// required to) continue to call Next until it is exhausted.
func (o *ordering) Advance(ev *baseEvent, evt *evTable, m ThreadID, gen uint64) (bool, error) {
	if o.initialGen == 0 {
		// Set the initial gen if necessary.
		o.initialGen = gen
	}

	var curCtx, newCtx schedCtx
	curCtx.M = m
	newCtx.M = m

	var ms *mState
	if m == NoThread {
		curCtx.P = NoProc
		curCtx.G = NoGoroutine