/**
*
* Copyright (c) 2006-2017, Speedment, Inc. 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.speedment.common.lazy;
import java.util.function.Supplier;
import static java.util.Objects.requireNonNull;
/**
* Generic lazy initialization class. The supplier must produce a non-null
* value.
*
* This class is thread safe. The Supplier is guaranteed to be called exactly
* one time following one or several calls to
* {@link #getOrCompute(java.util.function.Supplier) } by any number of
* threads.
*
* @author pemi
* @param <T> the type of the lazy initialized value
*/
public final class LazyReference<T> implements Lazy<T> {
private volatile T value;
private LazyReference() {
}
@Override
public T getOrCompute(Supplier<T> supplier) {
// With this local variable, we only need to do one volatile read most of the times
final T result = value;
return result != null ? result : maybeCompute(supplier);
}
private synchronized T maybeCompute(Supplier<T> supplier) {
if (value != null) {
return value;
}
value = requireNonNull(supplier.get());
return value;
}
public static <T> LazyReference<T> create() {
return new LazyReference<>();
}
}