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 java.util.concurrent.locks.ReentrantLock;
  import java.util.function.Supplier;
  import net.jcip.annotations.ThreadSafe;
  
  /** Holds a reference to an object that is initialized on first access. */
  @ThreadSafe
  public class LazyReference<T> {
  
    private final String name;
    private final Supplier<T> supplier;
    private final CycleDetector checker;
    private volatile T value;
    private final ReentrantLock lock = new ReentrantLock();
  
    public LazyReference(String name, Supplier<T> supplier, CycleDetector cycleDetector) {
      this.name = name;
      this.supplier = supplier;
      this.checker = cycleDetector;
    }
  
    public LazyReference(Supplier<T> supplier) {
      this(null, supplier, null);
    }
  
    public T get() {
      T t = value;
      if (t == null) {
        if (checker != null) {
          checker.onTryLock(this);
        }
        lock.lock();
        try {
          if (checker != null) {
            checker.onLockAcquired(this);
          }
          t = value;
          if (t == null) {
            value = t = supplier.get();
          }
        } finally {
          if (checker != null) {
            checker.onReleaseLock(this);
          }
          lock.unlock();
        }
      }
      return t;
    }
  
    public String getName() {
      return name;
    }
  }
  