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Remove unnecessary AtomicReference #110

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Remove unnecessary AtomicReference #110

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17 changes: 9 additions & 8 deletions core/src/main/java/com/spotify/metrics/core/SemanticMetricDistribution.java
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Original file line number Diff line number Diff line change
Expand Up @@ -27,7 +27,6 @@
import com.tdunning.math.stats.TDigest;

import java.nio.ByteBuffer;
import java.util.concurrent.atomic.AtomicReference;

/**
* Semantic Metric implementation of {@link Distribution}.
Expand All @@ -50,23 +49,24 @@
public class SemanticMetricDistribution implements Distribution {

private static final int COMPRESSION_DEFAULT_LEVEL = 100;
private final AtomicReference<TDigest> distRef;
private volatile TDigest dist;
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@rulle-io rulle-io Oct 15, 2021

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Since dist is covered by synchronized everywhere, does it really need to be a volatile?

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@spkrka spkrka Oct 18, 2021

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Line 85 references dist without being synchronized, so the read might see a stale copy

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@rulle-io rulle-io Oct 19, 2021

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I'd make it synchronized as well instead (like this e.g.).


SemanticMetricDistribution() {
this.distRef = new AtomicReference<>(create());
this.dist = create();
}

@Override
public synchronized void record(double val) {
distRef.get().add(val);
dist.add(val);
}

@Override
public ByteString getValueAndFlush() {
TDigest curVal;
TDigest nextVal = create();
synchronized (this) {
curVal = distRef.getAndSet(nextVal); // reset tdigest
curVal = dist;
dist = nextVal; // reset tdigest
}
ByteBuffer byteBuffer = ByteBuffer.allocate(curVal.smallByteSize());
curVal.asSmallBytes(byteBuffer);
Expand All @@ -75,13 +75,14 @@ public ByteString getValueAndFlush() {


@Override
public long getCount() {
return distRef.get().size();
// This needs to be synchronized because the dist object is not thread-safe
public synchronized long getCount() {
return dist.size();
}

@VisibleForTesting
TDigest tDigest() {
return distRef.get();
return dist;
}

private TDigest create() {
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