HHH-8680 Relax synchronized block in TableGenerator#generate

hibernate-core/src/main/java/org/hibernate/id/enhanced/NoopOptimizer.java

@@ -30,9 +30,14 @@ import org.hibernate.id.IntegralDataTypeHolder;
 /**
  * An optimizer that performs no optimization.  The database is hit for
  * every request.
+ *
+ * @deprecated This is the fallback Optimizer chosen when we fail to instantiate one
+ * of the proper implementations. Using this implementation is probably a performance
+ * problem.
  */
-public class NoopOptimizer extends AbstractOptimizer {
+@Deprecated
-	private IntegralDataTypeHolder lastSourceValue;
+public final class NoopOptimizer extends AbstractOptimizer {
+	private volatile IntegralDataTypeHolder lastSourceValue;
 
 	/**
 	 * Constructs a NoopOptimizer
@@ -45,7 +50,7 @@ public class NoopOptimizer extends AbstractOptimizer {
 	}
 
 	@Override
-	public Serializable generate(AccessCallback callback) {
+	public synchronized Serializable generate(AccessCallback callback) {
 		// IMPL NOTE : it is incredibly important that the method-local variable be used here to
 		//		avoid concurrency issues.
 		IntegralDataTypeHolder value = null;

hibernate-core/src/main/java/org/hibernate/id/enhanced/Optimizer.java

@@ -44,6 +44,9 @@ public interface Optimizer {
 	/**
 	 * Generate an identifier value accounting for this specific optimization.
 	 *
+	 * All known implementors are synchronized. Consider carefully if a new
+	 * implementation could drop this requirement.
+	 *
 	 * @param callback Callback to access the underlying value source.
 	 * @return The generated identifier value.
 	 */

hibernate-core/src/main/java/org/hibernate/id/enhanced/TableGenerator.java

@@ -525,7 +525,7 @@ public class TableGenerator implements PersistentIdentifierGenerator, Configurab
 	}
 
 	@Override
-	public synchronized Serializable generate(final SessionImplementor session, Object obj) {
+	public Serializable generate(final SessionImplementor session, final Object obj) {
 		final SqlStatementLogger statementLogger = session.getFactory().getServiceRegistry()
 				.getService( JdbcServices.class )
 				.getSqlStatementLogger();