001/*
002 * Units of Measurement Reference Implementation
003 * Copyright (c) 2005-2021, Jean-Marie Dautelle, Werner Keil, Otavio Santana.
004 *
005 * All rights reserved.
006 *
007 * Redistribution and use in source and binary forms, with or without modification,
008 * are permitted provided that the following conditions are met:
009 *
010 * 1. Redistributions of source code must retain the above copyright notice,
011 *    this list of conditions and the following disclaimer.
012 *
013 * 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions
014 *    and the following disclaimer in the documentation and/or other materials provided with the distribution.
015 *
016 * 3. Neither the name of JSR-385, Indriya nor the names of their contributors may be used to endorse or promote products
017 *    derived from this software without specific prior written permission.
018 *
019 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
020 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
021 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
022 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
023 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
024 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
025 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
026 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
027 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
028 * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
029 */
030package tech.units.indriya.internal.function;
031
032import static org.apiguardian.api.API.Status.INTERNAL;
033
034import java.util.Objects;
035import java.util.function.Supplier;
036
037import org.apiguardian.api.API;
038
039/**
040 * Holder of an instance of type T, supporting the <em>compute-if-absent</em> idiom in a thread-safe manner.
041 * <p>
042 * Not serializable!     
043 * 
044 * @author Andi Huber
045 * @since 2.0.3
046 */
047@API(status=INTERNAL)
048public class Lazy<T> {
049    private final Supplier<? extends T> supplier;
050    private T value;
051    private boolean memorized;
052
053    public Lazy(Supplier<? extends T> supplier) {
054        this.supplier = Objects.requireNonNull(supplier, "supplier is required");
055    }
056
057    public boolean isMemorized() {
058        synchronized (this) {
059            return memorized;    
060        }
061    }
062
063    public void clear() {
064        synchronized (this) {
065            this.memorized = false;
066            this.value = null;
067        }
068    }
069
070    public T get() {
071        synchronized (this) {
072            if(memorized) {
073                return value;
074            }
075            memorized = true;
076            return value = supplier.get();    
077        }
078    }
079    
080    public void set(T value) {
081        synchronized (this) {
082            if(memorized) {
083                throw new IllegalStateException(
084                        String.format("cannot set value '%s' on Lazy that has already memoized a value", ""+value));
085            }
086            memorized = true;
087            this.value = value;
088        }
089    }
090}