001/*
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018package org.apache.hadoop.hbase.replication.master;
019
020import org.apache.yetus.audience.InterfaceAudience;
021
022/**
023 * A barrier to guard the execution of {@link ReplicationLogCleaner}.
024 * <p/>
025 * The reason why we introduce this class is because there could be race between
026 * {@link org.apache.hadoop.hbase.master.replication.AddPeerProcedure} and
027 * {@link ReplicationLogCleaner}. See HBASE-27214 for more details.
028 */
029@InterfaceAudience.Private
030public class ReplicationLogCleanerBarrier {
031
032  private enum State {
033    // the cleaner is not running
034    NOT_RUNNING,
035    // the cleaner is running
036    RUNNING,
037    // the cleaner is disabled
038    DISABLED
039  }
040
041  private State state = State.NOT_RUNNING;
042
043  // we could have multiple AddPeerProcedure running at the same time, so here we need to do
044  // reference counting.
045  private int numberDisabled = 0;
046
047  public synchronized boolean start() {
048    if (state == State.NOT_RUNNING) {
049      state = State.RUNNING;
050      return true;
051    }
052    if (state == State.DISABLED) {
053      return false;
054    }
055    throw new IllegalStateException("Unexpected state " + state);
056  }
057
058  public synchronized void stop() {
059    if (state != State.RUNNING) {
060      throw new IllegalStateException("Unexpected state " + state);
061    }
062    state = State.NOT_RUNNING;
063  }
064
065  public synchronized boolean disable() {
066    if (state == State.RUNNING) {
067      return false;
068    }
069    if (state == State.NOT_RUNNING) {
070      state = State.DISABLED;
071    }
072    numberDisabled++;
073    return true;
074  }
075
076  public synchronized void enable() {
077    if (state != State.DISABLED) {
078      throw new IllegalStateException("Unexpected state " + state);
079    }
080    numberDisabled--;
081    if (numberDisabled == 0) {
082      state = State.NOT_RUNNING;
083    }
084  }
085}