mosche opened a new issue, #3940:
URL: https://github.com/apache/logging-log4j2/issues/3940
## Description
We observed this in Elasticsearch when attempting to upgrade to log4j 2.25.1.
In rare cases we drop stacktraces we don't care about on async response
listeners prior to sending them over the wire. If these exceptions are also
logged, we might hit an ArrayIndexOutOfBoundsException such as shown below.
## Configuration
**Version:** 2.25.1
**Operating system:** max OS, Linux 6.11.0-1017-gcp (amd64)
**JDK:** JDK 21, 24, 25
## Logs
```
java.lang.ArrayIndexOutOfBoundsException: Index 0 out of bounds for length 0
at
org.apache.logging.log4j.core.pattern.ThrowableStackTraceRenderer.renderStackTraceElements(ThrowableStackTraceRenderer.java:169)
at
org.apache.logging.log4j.core.pattern.ThrowableStackTraceRenderer.renderThrowable(ThrowableStackTraceRenderer.java:110)
at
org.apache.logging.log4j.core.pattern.ThrowableStackTraceRenderer.renderThrowable(ThrowableStackTraceRenderer.java:87)
at
org.apache.logging.log4j.core.pattern.ThrowableStackTraceRenderer.renderThrowable(ThrowableStackTraceRenderer.java:59)
at
org.apache.logging.log4j.core.pattern.Main.lambda$main$0(Main.java:23)
at
java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:545)
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:328)
at
java.base/java.util.concurrent.ThreadPerTaskExecutor$ThreadBoundFuture.run(ThreadPerTaskExecutor.java:323)
at java.base/java.lang.VirtualThread.run(VirtualThread.java:456)
```
## Reproduction
```java
package org.apache.logging.log4j.core.pattern;
import org.apache.logging.log4j.core.impl.ThrowableFormatOptions;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.Executors;
import static java.util.concurrent.TimeUnit.SECONDS;
public class Main {
public static void main(String[] args) throws Exception {
var stackTraceRenderer =
ThrowableStackTraceRendererFactory.INSTANCE.createStackTraceRenderer(ThrowableFormatOptions.newInstance(null));
var executor = Executors.newVirtualThreadPerTaskExecutor();
for (int i = 0; i < 10; i++) {
var latch = new CountDownLatch(2);
var exception = new RuntimeException("exception");
executor.submit(() -> {
try {
stackTraceRenderer.renderThrowable(new StringBuilder(),
exception, System.lineSeparator());
latch.countDown();
} catch (Throwable e) {
e.printStackTrace();
}
});
executor.submit(() -> {
exception.setStackTrace(new StackTraceElement[0]);
latch.countDown();
});
if (latch.await(10, SECONDS) == false) {
throw new IllegalStateException("timed out waiting for tasks
to complete");
}
}
}
}
```
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