code: public static boolean callbacksRegistered() {
          if (TraceComponent.isAnyTracingEnabled() && tc.isEntryEnabled())
              Tr.entry(tc, "callbacksRegistered");
  
          if (_syncLevel < 0) {
              if (TraceComponent.isAnyTracingEnabled() && tc.isEntryEnabled())
                  Tr.exit(tc, "callbacksRegistered", Boolean.FALSE);
              return false;
          }
  
          final int maxLevels = _syncLevels.size();
          for (int level = 0; level < maxLevels; level++) {
              final ArrayList syncs = _syncLevels.get(_syncLevel);
  
              if (syncs != null && !syncs.isEmpty()) {
                  if (TraceComponent.isAnyTracingEnabled() && tc.isEntryEnabled())
                      Tr.exit(tc, "callbacksRegistered", Boolean.TRUE);
                  return true;
              }
          }
  
          if (TraceComponent.isAnyTracingEnabled() && tc.isEntryEnabled())
              Tr.exit(tc, "callbacksRegistered", Boolean.FALSE);
          return false;
      }
docs: which can still be called otherwise false.