private void cleanupSentinels() {
    cleanupSentinels(this.snapshotHandlers);
    cleanupCompletedRestoreInMap();
    cleanupCompletedSnapshotInMap();
  }
Removes "abandoned" snapshot/restore requests. As part of the HBaseAdmin snapshot/restore API
the operation status is checked until completed, and the in-progress maps are cleaned up when
the status of a completed task is requested. To avoid having sentinels staying around for long
time if something client side is failed, each operation tries to clean up the in-progress maps
sentinels finished from a long time.
hbase-server/src/main/java/org/apache/hadoop/hbase/master/snapshot/SnapshotManager.java