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There is a newer version: 2.0.0-rc-1

/*
 * Copyright 2013 the original author or authors.
 *
 * Licensed 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 ratpack.registry.internal;

import ratpack.func.Factory;

import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class LazyRegistryEntry implements RegistryEntry {

  private final Class type;
  private final Factory factory;
  private final Lock lock = new ReentrantLock();

  private T object;

  public LazyRegistryEntry(Class type, Factory factory) {
    this.type = type;
    this.factory = factory;
  }

  @Override
  public Class getType() {
    return type;
  }

  @Override
  public T get() {
    if (object == null) {
      lock.lock();
      try {
        //noinspection ConstantConditions
        if (object == null) {
          object = factory.create();
        }
      } finally {
        lock.unlock();
      }
    }
    return object;
  }
}