/*
    * Copyright 2009 Red Hat, Inc.
    *
    * Red Hat 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.jboss.netty.util.internal;
  
  import java.util.concurrent.atomic.AtomicBoolean;
  import java.util.concurrent.atomic.AtomicLong;
  
  import org.jboss.netty.logging.InternalLogger;
  import org.jboss.netty.logging.InternalLoggerFactory;
  
  /**
   * Warn when user creates too many instances to avoid {@link OutOfMemoryError}.
   *
   * @author <a href="http://www.jboss.org/netty/">The Netty Project</a>
   * @author <a href="http://gleamynode.net/">Trustin Lee</a>
   * @version $Rev: 2234 $, $Date: 2010-04-06 18:23:25 +0900 (Tue, 06 Apr 2010) $
   */
  public class SharedResourceMisuseDetector {
  
      private static final int MAX_ACTIVE_INSTANCES = 256;
      private static final InternalLogger logger =
          InternalLoggerFactory.getInstance(SharedResourceMisuseDetector.class);
  
      private final Class<?> type;
      private final AtomicLong activeInstances = new AtomicLong();
      private final AtomicBoolean logged = new AtomicBoolean();
  
      public SharedResourceMisuseDetector(Class<?> type) {
          if (type == null) {
              throw new NullPointerException("type");
          }
          this.type = type;
      }
  
      public void increase() {
          if (activeInstances.incrementAndGet() > MAX_ACTIVE_INSTANCES) {
              if (logged.compareAndSet(false, true)) {
                  logger.warn(
                          "You are creating too many " + type.getSimpleName() +
                          " instances.  " + type.getSimpleName() +
                          " is a shared resource that must be reused across the" +
                          " application, so that only a few instances are created.");
              }
          }
      }
  
      public void decrease() {
          activeInstances.decrementAndGet();
      }
  }