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Make memory fence in `ByteBufferGuard` explicit (#12290)

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Petr Portnov | PROgrm_JARvis 2023-06-01 14:41:06 +03:00 committed by GitHub
parent 40b582ab18
commit 45110a6a46
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2 changed files with 6 additions and 8 deletions
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2
lucene/CHANGES.txt
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@ -156,6 +156,8 @@ Improvements
* GITHUB#12333: NumericLeafComparator#competitiveIterator makes better use of a "search after" value when paginating.
(Chaitanya Gohel)
* GITHUB#12290: Make memory fence in ByteBufferGuard explicit using `VarHandle.fullFence()`
Optimizations
---------------------

12
lucene/core/src/java/org/apache/lucene/store/ByteBufferGuard.java
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@ -17,11 +17,11 @@
package org.apache.lucene.store;
import java.io.IOException;
import java.lang.invoke.VarHandle;
import java.nio.ByteBuffer;
import java.nio.FloatBuffer;
import java.nio.IntBuffer;
import java.nio.LongBuffer;
import java.util.concurrent.atomic.AtomicInteger;
/**
* A guard that is created for every {@link ByteBufferIndexInput} that tries on best effort to
@ -49,9 +49,6 @@ final class ByteBufferGuard {
/** Not volatile; see comments on visibility below! */
private boolean invalidated = false;
/** Used as a store-store barrier; see comments below! */
private final AtomicInteger barrier = new AtomicInteger();
/**
* Creates an instance to be used for a single {@link ByteBufferIndexInput} which must be shared
* by all of its clones.
@ -69,10 +66,9 @@ final class ByteBufferGuard {
// the "invalidated" field update visible to other threads. We specifically
// don't make "invalidated" field volatile for performance reasons, hoping the
// JVM won't optimize away reads of that field and hardware should ensure
// caches are in sync after this call. This isn't entirely "fool-proof"
// (see LUCENE-7409 discussion), but it has been shown to work in practice
// and we count on this behavior.
barrier.lazySet(0);
// caches are in sync after this call.
// For previous implementation (based on `AtomicInteger#lazySet(0)`) see LUCENE-7409.
VarHandle.fullFence();
// we give other threads a bit of time to finish reads on their ByteBuffer...:
Thread.yield();
// finally unmap the ByteBuffers: