docs: @Override
      public void generateSkinCssFile(DynamicSkinInstanceData data) {
          final String cssInstanceKey = getCssInstanceKey(data);
          synchronized (cssInstanceKey) {
              if (instanceKeysForExistingCss.contains(cssInstanceKey)) {
                  /*
                   * Two or more threads needing the same CSS file managed to invoke
                   * this method.  An earlier thread has already generated the file
                   * we need.  Concurrency features of the CopyOnWriteArraySet
                   * (compiledCssFilepaths) guarantee that we will enter this if {}
                   * block (and exit) for a filePathname that's been successfully
                   * generated by another thread.
                   */
                  return;
              }
              try {
                  if (!cssSkinFailureCache.getKeysWithExpiryCheck().contains(cssInstanceKey)) {
                      createLessIncludeFile(data);
                      processLessFile(data);
                      if (!supportsRetainmentOfNonCurrentCss()) {
                          instanceKeysForExistingCss.clear();
                      }
                      instanceKeysForExistingCss.add(cssInstanceKey);
                  } else {
                      // Though this should never happen except when developers are modifying the LESS
                      // files and make a mistake,
                      // if we previously tried to create the CSS file and failed for some reason,
                      // don't try to compile it
                      // again for a bit since the process is so processor intensive. It would
                      // virtually hang the uPortal
                      // service trying to compile a bad LESS file repeatedly on different threads.
                      logger.warn(
                              "Skipping generation of CSS file {} due to previous LESS compilation failures",
                              cssInstanceKey);
                  }
              } catch (Exception e) {
                  cssSkinFailureCache.put(new Element(cssInstanceKey, cssInstanceKey));
                  throw new RuntimeException(
                          "Error compiling the LESS file to create:  " + cssInstanceKey, e);
              }
          }
      }