LazySupplier.java
- /*
- * *************************************************************************************************************************************************************
- *
- * TheseFoolishThings: Miscellaneous utilities
- * http://tidalwave.it/projects/thesefoolishthings
- *
- * Copyright (C) 2009 - 2024 by Tidalwave s.a.s. (http://tidalwave.it)
- *
- * *************************************************************************************************************************************************************
- *
- * 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.
- *
- * *************************************************************************************************************************************************************
- *
- * git clone https://bitbucket.org/tidalwave/thesefoolishthings-src
- * git clone https://github.com/tidalwave-it/thesefoolishthings-src
- *
- * *************************************************************************************************************************************************************
- */
- package it.tidalwave.util;
- import javax.annotation.Nonnull;
- import javax.annotation.concurrent.ThreadSafe;
- import java.util.function.Supplier;
- import it.tidalwave.util.annotation.VisibleForTesting;
- import lombok.EqualsAndHashCode;
- import lombok.Getter;
- import lombok.RequiredArgsConstructor;
- /***************************************************************************************************************************************************************
- *
- * A supplier of an object that is lazily evaluated (when its value is requested for the first time). It warranties
- * that the real wrapped supplier is called only once.
- *
- * @author Fabrizio Giudici
- * @since 3.2-ALPHA-13
- *
- **************************************************************************************************************************************************************/
- @ThreadSafe @RequiredArgsConstructor(staticName = "of") @EqualsAndHashCode(of = {"ref", "initialized"})
- public class LazySupplier<T> implements Supplier<T>
- {
- @Nonnull
- private final Supplier<T> supplier;
- @VisibleForTesting volatile T ref = null;
- @Getter
- @VisibleForTesting volatile boolean initialized;
- /** {@inheritDoc} */
- @Override @Nonnull
- public synchronized T get()
- {
- // AtomicReference.updateAndGet() not good because in case of contention it might call supplier multiple times
- // We don't mess with double check for null since nowadays synchronized is fast
- if (ref == null)
- {
- ref = supplier.get();
- initialized = true;
- }
- return ref;
- }
- public synchronized void clear()
- {
- ref = null;
- }
- public void set (@Nonnull final T ref)
- {
- this.ref = ref;
- }
- @Nonnull
- public String toString()
- {
- return String.format("LazySupplier(%s)", (ref == null && !initialized) ? "<not initialised>" : ref);
- }
- }