ZoieIndexDeletionPolicy.java

package proj.zoie.impl.indexing.internal;

/**
 * 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.
 */
import java.io.IOException;
import java.util.Collection;
import java.util.HashMap;
import java.util.List;

import org.apache.lucene.index.IndexCommit;
import org.apache.lucene.index.IndexDeletionPolicy;

/**
 * @author ymatsuda
 *
 */
public class ZoieIndexDeletionPolicy extends IndexDeletionPolicy {
  private IndexCommit _lastCommit;
  private final HashMap<String, Snapshot> _currentSnapshots = new HashMap<String, Snapshot>();

  public ZoieIndexDeletionPolicy() {
    _lastCommit = null;
  }

  @Override
  public void onInit(List<? extends IndexCommit> commits) throws IOException {
    processCommits(commits);
  }

  @Override
  public void onCommit(List<? extends IndexCommit> commits) throws IOException {
    processCommits(commits);
  }

  private synchronized void processCommits(List<? extends IndexCommit> commits) {
    int size = commits.size();
    if (size == 0) return;

    IndexCommit indexCommit = null;
    for (Object commit : commits) {
      indexCommit = (IndexCommit) commit;
      if (--size > 0 && !_currentSnapshots.containsKey(indexCommit.getSegmentsFileName())) {
        indexCommit.delete();
      }
    }
    _lastCommit = indexCommit;
  }

  public synchronized Snapshot getSnapshot() {
    if (_lastCommit == null) return null; // no commit yet

    Snapshot snapshot;
    synchronized (_currentSnapshots) {
      String name = _lastCommit.getSegmentsFileName();
      snapshot = _currentSnapshots.get(name);
      if (snapshot == null) {
        snapshot = new Snapshot(_lastCommit);
        _currentSnapshots.put(name, snapshot);
      } else {
        snapshot.incRef();
      }
    }
    return snapshot;
  }

  public class Snapshot {
    private final IndexCommit _commit;
    private int _refcount;

    public Snapshot(IndexCommit commit) {
      _commit = commit;
      _refcount = 1;
    }

    public Collection<String> getFileNames() throws IOException {
      return _commit.getFileNames();
    }

    public void close() {
      decRef();
    }

    private synchronized void incRef() {
      _refcount++;
    }

    private synchronized void decRef() {
      if (--_refcount <= 0) {
        synchronized (_currentSnapshots) {
          _currentSnapshots.remove(_commit.getSegmentsFileName());
        }
      }
    }

    @Override
    public void finalize() {
      _refcount = 0;
      close();
    }
  }
}