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Remove use of AtomicReferenceArray in RadixTreeCache #10600

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Remove use of AtomicReferenceArray in RadixTreeCache #10600

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30 changes: 6 additions & 24 deletions internal-api/src/main/java/datadog/trace/api/cache/RadixTreeCache.java
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Original file line number Diff line number Diff line change
@@ -1,8 +1,6 @@
package datadog.trace.api.cache;

import datadog.trace.bootstrap.instrumentation.api.UTF8BytesString;
import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
import java.util.concurrent.atomic.AtomicReferenceArray;
import java.util.function.IntFunction;

/** Sparse cache of values associated with a small integer */
Expand All @@ -25,11 +23,11 @@ public final class RadixTreeCache<T> {
private final int shift;
private final int mask;

private final AtomicReferenceArray<Object[]> tree;
private final Object[][] tree;
private final IntFunction<T> mapper;

public RadixTreeCache(int level1, int level2, IntFunction<T> mapper, int... commonValues) {
this.tree = new AtomicReferenceArray<>(level1);
this.tree = new Object[level1][];
this.mapper = mapper;
this.level1 = level1;
this.level2 = level2;
Expand All @@ -50,31 +48,15 @@ public T get(int primitive) {
}

@SuppressWarnings("unchecked")
@SuppressFBWarnings("DCN") // only interested in catching NullPointerException (see note below)
private T computeIfAbsent(int prefix, int primitive) {
Object[] page = tree.get(prefix);
if (null == page) {
try {
page = new Object[level2];
if (!tree.compareAndSet(prefix, null, page)) {
page = tree.get(prefix);
}
} catch (NullPointerException e) {
// Intermittent NPE observed in JDK code on Semeru 11.0.29: java.lang.NullPointerException:
// at j.l.i.ArrayVarHandle$...Operations$OpObject.computeOffset(ArrayVarHandle.java:142)
// at j.l.i.ArrayVarHandle$...Operations$OpObject.compareAndSet(ArrayVarHandle.java:201)
// at j.u.c.atomic.AtomicReferenceArray.compareAndSet(AtomicReferenceArray.java:152)
// at datadog.trace.api.cache.RadixTreeCache.computeIfAbsent(RadixTreeCache.java:59)
// Location indicates JDK's VarHandle used to access the backing array has returned null
// To mitigate this rare JDK bug we still map the primitive but skip caching the result
return mapper.apply(primitive);
}
Object[] page = tree[prefix];
if (page == null) {
page = tree[prefix] = new Object[level2]; // tolerate race to cache sub-array
}
// it's safe to race here
int suffix = primitive & mask;
Object cached = page[suffix];
if (cached == null) {
cached = page[suffix] = mapper.apply(primitive);
cached = page[suffix] = mapper.apply(primitive); // tolerate race to cache value
}
return (T) cached;
}
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