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 com.datastax.oss.driver.internal.core.util.concurrent;
  
  import com.datastax.oss.driver.shaded.guava.common.annotations.VisibleForTesting;
  import com.datastax.oss.driver.shaded.guava.common.collect.ImmutableList;
  import java.util.List;
  import java.util.concurrent.CopyOnWriteArrayList;
  import java.util.concurrent.locks.ReadWriteLock;
  import java.util.concurrent.locks.ReentrantReadWriteLock;
  import java.util.function.Consumer;
  import net.jcip.annotations.GuardedBy;
  import net.jcip.annotations.ThreadSafe;
  
  /**
   * Filters a list of events, accumulating them during an initialization period.
   *
   * <p>It has three states:
   *
   * <ul>
   *   <li>Not started: events are discarded.
   *   <li>Started: events accumulate but are not propagated to the end consumer yet.
   *   <li>Ready: all accumulated events are flushed to the end consumer; subsequent events are
   *       propagated directly. The order of events is preserved at all times.
   * </ul>
   */
  @ThreadSafe
  public class ReplayingEventFilter<EventT> {
  
    private enum State {
      NEW,
      STARTED,
      READY
    }
  
    private final Consumer<EventT> consumer;
  
    // Exceptionally, we use a lock: it will rarely be contended, and if so for only a short period.
    private final ReadWriteLock stateLock = new ReentrantReadWriteLock();
  
    @GuardedBy("stateLock")
    private State state;
  
    @GuardedBy("stateLock")
    private final List<EventT> recordedEvents;
  
    public ReplayingEventFilter(Consumer<EventT> consumer) {
      this.consumer = consumer;
      this.state = State.NEW;
      this.recordedEvents = new CopyOnWriteArrayList<>();
    }
  
    public void start() {
      stateLock.writeLock().lock();
      try {
        state = State.STARTED;
      } finally {
        stateLock.writeLock().unlock();
      }
    }
  
    public void markReady() {
      stateLock.writeLock().lock();
      try {
        state = State.READY;
        for (EventT event : recordedEvents) {
          consumer.accept(event);
        }
      } finally {
        recordedEvents.clear();
        stateLock.writeLock().unlock();
      }
    }
  
    public void accept(EventT event) {
      stateLock.readLock().lock();
      try {
        switch (state) {
          case NEW:
            break;
          case STARTED:
            recordedEvents.add(event);
            break;
          case READY:
            consumer.accept(event);
            break;
        }
      } finally {
        stateLock.readLock().unlock();
      }
    }
  
    @VisibleForTesting
    public List<EventT> recordedEvents() {
      stateLock.readLock().lock();
      try {
        return ImmutableList.copyOf(recordedEvents);
      } finally {
        stateLock.readLock().unlock();
      }
    }
  }
  