code: public static ArchTaskExecutor getInstance() {
          if (sInstance != null) {
              return sInstance;
          }
          synchronized (ArchTaskExecutor.class) {
              if (sInstance == null) {
                  sInstance = new ArchTaskExecutor();
              }
          }
          return sInstance;
      }
docs: Returns an instance of the task executor.
  
  @return The singleton ArchTaskExecutor.