发现 zeromq 的 yqueue_t 模板类，其数据存储理念设计得非常妙。借这一理念，按照 STL 的泛型类 queue 的接口标准，我设计了一个线程安全的 单生产者/单消费者（单线程push/单线程pop） FIFO 队列，以此满足更为广泛的应用。
1. 数据存储理念的结构图
- 队列的整体结构上，使用链表的方式，将多个固定长度的 chunk 串联起来；
- 每个 chunk 则可用于存储队列所需要的元素；
- 增加一个可交换的 chunk 单元，利于内存复用；
- 队列使用时，支持 单个线程的 push（生产） 和 单个线程 pop（消费）的并发操作（内部并未加锁）。
2. 源码 （xspsc_queue.h）
/**
* The MIT License (MIT)
* Copyright (c) 2019, Gaaagaa All rights reserved.
*
* Permission is hereby granted, free of charge, to any person obtaining a copy of
* this software and associated documentation files (the "Software"), to deal in
* the Software without restriction, including without limitation the rights to
* use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
* of the Software, and to permit persons to whom the Software is furnished to do
* so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in all
* copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
* FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
* COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
* IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/
/**
* @file xspsc_queue.h
* Copyright (c) 2019, Gaaagaa All rights reserved.
*
* @author ：Gaaagaa
* @date : 2019-11-29
* @version : 1.0.0.0
* @brief : 实现双线程安全的 单生产者/单消费者 FIFO 队列。
*/
#ifndef __XSPSC_QUEUE_H__
#define __XSPSC_QUEUE_H__
#include <memory>
#include <atomic>
#include <cassert>
////////////////////////////////////////////////////////////////////////////////
// x_spsc_queue_t : single producer/single consumer FIFO queue
/**
* @class x_spsc_queue_t
* @brief 双线程安全的 单生产者/单消费者 FIFO队列。
*
* @param [in ] __object_t : 队列存储的对象类型。
* @param [in ] __chunk_size : 队列中的存储块可容纳对象的数量。
* @param [in ] __allocator_t : 对象分配器。
*/
template< typename __object_t,
size_t __chunk_size,
typename __allocator_t = std::allocator< __object_t > >
class x_spsc_queue_t : protected __allocator_t
{
static_assert(__chunk_size >= 4,
"__chunk_size size value must be greater than or equal to 4!");
// common data types
public:
typedef __object_t value_type;
using x_object_t = __object_t;
private:
/**
* @struct x_chunk_t
* @brief 存储对象节点的连续内存块结构体。
*/
typedef struct x_chunk_t
{
x_chunk_t * xnext_ptr; ///< 指向后一内存块节点
x_object_t * xot_array; ///< 当前内存块中的对象节点数组
} x_chunk_t;
#ifdef _MSC_VER
using ssize_t = std::intptr_t;
#endif // _MSC_VER
using x_chunk_ptr_t = x_chunk_t *;
using x_atomic_ptr_t = std::atomic< x_chunk_ptr_t >;
using x_atomic_size_t = std::atomic< size_t >;
using x_allocator_t = __allocator_t;
using x_chunk_alloc_t = typename std::allocator_traits<
x_allocator_t >::template
rebind_alloc< x_chunk_t >;
// constructor/destructor
public:
explicit x_spsc_queue_t(void)
: m_chk_front(nullptr)
, m_pos_front(0)
, m_chk_back(nullptr)
, m_pos_back(0)
, m_xst_size(0)
, m_chk_stored(nullptr)
{
m_chk_front = m_chk_back = alloc_chunk();
}
~x_spsc_queue_t(void)
{
while (size() > 0)
pop();
assert(m_chk_front == m_chk_back);
free_chunk(m_chk_front);
free_chunk(m_chk_stored.exchange(nullptr));
m_chk_front = nullptr;
m_pos_front = 0;
m_chk_back = nullptr;
m_pos_back = 0;
}
x_spsc_queue_t(x_spsc_queue_t && xobject) = delete;
x_spsc_queue_t & operator = (x_spsc_queue_t && xobject) = delete;
x_spsc_queue_t(const x_spsc_queue_t & xobject) = delete;
x_spsc_queue_t & operator = (const x_spsc_queue_t & xobject) = delete;
// public interfaces
public:
/**********************************************************/
/**
* @brief 当前队列中的对象数量。
*/
inline size_t size(void) const
{
return m_xst_size;
}
/**********************************************************/
/**
* @brief 判断队列是否为空。
*/
inline bool empty(void) const
{
return (0 == size());
}
/**********************************************************/
/**
* @brief 向队列后端压入一个对象。
*/
void push(const x_object_t & xobject)
{
move_back_pos();
x_allocator_t::construct(
&m_chk_back->xot_array[m_pos_back], xobject);
m_xst_size.fetch_add(1);
}
/**********************************************************/
/**
* @brief 向队列后端压入一个对象。
*/
void push(x_object_t && xobject)
{
move_back_pos();
x_allocator_t::construct(
&m_chk_back->xot_array[m_pos_back],
std::forward< x_object_t >(xobject));
m_xst_size.fetch_add(1);
}
/**********************************************************/
/**
* @brief 从队列前端弹出一个对象。
*/
void pop(void)
{
assert(!empty());
m_xst_size.fetch_sub(1);
x_allocator_t::destroy(&m_chk_front->xot_array[m_pos_front]);
move_front_pos();
}
/**********************************************************/
/**
* @brief 返回队列前端对象。
*/
inline x_object_t & front(void)
{
assert(!empty());
return m_chk_front->xot_array[m_pos_front];
}
/**********************************************************/
/**
* @brief 返回队列前端对象。
*/
inline const x_object_t & front(void) const
{
assert(!empty());
return m_chk_front->xot_array[m_pos_front];
}
/**********************************************************/
/**
* @brief 返回队列后端对象。
*/
inline x_object_t & back(void)
{
assert(!empty());
return m_chk_back->xot_array[m_pos_back];
}
/**********************************************************/
/**
* @brief 返回队列后端对象。
*/
inline const x_object_t & back(void) const
{
assert(!empty());
return m_chk_back->xot_array[m_pos_back];
}
// internal invoking
private:
/**********************************************************/
/**
* @brief 申请一个存储对象节点的内存块。
*/
x_chunk_ptr_t alloc_chunk(void)
{
x_chunk_alloc_t xchunk_allocator(*(x_allocator_t *)this);
x_chunk_ptr_t xchunk_ptr = xchunk_allocator.allocate(1);
assert(nullptr != xchunk_ptr);
if (nullptr != xchunk_ptr)
{
xchunk_ptr->xot_array = x_allocator_t::allocate(__chunk_size);
assert(nullptr != xchunk_ptr->xot_array);
if (nullptr != xchunk_ptr->xot_array)
{
xchunk_ptr->xnext_ptr = nullptr;
}
else
{
xchunk_allocator.deallocate(xchunk_ptr, 1);
xchunk_ptr = nullptr;
}
}
return xchunk_ptr;
}
/**********************************************************/
/**
* @brief 释放一个存储对象节点的内存块。
*/
void free_chunk(x_chunk_ptr_t xchunk_ptr)
{
if (nullptr != xchunk_ptr)
{
if (nullptr != xchunk_ptr->xot_array)
{
x_allocator_t::deallocate(xchunk_ptr->xot_array, __chunk_size);
}
x_chunk_alloc_t xchunk_allocator(*(x_allocator_t *)this);
xchunk_allocator.deallocate(xchunk_ptr, 1);
}
}
/**********************************************************/
/**
* @brief 将前端位置向后移（该接口仅由 pop() 接口调用）。
*/
void move_front_pos(void)
{
if (++m_pos_front == __chunk_size)
{
x_chunk_ptr_t xchunk_ptr = m_chk_front;
m_chk_front = m_chk_front->xnext_ptr;
assert(nullptr != m_chk_front);
m_pos_front = 0;
free_chunk(m_chk_stored.exchange(xchunk_ptr));
}
}
/**********************************************************/
/**
* @brief 将后端位置向后移（该接口仅由 push() 接口调用）。
*/
void move_back_pos(void)
{
if (++m_pos_back == __chunk_size)
{
x_chunk_ptr_t xchunk_ptr = m_chk_stored.exchange(nullptr);
if (nullptr != xchunk_ptr)
{
xchunk_ptr->xnext_ptr = nullptr;
m_chk_back->xnext_ptr = xchunk_ptr;
}
else
{
m_chk_back->xnext_ptr = alloc_chunk();
}
m_chk_back = m_chk_back->xnext_ptr;
m_pos_back = 0;
}
}
// data members
protected:
x_chunk_ptr_t m_chk_front; ///< 内存块链表的前端块
ssize_t m_pos_front; ///< 队列中的前端对象位置
x_chunk_ptr_t m_chk_back; ///< 内存块链表的后端块
ssize_t m_pos_back; ///< 队列中的后端对象位置
x_atomic_size_t m_xst_size; ///< 队列中的有效对象数量
x_atomic_ptr_t m_chk_stored; ///< 用于保存临时内存块（备用缓存块）
};
////////////////////////////////////////////////////////////////////////////////
#endif // __XSPSC_QUEUE_H__
3. 使用示例
#include "xspsc_queue.h"
#include <iostream>
#include <thread>
#include <chrono>
#include <list>
////////////////////////////////////////////////////////////////////////////////
int main(int argc, char * argv[])
{
using x_int_queue_t = x_spsc_queue_t< int, 8 >;
x_int_queue_t spsc;
std::cout << "sizeof(x_int_queue_t) : " << sizeof(x_int_queue_t) << std::endl;
bool b_push_finished = false;
std::thread xthread_in([&spsc, &b_push_finished](void) -> void
{
for (int i = 1; i < 10000; ++i)
{
spsc.push(i);
std::this_thread::sleep_for(std::chrono::milliseconds(1));
}
b_push_finished = true;
});
std::thread xthread_out([&spsc, &b_push_finished](void) -> void
{
while (true)
{
if (!spsc.empty())
{
std::cout << spsc.size() << " : " << spsc.front() << std::endl;
spsc.pop();
std::this_thread::sleep_for(std::chrono::milliseconds(1));
}
else if (b_push_finished)
{
break;
}
}
});
if (xthread_in.joinable())
{
xthread_in.join();
}
if (xthread_out.joinable())
{
xthread_out.join();
}
return 0;
}