001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.juneau.rest.server.sse;
018
019
020import java.io.*;
021import java.time.*;
022import java.util.concurrent.*;
023import java.util.concurrent.atomic.*;
024
025import org.apache.juneau.marshall.sse.*;
026import static org.apache.juneau.commons.utils.Shorts.*;
027
028/**
029 * Scheduled SSE heartbeat.
030 */
031@SuppressWarnings({
032   "resource" // start() returns the SseHeartbeat to the caller, who closes it
033})
034public class SseHeartbeat implements Runnable, AutoCloseable {
035
036   /**
037    * Starts a heartbeat.
038    *
039    * @param scheduler The scheduler. Must not be <jk>null</jk>.
040    * @param writer The writer. Must not be <jk>null</jk>.
041    * @param interval The heartbeat interval. Must not be <jk>null</jk>.
042    * @return The heartbeat handle.
043    */
044   public static SseHeartbeat start(ScheduledExecutorService scheduler, Writer writer, Duration interval) {
045      var heartbeat = new SseHeartbeat(writer);
046      var i = reqnn("interval", interval).toMillis();
047      req(i > 0, "interval must be > 0.");
048      heartbeat.future = scheduler.scheduleAtFixedRate(heartbeat, i, i, TimeUnit.MILLISECONDS);
049      return heartbeat;
050   }
051
052   private final Writer writer;
053   private final AtomicBoolean closed;
054   private ScheduledFuture<?> future;
055
056   /**
057    * Constructor.
058    *
059    * @param writer The writer. Must not be <jk>null</jk>.
060    */
061   public SseHeartbeat(Writer writer) {
062      this.writer = reqnn("writer", writer);
063      closed = new AtomicBoolean();
064   }
065
066   @Override /* Runnable */
067   public void run() {
068      if (closed.get())
069         return;
070      try {
071         SseSerializer.writeComment(writer, "ping");
072      } catch (IOException e) {
073         close();
074      }
075   }
076
077   @Override /* AutoCloseable */
078   public void close() {
079      if (closed.compareAndSet(false, true) && future != null)
080         future.cancel(false);
081   }
082}