trace.go
func (t *trace) Finish() {
	if t.err {
		incrError(t)
	}
	incr(t)
	duration(t)
	if t.err {
		incrError(t)
	}
	t.trace.Finish()
}
func (t *trace) Finish() {
	if t.err {
		incrError(t)
	}
	incr(t)
	duration(t)
	if t.err {
		incrError(t)
	}
	t.trace.Finish()
}
// Finish declares that this trace is complete.
// The trace should not be used after calling this method.