| // Copyright 2016 The Bazel Authors. All Rights Reserved. |
| // |
| // 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.google.testing.junit.runner.util; |
| |
| /** |
| * Returns a {@link Supplier} which caches the instance retrieved during the first call to |
| * {@code get()} and returns that value on subsequent calls to {@code get()}. See: |
| * <a href="http://en.wikipedia.org/wiki/Memoization">memoization</a>. |
| * |
| * <p>The returned supplier is thread-safe. The delegate's {@code get()} method will be invoked at |
| * most once. |
| * |
| * <p>The returned supplier is not serializable. |
| */ |
| public class MemoizingSupplier<T> implements Supplier<T> { |
| private final Supplier<T> delegate; |
| private volatile boolean initialized; |
| private T instance; |
| |
| public MemoizingSupplier(Supplier<T> delegate) { |
| this.delegate = delegate; |
| } |
| |
| @Override |
| public T get() { |
| if (!initialized) { |
| synchronized (this) { |
| if (!initialized) { |
| initialized = true; |
| instance = delegate.get(); |
| } |
| } |
| } |
| return instance; |
| } |
| } |
| |