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HHH-18377 UUID Version 6 & UUID Version 7 implementations
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‎hibernate-core/src/main/java/org/hibernate/id/uuid/UuidV6ValueGenerator.java‎

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/*
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* Hibernate, Relational Persistence for Idiomatic Java
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*
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* License: GNU Lesser General Public License (LGPL), version 2.1 or later.
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* See the lgpl.txt file in the root directory or <http://www.gnu.org/licenses/lgpl-2.1.html>.
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*/
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package org.hibernate.id.uuid;
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import java.security.SecureRandom;
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import java.time.Duration;
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import java.time.Instant;
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import java.time.LocalDate;
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import java.time.ZoneId;
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import java.util.UUID;
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import java.util.concurrent.atomic.AtomicLong;
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import java.util.concurrent.locks.Lock;
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import java.util.concurrent.locks.ReentrantLock;
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import org.hibernate.engine.spi.SharedSessionContractImplementor;
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import org.hibernate.id.UUIDGenerationStrategy;
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/**
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* Implements a <a href="https://datatracker.ietf.org/doc/html/rfc9562#name-uuid-version-6">UUID Version 6</a> generation strategy as defined by the {@link UUID#randomUUID()} method.
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*
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* @author Cedomir Igaly
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*/
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public class UuidV6ValueGenerator implements UUIDGenerationStrategy, UuidValueGenerator {
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private static final Instant EPOCH_1582;
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static {
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EPOCH_1582 = LocalDate.of( 1582, 10, 15 )
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.atStartOfDay( ZoneId.of( "UTC" ) )
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.toInstant();
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}
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private static class Holder {
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static final SecureRandom numberGenerator = new SecureRandom();
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}
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public static final UuidV6ValueGenerator INSTANCE = new UuidV6ValueGenerator();
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private final Lock lock = new ReentrantLock( true );
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private long currentTimestamp;
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private final AtomicLong clockSequence = new AtomicLong( 0 );
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public UuidV6ValueGenerator() {
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this( getCurrentTimestamp(), 0 );
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}
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public UuidV6ValueGenerator(final long currentTimestamp, final long clockSequence) {
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this.currentTimestamp = currentTimestamp;
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this.clockSequence.set( clockSequence );
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}
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/**
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* A variant 6
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*/
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@Override
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public int getGeneratedVersion() {
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// UUIDv6 is a field-compatible version of UUIDv1, reordered for improved DB locality
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return 6;
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}
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/**
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* Delegates to {@link UUID#randomUUID()}
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*/
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@Override
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public UUID generateUUID(SharedSessionContractImplementor session) {
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return generateUuid( session );
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}
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/**
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* <ul>
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* <li>32 bits - the most significant 32 bits of the 60-bit starting timestamp.</li>
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* <li>16 bits - the middle 16 bits of the 60-bit starting timestamp.</li>
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* <li>4 bits - version field, set to 0b0110 (6).</li>
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* <li>12 bits - the least significant 12 bits from the 60-bit starting timestamp.</li>
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* <li>2 bits - variant field, set to 0b10.</li>
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* <li>14 bits - the clock sequence, resets to 0 when timestamp changes. </li>
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* <li>48 bits - pseudorandom data to provide uniqueness.</li>
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* </ul>
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*
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* @param session session
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*
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* @return UUID version 6
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* @see UuidValueGenerator#generateUuid(SharedSessionContractImplementor)
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*/
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@Override
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public UUID generateUuid(SharedSessionContractImplementor session) {
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final long currentTimestamp = getCurrentTimestamp();
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return new UUID(
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currentTimestamp << 4 & 0xFFFF_FFFF_FFFF_0000L
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| 0x6000L
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| currentTimestamp & 0x0FFFL,
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0x8000_0000_0000_0000L
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| ( getSequence( currentTimestamp ) & 0x3FFFL ) << 48
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| Holder.numberGenerator.nextLong() & 0xFFFF_FFFF_FFFFL
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);
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}
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private long getSequence(final long currentTimestamp) {
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lock.lock();
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try {
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if ( this.currentTimestamp > currentTimestamp ) {
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this.currentTimestamp = currentTimestamp;
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clockSequence.set( 0 );
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}
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}
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finally {
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lock.unlock();
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}
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return clockSequence.getAndIncrement();
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}
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private static long getCurrentTimestamp() {
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final Duration duration = Duration.between( EPOCH_1582, Instant.now() );
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return duration.toSeconds() * 10_000_000 + duration.toNanosPart() / 100;
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}
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}

‎hibernate-core/src/main/java/org/hibernate/id/uuid/UuidV7ValueGenerator.java‎

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/*
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* Hibernate, Relational Persistence for Idiomatic Java
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*
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* License: GNU Lesser General Public License (LGPL), version 2.1 or later.
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* See the lgpl.txt file in the root directory or <http://www.gnu.org/licenses/lgpl-2.1.html>.
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*/
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package org.hibernate.id.uuid;
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import java.security.SecureRandom;
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import java.time.Duration;
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import java.time.Instant;
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import java.util.UUID;
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import java.util.concurrent.atomic.AtomicLong;
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import java.util.concurrent.locks.Lock;
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import java.util.concurrent.locks.ReentrantLock;
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import org.hibernate.engine.spi.SharedSessionContractImplementor;
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import org.hibernate.id.UUIDGenerationStrategy;
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import static java.time.Instant.EPOCH;
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import static java.time.temporal.ChronoUnit.MILLIS;
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/**
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* Implements a <a href="https://datatracker.ietf.org/doc/html/rfc9562#name-uuid-version-7">UUID Version 7</a> generation strategy as defined by the {@link UUID#randomUUID()} method.
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*
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* @author Cedomir Igaly
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*/
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public class UuidV7ValueGenerator implements UUIDGenerationStrategy, UuidValueGenerator {
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public static final UuidV7ValueGenerator INSTANCE = new UuidV7ValueGenerator();
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private static class Holder {
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static final SecureRandom numberGenerator = new SecureRandom();
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}
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private final Lock lock = new ReentrantLock( true );
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private Duration currentTimestamp;
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private final AtomicLong clockSequence;
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public UuidV7ValueGenerator() {
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this( getCurrentTimestamp(), 0 );
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}
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public UuidV7ValueGenerator(final Duration currentTimestamp, final long clockSequence) {
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this.currentTimestamp = currentTimestamp;
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this.clockSequence = new AtomicLong( clockSequence );
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}
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/**
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* A variant 7
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*/
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@Override
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public int getGeneratedVersion() {
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/*
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* UUIDv7 features a time-ordered value field derived from the widely implemented and well-
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* known Unix Epoch timestamp source, the number of milliseconds since midnight 1 Jan 1970 UTC,
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* leap seconds excluded.
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*/
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return 7;
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}
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/**
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* Delegates to {@link UUID#randomUUID()}
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*/
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@Override
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public UUID generateUUID(SharedSessionContractImplementor session) {
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return generateUuid( session );
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}
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/**
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* <ul>
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* <li>48 bits - 48-bit big-endian unsigned number of the Unix Epoch timestamp in milliseconds.</li>
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* <li>4 bits - version field, set to 0b0111 (7).</li>
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* <li>
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* 12 bits - sub-milliseconds part of timestamp (resolution approximately 1/4 of millisecond)
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* to guarantee additional monotonicity.
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* </li>
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* <li>2 bits - variant field, set to 0b10.</li>
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* <li>14 bits - counter to guarantee additional monotonicity, resets to 0 when timestamp changes. </li>
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* <li>48 bits - pseudorandom data to provide uniqueness.</li>
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* </ul>
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*
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* @param session session
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*
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* @return UUID version 7
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* @see UuidValueGenerator#generateUuid(SharedSessionContractImplementor)
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*/
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@Override
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public UUID generateUuid(SharedSessionContractImplementor session) {
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final Duration currentTimestamp = getCurrentTimestamp();
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final long seq = getSequence( currentTimestamp );
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final long millis = currentTimestamp.getSeconds() * 1000 + currentTimestamp.getNano() / 1_000_000;
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final long nanosPart = Math.round( ( currentTimestamp.getNano() % 1_000_000L ) * 0.004096 );
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return new UUID(
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millis << 16 & 0xFFFF_FFFF_FFFF_0000L | 0x7000L | nanosPart & 0xFFFL,
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0x8000_0000_0000_0000L | ( seq & 0x3FFFL ) << 48 | Holder.numberGenerator.nextLong() & 0xFFFF_FFFF_FFFFL
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);
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}
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private long getSequence(final Duration currentTimestamp) {
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lock.lock();
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try {
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if ( !this.currentTimestamp.equals( currentTimestamp ) ) {
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this.currentTimestamp = currentTimestamp;
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clockSequence.set( 0 );
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}
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}
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finally {
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lock.unlock();
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}
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return clockSequence.getAndIncrement();
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}
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private static Duration getCurrentTimestamp() {
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return Duration.between( EPOCH, Instant.now() ).truncatedTo( MILLIS );
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}
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}

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