C++单例模式代码实现与分析
目录
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.
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* 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
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* THE SOFTWARE.
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#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 size
if (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