Method push

src/bthread/id.cpp:38–54

    SmallQueue() : _begin(0), _size(0), _full(NULL) {}
    
    void push(const T& val) {
        if (_full != NULL && !_full->empty()) {
            _full->push_back(val);
        } else if (_size < N) {
            int tail = _begin + _size;
            if (tail >= N) {
                tail -= N;
            }
            _c[tail] = val;
            ++_size;
        } else {
            if (_full == NULL) {
                _full = new std::deque<T>;
            }
            _full->push_back(val);
        }
    }
    bool pop(T* val) {
        if (_size > 0) {
            *val = _c[_begin];