Method update

sql/set_var.cc:174–193

}

bool sys_var::update(THD *thd, set_var *var)
{
  enum_var_type type= var->type;
  if (type == OPT_GLOBAL || scope() == GLOBAL)
  {
    /*
      Yes, both locks need to be taken before an update, just as
      both are taken to get a value. If we'll take only 'guard' here,
      then value_ptr() for strings won't be safe in SHOW VARIABLES anymore,
      to make it safe we'll need value_ptr_unlock().
    */
    AutoWLock lock1(&PLock_global_system_variables);
    AutoWLock lock2(guard);
    return global_update(thd, var) ||
      (on_update && on_update(this, thd, OPT_GLOBAL));
  }
  else
    return session_update(thd, var) ||
      (on_update && on_update(this, thd, OPT_SESSION));
}

uchar *sys_var::session_value_ptr(THD *thd, LEX_STRING *base)
{