fix: correctly detect Disruptor major version

log4j-core/src/main/java/org/apache/logging/log4j/core/async/DisruptorUtil.java

@@ -50,8 +50,19 @@ final class DisruptorUtil {
     static final boolean ASYNC_CONFIG_SYNCHRONIZE_ENQUEUE_WHEN_QUEUE_FULL = PropertiesUtil.getProperties()
             .getBooleanProperty("AsyncLoggerConfig.SynchronizeEnqueueWhenQueueFull", true);
 
-    static final int DISRUPTOR_MAJOR_VERSION =
-            LoaderUtil.isClassAvailable("com.lmax.disruptor.SequenceReportingEventHandler") ? 3 : 4;
+    static final int DISRUPTOR_MAJOR_VERSION = detectDisruptorMajorVersion();
+
+    // TODO: replace with LoaderUtil.isClassAvailable() when TCCL is removed
+    // See: https://github.com/apache/logging-log4j2/issues/3706
+    private static int detectDisruptorMajorVersion() {
+        try {
+            Class.forName(
+                    "com.lmax.disruptor.SequenceReportingEventHandler", true, DisruptorUtil.class.getClassLoader());
+            return 3;
+        } catch (final ClassNotFoundException e) {
+            return 4;
+        }
+    }
 
     private DisruptorUtil() {}
 

log4j-osgi-test/pom.xml

@@ -257,6 +257,7 @@
                 <include>org.apache.logging.log4j.osgi.tests.DisruptorTest</include>
               </includes>
               <systemPropertyVariables>
+                <log4j2.asyncLoggerExceptionHandler>org.apache.logging.log4j.osgi.tests.DisruptorTest$TestExceptionHandler</log4j2.asyncLoggerExceptionHandler>
                 <log4j2.contextSelector>org.apache.logging.log4j.core.async.BasicAsyncLoggerContextSelector</log4j2.contextSelector>
               </systemPropertyVariables>
             </configuration>
@@ -291,6 +292,7 @@
                 <include>org.apache.logging.log4j.osgi.tests.DisruptorTest</include>
               </includes>
               <systemPropertyVariables>
+                <log4j2.asyncLoggerExceptionHandler>org.apache.logging.log4j.osgi.tests.DisruptorTest$TestExceptionHandler</log4j2.asyncLoggerExceptionHandler>
                 <log4j2.contextSelector>org.apache.logging.log4j.core.async.BasicAsyncLoggerContextSelector</log4j2.contextSelector>
               </systemPropertyVariables>
             </configuration>

log4j-osgi-test/src/test/java/org/apache/logging/log4j/osgi/tests/DisruptorTest.java

@@ -17,19 +17,26 @@
 package org.apache.logging.log4j.osgi.tests;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertTrue;
 import static org.ops4j.pax.exam.CoreOptions.junitBundles;
 import static org.ops4j.pax.exam.CoreOptions.linkBundle;
 import static org.ops4j.pax.exam.CoreOptions.options;
 
+import com.lmax.disruptor.ExceptionHandler;
+import java.io.IOException;
+import java.net.URL;
+import java.util.concurrent.atomic.AtomicReference;
 import org.apache.logging.log4j.Level;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 import org.apache.logging.log4j.core.LogEvent;
 import org.apache.logging.log4j.core.LoggerContext;
 import org.apache.logging.log4j.core.async.AsyncLoggerContext;
+import org.apache.logging.log4j.core.async.RingBufferLogEvent;
 import org.junit.Test;
 import org.junit.runner.RunWith;
+import org.junitpioneer.jupiter.Issue;
 import org.ops4j.pax.exam.Option;
 import org.ops4j.pax.exam.junit.PaxExam;
 import org.ops4j.pax.exam.spi.reactors.ExamReactorStrategy;
@@ -39,6 +46,8 @@
 @ExamReactorStrategy(PerClass.class)
 public class DisruptorTest {
 
+    private static final int MESSAGE_COUNT = 128;
+
     @org.ops4j.pax.exam.Configuration
     public Option[] config() {
         return options(
@@ -59,26 +68,87 @@ public Option[] config() {
     }
 
     @Test
-    public void testDisruptorLog() {
-        // Logger context
-        LoggerContext context = getLoggerContext();
-        assertTrue("LoggerContext is an instance of AsyncLoggerContext", context instanceof AsyncLoggerContext);
-        final CustomConfiguration custom = (CustomConfiguration) context.getConfiguration();
-        // Logging
-        final Logger logger = LogManager.getLogger(getClass());
-        logger.info("Hello OSGI from Log4j2!");
-
-        context.stop();
-        assertEquals(1, custom.getEvents().size());
-        final LogEvent event = custom.getEvents().get(0);
-        assertEquals("Hello OSGI from Log4j2!", event.getMessage().getFormattedMessage());
-        assertEquals(Level.INFO, event.getLevel());
-        custom.clearEvents();
+    @Issue("https://github.com/apache/logging-log4j2/issues/3706")
+    public void testDisruptorLog() throws IOException {
+        ClassLoader threadContextClassLoader = Thread.currentThread().getContextClassLoader();
+        ClassLoader classLoader = createClassLoader();
+        try {
+            // Set the context classloader to an empty classloader, so attempts to use the TCCL will not find any
+            // classes.
+            Thread.currentThread().setContextClassLoader(classLoader);
+            // Logger context
+            LoggerContext context = getLoggerContext();
+            assertTrue("LoggerContext is an instance of AsyncLoggerContext", context instanceof AsyncLoggerContext);
+            final CustomConfiguration custom = (CustomConfiguration) context.getConfiguration();
+            // Logging
+            final Logger logger = LogManager.getLogger(getClass());
+            for (int i = 0; i < MESSAGE_COUNT; i++) {
+                logger.info("Hello OSGI from Log4j2! {}", i);
+            }
+
+            context.stop();
+            assertEquals(MESSAGE_COUNT, custom.getEvents().size());
+            for (int i = 0; i < MESSAGE_COUNT; i++) {
+                final LogEvent event = custom.getEvents().get(i);
+                assertEquals(
+                        "Message nr " + i,
+                        "Hello OSGI from Log4j2! " + i,
+                        event.getMessage().getFormattedMessage());
+                assertEquals(Level.INFO, event.getLevel());
+            }
+            custom.clearEvents();
+            assertNull("Asynchronous exception", TestExceptionHandler.exception.get());
+        } finally {
+            Thread.currentThread().setContextClassLoader(threadContextClassLoader);
+        }
+    }
+
+    private static ClassLoader createClassLoader() {
+        // We want a classloader capable only of loading TestExceptionHandler.
+        // This is needed to detect exceptions thrown by the asynchronous thread.
+        return new ClassLoader() {
+            @Override
+            public Class<?> loadClass(String name) throws ClassNotFoundException {
+                if (name.equals(TestExceptionHandler.class.getName())) {
+                    return TestExceptionHandler.class;
+                }
+                throw new ClassNotFoundException(name);
+            }
+
+            @Override
+            public URL getResource(String name) {
+                return null; // No resources available.
+            }
+        };
     }
 
     private static LoggerContext getLoggerContext() {
         final LoggerContext ctx = (LoggerContext) LogManager.getContext(false);
         assertEquals("AsyncDefault", ctx.getName());
         return ctx;
     }
+
+    public static class TestExceptionHandler implements ExceptionHandler<RingBufferLogEvent> {
+
+        private static final AtomicReference<Throwable> exception = new AtomicReference<>();
+
+        @Override
+        public void handleEventException(Throwable ex, long sequence, RingBufferLogEvent event) {
+            setException(ex);
+        }
+
+        @Override
+        public void handleOnStartException(Throwable ex) {
+            setException(ex);
+        }
+
+        @Override
+        public void handleOnShutdownException(Throwable ex) {
+            setException(ex);
+        }
+
+        private static void setException(Throwable ex) {
+            exception.compareAndSet(null, ex);
+        }
+    }
 }

src/changelog/.2.x.x/3706_disruptor-tccl.xml

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<entry xmlns="https://logging.apache.org/xml/ns"
+       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xsi:schemaLocation="
+           https://logging.apache.org/xml/ns
+           https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
+       type="fixed">
+  <issue id="3706" link="https://github.com/apache/logging-log4j2/issues/3706"/>
+  <description format="asciidoc">
+    Fix detection of the Disruptor major version in some environments.
+  </description>
+</entry>