// 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;
}
}