public void scheduleTombstone(LocalRegion r, RegionEntry entry, VersionTag destroyedVersion) {
    if (entry.getVersionStamp() == null) {
      logger.warn(
          "Detected an attempt to schedule a tombstone for an entry that is not versioned in region "
              + r.getFullPath(),
          new Exception("stack trace"));
      return;
    }
    Tombstone ts = new Tombstone(entry, r, destroyedVersion);
    getSweeper(r).scheduleTombstone(ts);
  }
Tombstones are markers placed in destroyed entries in order to keep the entry around for a
while so that it's available for concurrent modification detection.

@param r the region holding the entry
@param entry the region entry that holds the tombstone
@param destroyedVersion the version that was destroyed
geode-core/src/main/java/org/apache/geode/internal/cache/TombstoneService.java