afedulov commented on code in PR #20757: URL: https://github.com/apache/flink/pull/20757#discussion_r974320992
########## flink-core/src/main/java/org/apache/flink/api/connector/source/lib/util/GatedRateLimiter.java: ########## @@ -0,0 +1,64 @@ +/* + * 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.flink.api.connector.source.lib.util; + +import java.util.concurrent.CompletableFuture; +import java.util.concurrent.CompletionStage; + +/** + * An implementation of {@link RateLimiter} that completes defined number of futures in-between the + * external notification events. The first cycle completes immediately, without waiting for the + * external notifications. + */ +public class GatedRateLimiter implements RateLimiter { + + private final int capacityPerCycle; + private int capacityLeft; + + /** + * Instantiates a new GatedRateLimiter. + * + * @param capacityPerCycle The number of completed futures per cycle. + */ + public GatedRateLimiter(int capacityPerCycle) { + this.capacityPerCycle = capacityPerCycle; + this.capacityLeft = capacityPerCycle + 1; + } + + CompletableFuture<Void> gatingFuture; + + @Override + public CompletionStage<Void> acquire() { + if (capacityLeft-- > 0) { + return CompletableFuture.completedFuture(null); + } else { + if (gatingFuture == null) { + gatingFuture = new CompletableFuture<>(); + } + return gatingFuture; + } + } + + @Override + public void notifyCheckpointComplete(long checkpointId) { + capacityLeft = capacityPerCycle - 1; Review Comment: Let me try to clarify what is going on: - The goal is to always emit "capacity" values per cycle. - The first cycle after the start emits the "capacity" number the elements immediately, without waiting for the checkpoint. This is why the constructor initially gives capacity one more element - the future that is normally completed in the notifyCheckpointComplete has to be completed immediately in the first run. - Subsequent cycles produce the same number of elements but all of them are only released when the gating future completes. In `notifyCheckpointComplete` the new cycle starts. The gating future completes, causing the release of the first element of the new cycle; since the first result has just been emitted by the gating future, the remaining capacity available to the acquire method needs to be reduced by one. The gating future basically always "belongs" to the new cycle, triggered by the checkpoint. It emits an element, hence -1. Since in the first cycle we do not have the gating future, we add +1 to "emulate" it. Hope it makes sense. You can check that it works correctly here: [DataGeneratorPerCheckpoint](https://github.com/apache/flink/blob/608a43d28e0f5c0fef097b6581d8bb43ce983605/flink-examples/flink-examples-streaming/src/main/java/org/apache/flink/streaming/examples/datagen/DataGeneratorPerCheckpoint.java#L36) -- 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. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
