ndimiduk commented on a change in pull request #2454: URL: https://github.com/apache/hbase/pull/2454#discussion_r499865060
########## File path: hbase-server/src/main/java/org/apache/hadoop/hbase/master/normalizer/RegionNormalizerWorkQueue.java ########## @@ -0,0 +1,244 @@ +/* + * 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.hadoop.hbase.master.normalizer; + +import java.util.Collection; +import java.util.Collections; +import java.util.Iterator; +import java.util.LinkedHashSet; +import java.util.Queue; +import java.util.Set; +import java.util.concurrent.BlockingQueue; +import java.util.concurrent.locks.Condition; +import java.util.concurrent.locks.ReentrantLock; +import org.apache.yetus.audience.InterfaceAudience; + +/** + * A specialized collection that holds pending work for the {@link RegionNormalizerWorker}. It is + * an ordered collection class that has the following properties: + * <ul> + * <li>Guarantees uniqueness of elements, as a {@link Set}.</li> + * <li>Consumers retrieve objects from the head, as a {@link Queue}, via {@link #take()}.</li> + * <li>Work is retrieved on a FIFO policy.</li> + * <li>Work retrieval blocks the calling thread until new work is available, as a + * {@link BlockingQueue}.</li> + * <li>Allows a producer to insert an item at the head of the queue, if desired.</li> + * </ul> + * Assumes low-frequency and low-parallelism concurrent access, so protects state using a + * simplistic synchronization strategy. + */ [email protected] +class RegionNormalizerWorkQueue<E> { + + /** Underlying storage structure that gives us the Set behavior and FIFO retrieval policy. */ + private LinkedHashSet<E> delegate; + + // the locking structure used here follows the example found in LinkedBlockingQueue. The + // difference is that our locks guard access to `delegate` rather than the head node. + + /** Lock held by take, poll, etc */ + private final ReentrantLock takeLock; + + /** Wait queue for waiting takes */ + private final Condition notEmpty; + + /** Lock held by put, offer, etc */ + private final ReentrantLock putLock; + + public RegionNormalizerWorkQueue() { + delegate = new LinkedHashSet<>(); + takeLock = new ReentrantLock(); + notEmpty = takeLock.newCondition(); + putLock = new ReentrantLock(); + } + + /** + * Signals a waiting take. Called only from put/offer (which do not + * otherwise ordinarily lock takeLock.) + */ + private void signalNotEmpty() { + final ReentrantLock takeLock = this.takeLock; + takeLock.lock(); + try { + notEmpty.signal(); + } finally { + takeLock.unlock(); + } + } + + /** + * Locks to prevent both puts and takes. + */ + private void fullyLock() { + putLock.lock(); + takeLock.lock(); + } + + /** + * Unlocks to allow both puts and takes. + */ + private void fullyUnlock() { Review comment: I looked but did not find one. I'd be happy to replace this class with something off-the-shelf. ---------------------------------------------------------------- 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: [email protected]
