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Make Uuids have better random distribution #494

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Merged
merged 2 commits into from
Apr 4, 2025
Merged

Make Uuids have better random distribution #494

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fcec90c
Make Uuids use ThreadLocalRandom
dkropachev Apr 4, 2025
7bc5cfc
Fix `Uuids.random` to get better distribution
dkropachev Apr 4, 2025
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13 changes: 10 additions & 3 deletions core/src/main/java/com/datastax/oss/driver/api/core/uuid/Uuids.java
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Original file line number Diff line number Diff line change
Expand Up @@ -39,6 +39,7 @@
import java.util.Set;
import java.util.SplittableRandom;
import java.util.UUID;
import java.util.concurrent.ThreadLocalRandom;
import java.util.concurrent.atomic.AtomicLong;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
Expand Down Expand Up @@ -232,7 +233,7 @@ private static String getProcessPiece() {
}
}
if (pid == null) {
pid = new Random().nextInt();
pid = ThreadLocalRandom.current().nextInt();
LOG.warn("Could not determine PID, falling back to a random integer: {}", pid);
}
ClassLoader loader = Uuids.class.getClassLoader();
Expand Down Expand Up @@ -281,7 +282,7 @@ private static long makeClockSeqAndNode() {
*/
@NonNull
public static UUID random() {
return random(new Random());
return random(ThreadLocalRandom.current());
}

/**
Expand All @@ -300,7 +301,13 @@ public static UUID random() {
@NonNull
public static UUID random(@NonNull Random random) {
byte[] data = new byte[16];
random.nextBytes(data);
for (int i = 0; i < 16; i += 4) {
int rnd = random.nextInt();
data[i] = (byte) (rnd >>> 24);
data[i + 1] = (byte) (rnd >>> 16);
data[i + 2] = (byte) (rnd >>> 8);
data[i + 3] = (byte) rnd;
}
return buildUuid(data, 4);
}

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