/*
 * Copyright 2000-2013 JetBrains s.r.o.
 *
 * 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 com.intellij.openapi.util;

import org.jetbrains.annotations.NotNull;

/**
 * @author peter
 */
public abstract class AtomicNotNullLazyValue<T> extends NotNullLazyValue<T> {
  private static final RecursionGuard ourGuard = RecursionManager.createGuard("AtomicNotNullLazyValue");
  private volatile T myValue;

  @Override
  @NotNull
  public final T getValue() {
    T value = myValue;
    if (value != null) {
      return value;
    }
    //noinspection SynchronizeOnThis
    synchronized (this) {
      value = myValue;
      if (value == null) {
        RecursionGuard.StackStamp stamp = ourGuard.markStack();
        value = compute();
        if (stamp.mayCacheNow()) {
          myValue = value;
        }
      }
    }
    return value;
  }
}