docs: private void cleanCache() {
          Iterator<Entry<String, Object>> iterator = cacheManager.getCache().entrySet().iterator();
          int cacheChanged = 0;
          int i = 0;
          while (iterator.hasNext()) {
              cacheChanged += removeExpiredItem(iterator);
              i++;
              if (i == 2000) {
                  i = 0;
                  try {
                      Thread.sleep(0);// 触发操作系统立刻重新进行一次CPU竞争, 让其它线程获得CPU控制权的权力。
                  } catch (InterruptedException e) {
                      logger.error(e.getMessage(), e);
                  }
              }
          }
          if (cacheChanged > 0) {
              cacheChange(cacheChanged);
          }
      }