code: public static long getElapsed(final String taskTitle) {
          final long currentTimeMillis = System.currentTimeMillis();
  
          if (StringUtils.isBlank(taskTitle)) {
              return -1;
          }
  
          final Stopwatch root = STOPWATCH.get();
  
          if (null == root) {
              return -1;
          }
  
          final Stopwatch stopwatch = get(root, taskTitle);
  
          if (null == stopwatch) {
              return -1;
          }
  
          if (stopwatch.isEnded()) {
              return stopwatch.getElapsedTime();
          }
  
          return currentTimeMillis - stopwatch.getStartTime();
      }
docs: Gets elapsed time from the specified parent stopwatch with the specified task title.
  
  @param taskTitle the specified task title
  @return <ul>
  <li>{@linkplain org.b3log.latke.util.Stopwatchs.Stopwatch#getElapsedTime() elapsed time} of the found task if it
  {@linkplain org.b3log.latke.util.Stopwatchs.Stopwatch#isEnded() is ended}</li>
  <li>{@linkplain System#currentTimeMillis() the current time} subtracts
  {@linkplain org.b3log.latke.util.Stopwatchs.Stopwatch#startTime the start time} of the found task if it
  {@linkplain org.b3log.latke.util.Stopwatchs.Stopwatch#isRunning() is running} </li>
  <li>{@code -1} if not found any stopwatch corresponding to the specified task title</li>
  </ul>