vvcephei commented on a change in pull request #8497: URL: https://github.com/apache/kafka/pull/8497#discussion_r411672041
########## File path: streams/src/main/java/org/apache/kafka/streams/processor/internals/assignment/ValidClientsByTaskLoadQueue.java ########## @@ -0,0 +1,108 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one or more + * contributor license agreements. See the NOTICE file distributed with + * this work for additional information regarding copyright ownership. + * The ASF licenses this file to You 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. + */ +package org.apache.kafka.streams.processor.internals.assignment; + +import java.util.Collection; +import java.util.HashSet; +import java.util.LinkedList; +import java.util.List; +import java.util.Map; +import java.util.PriorityQueue; +import java.util.Set; +import java.util.UUID; +import java.util.function.BiFunction; +import org.apache.kafka.streams.processor.TaskId; + +/** + * Wraps a priority queue of clients and returns the next valid candidate(s) based on the current task assignment + */ +class ValidClientsByTaskLoadQueue { + private final PriorityQueue<UUID> clientsByTaskLoad; + private final BiFunction<UUID, TaskId, Boolean> validClientCriteria; + private final Set<UUID> uniqueClients = new HashSet<>(); + + ValidClientsByTaskLoadQueue(final Map<UUID, ClientState> clientStates, + final BiFunction<UUID, TaskId, Boolean> validClientCriteria) { + clientsByTaskLoad = getClientPriorityQueueByTaskLoad(clientStates); + this.validClientCriteria = validClientCriteria; + } + + /** += * @return the next least loaded client that satisfies the given criteria, or null if none do + */ + UUID poll(final TaskId task) { + final List<UUID> validClient = poll(task, 1); + return validClient.isEmpty() ? null : validClient.get(0); + } + + /** + * @return the next N <= {@code numClientsPerTask} clients in the underlying priority queue that are valid + * candidates for the given task + */ + List<UUID> poll(final TaskId task, final int numClients) { + final List<UUID> nextLeastLoadedValidClients = new LinkedList<>(); + final Set<UUID> invalidPolledClients = new HashSet<>(); + while (nextLeastLoadedValidClients.size() < numClients) { + UUID candidateClient; + while (true) { + candidateClient = clientsByTaskLoad.poll(); + if (candidateClient == null) { + offerAll(invalidPolledClients); + return nextLeastLoadedValidClients; + } + + if (validClientCriteria.apply(candidateClient, task)) { + nextLeastLoadedValidClients.add(candidateClient); + break; + } else { + invalidPolledClients.add(candidateClient); + } + } + } + offerAll(invalidPolledClients); + return nextLeastLoadedValidClients; + } + + void offerAll(final Collection<UUID> clients) { + for (final UUID client : clients) { + offer(client); + } + } + + void offer(final UUID client) { + if (uniqueClients.contains(client)) { Review comment: I think it's just a computer-sciencey matter of principle. `clientsByTaskLoad` is a linear collection, so every `offer` would become `O(n)` if we did a `contains` call on it every time. Right now, it's only `O(n)` when we need to remove the prior record for the same client, and `O(log(n))` otherwise. Does it really matter? I'm not sure. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org
