src/main/java/org/apache/sling/graphql/helpers/lazyloading/LazyLoadingField.java

/*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 ~ Licensed to the Apache Software Foundation (ASF) under one
 ~ or more contributor license agreements.  See the NOTICE file
 ~ distributed with this work for additional information
 ~ regarding copyright ownership.  The ASF licenses this file
 ~ to you 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 org.apache.sling.graphql.helpers.lazyloading;

import java.util.function.Supplier;

/** Helper for a single lazy-loading value */
public class LazyLoadingField<T> {

    @SuppressWarnings("squid:S3077")
    // The Supplier itself is immutable, just "volatile" is fine
    private volatile Supplier<T> supplier;

    private T value;

    public LazyLoadingField(Supplier<T> supplier) {
        this.supplier = supplier;
    }

    public T get() {
        if(supplier != null) {
            synchronized(this) {
                if(supplier != null) {
                    value = supplier.get();
                    supplier = null;
                }
            }
        }
        return value;
    }
}