private void addToPendingAssignment(final HashMap<RegionInfo, RegionStateNode> regions,
    final Collection<RegionInfo> pendingRegions) {
    assignQueueLock.lock();
    try {
      for (RegionInfo hri : pendingRegions) {
        pendingAssignQueue.add(regions.get(hri));
      }
    } finally {
      assignQueueLock.unlock();
    }
  }
Add the assign operation to the assignment queue. The pending assignment operation will be
processed, and each region will be assigned by a server using the balancer.
hbase-server/src/main/java/org/apache/hadoop/hbase/master/assignment/AssignmentManager.java