runtime/master/src/main/java/org/apache/nemo/runtime/master/metric/MetricBroadcaster.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.apache.nemo.runtime.master.metric;

import org.eclipse.jetty.websocket.api.Session;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;

/**
 * MetricBroadcaster broadcast metric changes to the currently active WebSocket sessions.
 */
public final class MetricBroadcaster {
  private static final Logger LOG = LoggerFactory.getLogger(MetricBroadcaster.class.getName());
  private final Set<Session> sessions = ConcurrentHashMap.newKeySet();

  /**
   * Private constructor.
   */
  private MetricBroadcaster() {
  }

  /**
   * Getter for the singleton object.
   *
   * @return MetricBroadcaster object.
   */
  public static MetricBroadcaster getInstance() {
    return InstanceHolder.INSTANCE;
  }

  /**
   * Lazy class object holder for MetricBroadcaster class.
   */
  private static class InstanceHolder {
    private static final MetricBroadcaster INSTANCE = new MetricBroadcaster();
  }

  /**
   * Add a session to the session list.
   *
   * @param session a WebSocket session.
   */
  public synchronized void addSession(final Session session) {
    try {
      session.getRemote().sendString(MetricStore.getStore().dumpAllMetricToJson());
    } catch (final IOException e) {
      LOG.warn("Failed to send initial metric to newly connected session.");
    }
    sessions.add(session);
  }

  /**
   * Remove a session from the session list.
   *
   * @param session a WebSocket session.
   */
  public synchronized void removeSession(final Session session) {
    sessions.remove(session);
  }

  /**
   * Send text frame to each WebSocket session.
   *
   * @param text text to send.
   */
  public void broadcast(final String text) {
    for (final Session session : sessions) {
      try {
        session.getRemote().sendString(text);
      } catch (final IOException e) {
        LOG.warn("Failed to send string to remote session {}.", session.getRemoteAddress().toString());
      }
    }
  }

  /**
   * Send binary frame to each WebSocket session.
   *
   * @param bytes byte array to send.
   */
  public void broadcast(final byte[] bytes) {
    for (final Session session : sessions) {
      try {
        session.getRemote().sendBytes(ByteBuffer.wrap(bytes));
      } catch (final IOException e) {
        LOG.warn("Failed to send binary to remote session {}.", session.getRemoteAddress().toString());
      }
    }
  }

}