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.activemq.memory;
  
  import java.util.Iterator;
  import java.util.LinkedList;
  import java.util.List;
  import java.util.concurrent.CopyOnWriteArrayList;
  
  import org.apache.activemq.thread.Task;
  import org.apache.activemq.thread.TaskRunner;
  import org.apache.activemq.thread.TaskRunnerFactory;
  import org.apache.activemq.usage.Usage;
  import org.apache.activemq.usage.UsageListener;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  public class CacheEvictionUsageListener implements UsageListener {
  
      private static final Logger LOG = LoggerFactory.getLogger(CacheEvictionUsageListener.class);
  
      private final List<CacheEvictor> evictors = new CopyOnWriteArrayList<CacheEvictor>();
      private final int usageHighMark;
      private final int usageLowMark;
  
      private final TaskRunner evictionTask;
      private final Usage usage;
  
      public CacheEvictionUsageListener(Usage usage, int usageHighMark, int usageLowMark, TaskRunnerFactory taskRunnerFactory) {
          this.usage = usage;
          this.usageHighMark = usageHighMark;
          this.usageLowMark = usageLowMark;
          evictionTask = taskRunnerFactory.createTaskRunner(new Task() {
              public boolean iterate() {
                  return evictMessages();
              }
          }, "Cache Evictor: " + System.identityHashCode(this));
      }
  
      boolean evictMessages() {
          // Try to take the memory usage down below the low mark.
          LOG.debug("Evicting cache memory usage: {}", usage.getPercentUsage());
  
          List<CacheEvictor> list = new LinkedList<CacheEvictor>(evictors);
          while (list.size() > 0 && usage.getPercentUsage() > usageLowMark) {
  
              // Evenly evict messages from all evictors
              for (Iterator<CacheEvictor> iter = list.iterator(); iter.hasNext();) {
                  CacheEvictor evictor = iter.next();
                  if (evictor.evictCacheEntry() == null) {
                      iter.remove();
                  }
              }
          }
          return false;
      }
  
      public void onUsageChanged(Usage usage, int oldPercentUsage, int newPercentUsage) {
          // Do we need to start evicting cache entries? Usage > than the
          // high mark
          if (oldPercentUsage < newPercentUsage && usage.getPercentUsage() >= usageHighMark) {
              try {
                  evictionTask.wakeup();
              } catch (InterruptedException e) {
                  Thread.currentThread().interrupt();
              }
          }
      }
  
      public void add(CacheEvictor evictor) {
          evictors.add(evictor);
      }
  
      public void remove(CacheEvictor evictor) {
          evictors.remove(evictor);
      }
  }
  