I am trying to design thread-safe data structure that I cna use as a buffer in my application. Can you please give me comments about this code and what can be improved:

#include <deque>
#include <thread>
#include <mutex>
#include <condition_variable>

template <typename T>
class Buffer
{
public:
    void add(T num)
    {
        while (true)
        {
            std::unique_lock<std::mutex> locker(mu);
            buffer.push_back(num);
            locker.unlock();
            cond.notify_all();
            return;
        }
    }
    T remove()
    {
        while (true)
        {
            std::unique_lock<std::mutex> locker(mu);
            cond.wait(locker, [this](){return buffer.size() > 0;});
            T back = buffer.back();
            buffer.pop_back();
            locker.unlock();
            cond.notify_all();
            return back;
        }
    }
    int size()
    {
        std::unique_lock<std::mutex> locker(mu);
        int s = buffer.size();
        locker.unlock();
        return s;
    }
private:
    std::mutex mu;
    std::condition_variable cond;

    std::deque<T> buffer;
};