MySQL中为什么慢日志中的select 的lock time也有值？

lock_utime=  (thd->utime_after_lock - thd->start_utime);


void set_time_after_lock()
  {
    utime_after_lock= my_micro_time();
    MYSQL_SET_STATEMENT_LOCK_TIME(m_statement_psi, (utime_after_lock - start_utime));
  }

void thd_storage_lock_wait(THD *thd, long long value)
{
  thd->utime_after_lock+= value;
}

/**
  Return time in microseconds.

  @remark This function is to be used to measure performance in
  micro seconds.

  @retval Number of microseconds since the Epoch, 1970-01-01 00:00:00 +0000 (UTC)
*/

ulonglong my_micro_time()



MYSQL_LOCK *mysql_lock_tables(THD *thd, TABLE **tables, size_t count, uint flags)
{
  int rc;
  MYSQL_LOCK *sql_lock;
  ulong timeout= (flags & MYSQL_LOCK_IGNORE_TIMEOUT) ?
    LONG_TIMEOUT : thd->variables.lock_wait_timeout;

  DBUG_ENTER("mysql_lock_tables");

  if (lock_tables_check(thd, tables, count, flags))
    DBUG_RETURN(NULL);

  if (! (sql_lock= get_lock_data(thd, tables, count, GET_LOCK_STORE_LOCKS)))
    DBUG_RETURN(NULL);

  THD_STAGE_INFO(thd, stage_system_lock);
  DBUG_PRINT("info", ("thd->proc_info %s", thd->proc_info));
  if (sql_lock->table_count && lock_external(thd, sql_lock->table,
                                             sql_lock->table_count))
  {
    /* Clear the lock type of all lock data to avoid reusage. */
    reset_lock_data_and_free(&sql_lock);
    goto end;
  }

  /* Copy the lock data array. thr_multi_lock() reorders its contents. */
  memcpy(sql_lock->locks + sql_lock->lock_count, sql_lock->locks,
         sql_lock->lock_count * sizeof(*sql_lock->locks));
  /* Lock on the copied half of the lock data array. */
  rc= thr_lock_errno_to_mysql[(int) thr_multi_lock(sql_lock->locks +
                                                   sql_lock->lock_count,
                                                   sql_lock->lock_count,
                                                   &thd->lock_info, timeout)];

  DBUG_EXECUTE_IF("mysql_lock_tables_kill_query",
                  thd->killed= THD::KILL_QUERY;);

  if (rc)
  {
    if (sql_lock->table_count)
      (void) unlock_external(thd, sql_lock->table, sql_lock->table_count);
    reset_lock_data_and_free(&sql_lock);
    if (! thd->killed)
      my_error(rc, MYF(0));
  }

end:
  if (!(flags & MYSQL_OPEN_IGNORE_KILLED) && thd->killed)
  {
    thd->send_kill_message();
    if (sql_lock)
    {
      mysql_unlock_tables(thd, sql_lock);
      sql_lock= 0;
    }
  }

  if (thd->variables.session_track_transaction_info > TX_TRACK_NONE)
    track_table_access(thd, tables, count);

  thd->set_time_after_lock();
  DBUG_RETURN(sql_lock);
}