c++ - 关于zeromq v 3.2.3的yqueue.hpp中push()的一个谜题

Question

最近，我正在尝试阅读 zeromq 3.2.3 版本的源代码。现在我对 yqueue.hpp 中的 push() 函数感到困惑？

源代码是:

//  Adds an element to the back end of the queue.
    inline void push ()
    {
        back_chunk = end_chunk;
        back_pos = end_pos;

        if (++end_pos != N)
            return;

        chunk_t *sc = spare_chunk.xchg (NULL);
        if (sc) {
            end_chunk->next = sc;
            sc->prev = end_chunk;
        } else {
            end_chunk->next = (chunk_t*) malloc (sizeof (chunk_t));
            alloc_assert (end_chunk->next);
            end_chunk->next->prev = end_chunk;
        }
        end_chunk = end_chunk->next;
        end_pos = 0;
    }

不断移动“end_pos”的位置，如果不等于N，“返回”。我对此感到困惑。有人可以为我解释一下吗？谢谢

Answer 1

变量 N 是此处定义的类模板的一部分:

template <typename T, int N> class yqueue_t

如果您查看类(class)顶部的评论，您就会明白 N 的确切含义:

//  yqueue is an efficient queue implementation. The main goal is
//  to minimise number of allocations/deallocations needed. Thus yqueue
//  allocates/deallocates elements in batches of N.
//
//  yqueue allows one thread to use push/back function and another one 
//  to use pop/front functions. However, user must ensure that there's no
//  pop on the empty queue and that both threads don't access the same
//  element in unsynchronised manner.
//
//  T is the type of the object in the queue.
//  N is granularity of the queue (how many pushes have to be done till
//  actual memory allocation is required).