What version of protobuf and what language are you using?
Version: main/v3.25.8
Language: Java

What operating system (Linux, Windows, ...) and version?
Linux

What runtime / compiler are you using (e.g., python version or gcc version)
Java17

What did you do?
On a Java webServer producing a lot of protoc2 messages, upgrade from 3.25.3 to 3.25.8

What did you expect to see
No functional change

What did you see instead?
Degraded performance, pinpointed to thread contention for method call Set.add in this code

private static final Set<String> loggedPre22TypeNames
      = Collections.synchronizedSet(new HashSet<String>()); // <-- synchronizedSet causing locking

static void warnPre22Gencode(Class<?> messageClass) {
    // ...
    if (!loggedPre22TypeNames.add(messageName)) {   //   <---- thread contention here
       return;
    }
    logger.warning(vulnerabilityMessage);
}

Related changes:

• https://github.com/protocolbuffers/protobuf/pull/20084/files Add a ExtensionsImmutable check poison pill
• Weaken Failure to warning in 320eafa
• Prevent multiple logging in https://github.com/protocolbuffers/protobuf/pull/21754/files

CC @esrauchg @zhangskz