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 }