core/src/main/java/com/orientechnologies/orient/core/storage/cache/local/OWOWCache.java
private void fireBackgroundDataFlushExceptionEvent(final Throwable e) {
    for (final WeakReference<OBackgroundExceptionListener> ref : backgroundExceptionListeners) {
      final OBackgroundExceptionListener listener = ref.get();
      if (listener != null) {
        listener.onException(e);
      }
    }
  }
private void fireBackgroundDataFlushExceptionEvent(final Throwable e) {
    for (final WeakReference<OBackgroundExceptionListener> ref : backgroundExceptionListeners) {
      final OBackgroundExceptionListener listener = ref.get();
      if (listener != null) {
        listener.onException(e);
      }
    }
  }
Fires event about exception is thrown in data flush thread