blur-store/src/main/java/org/apache/blur/store/blockcache_v2/cachevalue/DetachableCacheValue.java

/**
 * 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.blur.store.blockcache_v2.cachevalue;

import static org.apache.blur.metrics.MetricsConstants.CACHE;
import static org.apache.blur.metrics.MetricsConstants.DETACHES;
import static org.apache.blur.metrics.MetricsConstants.ORG_APACHE_BLUR;

import java.util.concurrent.TimeUnit;

import org.apache.blur.store.blockcache_v2.CacheValue;
import org.apache.blur.store.blockcache_v2.EvictionException;

import com.yammer.metrics.Metrics;
import com.yammer.metrics.core.Meter;
import com.yammer.metrics.core.MetricName;

public class DetachableCacheValue implements CacheValue {

  private static final Meter _detaches;

  static {
    _detaches = Metrics.newMeter(new MetricName(ORG_APACHE_BLUR, CACHE, DETACHES), DETACHES, TimeUnit.SECONDS);
  }

  private volatile CacheValue _baseCacheValue;

  public DetachableCacheValue(CacheValue cacheValue) {
    _baseCacheValue = cacheValue;
  }

  @Override
  public CacheValue detachFromCache() {
    if (_baseCacheValue instanceof ByteArrayCacheValue) {
      // already detached
      return null;
    } else if (_baseCacheValue instanceof UnsafeCacheValue) {
      final CacheValue result = _baseCacheValue;
      // No one is using this so don't copy
      // NULL out reference so just in case there can't be a seg fault.
      _baseCacheValue = null;
      _detaches.mark();
      return result;
    } else {
      throw new RuntimeException("Unsupported type of [" + _baseCacheValue + "]");
    }
  }

  @Override
  public int length() throws EvictionException {
    try {
      return _baseCacheValue.length();
    } catch (NullPointerException npe) {
      throw new EvictionException();
    }
  }

  @Override
  public void write(int position, byte[] buf, int offset, int length) {
    _baseCacheValue.write(position, buf, offset, length);
  }

  @Override
  public void read(int position, byte[] buf, int offset, int length) throws EvictionException {
    try {
      _baseCacheValue.read(position, buf, offset, length);
    } catch (NullPointerException npe) {
      throw new EvictionException();
    }
  }

  @Override
  public byte read(int position) throws EvictionException {
    try {
      return _baseCacheValue.read(position);
    } catch (NullPointerException npe) {
      throw new EvictionException();
    }
  }

  @Override
  public void release() {
    if (_baseCacheValue != null) {
      _baseCacheValue.release();
    }
  }

  @Override
  public short readShort(int position) throws EvictionException {
    try {
      return _baseCacheValue.readShort(position);
    } catch (NullPointerException npe) {
      throw new EvictionException();
    }
  }

  @Override
  public int readInt(int position) throws EvictionException {
    try {
      return _baseCacheValue.readInt(position);
    } catch (NullPointerException npe) {
      throw new EvictionException();
    }
  }

  @Override
  public long readLong(int position) throws EvictionException {
    try {
      return _baseCacheValue.readLong(position);
    } catch (NullPointerException npe) {
      throw new EvictionException();
    }
  }

  @Override
  public CacheValue trim(int length) {
    return this;
  }

  @Override
  public boolean isEvicted() {
    return _baseCacheValue == null;
  }

}