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    1   /*
    2    * Copyright 2009 Red Hat, Inc.
    3    *
    4    * Red Hat licenses this file to you under the Apache License, version 2.0
    5    * (the "License"); you may not use this file except in compliance with the
    6    * 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   * @author <a href="http://www.jboss.org/netty/">The Netty Project</a>
    28   * @author <a href="http://gleamynode.net/">Trustin Lee</a>
    29   * @version $Rev: 2234 $, $Date: 2010-04-06 18:23:25 +0900 (Tue, 06 Apr 2010) $
    30   */
    31  public class SharedResourceMisuseDetector {
    32
    33      private static final int MAX_ACTIVE_INSTANCES = 256;
    34      private static final InternalLogger logger =
    35          InternalLoggerFactory.getInstance(SharedResourceMisuseDetector.class);
    36
    37      private final Class<?> type;
    38      private final AtomicLong activeInstances = new AtomicLong();
    39      private final AtomicBoolean logged = new AtomicBoolean();
    40
    41      public SharedResourceMisuseDetector(Class<?> type) {
    42          if (type == null) {
    43              throw new NullPointerException("type");
    44          }
    45          this.type = type;
    46      }
    47
    48      public void increase() {
    49          if (activeInstances.incrementAndGet() > MAX_ACTIVE_INSTANCES) {
    50              if (logged.compareAndSet(false, true)) {
    51                  logger.warn(
    52                          "You are creating too many " + type.getSimpleName() +
    53                          " instances.  " + type.getSimpleName() +
    54                          " is a shared resource that must be reused across the" +
    55                          " application, so that only a few instances are created.");
    56              }
    57          }
    58      }
    59
    60      public void decrease() {
    61          activeInstances.decrementAndGet();
    62      }
    63  }