code: public boolean releaseLock(TransactionImpl tx, Object obj)
      {
          LockEntry writer = getWriter(obj);
          if (writer != null && writer.isOwnedBy(tx))
          {
              removeWriter(writer);
              return true;
          }
          if (hasReadLock(tx, obj))
          {
              removeReader(tx, obj);
              return true;
          }
          return false;
      }
docs: release a lock on Object obj for Transaction tx.
  @param tx the transaction releasing the lock
  @param obj the Object to be unlocked
  @return true if successful, else false