type SchedReqs struct {
	Thread    Constraint
	Proc      Constraint
	Goroutine Constraint
}

// Constraint represents a various presence requirements.
type Constraint uint8

const (
	MustNotHave Constraint = iota
	MayHave
	MustHave
)

// UserGoReqs is a common requirement among events that are running
// or are close to running user code.