func (t *target) nextTryLater() {
	t.tryAfter = time.Now().Add(t.tryInterval/2 + time.Duration(rand.Int63n(int64(t.tryInterval))))
	t.tryInterval = t.tryInterval * 3 / 2
	if t.tryInterval > maxInterval {
		t.tryInterval = maxInterval
	}
}
func (t *target) nextTryLater() {
	t.tryAfter = time.Now().Add(t.tryInterval/2 + time.Duration(rand.Int63n(int64(t.tryInterval))))
	t.tryInterval = t.tryInterval * 3 / 2
	if t.tryInterval > maxInterval {
		t.tryInterval = maxInterval
	}
}
// The delay at the nth retry is a random value in the range
// [i-i/2,i+i/2], where i = InitialInterval * 1.5^(n-1).