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/*
 * Copyright 2015 Async-IO.org
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * 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 CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */

package org.atmosphere.cpr;

import org.atmosphere.cache.BroadcastMessage;
import org.atmosphere.cache.BroadcasterCacheInspector;
import org.atmosphere.cache.CacheMessage;
import org.atmosphere.cache.DefaultBroadcasterCache;
import org.atmosphere.inject.AtmosphereConfigAware;

import java.util.List;

/**
 * A BroadcasterCache is a cache for broadcasted messages. When a Broadcaster is about to execute a broadcast operation
 * ({@link Broadcaster#broadcast(Object)}, the messages is cached, and the the write operation is executed. If the
 * write operation succeed, the message is removed from the cache. If the write operation fails for an
 * {@link AtmosphereResource}, the message stays in the cache so next time the client reconnects, the message can be sent
 * back to the client. BroadcasterCache is useful for applications that require that no messages are lost, e.g all
 * broadcasted message must be delivered to the client. If your application can survive lost messages, your don't need
 * to install a BroadcasterCache.
 * 

* A BroadcasterCache works the following way. The methods are always invoked from the application's {@link Broadcaster}. *

 *     1. When the Broadcaster is created, a unique BroadcasterCache is created and assigned to it as well. That means
 *     a BroadcasterCache is, by default, associated with a Broadcaster. You can share BroadcasterCache instances among
 *     Broadcasters as well.
 *     2. Just after the constructor has been invoked, the {@link #configure(BroadcasterConfig)} will get invoked, allowing
 *     the instance to configure itself based on a {@link BroadcasterConfig}.
 *     3. When {@link Broadcaster} starts, {@link #start()} will be invoked.
 *     4. Every time a {@link Broadcaster#broadcast(Object)} invocation occurs, the {@link #addToCache(String, String, org.atmosphere.cache.BroadcastMessage)}
 *     method will be invoked, allowing the instance to cache the object.
 *     5. If the write operation succeeds, the {@link #clearCache(String, String, org.atmosphere.cache.CacheMessage)} method will
 *     be invoked. If the write operation fail the cache won't be cleared, and the message will be available next time the
 *     client reconnects. An application that write a BroadcasterCache must make sure cached message aren't staying in the
 *     cache forever to prevent memory leaks.
 *     6. When a client reconnects, the {@link #retrieveFromCache(String, String)} method will be invoked.
 *     If messages are available, a {@link List} will be returned and written back to the client.
 *     7. When messages are added to the cache, an application can always customize the messages by creating {@link BroadcasterCacheInspector}
 *     and add them using {@link #inspector(org.atmosphere.cache.BroadcasterCacheInspector)}. BroadcasterCacheInspector
 *     will be invoked every time {@link #addToCache(String, String, org.atmosphere.cache.BroadcastMessage)} is executed.
 *     8. An application may decide that, at one point in time, stop caching message for a particular {@link AtmosphereResource} by invoking
 *     {@link #excludeFromCache(String, AtmosphereResource)}
 * 

*

*

* Implementations of this interface must be thread-safe. *

* A BroadcasterCache can be configured by invoking {@link org.atmosphere.cpr.BroadcasterConfig#setBroadcasterCache(BroadcasterCache)}, by * defining it in your web/application.xml or by using the {@link org.atmosphere.config.service.BroadcasterCacheService} annotation. * * @author Jeanfrancois Arcand */ public interface BroadcasterCache extends AtmosphereConfigAware { public static final String NULL = "null"; BroadcasterCache DEFAULT = new DefaultBroadcasterCache(); /** * This method is invoked when the Broadcaster is started. */ void start(); /** * This method is invoked when the Broadcaster is stopped. */ void stop(); /** * Clean resources associated with this instance. This method is useful when ExecutorServices are shared * and some future must be cancelled. This method will always be invoked when a {@link Broadcaster} gets destroyed. */ void cleanup(); /** * Start tracking messages associated with {@link AtmosphereResource} from the cache. * * @param broadcasterId The associated {@link Broadcaster#addAtmosphereResource(AtmosphereResource).getID} * @param uuid {@link AtmosphereResource#uuid} * @param message {@link BroadcastMessage}. * @return The {@link CacheMessage} */ CacheMessage addToCache(String broadcasterId, String uuid, BroadcastMessage message); /** * Retrieve messages associated with {@link AtmosphereResource}. * * * @param id The associated {@link org.atmosphere.cpr.Broadcaster#addAtmosphereResource(org.atmosphere.cpr.AtmosphereResource).getID} * @param uuid {@link org.atmosphere.cpr.AtmosphereResource} * @return a {@link List} of messages (String). */ List retrieveFromCache(String id, String uuid); /** * Remove the previously cached message. * * @param broadcasterId The {@link org.atmosphere.cpr.Broadcaster#getID()} * @param uuid an {@link org.atmosphere.cpr.AtmosphereResource#uuid()} * @param cache the {@link CacheMessage} */ BroadcasterCache clearCache(String broadcasterId, String uuid, CacheMessage cache); /** * Allow an application to exclude, or block, an {@link AtmosphereResource} to received cached message. * No new message will get sent to this client except the ones already cached. * * @param broadcasterId The {@link org.atmosphere.cpr.Broadcaster#getID()} * @param r an {@link AtmosphereResource} * @return this */ BroadcasterCache excludeFromCache(String broadcasterId, AtmosphereResource r); /** * Add a {@link org.atmosphere.cpr.AtmosphereResource#uuid()} to the list of active {@link org.atmosphere.cpr.AtmosphereResource} * Message will be cached for the resource associated with the uuid. * * @param broadcasterId The {@link org.atmosphere.cpr.Broadcaster#getID()} * @param uuid an {@link org.atmosphere.cpr.AtmosphereResource#uuid()} * @return this */ BroadcasterCache cacheCandidate(String broadcasterId, String uuid); /** * Add a {@link BroadcasterCacheInspector} that will be invoked before a message gets added to the cache. * * @param interceptor an instance of {@link BroadcasterCacheInspector} * @return this */ BroadcasterCache inspector(BroadcasterCacheInspector interceptor); /** * Add a {@link BroadcasterCacheListener} * * @param l a {@link BroadcasterCacheListener} * @return this */ BroadcasterCache addBroadcasterCacheListener(BroadcasterCacheListener l); /** * Remove a {@link BroadcasterCacheListener} * * @param l a {@link BroadcasterCacheListener} * @return this */ BroadcasterCache removeBroadcasterCacheListener(BroadcasterCacheListener l); }