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feat: Add ReassignmentHandler which is notified on client reassignment #242
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70 changes: 70 additions & 0 deletions
70
google/cloud/pubsublite/cloudpubsub/reassignment_handler.py
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# Copyright 2020 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 | ||
# | ||
# 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. | ||
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from abc import ABC, abstractmethod | ||
from typing import Set, Optional, Awaitable | ||
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from google.cloud.pubsublite.types import Partition | ||
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class ReassignmentHandler(ABC): | ||
""" | ||
A ReassignmentHandler is called any time a new partition assignment is received from the server. | ||
It will be called with both the previous and new assignments as decided by the backend. | ||
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The client library will not acknowledge the assignment until handleReassignment returns. The | ||
assigning backend will not assign any of the partitions in `before` to another server unless the | ||
assignment is acknowledged, or a client takes too long to acknowledged (currently 30 seconds from | ||
the time the assignment is sent from server's point of view). | ||
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Because of the above, as long as reassignment handling is processed quickly, it can be used to | ||
abort outstanding operations on partitions which are being assigned away from this client, or to | ||
pre-warm state which will be used by the MessageCallback. | ||
""" | ||
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@abstractmethod | ||
def handle_reassignment( | ||
self, before: Set[Partition], after: Set[Partition] | ||
) -> Optional[Awaitable]: | ||
""" | ||
Called with the previous and new assignment delivered to this client on an assignment change. | ||
The assignment will not be acknowledged until this method returns, so it should complete | ||
quickly, or the backend will assume it is non-responsive and assign all partitions away without | ||
waiting for acknowledgement. | ||
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handle_reassignment will only be called after no new message deliveries will be started for the partition. | ||
There may still be messages in flight on executors or in async callbacks. | ||
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Acks or nacks on messages from partitions being assigned away will have no effect. | ||
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This method will be called on an event loop and should not block. | ||
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Args: | ||
before: The previous assignment. | ||
after: The new assignment. | ||
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Returns: | ||
Either None or an Awaitable to be waited on before acknowledging reassignment. | ||
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Raises: | ||
GoogleAPICallError: To fail the client if raised. | ||
""" | ||
pass | ||
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class DefaultReassignmentHandler(ReassignmentHandler): | ||
def handle_reassignment( | ||
self, before: Set[Partition], after: Set[Partition] | ||
) -> Optional[Awaitable]: | ||
return None |
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Ditto comments from the Java PR.
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Copied over the docstring changes- python unfortunately cannot implement the stronger semantics around message delivery, but I've documented this.