Hey
I've found a leak possible in OracleJDK/OpenJDK which is impossible to find using MAT
I think the problem is that HPROF dump doesn't contain the information needed to find the leak, and therefor the problem is in HeapDumper.c code, and not in MAT
The leak is that Class::newInstance() is leaking the caller, since it is doing caller checks, and cache the caller forever (no WeakReference, which is the fix in my opinion)
For example, executing the following code:
package poc;
import java.io.ByteArrayOutputStream;
import java.lang.ref.WeakReference;
import java.net.URL;
import java.net.URLClassLoader;
public class Leak {
public static void main(String[] args) throws Exception {
WeakReference<ClassLoader> loader = getLoader();
while (loader.get() != null) {
System.gc();
Thread.sleep(1000);
}
}
public static void test() {
try {
// BUG(JDK-8206208): Leaks the caller in newInstanceCallerCache in Java9+
ByteArrayOutputStream.class.newInstance();
} catch (Exception e) {
e.printStackTrace();
}
}
private static WeakReference<ClassLoader> getLoader() throws Exception {
URL url = "" style="background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">Leak.class.getProtectionDomain().getCodeSource().getLocation();
URLClassLoader loader = new URLClassLoader(new URL[] {url}, null);
Class<?> workerClass = Class.forName("poc.Leak", true, loader);
workerClass.getDeclaredMethod("test").invoke(null);
loader.close();
return new WeakReference<>(loader);
}
}
will leak forever under current Java9/10/11
So this leak is reported and hopefully fixed before Java11 release, but the problem is that its invisible under MAT.
Because when I try to query using OQL and find those "faulty" classes, I don't see any members of newInstanceCallerCache under it
But when I'm with a debugger I do see them.
I'm sending this email to make sure the problem is indeed in JDK core code,
What do you think?
