C++单例模式代码实现与分析

1 代码

2 代码剖析

2.1 构造函数私有化

2.2 只能执行一次的代码

2.3 静态成员变量

2.4 智能指针

1 代码

下面的代码是https://github.com/Cambricon/CNStream 中的，

/************************************************************************** Copyright (C) [2022] by Cambricon, Inc. All rights reserved**  Licensed under the Apache License, Version 2.0 (the "License");*  you may not use this file except in compliance with the License.*  You may obtain a Copy of the License at**     http://www.apache.org/licenses/LICENSE-2.0** 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.*************************************************************************/#include "buf_surface.h"#include <algorithm>
#include <cstring>  // for memset
#include <memory>
#include <mutex>
#include <queue>
#include <string>
#include <thread>#include "glog/logging.h"#include "buf_surface_impl.h"
#include "nvis/infer_server.h"
#include "common/utils.hpp"namespace infer_server {class BufSurfaceService {public:static BufSurfaceService &Instance() {static std::once_flag s_flag;std::call_once(s_flag, [&] { instance_.reset(new BufSurfaceService); });return *instance_;}~BufSurfaceService() = default;int BufPoolCreate(void **pool, BufSurfaceCreateParams *params, uint32_t block_num) {if (pool && params && block_num) {MemPool *mempool = new MemPool();if (!mempool) {LOG(ERROR) << "[InferServer] [BufSurfaceService] BufPoolCreate(): new memory pool failed";return -1;}*pool = reinterpret_cast<void *>(mempool);if (mempool->Create(params, block_num) == 0) {return 0;}delete mempool;LOG(ERROR) << "[InferServer] [BufSurfaceService] BufPoolCreate(): Create memory pool failed";return -1;}return -1;}int BufPoolDestroy(void *pool) {if (pool) {MemPool *mempool = reinterpret_cast<MemPool *>(pool);if (mempool) {int ret = mempool->Destroy();if (ret != 0) {VLOG(3) << "[InferServer] [BufSurfaceService] BufPoolDestroy(): Destroy memory pool failed, ret = " << ret;return ret;}delete mempool;}return 0;}LOG(ERROR) << "[InferServer] [BufSurfaceService] BufPoolDestroy(): Pool is not existed";return -1;}int CreateFromPool(BufSurface **surf, void *pool) {if (surf && pool) {BufSurface surface;MemPool *mempool = reinterpret_cast<MemPool *>(pool);if (mempool->Alloc(&surface) < 0) {VLOG(4) << "[InferServer] [BufSurfaceService] CreateFromPool(): Create BufSurface from pool failed";return -1;}*surf = AllocSurface();if (!(*surf)) {mempool->Free(&surface);LOG(WARNING) << "[InferServer] [BufSurfaceService] CreateFromPool(): Alloc BufSurface failed";return -1;}*(*surf) = surface;return 0;}LOG(ERROR) << "[InferServer] [BufSurfaceService] CreateFromPool(): surf or pool is nullptr";return -1;}int Create(BufSurface **surf, BufSurfaceCreateParams *params) {if (surf && params) {if (CheckParams(params) < 0) {LOG(ERROR) << "[InferServer] [BufSurfaceService] Create(): Parameters are invalid";return -1;}BufSurface surface;if (CreateSurface(params, &surface) < 0) {LOG(ERROR) << "[InferServer] [BufSurfaceService] Create(): Create BufSurface failed";return -1;}*surf = AllocSurface();if (!(*surf)) {DestroySurface(&surface);LOG(ERROR) << "[InferServer] [BufSurfaceService] Create(): Alloc BufSurface failed";return -1;}*(*surf) = surface;return 0;}LOG(ERROR) << "[InferServer] [BufSurfaceService] Create(): surf or params is nullptr";return -1;}int Destroy(BufSurface *surf) {if (!surf) {LOG(ERROR) << "[InferServer] [BufSurfaceService] Destroy(): surf is nullptr";return -1;}if (surf->opaque) {MemPool *mempool = reinterpret_cast<MemPool *>(surf->opaque);int ret = mempool->Free(surf);FreeSurface(surf);if (ret) {LOG(ERROR) << "[InferServer] [BufSurfaceService] Destroy(): Free BufSurface back to memory pool failed";}return ret;}// created by BufSurfaceCreate()int ret = DestroySurface(surf);FreeSurface(surf);if (ret) {LOG(ERROR) << "[InferServer] [BufSurfaceService] Destroy(): Destroy BufSurface failed";}return ret;}int Memset(BufSurface *surf, int index, uint8_t value) {if (!surf) {LOG(ERROR) << "[InferServer] [BufSurfaceService] Memset(): BufSurface is nullptr";return -1;}if (index < -1 || index >= static_cast<int>(surf->batch_size)) {LOG(ERROR) << "[InferServer] [BufSurfaceService] Memset(): batch index is invalid";return -1;}for (uint32_t i = 0; i < surf->batch_size; i++) {if (index >= 0 && i != static_cast<uint32_t>(index)) continue;CUDA_SAFECALL(cudaMemset(surf->surface_list[i].data_ptr, value, surf->surface_list[i].data_size), "[InferServer] [BufSurfaceService] Memset(): failed", -1);}return 0;}int Copy(BufSurface *src_surf, BufSurface *dst_surf) {if (!src_surf || !dst_surf) {LOG(ERROR) << "[InferServer] [BufSurfaceService] Copy(): src or dst BufSurface is nullptr";return -1;}// check parameters, must be the same sizeif (src_surf->batch_size != dst_surf->batch_size) {LOG(ERROR) << "[InferServer] [BufSurfaceService] Copy(): src and dst BufSurface has different batch size";return -1;}dst_surf->pts = src_surf->pts;bool src_host = (src_surf->mem_type == BUF_MEMORY_HOST);bool dst_host = (dst_surf->mem_type == BUF_MEMORY_HOST);if ((!dst_host && !src_host) && (src_surf->device_id != dst_surf->device_id)) {LOG(ERROR) << "[InferServer] [BufSurfaceService] Copy(): src and dst BufSurface is on different device";return -1;}for (size_t i = 0; i < src_surf->batch_size; ++i) {CUDA_SAFECALL(MemcpyHD(dst_surf->surface_list[i].data_ptr, dst_surf->mem_type, src_surf->surface_list[i].data_ptr, src_surf->mem_type, dst_surf->surface_list[i].data_size),"[InferServer] [BufSurfaceService] Copy(): failed", -1);}return 0;}private:BufSurfaceService(const BufSurfaceService &) = delete;BufSurfaceService(BufSurfaceService &&) = delete;BufSurfaceService &operator=(const BufSurfaceService &) = delete;BufSurfaceService &operator=(BufSurfaceService &&) = delete;BufSurfaceService() = default;private:std::mutex mutex_;bool initialized_ = false;std::queue<BufSurface *> surfpool_;BufSurface *start_ = nullptr, *end_ = nullptr;static const int k_surfs_num_ = 256 * 1024;private:void CreateSurfsPool() {if (initialized_) return;start_ = reinterpret_cast<BufSurface *>(malloc(sizeof(BufSurface) * k_surfs_num_));if (!start_) {LOG(ERROR) << "[InferServer] [BufSurfaceService] CreateSurfsPool(): Create BufSurface pointers failed";return;}end_ = &start_[k_surfs_num_ - 1];for (int i = 0; i < k_surfs_num_; i++) surfpool_.push(&start_[i]);initialized_ = true;}BufSurface *AllocSurface() {std::unique_lock<std::mutex> lk(mutex_);if (!initialized_) CreateSurfsPool();if (!surfpool_.empty()) {BufSurface *res = surfpool_.front();surfpool_.pop();return res;}return reinterpret_cast<BufSurface *>(malloc(sizeof(BufSurface)));}void FreeSurface(BufSurface *surf) {std::unique_lock<std::mutex> lk(mutex_);if (surf >= start_ && surf <= end_) {surfpool_.push(surf);return;}::free(surf);}private:static std::unique_ptr<BufSurfaceService> instance_;};std::unique_ptr<BufSurfaceService> BufSurfaceService::instance_;}  // namespace extern "C" {int BufPoolCreate(void **pool, BufSurfaceCreateParams *params, uint32_t block_num) {return infer_server::BufSurfaceService::Instance().BufPoolCreate(pool, params, block_num);}int BufPoolDestroy(void *pool) { return infer_server::BufSurfaceService::Instance().BufPoolDestroy(pool); }int BufSurfaceCreateFromPool(BufSurface **surf, void *pool) {return infer_server::BufSurfaceService::Instance().CreateFromPool(surf, pool);}int BufSurfaceCreate(BufSurface **surf, BufSurfaceCreateParams *params) {return infer_server::BufSurfaceService::Instance().Create(surf, params);}int BufSurfaceDestroy(BufSurface *surf) { return infer_server::BufSurfaceService::Instance().Destroy(surf); }int BufSurfaceMemSet(BufSurface *surf, int index, uint8_t value) {return infer_server::BufSurfaceService::Instance().Memset(surf, index, value);}int BufSurfaceCopy(BufSurface *src_surf, BufSurface *dst_surf) {return infer_server::BufSurfaceService::Instance().Copy(src_surf, dst_surf);}};  // extern "C"

2 代码剖析

简单看一下代码，看一下他怎么实现的单例模式

2.1 构造函数私有化

    private:BufSurfaceService(const BufSurfaceService &) = delete;BufSurfaceService(BufSurfaceService &&) = delete;BufSurfaceService &operator=(const BufSurfaceService &) = delete;BufSurfaceService &operator=(BufSurfaceService &&) = delete;BufSurfaceService() = default;

把所有的构造函数都声明成私有的，这样让用户只能通过下面的函数去实例化

        static BufSurfaceService &Instance() {static std::once_flag s_flag;std::call_once(s_flag, [&] { instance_.reset(new BufSurfaceService); });return *instance_;}

2.2 只能执行一次的代码

        static BufSurfaceService &Instance() {static std::once_flag s_flag;std::call_once(s_flag, [&] { instance_.reset(new BufSurfaceService); });return *instance_;}

这地方用了call_once保证后面的lambda表达式只会被执行一次。

2.3 静态成员变量

    private:static std::unique_ptr<BufSurfaceService> instance_;};std::unique_ptr<BufSurfaceService> BufSurfaceService::instance_;}  // namespace

类里面声明了一个静态成员变量，并且在类外面对他进行了定义，但是这里只是给这个智能指针本身分配了内存，并没给他赋值，在调用Instance()函数的时候再给他赋值。

2.4 智能指针

    private:static std::unique_ptr<BufSurfaceService> instance_;};std::unique_ptr<BufSurfaceService> BufSurfaceService::instance_;}  // namespace

这里的静态成员变量用的智能指针，防止内存泄漏。

参考文献：

C++_单例模式_c++单例模式-CSDN博客

C++ 设计模式——单例模式_c++ 单例模式-CSDN博客

GitHub - Cambricon/CNStream: CNStream is a streaming framework for building Cambricon machine learning pipelines http://forum.cambricon.com https://gitee.com/SolutionSDK/CNStream