content: /*
   * 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.distributedlog.logsegment;
  
  
  import com.google.common.base.Ticker;
  import com.google.common.cache.Cache;
  import com.google.common.cache.CacheBuilder;
  import com.google.common.cache.RemovalListener;
  import com.google.common.cache.RemovalNotification;
  import java.util.concurrent.TimeUnit;
  import org.apache.distributedlog.DistributedLogConfiguration;
  import org.apache.distributedlog.LogSegmentMetadata;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  
  /**
   * Cache the log segment metadata.
   */
  public class LogSegmentMetadataCache implements RemovalListener<String, LogSegmentMetadata> {
  
      private static final Logger logger = LoggerFactory.getLogger(LogSegmentMetadataCache.class);
  
      private final Cache<String, LogSegmentMetadata> cache;
      private final boolean isCacheEnabled;
  
      public LogSegmentMetadataCache(DistributedLogConfiguration conf,
                                     Ticker ticker) {
          cache = CacheBuilder.newBuilder()
                  .concurrencyLevel(conf.getNumWorkerThreads())
                  .initialCapacity(1024)
                  .expireAfterAccess(conf.getLogSegmentCacheTTLMs(), TimeUnit.MILLISECONDS)
                  .maximumSize(conf.getLogSegmentCacheMaxSize())
                  .removalListener(this)
                  .ticker(ticker)
                  .recordStats()
                  .build();
          this.isCacheEnabled = conf.isLogSegmentCacheEnabled();
          logger.info("Log segment cache is enabled = {}", this.isCacheEnabled);
      }
  
      /**
       * Add the log <i>segment</i> of <i>path</i> to the cache.
       *
       * @param path the path of the log segment
       * @param segment log segment metadata
       */
      public void put(String path, LogSegmentMetadata segment) {
          if (isCacheEnabled) {
              cache.put(path, segment);
          }
      }
  
      /**
       * Invalid the cache entry associated with <i>path</i>.
       *
       * @param path the path of the log segment
       */
      public void invalidate(String path) {
          if (isCacheEnabled) {
              cache.invalidate(path);
          }
      }
  
      /**
       * Retrieve the log segment of <i>path</i> from the cache.
       *
       * @param path the path of the log segment.
       * @return log segment metadata if exists, otherwise null.
       */
      public LogSegmentMetadata get(String path) {
          return cache.getIfPresent(path);
      }
  
      @Override
      public void onRemoval(RemovalNotification<String, LogSegmentMetadata> notification) {
          if (notification.wasEvicted()) {
              if (logger.isDebugEnabled()) {
                  logger.debug("Log segment of {} was evicted.", notification.getKey());
              }
          }
      }
  }
  