From 3e17be98324a2aed8d18aab573c11a846e40c106 Mon Sep 17 00:00:00 2001
From: Sanne Grinovero <sanne@hibernate.org>
Date: Sun, 11 Aug 2019 21:50:15 +0100
Subject: [PATCH] HHH-13562 List of TransactionObserver for
 JdbcResourceLocalTransactionCoordinatorImpl should be lazily initialized

---
 ...esourceLocalTransactionCoordinatorImpl.java | 18 ++++++++++++++----
 .../SessionWithSharedConnectionTest.java       |  4 +++-
 2 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/hibernate-core/src/main/java/org/hibernate/resource/transaction/backend/jdbc/internal/JdbcResourceLocalTransactionCoordinatorImpl.java b/hibernate-core/src/main/java/org/hibernate/resource/transaction/backend/jdbc/internal/JdbcResourceLocalTransactionCoordinatorImpl.java
index 1bbde93579..a637c01c19 100644
--- a/hibernate-core/src/main/java/org/hibernate/resource/transaction/backend/jdbc/internal/JdbcResourceLocalTransactionCoordinatorImpl.java
+++ b/hibernate-core/src/main/java/org/hibernate/resource/transaction/backend/jdbc/internal/JdbcResourceLocalTransactionCoordinatorImpl.java
@@ -7,6 +7,7 @@
 package org.hibernate.resource.transaction.backend.jdbc.internal;
 
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.List;
 import javax.persistence.RollbackException;
 import javax.transaction.Status;
@@ -50,7 +51,7 @@ public class JdbcResourceLocalTransactionCoordinatorImpl implements TransactionC
 
 	private int timeOut = -1;
 
-	private final transient List<TransactionObserver> observers;
+	private transient List<TransactionObserver> observers = null;
 
 	/**
 	 * Construct a ResourceLocalTransactionCoordinatorImpl instance.  package-protected to ensure access goes through
@@ -62,7 +63,6 @@ public class JdbcResourceLocalTransactionCoordinatorImpl implements TransactionC
 			TransactionCoordinatorBuilder transactionCoordinatorBuilder,
 			TransactionCoordinatorOwner owner,
 			JdbcResourceTransactionAccess jdbcResourceTransactionAccess) {
-		this.observers = new ArrayList<>();
 		this.transactionCoordinatorBuilder = transactionCoordinatorBuilder;
 		this.jdbcResourceTransactionAccess = jdbcResourceTransactionAccess;
 		this.transactionCoordinatorOwner = owner;
@@ -81,7 +81,12 @@ public class JdbcResourceLocalTransactionCoordinatorImpl implements TransactionC
 	 * @return TransactionObserver
 	 */
 	private Iterable<TransactionObserver> observers() {
-		return new ArrayList<>( observers );
+		if ( observers == null || observers.isEmpty() ) {
+			return Collections.emptyList();
+		}
+		else {
+			return new ArrayList<>( observers );
+		}
 	}
 
 	@Override
@@ -203,12 +208,17 @@ public class JdbcResourceLocalTransactionCoordinatorImpl implements TransactionC
 
 	@Override
 	public void addObserver(TransactionObserver observer) {
+		if ( observers == null ) {
+			observers = new ArrayList<>( 6 );
+		}
 		observers.add( observer );
 	}
 
 	@Override
 	public void removeObserver(TransactionObserver observer) {
-		observers.remove( observer );
+		if ( observers != null ) {
+			observers.remove( observer );
+		}
 	}
 
 	/**
diff --git a/hibernate-core/src/test/java/org/hibernate/sharedSession/SessionWithSharedConnectionTest.java b/hibernate-core/src/test/java/org/hibernate/sharedSession/SessionWithSharedConnectionTest.java
index 703174f6f8..ebec824f32 100644
--- a/hibernate-core/src/test/java/org/hibernate/sharedSession/SessionWithSharedConnectionTest.java
+++ b/hibernate-core/src/test/java/org/hibernate/sharedSession/SessionWithSharedConnectionTest.java
@@ -270,7 +270,9 @@ public class SessionWithSharedConnectionTest extends BaseCoreFunctionalTestCase
 		}
 		assertNotNull("Observers field was not found", field);
 
-		assertEquals(0, ((Collection) field.get(((SessionImplementor) session).getTransactionCoordinator())).size());
+		//Some of these collections could be lazily initialize: check for null before invoking size()
+		final Collection collection = (Collection) field.get( ( (SessionImplementor) session ).getTransactionCoordinator() );
+		assertTrue(collection == null || collection.size() == 0 );
 
 		//open secondary sessions with managed options and immediately close
 		Session secondarySession;