content: /*
   * The Alluxio Open Foundation licenses this work under the Apache License, version 2.0
   * (the "License"). You may not use this work except in compliance with the License, which is
   * available at www.apache.org/licenses/LICENSE-2.0
   *
   * This software is distributed on an "AS IS" basis, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
   * either express or implied, as more fully set forth in the License.
   *
   * See the NOTICE file distributed with this work for information regarding copyright ownership.
   */
  
  package alluxio.master.journal;
  
  import alluxio.collections.ConcurrentHashSet;
  import alluxio.master.Master;
  import alluxio.master.journal.sink.JournalSink;
  import alluxio.metrics.MetricKey;
  import alluxio.metrics.MetricsSystem;
  import alluxio.resource.LockResource;
  
  import com.google.common.base.Preconditions;
  
  import java.util.Collections;
  import java.util.HashSet;
  import java.util.Map;
  import java.util.Set;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.locks.ReentrantReadWriteLock;
  import javax.annotation.Nullable;
  import javax.annotation.concurrent.ThreadSafe;
  
  /**
   * Base implementation for journal systems.
   */
  @ThreadSafe
  public abstract class AbstractJournalSystem implements JournalSystem {
    private boolean mRunning = false;
  
    private final ReentrantReadWriteLock mSinkLock = new ReentrantReadWriteLock();
    private final Map<String, Set<JournalSink>> mJournalSinks = new ConcurrentHashMap<>();
    private final Set<JournalSink> mAllJournalSinks = new ConcurrentHashSet<>();
  
    @Override
    public synchronized void start() {
      Preconditions.checkState(!mRunning, "Journal is already running");
      startInternal();
      mRunning = true;
    }
  
    @Override
    public synchronized void stop() {
      Preconditions.checkState(mRunning, "Journal is not running : " + this);
      mAllJournalSinks.forEach(JournalSink::beforeShutdown);
      mRunning = false;
      stopInternal();
    }
  
    @Override
    public void addJournalSink(Master master, JournalSink journalSink) {
      try (LockResource r = new LockResource(mSinkLock.writeLock())) {
        mJournalSinks.computeIfAbsent(master.getName(), (key) -> new HashSet<>()).add(journalSink);
        mAllJournalSinks.add(journalSink);
      }
    }
  
    @Override
    public void removeJournalSink(Master master, JournalSink journalSink) {
      try (LockResource r = new LockResource(mSinkLock.writeLock())) {
        Set<JournalSink> sinks = mJournalSinks.get(master.getName());
        if (sinks != null) {
          sinks.remove(journalSink);
          if (sinks.isEmpty()) {
            mJournalSinks.remove(master.getName());
          }
        }
        // Compute the full set of sinks on removal. Simply removing it may be incorrect, if the same
        // sink is associated with other masters.
        mAllJournalSinks.clear();
        for (Set<JournalSink> s : mJournalSinks.values()) {
          mAllJournalSinks.addAll(s);
        }
      }
    }
  
    @Override
    public Set<JournalSink> getJournalSinks(@Nullable Master master) {
      try (LockResource r = new LockResource(mSinkLock.readLock())) {
        if (master == null) {
          return mAllJournalSinks;
        }
        return mJournalSinks.getOrDefault(master.getName(), Collections.emptySet());
      }
    }
  
    /**
     * Starts the journal system.
     */
    protected abstract void startInternal();
  
    /**
     * Stops the journal system.
     */
    protected abstract void stopInternal();
  
    protected void registerMetrics() {
      Map<String, Long> sequenceNumber = getCurrentSequenceNumbers();
      for (String masterName : sequenceNumber.keySet()) {
        MetricsSystem.registerGaugeIfAbsent(
            MetricKey.MASTER_JOURNAL_SEQUENCE_NUMBER.getName() + "." + masterName,
            () -> getCurrentSequenceNumbers().get(masterName));
      }
    }
  }
  