From 6ff15ff3fb78af44d052462af6929e489880332b Mon Sep 17 00:00:00 2001
From: Sanne Grinovero <sanne@hibernate.org>
Date: Mon, 17 Jul 2023 19:16:43 +0100
Subject: [PATCH] HHH-16911 Integration test for empty SessionFactory to not
 leak the CL

---
 .../HibernateClassLoaderLeaksTest.java        | 71 +++++++++++++++++++
 .../HibernateLoadingTestAction.java           | 58 +++++++++++++++
 2 files changed, 129 insertions(+)
 create mode 100644 hibernate-core/src/test/java/org/hibernate/orm/test/bootstrap/registry/classloading/HibernateClassLoaderLeaksTest.java
 create mode 100644 hibernate-core/src/test/java/org/hibernate/orm/test/bootstrap/registry/classloading/HibernateLoadingTestAction.java

diff --git a/hibernate-core/src/test/java/org/hibernate/orm/test/bootstrap/registry/classloading/HibernateClassLoaderLeaksTest.java b/hibernate-core/src/test/java/org/hibernate/orm/test/bootstrap/registry/classloading/HibernateClassLoaderLeaksTest.java
new file mode 100644
index 0000000000..fe13eab671
--- /dev/null
+++ b/hibernate-core/src/test/java/org/hibernate/orm/test/bootstrap/registry/classloading/HibernateClassLoaderLeaksTest.java
@@ -0,0 +1,71 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later
+ * See the lgpl.txt file in the root directory or http://www.gnu.org/licenses/lgpl-2.1.html
+ */
+package org.hibernate.orm.test.bootstrap.registry.classloading;
+
+import java.sql.Driver;
+import java.sql.DriverManager;
+import java.sql.SQLException;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+import org.hibernate.dialect.H2Dialect;
+
+import org.hibernate.testing.orm.junit.RequiresDialect;
+import org.junit.Assert;
+import org.junit.jupiter.api.AfterAll;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Verifies that Hibernate ORM won't leak the classloader.
+ * We only test in H2 to save some time; we also need to avoid
+ * leaks by JDBC drivers, and since these aren't our responsibility
+ * it's best to focus on a single DB.
+ */
+@RequiresDialect(H2Dialect.class)
+public class HibernateClassLoaderLeaksTest {
+
+	private static Set<Driver> knownDrivers;
+
+	@BeforeAll
+	public static void prepareForClassLoaderLeakTest() {
+		final String property = System.getProperty( "log4j2.disableJmx" );
+		Assert.assertEquals( "To be able to test against leaks, the system property 'log4j2.disableJmx' must be set to true",
+							 "true", property );
+
+		//Attempt to workaround the mess of DriverManager leaks by clearing it before the test;
+		//it will most certainly re-register all drivers again within the test running context,
+		//but that will imply that the isolated classloader will also have permission to de-register them.
+		knownDrivers = DriverManager.drivers().collect( Collectors.toUnmodifiableSet() );
+		knownDrivers.forEach( HibernateClassLoaderLeaksTest::cleanup );
+	}
+
+	@AfterAll
+	public static void restoreRegisteredDrivers() throws SQLException {
+		if ( knownDrivers != null ) {
+			for ( Driver driver : knownDrivers ) {
+				DriverManager.registerDriver( driver );
+			}
+		}
+	}
+
+	@Test
+	public void hibernateDoesNotLeakClassloader() {
+		ClassLoaderLeakDetector.assertNotLeakingAction( HibernateLoadingTestAction.class.getName() );
+	}
+
+	private static void cleanup(Driver driver) {
+		System.out.println( "Attempting de-registration of driver: " + driver );
+		try {
+			DriverManager.deregisterDriver( driver );
+		}
+		catch ( SQLException e ) {
+			throw new RuntimeException( e );
+		}
+	}
+
+}
diff --git a/hibernate-core/src/test/java/org/hibernate/orm/test/bootstrap/registry/classloading/HibernateLoadingTestAction.java b/hibernate-core/src/test/java/org/hibernate/orm/test/bootstrap/registry/classloading/HibernateLoadingTestAction.java
new file mode 100644
index 0000000000..44729b558e
--- /dev/null
+++ b/hibernate-core/src/test/java/org/hibernate/orm/test/bootstrap/registry/classloading/HibernateLoadingTestAction.java
@@ -0,0 +1,58 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later
+ * See the lgpl.txt file in the root directory or http://www.gnu.org/licenses/lgpl-2.1.html
+ */
+package org.hibernate.orm.test.bootstrap.registry.classloading;
+
+import java.sql.Driver;
+import java.sql.DriverManager;
+import java.sql.SQLException;
+import java.util.HashMap;
+import java.util.Map;
+
+import org.hibernate.jpa.boot.spi.Bootstrap;
+import org.hibernate.orm.test.jpa.BaseEntityManagerFunctionalTestCase;
+
+import jakarta.persistence.EntityManagerFactory;
+
+/**
+ * A Runnable which initializes an EntityManagerFactory;
+ * this is meant to test against classloader leaks, so needs
+ * to be packaged as a Runnable rather than using our usual
+ * testing facilities.
+ */
+public class HibernateLoadingTestAction extends NotLeakingTestAction implements Runnable {
+
+	@Override
+	public void run() {
+		super.run(); //for basic sanity self-check
+		final Map config = new HashMap();
+		EntityManagerFactory emf = Bootstrap.getEntityManagerFactoryBuilder(
+				new BaseEntityManagerFunctionalTestCase.TestingPersistenceUnitDescriptorImpl( getClass().getSimpleName() ),
+				config
+		).build();
+		try {
+			emf.close();
+		}
+		finally {
+			cleanupJDBCDrivers();
+		}
+	}
+
+	private void cleanupJDBCDrivers() {
+		DriverManager.drivers().forEach( this::deregister );
+	}
+
+	private void deregister(final Driver driver) {
+		System.out.println( "Unregistering driver: " +driver);
+		try {
+			DriverManager.deregisterDriver( driver );
+		}
+		catch ( SQLException e ) {
+			throw new RuntimeException( e );
+		}
+	}
+
+}