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1   /*
2    * Copyright 2013 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  
17  package io.netty.channel;
18  
19  import io.netty.util.internal.InternalThreadLocalMap;
20  
21  import java.util.Map;
22  import java.util.WeakHashMap;
23  
24  /**
25   * Skeleton implementation of a {@link ChannelHandler}.
26   */
27  public abstract class ChannelHandlerAdapter implements ChannelHandler {
28  
29      // Not using volatile because it's used only for a sanity check.
30      boolean added;
31  
32      /**
33       * Throws {@link IllegalStateException} if {@link ChannelHandlerAdapter#isSharable()} returns {@code true}
34       */
35      protected void ensureNotSharable() {
36          if (isSharable()) {
37              throw new IllegalStateException("ChannelHandler " + getClass().getName() + " is not allowed to be shared");
38          }
39      }
40  
41      /**
42       * Return {@code true} if the implementation is {@link Sharable} and so can be added
43       * to different {@link ChannelPipeline}s.
44       */
45      public boolean isSharable() {
46          /**
47           * Cache the result of {@link Sharable} annotation detection to workaround a condition. We use a
48           * {@link ThreadLocal} and {@link WeakHashMap} to eliminate the volatile write/reads. Using different
49           * {@link WeakHashMap} instances per {@link Thread} is good enough for us and the number of
50           * {@link Thread}s are quite limited anyway.
51           *
52           * See <a href="https://github.com/netty/netty/issues/2289">#2289</a>.
53           */
54          Class<?> clazz = getClass();
55          Map<Class<?>, Boolean> cache = InternalThreadLocalMap.get().handlerSharableCache();
56          Boolean sharable = cache.get(clazz);
57          if (sharable == null) {
58              sharable = clazz.isAnnotationPresent(Sharable.class);
59              cache.put(clazz, sharable);
60          }
61          return sharable;
62      }
63  
64      /**
65       * Do nothing by default, sub-classes may override this method.
66       */
67      @Override
68      public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
69          // NOOP
70      }
71  
72      /**
73       * Do nothing by default, sub-classes may override this method.
74       */
75      @Override
76      public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
77          // NOOP
78      }
79  
80      /**
81       * Calls {@link ChannelHandlerContext#fireExceptionCaught(Throwable)} to forward
82       * to the next {@link ChannelHandler} in the {@link ChannelPipeline}.
83       *
84       * Sub-classes may override this method to change behavior.
85       */
86      @Override
87      public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
88          ctx.fireExceptionCaught(cause);
89      }
90  }