聊聊claudb的NotificationManager

public class NotificationManager implements PatternSubscriptionSupport {

  private final DBServerContext server;
  private final ExecutorService executor = Executors.newSingleThreadExecutor();

  public NotificationManager(DBServerContext server) {
    this.server = server;
  }

  public void start() {
    // nothing to do
  }

  public void stop() {
    executor.shutdown();
  }

  public void enqueue(Event event) {
    executor.execute(() -> patternPublish(server, event.getChannel(), event.getValue()));
  }
}

public interface PatternSubscriptionSupport extends BaseSubscriptionSupport {
  String PSUBSCRIPTION_PREFIX = "psubscription:";
  String PMESSAGE = "pmessage";

  //......

  default int patternPublish(DBServerContext server, String channel, SafeString message) {
    int count = 0;
    for (Tuple2<String, ImmutableSet<SafeString>> entry : getPatternSubscriptions(server.getAdminDatabase(), channel)) {
      count += publish(server, entry.get2(), toPatternMessage(entry.get1(), channel, message));
    }
    return count;
  }

  default ImmutableSet<Tuple2<String, ImmutableSet<SafeString>>> getPatternSubscriptions(Database admin, String channel) {
    return getPatternSubscriptions(admin).entries().filter(subscriptionApplyTo(channel));
  }

  //......

}

public interface BaseSubscriptionSupport
{
  default void addSubscription(String suffix, Database admin, String sessionId, SafeString channel) {
    admin.merge(safeKey(suffix + channel), set(safeString(sessionId)),
        (oldValue, newValue) -> set(oldValue.getSet().appendAll(newValue.getSet())));
  }

  default void removeSubscription(String suffix, Database admin, String sessionId, SafeString channel) {
      admin.merge(safeKey(suffix + channel), set(safeString(sessionId)),
        (oldValue, newValue) -> set(oldValue.getSet().removeAll(newValue.getSet())));
  }

  default int publish(DBServerContext server, ImmutableSet<SafeString> clients, RedisToken message) {
    clients.forEach(client -> server.publish(client.toString(), message));
    return clients.size();
  }
}

public class ClauDB extends RespServerContext implements DBServerContext {

  private static final String STATE = "state";

  private static final Logger LOGGER = LoggerFactory.getLogger(ClauDB.class);

  private DatabaseCleaner cleaner;
  private Option<PersistenceManager> persistence;
  private Option<NotificationManager> notifications;

  private final DBConfig config;

  public ClauDB() {
    this(DEFAULT_HOST, DEFAULT_PORT);
  }

  public ClauDB(String host, int port) {
    this(host, port, DBConfig.builder().build());
  }

  public ClauDB(String host, int port, DBConfig config) {
    super(host, port, new DBCommandSuite(), new DBSessionListener());
    this.config = config;
  }

  //......

  @Override
  public void publish(String sourceKey, RedisToken message) {
    Session session = getSession(sourceKey);
    if (session != null) {
      session.publish(message);
    }
  }

  //......

}