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Make SLOT_MASK a true constant expression #92

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Merged
mcculls merged 1 commit into from
Jun 19, 2026
Merged

Make SLOT_MASK a true constant expression #92

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10 changes: 5 additions & 5 deletions utils/src/main/java/datadog/instrument/utils/ClassLoaderIndex.java
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Original file line number Diff line number Diff line change
Expand Up @@ -21,8 +21,9 @@ public final class ClassLoaderIndex {

// fixed-size hashtable of known class-loader keys (table size must be power of 2)
// this is tuned to support ~700 concurrent class-loaders with minimal collisions
private static final ClassLoaderKey[] KEYS = new ClassLoaderKey[1024];
private static final int SLOT_MASK = KEYS.length - 1;
private static final int INDEX_SIZE = 1024; // must be power of 2
private static final ClassLoaderKey[] KEYS = new ClassLoaderKey[INDEX_SIZE];
private static final int SLOT_MASK = INDEX_SIZE - 1;

private static final int MAX_HASH_ATTEMPTS = 10;

Expand Down Expand Up @@ -53,14 +54,13 @@ public static int getClassLoaderKeyId(ClassLoader cl) {
static ClassLoaderKey getClassLoaderKey(ClassLoader cl) {
final int hash = System.identityHashCode(cl);
final ClassLoaderKey[] keys = KEYS;
final int slotMask = SLOT_MASK;

int evictedSlot = -1;

// search by repeated hashing; stop when we find an empty slot,
// a matching slot, or we exhaust all attempts and re-use a slot
for (int i = 1, h = hash; true; i++, h = rehash(h)) {
int slot = slotMask & h;
int slot = SLOT_MASK & h;
ClassLoaderKey existing = keys[slot];
if (existing != null) {
// slot already used
Expand All @@ -82,7 +82,7 @@ static ClassLoaderKey getClassLoaderKey(ClassLoader cl) {
} else if (existingCL == null) {
// last hashed slot is itself evicted, re-use it
} else {
slot = slotMask & hash; // re-use first hashed slot
slot = SLOT_MASK & hash; // re-use first hashed slot
}
}
return (keys[slot] = new ClassLoaderKey(cl, hash));
Expand Down
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