glibc中本地时间的资源争用，为什么？

Question

我发现在多线程程序中使用localtime函数时存在资源争用。

但是函数中只有一个锁资源？可能是这个bug的根本原因是什么？

对此问题的任何建议或想法都表示赞赏。

代码如下所示，来自glibc，

struct tm *
localtime (t)
     const time_t *t;
{
  return __tz_convert (t, 1, &_tmbuf);  //tmbuf temp variable
}

struct tm *
__tz_convert (const time_t *timer, int use_localtime, struct tm *tp)
{
  long int leap_correction;
  int leap_extra_secs;

  if (timer == NULL)
    {
      __set_errno (EINVAL);
      return NULL;
    }

  __libc_lock_lock (tzset_lock);

  /* Update internal database according to current TZ setting.
     POSIX.1 8.3.7.2 says that localtime_r is not required to set tzname.
     This is a good idea since this allows at least a bit more parallelism.  */
  tzset_internal (tp == &_tmbuf && use_localtime, 1);

  if (__use_tzfile)
    __tzfile_compute (*timer, use_localtime, &leap_correction,
              &leap_extra_secs, tp);
  else
    {
      if (! __offtime (timer, 0, tp))
    tp = NULL;
      else
    __tz_compute (*timer, tp, use_localtime);
      leap_correction = 0L;
      leap_extra_secs = 0;
    }

  if (tp)
    {
      if (! use_localtime)
    {
      tp->tm_isdst = 0;
      tp->tm_zone = "GMT";
      tp->tm_gmtoff = 0L;
    }

      if (__offtime (timer, tp->tm_gmtoff - leap_correction, tp))
        tp->tm_sec += leap_extra_secs;
      else
    tp = NULL;
    }

  __libc_lock_unlock (tzset_lock);

  return tp;
}