This document is for Kombu's development version, which can be significantly different from previous releases. Get the stable docs here: 5.0.
Source code for kombu.common
"""Common Utilities."""
import os
import socket
import threading
from collections import deque
from contextlib import contextmanager
from functools import partial
from itertools import count
from uuid import NAMESPACE_OID, uuid3, uuid4, uuid5
from amqp import ChannelError, RecoverableConnectionError
from .entity import Exchange, Queue
from .log import get_logger
from .serialization import registry as serializers
from .utils.uuid import uuid
__all__ = ('Broadcast', 'maybe_declare', 'uuid',
'itermessages', 'send_reply',
'collect_replies', 'insured', 'drain_consumer',
'eventloop')
#: Prefetch count can't exceed short.
PREFETCH_COUNT_MAX = 0xFFFF
logger = get_logger(__name__)
_node_id = None
def get_node_id():
global _node_id
if _node_id is None:
_node_id = uuid4().int
return _node_id
def generate_oid(node_id, process_id, thread_id, instance):
ent = '{:x}-{:x}-{:x}-{:x}'.format(
node_id, process_id, thread_id, id(instance))
try:
ret = str(uuid3(NAMESPACE_OID, ent))
except ValueError:
ret = str(uuid5(NAMESPACE_OID, ent))
return ret
def oid_from(instance, threads=True):
return generate_oid(
get_node_id(),
os.getpid(),
threading.get_ident() if threads else 0,
instance,
)
[docs]class Broadcast(Queue):
"""Broadcast queue.
Convenience class used to define broadcast queues.
Every queue instance will have a unique name,
and both the queue and exchange is configured with auto deletion.
Arguments:
name (str): This is used as the name of the exchange.
queue (str): By default a unique id is used for the queue
name for every consumer. You can specify a custom
queue name here.
unique (bool): Always create a unique queue
even if a queue name is supplied.
**kwargs (Any): See :class:`~kombu.Queue` for a list
of additional keyword arguments supported.
"""
attrs = Queue.attrs + (('queue', None),)
def __init__(self,
name=None,
queue=None,
unique=False,
auto_delete=True,
exchange=None,
alias=None,
**kwargs):
if unique:
queue = '{}.{}'.format(queue or 'bcast', uuid())
else:
queue = queue or f'bcast.{uuid()}'
super().__init__(
alias=alias or name,
queue=queue,
name=queue,
auto_delete=auto_delete,
exchange=(exchange if exchange is not None
else Exchange(name, type='fanout')),
**kwargs
)
def declaration_cached(entity, channel):
return entity in channel.connection.client.declared_entities
[docs]def maybe_declare(entity, channel=None, retry=False, **retry_policy):
"""Declare entity (cached)."""
if retry:
return _imaybe_declare(entity, channel, **retry_policy)
return _maybe_declare(entity, channel)
def _ensure_channel_is_bound(entity, channel):
"""Make sure the channel is bound to the entity.
:param entity: generic kombu nomenclature, generally an exchange or queue
:param channel: channel to bind to the entity
:return: the updated entity
"""
is_bound = entity.is_bound
if not is_bound:
if not channel:
raise ChannelError(
f"Cannot bind channel {channel} to entity {entity}")
entity = entity.bind(channel)
return entity
def _maybe_declare(entity, channel):
# _maybe_declare sets name on original for autogen queues
orig = entity
_ensure_channel_is_bound(entity, channel)
if channel is None:
if not entity.is_bound:
raise ChannelError(
f"channel is None and entity {entity} not bound.")
channel = entity.channel
declared = ident = None
if channel.connection and entity.can_cache_declaration:
declared = channel.connection.client.declared_entities
ident = hash(entity)
if ident in declared:
return False
if not channel.connection:
raise RecoverableConnectionError('channel disconnected')
entity.declare(channel=channel)
if declared is not None and ident:
declared.add(ident)
if orig is not None:
orig.name = entity.name
return True
def _imaybe_declare(entity, channel, **retry_policy):
_ensure_channel_is_bound(entity, channel)
if not entity.channel.connection:
raise RecoverableConnectionError('channel disconnected')
return entity.channel.connection.client.ensure(
entity, _maybe_declare, **retry_policy)(entity, channel)
[docs]def drain_consumer(consumer, limit=1, timeout=None, callbacks=None):
"""Drain messages from consumer instance."""
acc = deque()
def on_message(body, message):
acc.append((body, message))
consumer.callbacks = [on_message] + (callbacks or [])
with consumer:
for _ in eventloop(consumer.channel.connection.client,
limit=limit, timeout=timeout, ignore_timeouts=True):
try:
yield acc.popleft()
except IndexError:
pass
[docs]def itermessages(conn, channel, queue, limit=1, timeout=None,
callbacks=None, **kwargs):
"""Iterator over messages."""
return drain_consumer(
conn.Consumer(queues=[queue], channel=channel, **kwargs),
limit=limit, timeout=timeout, callbacks=callbacks,
)
[docs]def eventloop(conn, limit=None, timeout=None, ignore_timeouts=False):
"""Best practice generator wrapper around ``Connection.drain_events``.
Able to drain events forever, with a limit, and optionally ignoring
timeout errors (a timeout of 1 is often used in environments where
the socket can get "stuck", and is a best practice for Kombu consumers).
``eventloop`` is a generator.
Examples:
>>> from kombu.common import eventloop
>>> def run(conn):
... it = eventloop(conn, timeout=1, ignore_timeouts=True)
... next(it) # one event consumed, or timed out.
...
... for _ in eventloop(conn, timeout=1, ignore_timeouts=True):
... pass # loop forever.
It also takes an optional limit parameter, and timeout errors
are propagated by default::
for _ in eventloop(connection, limit=1, timeout=1):
pass
See Also:
:func:`itermessages`, which is an event loop bound to one or more
consumers, that yields any messages received.
"""
for i in limit and range(limit) or count():
try:
yield conn.drain_events(timeout=timeout)
except socket.timeout:
if timeout and not ignore_timeouts: # pragma: no cover
raise
[docs]def send_reply(exchange, req, msg,
producer=None, retry=False, retry_policy=None, **props):
"""Send reply for request.
Arguments:
exchange (kombu.Exchange, str): Reply exchange
req (~kombu.Message): Original request, a message with
a ``reply_to`` property.
producer (kombu.Producer): Producer instance
retry (bool): If true must retry according to
the ``reply_policy`` argument.
retry_policy (Dict): Retry settings.
**props (Any): Extra properties.
"""
return producer.publish(
msg, exchange=exchange,
retry=retry, retry_policy=retry_policy,
**dict({'routing_key': req.properties['reply_to'],
'correlation_id': req.properties.get('correlation_id'),
'serializer': serializers.type_to_name[req.content_type],
'content_encoding': req.content_encoding}, **props)
)
[docs]def collect_replies(conn, channel, queue, *args, **kwargs):
"""Generator collecting replies from ``queue``."""
no_ack = kwargs.setdefault('no_ack', True)
received = False
try:
for body, message in itermessages(conn, channel, queue,
*args, **kwargs):
if not no_ack:
message.ack()
received = True
yield body
finally:
if received:
channel.after_reply_message_received(queue.name)
def _ensure_errback(exc, interval):
logger.error(
'Connection error: %r. Retry in %ss\n', exc, interval,
exc_info=True,
)
@contextmanager
def _ignore_errors(conn):
try:
yield
except conn.connection_errors + conn.channel_errors:
pass
def ignore_errors(conn, fun=None, *args, **kwargs):
"""Ignore connection and channel errors.
The first argument must be a connection object, or any other object
with ``connection_error`` and ``channel_error`` attributes.
Can be used as a function:
.. code-block:: python
def example(connection):
ignore_errors(connection, consumer.channel.close)
or as a context manager:
.. code-block:: python
def example(connection):
with ignore_errors(connection):
consumer.channel.close()
Note:
Connection and channel errors should be properly handled,
and not ignored. Using this function is only acceptable in a cleanup
phase, like when a connection is lost or at shutdown.
"""
if fun:
with _ignore_errors(conn):
return fun(*args, **kwargs)
return _ignore_errors(conn)
def revive_connection(connection, channel, on_revive=None):
if on_revive:
on_revive(channel)
[docs]def insured(pool, fun, args, kwargs, errback=None, on_revive=None, **opts):
"""Function wrapper to handle connection errors.
Ensures function performing broker commands completes
despite intermittent connection failures.
"""
errback = errback or _ensure_errback
with pool.acquire(block=True) as conn:
conn.ensure_connection(errback=errback)
# we cache the channel for subsequent calls, this has to be
# reset on revival.
channel = conn.default_channel
revive = partial(revive_connection, conn, on_revive=on_revive)
insured = conn.autoretry(fun, channel, errback=errback,
on_revive=revive, **opts)
retval, _ = insured(*args, **dict(kwargs, connection=conn))
return retval
class QoS:
"""Thread safe increment/decrement of a channels prefetch_count.
Arguments:
callback (Callable): Function used to set new prefetch count,
e.g. ``consumer.qos`` or ``channel.basic_qos``. Will be called
with a single ``prefetch_count`` keyword argument.
initial_value (int): Initial prefetch count value..
Example:
>>> from kombu import Consumer, Connection
>>> connection = Connection('amqp://')
>>> consumer = Consumer(connection)
>>> qos = QoS(consumer.qos, initial_prefetch_count=2)
>>> qos.update() # set initial
>>> qos.value
2
>>> def in_some_thread():
... qos.increment_eventually()
>>> def in_some_other_thread():
... qos.decrement_eventually()
>>> while 1:
... if qos.prev != qos.value:
... qos.update() # prefetch changed so update.
It can be used with any function supporting a ``prefetch_count`` keyword
argument::
>>> channel = connection.channel()
>>> QoS(channel.basic_qos, 10)
>>> def set_qos(prefetch_count):
... print('prefetch count now: %r' % (prefetch_count,))
>>> QoS(set_qos, 10)
"""
prev = None
def __init__(self, callback, initial_value):
self.callback = callback
self._mutex = threading.RLock()
self.value = initial_value or 0
def increment_eventually(self, n=1):
"""Increment the value, but do not update the channels QoS.
Note:
The MainThread will be responsible for calling :meth:`update`
when necessary.
"""
with self._mutex:
if self.value:
self.value = self.value + max(n, 0)
return self.value
def decrement_eventually(self, n=1):
"""Decrement the value, but do not update the channels QoS.
Note:
The MainThread will be responsible for calling :meth:`update`
when necessary.
"""
with self._mutex:
if self.value:
self.value -= n
if self.value < 1:
self.value = 1
return self.value
def set(self, pcount):
"""Set channel prefetch_count setting."""
if pcount != self.prev:
new_value = pcount
if pcount > PREFETCH_COUNT_MAX:
logger.warning('QoS: Disabled: prefetch_count exceeds %r',
PREFETCH_COUNT_MAX)
new_value = 0
logger.debug('basic.qos: prefetch_count->%s', new_value)
self.callback(prefetch_count=new_value)
self.prev = pcount
return pcount
def update(self):
"""Update prefetch count with current value."""
with self._mutex:
return self.set(self.value)
