Fix ClassCastException in LMAX Disruptor 3 initialization (#2768)

Co-authored-by: Volkan Yazıcı <[email protected]>
Co-authored-by: Piotr P. Karwasz <[email protected]>

Author: 3 people

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

@@ -36,7 +36,6 @@
 import org.apache.logging.log4j.core.util.Log4jThreadFactory;
 import org.apache.logging.log4j.core.util.Throwables;
 import org.apache.logging.log4j.message.Message;
-import org.apache.logging.log4j.util.LoaderUtil;
 
 /**
  * Helper class for async loggers: AsyncLoggerDisruptor handles the mechanics of working with the LMAX Disruptor, and
@@ -54,7 +53,11 @@ class AsyncLoggerDisruptor extends AbstractLifeCycle {
     private static EventHandler<RingBufferLogEvent> createEventHandler() {
         if (DisruptorUtil.DISRUPTOR_MAJOR_VERSION == 3) {
             try {
-                return LoaderUtil.newInstanceOf("org.apache.logging.log4j.core.async.RingBufferLogEventHandler");
+                return (EventHandler<RingBufferLogEvent>)
+                        // Avoid using `LoaderUtil`, which might choose an incorrect class loader – see #2768.
+                        Class.forName("org.apache.logging.log4j.core.async.RingBufferLogEventHandler")
+                                .getConstructor()
+                                .newInstance();
             } catch (final ReflectiveOperationException | LinkageError e) {
                 LOGGER.warn("Failed to create event handler for LMAX Disruptor 3.x, trying version 4.x.", e);
             }

src/changelog/.2.x.x/fix_disruptor3_cce.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<entry xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xmlns="https://logging.apache.org/xml/ns"
+       xsi:schemaLocation="https://logging.apache.org/xml/ns https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
+       type="fixed">
+  <issue id="2768" link="https://github.com/apache/logging-log4j2/pull/2768"/>
+  <description format="asciidoc">Fix `ClassCastException` in LMAX Disruptor 3 initialization</description>
+</entry>