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/*
 * Licensed to Elasticsearch under one or more contributor
 * license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright
 * ownership. Elasticsearch 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.elasticsearch.common.util;

import java.util.function.Supplier;

/**
 * A {@link Supplier} that caches its return value. This may be useful to make
 * a {@link Supplier} idempotent or for performance reasons if always returning
 * the same instance is acceptable.
 */
public final class CachedSupplier implements Supplier {

    private Supplier supplier;
    private T result;
    private boolean resultSet;

    public CachedSupplier(Supplier supplier) {
        this.supplier = supplier;
    }

    @Override
    public synchronized T get() {
        if (resultSet == false) {
            result = supplier.get();
            resultSet = true;
        }
        return result;
    }

}