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dispatcher.py
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dispatcher.py
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# Copyright 2017, Google LLC
#
# 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
#
# https://www.apache.org/licenses/LICENSE-2.0
#
# 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.
from __future__ import absolute_import
from __future__ import division
import collections
import itertools
import logging
import math
import threading
from google.cloud.pubsub_v1 import types
from google.cloud.pubsub_v1.subscriber._protocol import helper_threads
from google.cloud.pubsub_v1.subscriber._protocol import requests
_LOGGER = logging.getLogger(__name__)
_CALLBACK_WORKER_NAME = "Thread-CallbackRequestDispatcher"
_MAX_BATCH_SIZE = 100
"""The maximum number of requests to process and dispatch at a time."""
_MAX_BATCH_LATENCY = 0.01
"""The maximum amount of time in seconds to wait for additional request items
before processing the next batch of requests."""
_ACK_IDS_BATCH_SIZE = 2500
"""The maximum number of ACK IDs to send in a single StreamingPullRequest.
The backend imposes a maximum request size limit of 524288 bytes (512 KiB) per
acknowledge / modifyAckDeadline request. ACK IDs have a maximum size of 164
bytes, thus we cannot send more than o 524288/176 ~= 2979 ACK IDs in a single
StreamingPullRequest message.
Accounting for some overhead, we should thus only send a maximum of 2500 ACK
IDs at a time.
"""
class Dispatcher(object):
def __init__(self, manager, queue):
self._manager = manager
self._queue = queue
self._thread = None
self._operational_lock = threading.Lock()
def start(self):
"""Start a thread to dispatch requests queued up by callbacks.
Spawns a thread to run :meth:`dispatch_callback`.
"""
with self._operational_lock:
if self._thread is not None:
raise ValueError("Dispatcher is already running.")
worker = helper_threads.QueueCallbackWorker(
self._queue,
self.dispatch_callback,
max_items=_MAX_BATCH_SIZE,
max_latency=_MAX_BATCH_LATENCY,
)
# Create and start the helper thread.
thread = threading.Thread(name=_CALLBACK_WORKER_NAME, target=worker)
thread.daemon = True
thread.start()
_LOGGER.debug("Started helper thread %s", thread.name)
self._thread = thread
def stop(self):
with self._operational_lock:
if self._thread is not None:
# Signal the worker to stop by queueing a "poison pill"
self._queue.put(helper_threads.STOP)
self._thread.join()
self._thread = None
def dispatch_callback(self, items):
"""Map the callback request to the appropriate gRPC request.
Args:
action (str): The method to be invoked.
kwargs (Dict[str, Any]): The keyword arguments for the method
specified by ``action``.
Raises:
ValueError: If ``action`` isn't one of the expected actions
"ack", "drop", "lease", "modify_ack_deadline" or "nack".
"""
if not self._manager.is_active:
return
batched_commands = collections.defaultdict(list)
for item in items:
batched_commands[item.__class__].append(item)
_LOGGER.debug("Handling %d batched requests", len(items))
if batched_commands[requests.LeaseRequest]:
self.lease(batched_commands.pop(requests.LeaseRequest))
if batched_commands[requests.ModAckRequest]:
self.modify_ack_deadline(batched_commands.pop(requests.ModAckRequest))
# Note: Drop and ack *must* be after lease. It's possible to get both
# the lease and the ack/drop request in the same batch.
if batched_commands[requests.AckRequest]:
self.ack(batched_commands.pop(requests.AckRequest))
if batched_commands[requests.NackRequest]:
self.nack(batched_commands.pop(requests.NackRequest))
if batched_commands[requests.DropRequest]:
self.drop(batched_commands.pop(requests.DropRequest))
def ack(self, items):
"""Acknowledge the given messages.
Args:
items(Sequence[AckRequest]): The items to acknowledge.
"""
# If we got timing information, add it to the histogram.
for item in items:
time_to_ack = item.time_to_ack
if time_to_ack is not None:
self._manager.ack_histogram.add(time_to_ack)
# We must potentially split the request into multiple smaller requests
# to avoid the server-side max request size limit.
ack_ids = (item.ack_id for item in items)
total_chunks = int(math.ceil(len(items) / _ACK_IDS_BATCH_SIZE))
for _ in range(total_chunks):
request = types.StreamingPullRequest(
ack_ids=itertools.islice(ack_ids, _ACK_IDS_BATCH_SIZE)
)
self._manager.send(request)
# Remove the message from lease management.
self.drop(items)
def drop(self, items):
"""Remove the given messages from lease management.
Args:
items(Sequence[DropRequest]): The items to drop.
"""
self._manager.leaser.remove(items)
ordering_keys = (k.ordering_key for k in items if k.ordering_key)
self._manager.activate_ordering_keys(ordering_keys)
self._manager.maybe_resume_consumer()
def lease(self, items):
"""Add the given messages to lease management.
Args:
items(Sequence[LeaseRequest]): The items to lease.
"""
self._manager.leaser.add(items)
self._manager.maybe_pause_consumer()
def modify_ack_deadline(self, items):
"""Modify the ack deadline for the given messages.
Args:
items(Sequence[ModAckRequest]): The items to modify.
"""
# We must potentially split the request into multiple smaller requests
# to avoid the server-side max request size limit.
ack_ids = (item.ack_id for item in items)
seconds = (item.seconds for item in items)
total_chunks = int(math.ceil(len(items) / _ACK_IDS_BATCH_SIZE))
for _ in range(total_chunks):
request = types.StreamingPullRequest(
modify_deadline_ack_ids=itertools.islice(ack_ids, _ACK_IDS_BATCH_SIZE),
modify_deadline_seconds=itertools.islice(seconds, _ACK_IDS_BATCH_SIZE),
)
self._manager.send(request)
def nack(self, items):
"""Explicitly deny receipt of messages.
Args:
items(Sequence[NackRequest]): The items to deny.
"""
self.modify_ack_deadline(
[requests.ModAckRequest(ack_id=item.ack_id, seconds=0) for item in items]
)
self.drop([requests.DropRequest(*item) for item in items])