[SENTRY-1462] UpdateForwarder handling of failed updates is boken

• Type: Bug
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Affects Version/s: 1.7.0, 2.0.0
• Component/s: Hdfs Plugin
• Assignee: Unassigned
• Reporter: Alex Kolbasov
• Created: 07/Sep/16 23:11
• Updated: 24/Jul/17 15:36

Description

The UpdateFollower class has the following logic:

  private void spawnInitialUpdater(final Updateable<K> updateable,
      final int initUpdateRetryDelay) {
    K firstFullImage = null;
    try {
      firstFullImage = imageRetreiver.retrieveFullImage(INIT_SEQ_NUM);
    } catch (Exception e) {
      LOGGER.warn("InitialUpdater encountered exception !! ", e);
      firstFullImage = null;
      Thread initUpdater = new Thread() {
        @Override
        public void run() {
           ...
           Retry logic here
        }
  ...
}

There is no synchronization with this retry thread. More over it isn't clear what is the benefit of such async recovery.

For example, later in the code, handleUpdateNotification{} accesses updateable field without checking whether it is null or not, but even if it would, we may get inconsistency due to async nature of updates.