docs: synchronized public void prepareTransferMastership(int partitionId, int hostId) {
          // remove mastership for partition id, so when failure happen during the mastership transfer
          // this node can be elected as new master again.
          m_masterOfPartitions.remove(partitionId);
  
          if (exportLog.isDebugEnabled()) {
              exportLog.debug("Export stream masters on " + partitionId + " are going to migrate away");
          }
          ExportGeneration generation = m_generation.get();
          if (generation == null) {
              return;
          }
          generation.prepareTransferMastership(partitionId, hostId);
      }