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   /*
    * Copyright 2012 The Netty Project
    *
    * The Netty Project 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}.
   */
  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 (logger.isWarnEnabled()) {
                  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();
      }
  }