public synchronized boolean isTakingAnySnapshot() {
    return this.takingSnapshotLock.getReadHoldCount() > 0 || this.snapshotHandlers.size() > 0
      || this.snapshotToProcIdMap.size() > 0;
  }
The snapshot operation processing as following: <br>
1. Create a Snapshot Handler, and do some initialization; <br>
2. Put the handler into snapshotHandlers <br>
So when we consider if any snapshot is taking, we should consider both the takingSnapshotLock
and snapshotHandlers;
@return true to indicate that there're some running snapshots.
hbase-server/src/main/java/org/apache/hadoop/hbase/master/snapshot/SnapshotManager.java