1 /*
2 * *************************************************************************************************************************************************************
3 *
4 * TheseFoolishThings: Miscellaneous utilities
5 * http://tidalwave.it/projects/thesefoolishthings
6 *
7 * Copyright (C) 2009 - 2026 by Tidalwave s.a.s. (http://tidalwave.it)
8 *
9 * *************************************************************************************************************************************************************
10 *
11 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License.
12 * You may obtain a copy of the License at
13 *
14 * http://www.apache.org/licenses/LICENSE-2.0
15 *
16 * 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
17 * CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.
18 *
19 * *************************************************************************************************************************************************************
20 *
21 * git clone https://bitbucket.org/tidalwave/thesefoolishthings-src
22 * git clone https://github.com/tidalwave-it/thesefoolishthings-src
23 *
24 * *************************************************************************************************************************************************************
25 */
26 package it.tidalwave.messagebus.spi;
27
28 import java.lang.ref.WeakReference;
29 // import javax.annotation.concurrent.ThreadSafe;
30 import jakarta.annotation.Nonnull;
31 import java.util.List;
32 import java.util.Map;
33 import java.util.concurrent.ConcurrentHashMap;
34 import java.util.concurrent.CopyOnWriteArrayList;
35 import java.util.concurrent.Executor;
36 import java.util.concurrent.Executors;
37 import it.tidalwave.messagebus.MessageBus;
38 import lombok.Getter;
39 import lombok.extern.slf4j.Slf4j;
40
41 /***************************************************************************************************************************************************************
42 * An implementation of {@link MessageBus}. Messages are delivered by means of an {@link Executor}, according to a {@link MessageDelivery} strategy. A listener
43 * subscribed to a topic receives the messages of that class and of its subclasses (or implementations, if the topic is an interface); if a listener throws an
44 * exception, it is logged and the message is delivered to the other listeners anyway. This class is thread-safe.
45 * @author Fabrizio Giudici
46 **************************************************************************************************************************************************************/
47 /* @ThreadSafe */ @Slf4j @SuppressWarnings("this-escape")
48 public class SimpleMessageBus implements MessageBus
49 {
50 private final Map<Class<?>, List<WeakReference<Listener<?>>>> listenersMapByTopic = new ConcurrentHashMap<>();
51
52 private final MessageDelivery messageDelivery;
53
54 /***********************************************************************************************************************************************************
55 * The {@link Executor} used to deliver messages.
56 * @return the {@code Executor}
57 **********************************************************************************************************************************************************/
58 @Getter
59 private final Executor executor;
60
61 /***********************************************************************************************************************************************************
62 * Creates a new instance with a {@link SimpleAsyncMessageDelivery} strategy for delivery. It will use its own pool of 10 threads.
63 **********************************************************************************************************************************************************/
64 public SimpleMessageBus()
65 {
66 this(Executors.newFixedThreadPool(10));
67 }
68
69 /***********************************************************************************************************************************************************
70 * Creates a new instance given an executor and a {@link SimpleAsyncMessageDelivery} strategy for delivery.
71 * @param executor the {@link Executor}
72 **********************************************************************************************************************************************************/
73 public SimpleMessageBus (@Nonnull final Executor executor)
74 {
75 this(executor, new SimpleAsyncMessageDelivery());
76 }
77
78 /***********************************************************************************************************************************************************
79 * Creates a new instance given an executor and a strategy for delivery.
80 * @param executor the {@link Executor}
81 * @param messageDelivery the strategy for delivery
82 **********************************************************************************************************************************************************/
83 public SimpleMessageBus (@Nonnull final Executor executor, @Nonnull final MessageDelivery messageDelivery)
84 {
85 this.executor = executor;
86 this.messageDelivery = messageDelivery;
87 this.messageDelivery.initialize(this);
88 log.info("MessageBusSupport configured with {}", messageDelivery);
89 }
90
91 /***********************************************************************************************************************************************************
92 * {@inheritDoc}
93 **********************************************************************************************************************************************************/
94 @Override
95 public <T> void publish (@Nonnull final T message)
96 {
97 publish((Class<T>)message.getClass(), message);
98 }
99
100 /***********************************************************************************************************************************************************
101 * {@inheritDoc}
102 **********************************************************************************************************************************************************/
103 @Override
104 public <T> void publish (@Nonnull final Class<T> topic, @Nonnull final T message)
105 {
106 log.trace("publish({}, {})", topic, message);
107 messageDelivery.deliverMessage(topic, message);
108 }
109
110 /***********************************************************************************************************************************************************
111 * {@inheritDoc}
112 **********************************************************************************************************************************************************/
113 @Override
114 public <T> void subscribe (@Nonnull final Class<T> topic, @Nonnull final Listener<T> listener)
115 {
116 log.debug("subscribe({}, {})", topic, listener);
117 findListenersByTopic(topic).add(new WeakReference<>(listener));
118 }
119
120 /***********************************************************************************************************************************************************
121 * {@inheritDoc}
122 **********************************************************************************************************************************************************/
123 @Override
124 public void unsubscribe (@Nonnull final Listener<?> listener)
125 {
126 log.debug("unsubscribe({})", listener);
127
128 for (final var list : listenersMapByTopic.values())
129 {
130 list.removeIf(ref -> (ref.get() == null) || (ref.get() == listener));
131 }
132 }
133
134 /***********************************************************************************************************************************************************
135 * Dispatches a message to all the listeners subscribed to its topic, or to a supertype of it. It is called by the {@link MessageDelivery} strategy.
136 * @param <T> the static type of the topic
137 * @param topic the dynamic type of the topic
138 * @param message the message
139 **********************************************************************************************************************************************************/
140 protected <T> void dispatchMessage (@Nonnull final Class<T> topic, @Nonnull final T message)
141 {
142 for (final var e : listenersMapByTopic.entrySet())
143 {
144 if (e.getKey().isAssignableFrom(topic))
145 {
146 final List<WeakReference<MessageBus.Listener<T>>> listeners = (List)e.getValue();
147
148 for (final var listenerReference : listeners)
149 {
150 final var listener = listenerReference.get();
151
152 if (listener != null)
153 {
154 try
155 {
156 listener.notify(message);
157 }
158 catch (Throwable t)
159 {
160 log.warn("deliverMessage()", t);
161 }
162 }
163 }
164 }
165 }
166 }
167
168 /***********************************************************************************************************************************************************
169 * Returns the listeners subscribed to the given topic, creating the list if needed.
170 * @param <T> the static type of the topic
171 * @param topic the topic
172 * @return the listeners
173 **********************************************************************************************************************************************************/
174 @Nonnull
175 private <T> List<WeakReference<Listener<T>>> findListenersByTopic (@Nonnull final Class<T> topic)
176 {
177 return (List)listenersMapByTopic.computeIfAbsent(topic, t -> new CopyOnWriteArrayList<>());
178 }
179 }