code: public static InvocationStat getInvocationStat(InvocationStatDimension statDimension) {
          InvocationStat invocationStat = ALL_STATS.get(statDimension);
          if (invocationStat == null) {
              invocationStat = new ServiceExceptionInvocationStat(statDimension);
              InvocationStat old = ALL_STATS.putIfAbsent(statDimension, invocationStat);
              if (old != null) {
                  invocationStat = old;
              }
              for (InvocationStatListener listener : LISTENERS) {
                  listener.onAddInvocationStat(invocationStat);
              }
          }
          return invocationStat;
      }
docs: 根据Invocation获取InvocationStat
  该Invocation对应的InvocationStat会在被第一次获取（也就是刚被创建的时候）时被放入到Regulation中进行能力的持续调控。
  
  @param statDimension InvocationStatDimension
  @return InvocationStat