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Add flow control logic to publisher client
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| # Copyright 2020, Google LLC All rights reserved. | ||
| # | ||
| # 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 | ||
| # | ||
| # http://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. | ||
|
|
||
| import logging | ||
| import threading | ||
| import warnings | ||
|
|
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| from google.cloud.pubsub_v1 import types | ||
| from google.cloud.pubsub_v1.publisher import exceptions | ||
|
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|
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| _LOGGER = logging.getLogger(__name__) | ||
|
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| class FlowController(object): | ||
| """A class used to control the flow of messages passing through it. | ||
| Args: | ||
| settings (~google.cloud.pubsub_v1.types.PublishFlowControl): | ||
| Desired flow control configuration. | ||
| """ | ||
|
|
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| def __init__(self, settings): | ||
| self._settings = settings | ||
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| self._message_count = 0 | ||
| self._total_bytes = 0 | ||
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| # The lock is used to protect the internal state (message and byte count). | ||
| self._operational_lock = threading.Lock() | ||
|
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| # The condition for blocking the flow if capacity is exceeded. | ||
| self._has_capacity = threading.Condition(lock=self._operational_lock) | ||
|
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| def add(self, message): | ||
| """Add a message to flow control. | ||
| Adding a message updates the internal load statistics, and an action is | ||
| taken if these limits are exceeded (depending on the flow control settings). | ||
| Args: | ||
| message (:class:`~google.cloud.pubsub_v1.types.PubsubMessage`): | ||
| The message entering the flow control. | ||
| Raises: | ||
| :exception:`~pubsub_v1.publisher.exceptions.FlowControlLimitError`: | ||
| If adding a message exceeds flow control limits and the desired | ||
| action is :attr:`~google.cloud.pubsub_v1.types.LimitExceededBehavior.ERROR`. | ||
| """ | ||
| if self._settings.limit_exceeded_behavior == types.LimitExceededBehavior.IGNORE: | ||
| return | ||
|
|
||
| with self._operational_lock: | ||
| self._message_count += 1 | ||
| self._total_bytes += message.ByteSize() | ||
|
|
||
| if not self._is_overflow(): | ||
| return | ||
|
|
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| # We have an overflow, react. | ||
| if ( | ||
| self._settings.limit_exceeded_behavior | ||
| == types.LimitExceededBehavior.ERROR | ||
| ): | ||
| msg = ( | ||
| "Flow control limits exceeded " | ||
| "(messages: {} / {}, bytes: {} / {})." | ||
| ).format( | ||
| self._message_count, | ||
| self._settings.message_limit, | ||
| self._total_bytes, | ||
| self._settings.byte_limit, | ||
| ) | ||
| error = exceptions.FlowControlLimitError(msg) | ||
|
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| # Raising an error means rejecting a message, thus we need to deduct | ||
| # the latter's contribution to the total load. | ||
| self._message_count -= 1 | ||
| self._total_bytes -= message.ByteSize() | ||
| raise error | ||
|
|
||
| assert ( | ||
| self._settings.limit_exceeded_behavior | ||
| == types.LimitExceededBehavior.BLOCK | ||
| ) | ||
|
|
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| while self._is_overflow(): | ||
| _LOGGER.debug( | ||
| "Blocking until there is enough free capacity in the flow." | ||
| ) | ||
| self._has_capacity.wait() | ||
| _LOGGER.debug("Woke up from waiting on free capacity in the flow.") | ||
|
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| def release(self, message): | ||
| """Release a mesage from flow control. | ||
| Args: | ||
| message (:class:`~google.cloud.pubsub_v1.types.PubsubMessage`): | ||
| The message entering the flow control. | ||
| """ | ||
| if self._settings.limit_exceeded_behavior == types.LimitExceededBehavior.IGNORE: | ||
| return | ||
|
|
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| with self._operational_lock: | ||
| was_overflow = self._is_overflow() | ||
|
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| self._message_count -= 1 | ||
| self._total_bytes -= message.ByteSize() | ||
|
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| if self._message_count < 0 or self._total_bytes < 0: | ||
| warnings.warn( | ||
| "Releasing a message that was never added or already released.", | ||
| category=RuntimeWarning, | ||
| stacklevel=2, | ||
| ) | ||
| self._message_count = max(0, self._message_count) | ||
| self._total_bytes = max(0, self._total_bytes) | ||
|
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| if was_overflow and not self._is_overflow(): | ||
| _LOGGER.debug("Notifying threads waiting to add messages to flow.") | ||
| self._has_capacity.notify_all() | ||
|
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| def _is_overflow(self): | ||
| """Determine if the current message load exceeds flow control limits. | ||
| The method assumes that the caller has obtained ``_operational_lock``. | ||
| Returns: | ||
| bool | ||
| """ | ||
| return ( | ||
| self._message_count > self._settings.message_limit | ||
| or self._total_bytes > self._settings.byte_limit | ||
| ) |
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