private void assignQueueSignal() {
    assignQueueLock.lock();
    try {
      assignQueueFullCond.signal();
    } 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