content: /*
   * 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.kafka.server.util.timer;
  
  import org.apache.kafka.common.utils.Time;
  
  import java.util.concurrent.Delayed;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.atomic.AtomicInteger;
  import java.util.concurrent.atomic.AtomicLong;
  import java.util.function.Consumer;
  
  class TimerTaskList implements Delayed {
      private final Time time;
      private final AtomicInteger taskCounter;
      private final AtomicLong expiration;
  
      // TimerTaskList forms a doubly linked cyclic list using a dummy root entry
      // root.next points to the head
      // root.prev points to the tail
      private final TimerTaskEntry root;
  
      TimerTaskList(
          AtomicInteger taskCounter
      ) {
          this(taskCounter, Time.SYSTEM);
      }
  
      TimerTaskList(
          AtomicInteger taskCounter,
          Time time
      ) {
          this.time = time;
          this.taskCounter = taskCounter;
          this.expiration = new AtomicLong(-1L);
          this.root = new TimerTaskEntry(null, -1L);
          this.root.next = root;
          this.root.prev = root;
      }
  
      public boolean setExpiration(long expirationMs) {
          return expiration.getAndSet(expirationMs) != expirationMs;
      }
  
      public long getExpiration() {
          return expiration.get();
      }
  
      public synchronized void foreach(Consumer<TimerTask> f) {
          TimerTaskEntry entry = root.next;
          while (entry != root) {
              TimerTaskEntry nextEntry = entry.next;
              if (!entry.cancelled()) f.accept(entry.timerTask);
              entry = nextEntry;
          }
      }
  
      public void add(TimerTaskEntry timerTaskEntry) {
          boolean done = false;
          while (!done) {
              // Remove the timer task entry if it is already in any other list
              // We do this outside of the sync block below to avoid deadlocking.
              // We may retry until timerTaskEntry.list becomes null.
              timerTaskEntry.remove();
  
              synchronized (this) {
                  synchronized (timerTaskEntry) {
                      if (timerTaskEntry.list == null) {
                          // put the timer task entry to the end of the list. (root.prev points to the tail entry)
                          TimerTaskEntry tail = root.prev;
                          timerTaskEntry.next = root;
                          timerTaskEntry.prev = tail;
                          timerTaskEntry.list = this;
                          tail.next = timerTaskEntry;
                          root.prev = timerTaskEntry;
                          taskCounter.incrementAndGet();
                          done = true;
                      }
                  }
              }
          }
      }
  
      public synchronized void remove(TimerTaskEntry timerTaskEntry) {
          synchronized (timerTaskEntry) {
              if (timerTaskEntry.list == this) {
                  timerTaskEntry.next.prev = timerTaskEntry.prev;
                  timerTaskEntry.prev.next = timerTaskEntry.next;
                  timerTaskEntry.next = null;
                  timerTaskEntry.prev = null;
                  timerTaskEntry.list = null;
                  taskCounter.decrementAndGet();
              }
          }
      }
  
      public synchronized void flush(Consumer<TimerTaskEntry> f) {
          TimerTaskEntry head = root.next;
          while (head != root) {
              remove(head);
              f.accept(head);
              head = root.next;
          }
          expiration.set(-1L);
      }
  
      @Override
      public long getDelay(TimeUnit unit) {
          return unit.convert(Math.max(getExpiration() - time.hiResClockMs(), 0), TimeUnit.MILLISECONDS);
      }
  
      @Override
      public int compareTo(Delayed o) {
          TimerTaskList other = (TimerTaskList) o;
          return Long.compare(getExpiration(), other.getExpiration());
      }
  }
  