Feedback loop in Sound effects chain

Could anyone advise me, how to implement a function that checks if there is a feedback loop in effects chain? SoundEffect is the base class for effects that can process sound and have a subsequent effect (next)

struct SoundEffect {
virtual ~SoundEffect() = default;
virtual void process(float* buf, size_t num) = 0;
std::shared_ptr<SoundEffect> next;
};