c++ shared_ptr cyclic references by capturing shared_from_this()

cyclic_references.cc

#include <atomic>
#include <functional>
#include <iostream>
#include <memory>
using namespace std;

static std::atomic_int idGenerator{0};

struct Object {
    int id;
    Object() : id(idGenerator++) { cout << "Create " << id << endl; }
    virtual ~Object() { cout << "Destroy " << id << endl; }
};

class Timer : public Object {
   public:
    void async_wait(function<void()> callback) {
        callback_ = callback;
        // Assume running callback_() in another thread
        callback_();
    }

   private:
    function<void()> callback_;
};

class Producer : public Object, public enable_shared_from_this<Producer> {
   public:
    void startTimer() {
        auto self = shared_from_this();
        timer_->async_wait([this, self] { doSomething(); });
    }

   private:
    std::shared_ptr<Timer> timer_{make_shared<Timer>()};

    void doSomething() { timer_.reset(); }
};

int main() {
    auto producer = make_shared<Producer>();
    producer->startTimer();
}
// Outputs:
// ```
// Create 0
// Create 1
// ```
// No "Destroy" logs can be seen.