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/*
* Copyright © 2016-2025 The LmdbJava Open Source Project
*
* 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 org.lmdbjava;
/** Supports creating strong references in manner compatible with Java 8. */
public final class ReferenceUtil {
private ReferenceUtil() {}
/**
* Ensures that the object referenced by the given reference remains <em>strongly reachable</em>,
* regardless of any prior actions of the program that might otherwise cause the object to become
* unreachable. Thus, the referenced object is not reclaimable by garbage collection at least
* until after the invocation of this method.
*
* <p>Recent versions of the JDK have a nasty habit of prematurely deciding objects are
* unreachable (eg <a href="https://tinyurl.com/so26642153">StackOverflow question 26642153</a>.
*
* <p><code>java.lang.ref.Reference.reachabilityFence</code> offers a solution to this problem,
* but it was only introduced in Java 9. LmdbJava presently supports Java 8 and therefore this
* method provides an alternative.
*
* <p>This method is always implemented as a synchronization on {@code ref}. <b>It is the caller's
* responsibility to ensure that this synchronization will not cause deadlock.</b>
*
* @param ref the reference (null is acceptable but has no effect)
* @see <a href="https://github.com/netty/netty/pull/8410">Netty PR 8410</a>
*/
public static void reachabilityFence0(final Object ref) {
if (ref != null) {
synchronized (ref) {
// Empty synchronized is ok: https://stackoverflow.com/a/31933260/1151521
}
}
}
}