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Core Neural Networks Framework

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/*
 * Copyright (c) 2018 by Andrew Charneski.
 *
 * The author 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.simiacryptus.mindseye.lang;

import javax.annotation.Nonnull;
import java.util.concurrent.BlockingDeque;
import java.util.concurrent.LinkedBlockingDeque;
import java.util.function.Supplier;

/**
 * An asynchronous, settable reference buffer. Allows consumers to block until a value is availble.
 *
 * @param  the type parameter
 */
public class Singleton implements Supplier {
  private final BlockingDeque deque = new LinkedBlockingDeque<>();

  /**
   * Instantiates a new Singleton.
   */
  public Singleton() {
  }

  @Override
  public T get() {
    try {
      T take = deque.take();
      deque.add(take);
      return take;
    } catch (InterruptedException e) {
      throw new RuntimeException(e);
    }
  }

  /**
   * Set.
   *
   * @param obj the obj
   * @return the singleton
   */
  @Nonnull
  public Singleton set(T obj) {
    assert deque.isEmpty();
    deque.add(obj);
    return this;
  }
}