/**
* Copyright (C) 2013-2015 all@code-story.net
*
* 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 net.codestory.http.misc;
import java.util.function.*;
// Code copied from Google's Guava
//
public class MemoizingSupplier<T> implements Supplier<T> {
private final Supplier<T> delegate;
transient volatile boolean initialized;
// "value" does not need to be volatile; visibility piggy-backs
// on volatile read of "initialized".
transient T value;
private MemoizingSupplier(Supplier<T> delegate) {
this.delegate = delegate;
}
public static <T> Supplier<T> memoize(Supplier<T> delegate) {
return new MemoizingSupplier<>(delegate);
}
@Override
public T get() {
// A 2-field variant of Double Checked Locking.
if (!initialized) {
synchronized (this) {
if (!initialized) {
T t = delegate.get();
value = t;
initialized = true;
return t;
}
}
}
return value;
}
}