respawn_children()
            if self.sigcaught:
                signame = _signo_to_signame(self.sigcaught)
                LOG.info(_('Caught %s, stopping children'), signame)
            if not _is_sighup(self.sigcaught):
                break

            for pid in self.children:
                os.kill(pid, signal.SIGHUP)
            self.running = True
            self.sigcaught = None

        for pid in self.children:
            try:
                os.kill(pid, signal.SIGTERM)
            except OSError as exc:
                if exc.errno != errno.ESRCH:
                    raise

        # Wait for children to die
        if self.children:
            LOG.info(_('Waiting on %d children to exit'), len(self.children))
            while self.children:
                self._wait_child()

    def _wait_child(self):
        try:
            # Don't block if no child processes have exited
            pid, status = os.waitpid(0, os.WNOHANG)
            if not pid:
                return None
        except OSError as exc:
            if exc.errno not in (errno.EINTR, errno.ECHILD):
                raise
            return None

        if os.WIFSIGNALED(status):
            sig = os.WTERMSIG(status)
            LOG.info(_('Child %(pid)d killed by signal %(sig)d'),
                     dict(pid=pid, sig=sig))
        else:
            code = os.WEXITSTATUS(status)
            LOG.info(_('Child %(pid)s exited with status %(code)d'),
                     dict(pid=pid, code=code))

        if pid not in self.children:
            LOG.warning(_('pid %d not in child list'), pid)
            return None

        wrap = self.children.pop(pid)
        wrap.children.remove(pid)
        return wrap

 def _connect(self, params):
     """Connect to rabbit.  Re-establish any queues that may have
     been declared before if we are reconnecting.  Exceptions should
     be handled by the caller.
     """
     if self.connection:
         LOG.info(_("Reconnecting to AMQP server on "
                  "%(hostname)s:%(port)d") % params)
         try:
             self.connection.release()
         except self.connection_errors:
             pass
         # Setting this in case the next statement fails, though
         # it shouldn't be doing any network operations, yet.
         self.connection = None
     self.connection = kombu.connection.BrokerConnection(**params)
     self.connection_errors = self.connection.connection_errors
     if self.memory_transport:
         # Kludge to speed up tests.
         self.connection.transport.polling_interval = 0.0
     self.consumer_num = itertools.count(1)
     self.connection.connect()
     self.channel = self.connection.channel()
     # work around 'memory' transport bug in 1.1.3
     if self.memory_transport:
         self.channel._new_queue('ae.undeliver')
     for consumer in self.consumers:
         consumer.reconnect(self.channel)
     LOG.info(_('Connected to AMQP server on %(hostname)s:%(port)d') %
              params)

    def _process_data(self, ctxt, version, method, namespace, args):
        """Process a message in a new thread.

        If the proxy object we have has a dispatch method
        (see rpc.dispatcher.RpcDispatcher), pass it the version,
        method, and args and let it dispatch as appropriate.  If not, use
        the old behavior of magically calling the specified method on the
        proxy we have here.
        """
        ctxt.update_store()
        try:
            rval = self.proxy.dispatch(ctxt, version, method, namespace,
                                       **args)
            # Check if the result was a generator
            if inspect.isgenerator(rval):
                for x in rval:
                    ctxt.reply(x, None, connection_pool=self.connection_pool)
            else:
                ctxt.reply(rval, None, connection_pool=self.connection_pool)
            # This final None tells multicall that it is done.
            ctxt.reply(ending=True, connection_pool=self.connection_pool)
        except rpc_common.ClientException as e:
            LOG.debug(_('Expected exception during message handling (%s)') %
                      e._exc_info[1])
            ctxt.reply(None, e._exc_info,
                       connection_pool=self.connection_pool,
                       log_failure=False)
        except Exception:
            # sys.exc_info() is deleted by LOG.exception().
            exc_info = sys.exc_info()
            LOG.error(_('Exception during message handling'),
                      exc_info=exc_info)
            ctxt.reply(None, exc_info, connection_pool=self.connection_pool)

def _multi_send(method, context, topic, msg, timeout=None, envelope=False, _msg_id=None):
    """Wraps the sending of messages.

    Dispatches to the matchmaker and sends message to all relevant hosts.
    """
    conf = CONF
    LOG.debug(_("%(msg)s") % {"msg": " ".join(map(pformat, (topic, msg)))})

    queues = _get_matchmaker().queues(topic)
    LOG.debug(_("Sending message(s) to: %s"), queues)

    # Don't stack if we have no matchmaker results
    if not queues:
        LOG.warn(_("No matchmaker results. Not casting."))
        # While not strictly a timeout, callers know how to handle
        # this exception and a timeout isn't too big a lie.
        raise rpc_common.Timeout(_("No match from matchmaker."))

    # This supports brokerless fanout (addresses > 1)
    for queue in queues:
        (_topic, ip_addr) = queue
        _addr = "tcp://%s:%s" % (ip_addr, conf.rpc_zmq_port)

        if method.__name__ == "_cast":
            eventlet.spawn_n(method, _addr, context, _topic, msg, timeout, envelope, _msg_id)
            return
        return method(_addr, context, _topic, msg, timeout, envelope)

        def inner(*args, **kwargs):
            with lock(name, lock_file_prefix, external, lock_path):
                LOG.debug(_('Got semaphore / lock "%(function)s"'),
                          {'function': f.__name__})
                return f(*args, **kwargs)

            LOG.debug(_('Semaphore / lock released "%(function)s"'),
                      {'function': f.__name__})

 def _error_callback(exc):
     if isinstance(exc, qpid_exceptions.Empty):
         LOG.debug(_('Timed out waiting for RPC response: %s') %
                   str(exc))
         raise rpc_common.Timeout()
     else:
         LOG.exception(_('Failed to consume message from queue: %s') %
                       str(exc))

 def _error_callback(exc):
     if isinstance(exc, socket.timeout):
         LOG.debug(_('Timed out waiting for RPC response: %s') %
                   str(exc))
         raise rpc_common.Timeout()
     else:
         LOG.exception(_('Failed to consume message from queue: %s') %
                       str(exc))
         info['do_consume'] = True

def notify(context, publisher_id, event_type, priority, payload):
    """Sends a notification using the specified driver

    :param publisher_id: the source worker_type.host of the message
    :param event_type:   the literal type of event (ex. Instance Creation)
    :param priority:     patterned after the enumeration of Python logging
                         levels in the set (DEBUG, WARN, INFO, ERROR, CRITICAL)
    :param payload:       A python dictionary of attributes

    Outgoing message format includes the above parameters, and appends the
    following:

    message_id
      a UUID representing the id for this notification

    timestamp
      the GMT timestamp the notification was sent at

    The composite message will be constructed as a dictionary of the above
    attributes, which will then be sent via the transport mechanism defined
    by the driver.

    Message example::

        {'message_id': str(uuid.uuid4()),
         'publisher_id': 'compute.host1',
         'timestamp': timeutils.utcnow(),
         'priority': 'WARN',
         'event_type': 'compute.create_instance',
         'payload': {'instance_id': 12, ... }}

    """
    if priority not in log_levels:
        raise BadPriorityException(
            _('%s not in valid priorities') % priority)

    # Ensure everything is JSON serializable.
    payload = jsonutils.to_primitive(payload, convert_instances=True)

    msg = dict(message_id=str(uuid.uuid4()),
               publisher_id=publisher_id,
               event_type=event_type,
               priority=priority,
               payload=payload,
               timestamp=str(timeutils.utcnow()))

    for driver in _get_drivers():
        try:
            driver.notify(context, msg)
        except Exception as e:
            LOG.exception(_("Problem '%(e)s' attempting to "
                            "send to notification system. "
                            "Payload=%(payload)s")
                          % dict(e=e, payload=payload))

    def reconnect(self):
        """Handles reconnecting and re-establishing queues.
        Will retry up to self.max_retries number of times.
        self.max_retries = 0 means to retry forever.
        Sleep between tries, starting at self.interval_start
        seconds, backing off self.interval_stepping number of seconds
        each attempt.
        """

        attempt = 0
        while True:
            params = self.params_list[attempt % len(self.params_list)]
            attempt += 1
            try:
                self._connect(params)
                return
            except (IOError, self.connection_errors) as e:
                pass
            except Exception as e:
                # NOTE(comstud): Unfortunately it's possible for amqplib
                # to return an error not covered by its transport
                # connection_errors in the case of a timeout waiting for
                # a protocol response.  (See paste link in LP888621)
                # So, we check all exceptions for 'timeout' in them
                # and try to reconnect in this case.
                if 'timeout' not in str(e):
                    raise

            log_info = {}
            log_info['err_str'] = str(e)
            log_info['max_retries'] = self.max_retries
            log_info.update(params)

            if self.max_retries and attempt == self.max_retries:
                msg = _('Unable to connect to AMQP server on '
                        '%(hostname)s:%(port)d after %(max_retries)d '
                        'tries: %(err_str)s') % log_info
                LOG.error(msg)
                raise rpc_common.RPCException(msg)

            if attempt == 1:
                sleep_time = self.interval_start or 1
            elif attempt > 1:
                sleep_time += self.interval_stepping
            if self.interval_max:
                sleep_time = min(sleep_time, self.interval_max)

            log_info['sleep_time'] = sleep_time
            LOG.error(_('AMQP server on %(hostname)s:%(port)d is '
                        'unreachable: %(err_str)s. Trying again in '
                        '%(sleep_time)d seconds.') % log_info)
            time.sleep(sleep_time)

    def register(self, proxy, in_addr, zmq_type_in, in_bind=True, subscribe=None):

        LOG.info(_("Registering reactor"))

        if zmq_type_in not in (zmq.PULL, zmq.SUB):
            raise RPCException("Bad input socktype")

        # Items push in.
        inq = ZmqSocket(in_addr, zmq_type_in, bind=in_bind, subscribe=subscribe)

        self.proxies[inq] = proxy
        self.sockets.append(inq)

        LOG.info(_("In reactor registered"))