void setModificationStamp(int fileId, long stamp) {
      int offset = fieldOffset(fileId, FLAGS_FIELD_NO);
      intFieldsArray.updateAndGet(offset, oldInt -> (oldInt & VirtualFileSystemEntry.ALL_FLAGS_MASK) |
                                                    ((int)stamp & ~VirtualFileSystemEntry.ALL_FLAGS_MASK));
    }
void setModificationStamp(int fileId, long stamp)