func lockextra(nilokay bool) *m {
	const locked = 1

	incr := false
	for {
		old := extraM.Load()
		if old == locked {
			osyield_no_g()
			continue
		}
		if old == 0 && !nilokay {
			if !incr {
				// Add 1 to the number of threads
				// waiting for an M.
				// This is cleared by newextram.
				extraMWaiters.Add(1)
				incr = true
			}
			usleep_no_g(1)
			continue
		}

	}
}

func TestMakeFuncInterface(t *testing.T) {
	fn := func(i int) int { return i }
	incr := func(in []Value) []Value {
		return []Value{ValueOf(int(in[0].Int() + 1))}
	}
	fv := MakeFunc(TypeOf(fn), incr)
	ValueOf(&fn).Elem().Set(fv)
	if r := fn(2); r != 3 {
		t.Errorf("Call returned %d, want 3", r)
	}