RoundRobinAsyncMessageDelivery.java

/*
 * *************************************************************************************************************************************************************
 *
 * TheseFoolishThings: Miscellaneous utilities
 * http://tidalwave.it/projects/thesefoolishthings
 *
 * Copyright (C) 2009 - 2026 by Tidalwave s.a.s. (http://tidalwave.it)
 *
 * *************************************************************************************************************************************************************
 *
 * 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.
 *
 * *************************************************************************************************************************************************************
 *
 * git clone https://bitbucket.org/tidalwave/thesefoolishthings-src
 * git clone https://github.com/tidalwave-it/thesefoolishthings-src
 *
 * *************************************************************************************************************************************************************
 */
package it.tidalwave.messagebus.spi;

import jakarta.annotation.Nonnull;
import it.tidalwave.messagebus.spi.MultiQueue.TopicAndMessage;
import lombok.Getter;
import lombok.Setter;
import lombok.ToString;
import lombok.extern.slf4j.Slf4j;

/***************************************************************************************************************************************************************
 * An implementation of {@link MessageDelivery} that keeps a queue of messages for each topic, and dispatches them in a round-robin fashion, topic by topic, so
 * a topic with many messages doesn't starve the others (see {@link MultiQueue}). Messages are dispatched by a number of workers, each of them permanently
 * running in a thread of the {@link java.util.concurrent.Executor} of the {@link SimpleMessageBus}.
 * @author  Fabrizio Giudici
 * @since   2.2
 **************************************************************************************************************************************************************/
@Slf4j @ToString(of = "workers")
public class RoundRobinAsyncMessageDelivery implements MessageDelivery
  {
    @Nonnull
    private SimpleMessageBus messageBusSupport;
    
    /***********************************************************************************************************************************************************
     * The number of workers that dispatch messages.
     * @return            the number of workers
     **********************************************************************************************************************************************************/
    @Getter @Setter
    private int workers = 10;
    
    private final MultiQueue multiQueue = new MultiQueue();
    
    /***********************************************************************************************************************************************************
     * The code run by each worker: it repeatedly removes the next message from the {@link MultiQueue}, waiting if none is available, and dispatches it by means
     * of the {@link SimpleMessageBus}. It terminates when the thread is interrupted.
     **********************************************************************************************************************************************************/
    private final Runnable dispatcher = new Runnable()
      {
        @Override
        public void run() 
          {
            for (;;)
              {
                try 
                  {
                    dispatchMessage(multiQueue.remove());
                  } 
                catch (InterruptedException e) 
                  {
                    break;
                  }
              }
          }
        
        private <T> void dispatchMessage (@Nonnull final TopicAndMessage<T> tam)
          {
            messageBusSupport.dispatchMessage(tam.getTopic(), tam.getMessage());
          }
      };

    /***********************************************************************************************************************************************************
     * {@inheritDoc}
     **********************************************************************************************************************************************************/
    @Override
    public void initialize (@Nonnull final SimpleMessageBus messageBusSupport)
      {
        this.messageBusSupport = messageBusSupport;
        final var executor = this.messageBusSupport.getExecutor();
        
        for (var i = 0; i < workers; i++)
          {
            executor.execute(dispatcher);
          }
      }
    
    /***********************************************************************************************************************************************************
     * {@inheritDoc}
     **********************************************************************************************************************************************************/
    @Override
    public <T> void deliverMessage (@Nonnull final Class<T> topic, @Nonnull final T message)
      {
        multiQueue.add(topic, message);
      }
  }