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1   /*
2    * Copyright 2012 The Netty Project
3    *
4    * The Netty Project licenses this file to you under the Apache License,
5    * version 2.0 (the "License"); you may not use this file except in compliance
6    * with the License. You may obtain a copy of the License at:
7    *
8    *   http://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
12   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
13   * License for the specific language governing permissions and limitations
14   * under the License.
15   */
16  package org.jboss.netty.util.internal;
17  
18  import java.util.concurrent.atomic.AtomicBoolean;
19  import java.util.concurrent.atomic.AtomicLong;
20  
21  import org.jboss.netty.logging.InternalLogger;
22  import org.jboss.netty.logging.InternalLoggerFactory;
23  
24  /**
25   * Warn when user creates too many instances to avoid {@link OutOfMemoryError}.
26   */
27  public class SharedResourceMisuseDetector {
28  
29      private static final int MAX_ACTIVE_INSTANCES = 256;
30      private static final InternalLogger logger =
31          InternalLoggerFactory.getInstance(SharedResourceMisuseDetector.class);
32  
33      private final Class<?> type;
34      private final AtomicLong activeInstances = new AtomicLong();
35      private final AtomicBoolean logged = new AtomicBoolean();
36  
37      public SharedResourceMisuseDetector(Class<?> type) {
38          if (type == null) {
39              throw new NullPointerException("type");
40          }
41          this.type = type;
42      }
43  
44      public void increase() {
45          if (activeInstances.incrementAndGet() > MAX_ACTIVE_INSTANCES) {
46              if (logger.isWarnEnabled()) {
47                  if (logged.compareAndSet(false, true)) {
48                      logger.warn(
49                              "You are creating too many " + type.getSimpleName() +
50                              " instances.  " + type.getSimpleName() +
51                              " is a shared resource that must be reused across the" +
52                              " application, so that only a few instances are created.");
53                  }
54              }
55          }
56      }
57  
58      public void decrease() {
59          activeInstances.decrementAndGet();
60      }
61  }