@Override
  protected void snapshotRegions(List<Pair<RegionInfo, ServerName>> regions) throws IOException {
    Set<String> regionServers = new HashSet<>(regions.size());
    for (Pair<RegionInfo, ServerName> region : regions) {
      if (region != null && region.getFirst() != null && region.getSecond() != null) {
        RegionInfo hri = region.getFirst();
        if (hri.isOffline() && (hri.isSplit() || hri.isSplitParent())) continue;
        regionServers.add(region.getSecond().toString());
      }
    }

    // start the snapshot on the RS
    Procedure proc = coordinator.startProcedure(this.monitor, this.snapshot.getName(),
      this.snapshot.toByteArray(), Lists.newArrayList(regionServers));
    if (proc == null) {
      String msg =
        "Failed to submit distributed procedure for snapshot '" + snapshot.getName() + "'";
      LOG.error(msg);
      throw new HBaseSnapshotException(msg);
    }

    try {
      // wait for the snapshot to complete. A timer thread is kicked off that should cancel this
      // if it takes too long.
      proc.waitForCompleted();
      LOG.info("Done waiting - online snapshot for " + this.snapshot.getName());

      // Take the offline regions as disabled
      for (Pair<RegionInfo, ServerName> region : regions) {
        RegionInfo regionInfo = region.getFirst();
        if (
          regionInfo.isOffline() && (regionInfo.isSplit() || regionInfo.isSplitParent())
            && RegionReplicaUtil.isDefaultReplica(regionInfo)
        ) {
          LOG.info("Take disabled snapshot of offline region=" + regionInfo);
          snapshotDisabledRegion(regionInfo);
        }
      }
      // handle the mob files if any.
      boolean mobEnabled = MobUtils.hasMobColumns(htd);
      if (mobEnabled) {
        LOG.info("Taking snapshot for mob files in table " + htd.getTableName());
        // snapshot the mob files as a offline region.
        RegionInfo mobRegionInfo = MobUtils.getMobRegionInfo(htd.getTableName());
        snapshotMobRegion(mobRegionInfo);
      }
    } catch (InterruptedException e) {
      ForeignException ee =
        new ForeignException("Interrupted while waiting for snapshot to finish", e);
      monitor.receive(ee);
      Thread.currentThread().interrupt();
    } catch (ForeignException e) {
      monitor.receive(e);
    }
  }
This method kicks off a snapshot procedure. Other than that it hangs around for various phases
to complete.
hbase-server/src/main/java/org/apache/hadoop/hbase/master/snapshot/EnabledTableSnapshotHandler.java