public Map<ServerName, List<RegionInfo>>
    getSnapShotOfAssignment(final Collection<RegionInfo> regions) {
    return regionStates.getSnapShotOfAssignment(regions);
  }
Usually run by the Master in reaction to server crash during normal processing. Can also be
invoked via external RPC to effect repair; in the latter case, the 'force' flag is set so we
push through the SCP though context may indicate already-running-SCP (An old SCP may have
exited abnormally, or damaged cluster may still have references in hbase:meta to 'Unknown
Servers' -- servers that are not online or in dead servers list, etc.)
@param force Set if the request came in externally over RPC (via hbck2). Force means run the
             SCP even if it seems as though there might be an outstanding SCP running.
@return pid of scheduled SCP or {@link Procedure#NO_PROC_ID} if none scheduled.
hbase-server/src/main/java/org/apache/hadoop/hbase/master/assignment/AssignmentManager.java