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ReferenceUtil.java
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50 lines (47 loc) · 2.38 KB
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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 works because HotSpot JIT-compilers prune dead locals based on method bytecode
* analysis rather than optimized IR. As Vladimir Ivanov explains: "any usage of a local extends
* its live range, even if that usage is eliminated in generated code". The method call at the
* bytecode level is sufficient to keep the object alive through safepoints, preventing premature
* garbage collection during native operations.
*
* @param ref the reference
* @see <a href="https://mail.openjdk.org/pipermail/core-libs-dev/2018-February/051312.html">
* Vladimir Ivanov on reachabilityFence implementation</a>
*/
public static void reachabilityFence0(final Object ref) {
// Empty method body is intentional - the method call itself at bytecode level
// extends the object's live range per HotSpot JIT behavior
}
}