JniCallback checks the input object instead of the NewGlobalRef result #14974

File: java/rocksjni/jnicallback.cc

Function: JniCallback::JniCallback

The base callback wrapper creates a global reference for the Java callback object, but the null check tests the input local reference instead of the NewGlobalRef result:

assert(jcallback_obj != nullptr);
m_jcallback_obj = env->NewGlobalRef(jcallback_obj);
if (jcallback_obj == nullptr) {
  // exception thrown: OutOfMemoryError
  return;
}

NewGlobalRef can return null, typically with an OutOfMemoryError pending.
In normal calls jcallback_obj is non-null, so this guard never catches a
failed global-reference allocation. The object is left with
m_jcallback_obj == nullptr while derived callback constructors continue to run
and native factory functions can still return a native handle.

This base class is shared by multiple RocksJava callback bridges, including
comparators, loggers, event listeners, table filters, WAL filters, trace
writers, transaction notifiers, and write-batch handlers.

Suggested fix

At minimum, check the returned global reference:

 assert(jcallback_obj != nullptr);
 m_jcallback_obj = env->NewGlobalRef(jcallback_obj);
-if (jcallback_obj == nullptr) {
+if (m_jcallback_obj == nullptr) {
   // exception thrown: OutOfMemoryError
   return;
 }

Because a C++ base constructor cannot stop the derived constructor body from
running, the callback constructors or factory functions should also propagate
construction failure before using or returning the callback object.