in glog.go [469:485]
func (l *loggingT) setVState(verbosity Level, filter []modulePat, setFilter bool) {
// Turn verbosity off so V will not fire while we are in transition.
logging.verbosity.set(0)
// Ditto for filter length.
atomic.StoreInt32(&logging.filterLength, 0)
// Set the new filters and wipe the pc->Level map if the filter has changed.
if setFilter {
logging.vmodule.filter = filter
logging.vmap = make(map[uintptr]Level)
}
// Things are consistent now, so enable filtering and verbosity.
// They are enabled in order opposite to that in V.
atomic.StoreInt32(&logging.filterLength, int32(len(filter)))
logging.verbosity.set(verbosity)
}