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# Copyright 2010 United States Government as represented by the
# Administrator of the National Aeronautics and Space Administration.
# All Rights Reserved.
# Copyright 2013 Red Hat, Inc.
# Copyright 2013 New Dream Network, LLC (DreamHost)
# Licensed under the Apache License, Version 2.0 (the "License"); you may
# not use this file except in compliance with the License. You may obtain
# a copy of the License at
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations
# under the License.
__all__ = [
import abc
import functools
import inspect
import logging
import threading
import traceback
from oslo_config import cfg
from oslo_service import service
from oslo_utils import eventletutils
from oslo_utils import timeutils
import six
from stevedore import driver
from oslo_messaging._drivers import base as driver_base
from oslo_messaging._i18n import _LW, _LI
from oslo_messaging import exceptions
LOG = logging.getLogger(__name__)
# The default number of seconds of waiting after which we will emit a log
# message
_pool_opts = [
help='Size of executor thread pool.'),
class MessagingServerError(exceptions.MessagingException):
"""Base class for all MessageHandlingServer exceptions."""
class ExecutorLoadFailure(MessagingServerError):
"""Raised if an executor can't be loaded."""
def __init__(self, executor, ex):
msg = 'Failed to load executor "%s": %s' % (executor, ex)
super(ExecutorLoadFailure, self).__init__(msg)
self.executor = executor
self.ex = ex
class ServerListenError(MessagingServerError):
"""Raised if we failed to listen on a target."""
def __init__(self, target, ex):
msg = 'Failed to listen on target "%s": %s' % (target, ex)
super(ServerListenError, self).__init__(msg) = target
self.ex = ex
class TaskTimeout(MessagingServerError):
"""Raised if we timed out waiting for a task to complete."""
class _OrderedTask(object):
"""A task which must be executed in a particular order.
A caller may wait for this task to complete by calling
A caller may run this task with `run_once`, which will ensure that however
many times the task is called it only runs once. Simultaneous callers will
block until the running task completes, which means that any caller can be
sure that the task has completed after run_once returns.
INIT = 0 # The task has not yet started
RUNNING = 1 # The task is running somewhere
COMPLETE = 2 # The task has run somewhere
def __init__(self, name):
"""Create a new _OrderedTask.
:param name: The name of this task. Used in log messages.
super(_OrderedTask, self).__init__()
self._name = name
self._cond = threading.Condition()
self._state = self.INIT
def _wait(self, condition, msg, log_after, timeout_timer):
"""Wait while condition() is true. Write a log message if condition()
has not become false within `log_after` seconds. Raise TaskTimeout if
timeout_timer expires while waiting.
log_timer = None
if log_after != 0:
log_timer = timeutils.StopWatch(duration=log_after)
while condition():
if log_timer is not None and log_timer.expired():
LOG.warning(_LW('Possible hang: %s'), msg)
# Only log once. After than we wait indefinitely without
# logging.
log_timer = None
if timeout_timer is not None and timeout_timer.expired():
raise TaskTimeout(msg)
timeouts = []
if log_timer is not None:
if timeout_timer is not None:
wait = None
if timeouts:
wait = min(timeouts)
def complete(self):
return self._state == self.COMPLETE
def wait_for_completion(self, caller, log_after, timeout_timer):
"""Wait until this task has completed.
:param caller: The name of the task which is waiting.
:param log_after: Emit a log message if waiting longer than `log_after`
:param timeout_timer: Raise TaskTimeout if StopWatch object
`timeout_timer` expires while waiting.
with self._cond:
msg = '%s is waiting for %s to complete' % (caller, self._name)
self._wait(lambda: not self.complete,
msg, log_after, timeout_timer)
def run_once(self, fn, log_after, timeout_timer):
"""Run a task exactly once. If it is currently running in another
thread, wait for it to complete. If it has already run, return
immediately without running it again.
:param fn: The task to run. It must be a callable taking no arguments.
It may optionally return another callable, which also takes
no arguments, which will be executed after completion has
been signaled to other threads.
:param log_after: Emit a log message if waiting longer than `log_after`
:param timeout_timer: Raise TaskTimeout if StopWatch object
`timeout_timer` expires while waiting.
with self._cond:
if self._state == self.INIT:
self._state = self.RUNNING
# Note that nothing waits on RUNNING, so no need to notify
# We need to release the condition lock before calling out to
# prevent deadlocks. Reacquire it immediately afterwards.
post_fn = fn()
self._state = self.COMPLETE
if post_fn is not None:
# Release the condition lock before calling out to prevent
# deadlocks. Reacquire it immediately afterwards.
elif self._state == self.RUNNING:
msg = ('%s is waiting for another thread to complete'
% self._name)
self._wait(lambda: self._state == self.RUNNING,
msg, log_after, timeout_timer)
class _OrderedTaskRunner(object):
"""Mixin for a class which executes ordered tasks."""
def __init__(self, *args, **kwargs):
super(_OrderedTaskRunner, self).__init__(*args, **kwargs)
# Get a list of methods on this object which have the _ordered
# attribute
self._tasks = [name
for (name, member) in inspect.getmembers(self)
if inspect.ismethod(member) and
getattr(member, '_ordered', False)]
self._reset_lock = threading.Lock()
def reset_states(self):
# Create new task states for tasks in reset
self._states = {task: _OrderedTask(task) for task in self._tasks}
def decorate_ordered(fn, state, after, reset_after):
def wrapper(self, *args, **kwargs):
# If the reset_after state has already completed, reset state so
# we can run again.
# NOTE(mdbooth): This is ugly and requires external locking to be
# deterministic when using multiple threads. Consider a thread that
# does: server.stop(), server.wait(). If another thread causes a
# reset between stop() and wait(), this will not have the intended
# behaviour. It is safe without external locking, if the caller
# instantiates a new object.
with self._reset_lock:
if (reset_after is not None and
# Store the states we started with in case the state wraps on us
# while we're sleeping. We must wait and run_once in the same
# epoch. If the epoch ended while we were sleeping, run_once will
# safely do nothing.
states = self._states
log_after = kwargs.pop('log_after', DEFAULT_LOG_AFTER)
timeout = kwargs.pop('timeout', None)
timeout_timer = None
if timeout is not None:
timeout_timer = timeutils.StopWatch(duration=timeout)
# Wait for the given preceding state to complete
if after is not None:
log_after, timeout_timer)
# Run this state
states[state].run_once(lambda: fn(self, *args, **kwargs),
log_after, timeout_timer)
return wrapper
def ordered(after=None, reset_after=None):
"""A method which will be executed as an ordered task. The method will be
called exactly once, however many times it is called. If it is called
multiple times simultaneously it will only be called once, but all callers
will wait until execution is complete.
If `after` is given, this method will not run until `after` has completed.
If `reset_after` is given and the target method has completed, allow this
task to run again by resetting all task states.
:param after: Optionally, the name of another `ordered` method. Wait for
the completion of `after` before executing this method.
:param reset_after: Optionally, the name of another `ordered` method. Reset
all states when calling this method if `reset_after`
has completed.
def _ordered(fn):
# Set an attribute on the method so we can find it later
setattr(fn, '_ordered', True)
state = fn.__name__
return _OrderedTaskRunner.decorate_ordered(fn, state, after,
return _ordered
class MessageHandlingServer(service.ServiceBase, _OrderedTaskRunner):
"""Server for handling messages.
Connect a transport to a dispatcher that knows how to process the
message using an executor that knows how the app wants to create
new tasks.
def __init__(self, transport, dispatcher, executor='blocking'):
"""Construct a message handling server.
The dispatcher parameter is a DispatcherBase instance which is used
for routing request to endpoint for processing.
The executor parameter controls how incoming messages will be received
and dispatched. By default, the most simple executor is used - the
blocking executor. It handles only one message at once. It's
recommended to use threading or eventlet.
:param transport: the messaging transport
:type transport: Transport
:param dispatcher: has a dispatch() method which is invoked for each
incoming request
:type dispatcher: DispatcherBase
:param executor: name of message executor - for example
'eventlet', 'blocking'
:type executor: str
self.conf = transport.conf
self.transport = transport
self.dispatcher = dispatcher
self.executor_type = executor
if self.executor_type == 'blocking':
# NOTE(sileht): We keep blocking as default to not enforce the
# application to use threading or eventlet. Because application
# have to be preprepared accordingly for each one (monkeypatching,
# threadsafe, ...)"blocking executor handles only one message at "
"once. threading or eventlet executor is "
self.listener = None
mgr = driver.DriverManager('oslo.messaging.executors',
except RuntimeError as ex:
raise ExecutorLoadFailure(self.executor_type, ex)
self._executor_cls = mgr.driver
self._work_executor = None
self._started = False
super(MessageHandlingServer, self).__init__()
def _on_incoming(self, incoming):
"""Handles on_incoming event
:param incoming: incoming request.
self._work_executor.submit(self._process_incoming, incoming)
def _process_incoming(self, incoming):
"""Perform processing incoming request
:param incoming: incoming request.
def _create_listener(self):
"""Creates listener object for polling requests
:return: MessageListenerAdapter
def start(self, override_pool_size=None):
"""Start handling incoming messages.
This method causes the server to begin polling the transport for
incoming messages and passing them to the dispatcher. Message
processing will continue until the stop() method is called.
The executor controls how the server integrates with the applications
I/O handling strategy - it may choose to poll for messages in a new
process, thread or co-operatively scheduled coroutine or simply by
registering a callback with an event loop. Similarly, the executor may
choose to dispatch messages in a new thread, coroutine or simply the
current thread.
# Warn that restarting will be deprecated
if self._started:
LOG.warning(_LW('Restarting a MessageHandlingServer is inherently '
'racy. It is deprecated, and will become a noop '
'in a future release of oslo.messaging. If you '
'need to restart MessageHandlingServer you should '
'instantiate a new object.'))
self._started = True
executor_opts = {}
if self.executor_type == "threading":
executor_opts["max_workers"] = (
override_pool_size or self.conf.executor_thread_pool_size
elif self.executor_type == "eventlet":
what="the 'oslo.messaging eventlet executor'")
executor_opts["max_workers"] = (
override_pool_size or self.conf.executor_thread_pool_size
self._work_executor = self._executor_cls(**executor_opts)
self.listener = self._create_listener()
except driver_base.TransportDriverError as ex:
raise ServerListenError(, ex)
def stop(self):
"""Stop handling incoming messages.
Once this method returns, no new incoming messages will be handled by
the server. However, the server may still be in the process of handling
some messages, and underlying driver resources associated to this
server are still in use. See 'wait' for more details.
self._started = False
def wait(self):
"""Wait for message processing to complete.
After calling stop(), there may still be some existing messages
which have not been completely processed. The wait() method blocks
until all message processing has completed.
Once it's finished, the underlying driver resources associated to this
server are released (like closing useless network connections).
# Close listener connection after processing all messages
def reset(self):
"""Reset service.
Called in case service running in daemon mode receives SIGHUP.
# TODO(sergey.vilgelm): implement this method