C++API搭建Tensorrt深度解析及构建模板(构建引擎/序列化与反序列化/推理)

　　好久没写一篇关于使用C++ API搭建构建Tensorrt的文章了，而本篇文章该说些什么了，也不想像很多博客介绍Tensorrt的C++API，直接来几个步骤，然后如何搭建网络，构造engine，需要前提logger等。

为此，本篇博客为了减少下载什么pth，根据什么onnx等不必要麻烦，我们将从torch构建一个简单网络， 并将其转换wts格式，然后通过C++API调用wts(权重)建立如何构建tensorrt的网络的一个模板。

至于简单使用tensorrt搭建实列，可参考“使用tensorRT C++ API搭建MLP网络详解”文章，该篇文章简单介绍了visual studio环境搭建。、

一.python搭建网络，得到权重wts

因其搭建简单网络，我将不在介绍，直接根据代码可实现网络搭建，也不必要训练，直接保存pth，构建wts即可，以下为python构建wts代码。

from torch import nn
import torch
import struct
from torchsummary import summary
import numpy as np
import cv2


class TRY(nn.Module):
    def __init__(            self    ):
        super(TRY, self).__init__()
        self.cov1=nn.Conv2d(3,64,3,1)
        self.r1=nn.ReLU(inplace=True)
        self.conv2=nn.Conv2d(64,2,3,1)


    def forward(self, x) :
        x = self.cov1(x)
        x = self.r1(x)
        x = self.conv2(x)
        return x

def transform(img):
    img = img.astype('float32')
    img -= 127.5
    img *= 0.0078125
    img = np.transpose(img, (2, 0, 1))
    img = np.expand_dims(img, axis=0)

    return img


def infer(img=None):

    net = torch.load('./try.pth')
    net = net.cuda()
    net = net.eval()
    print('model: ', net)
    # print('state dict: ', net.state_dict().keys())
    if img is None:
        tmp = torch.ones(1, 3, 224, 224).cuda()
    else:
        if isinstance(img, str):
            img = cv2.imread(img)
        tmp = transform(img)
        tmp = torch.from_numpy(tmp).cuda()

    print('input: ', tmp)
    out = net(tmp)
    out_index = torch.argmax(out).cpu().numpy()
    print('output_index:', out_index)

    summary(net, (3, 224, 224))
    # return
    f = open("try.wts", 'w')
    f.write("{}\n".format(len(net.state_dict().keys())))
    for k, v in net.state_dict().items():
        print('key: ', k)
        print('value: ', v.shape)
        vr = v.reshape(-1).cpu().numpy()
        f.write("{} {}".format(k, len(vr)))
        for vv in vr:
            f.write(" ")
            f.write(struct.pack(">f", float(vv)).hex())
        f.write("\n")


def main_createnet():
    print('cuda device count: ', torch.cuda.device_count())
    net = TRY()
    net = net.eval()
    net = net.cuda()
    print(net)
    tmp = torch.ones(2, 3, 224, 224).cuda()

    out = net(tmp)
    print('out:', out.shape)
    torch.save(net, "./try.pth")


if __name__ == '__main__':
    # main_createnet()
    infer(img='../dog.png')

以上代码可获得wts文件，基于此文件，我们将继续搭建tensorrt网络模板。

二.构建tensorrt网络模板

本次使用tensorrt版本为8.2左右。

搭建tensorrt网络模板前，我先推荐大神git上的code，建议读者拜读，可点击code查阅。

我将通过网络图重点介绍某些功能，具体说明已在代码中给出注释。

 ①构建logger信息，简单构建可用以下代码，来源于官网，不必纠结。

class Logger : public ILogger
{
    void log(Severity severity, const char* msg) noexcept override
    {
        // suppress info-level messages
        if (severity <= Severity::kWARNING)
            std::cout << msg << std::endl;
    }
} gLogger;

②createEngine实际内部调用torch构建网络转换为wts加载，搭建网络，并创造了engine，此时想用engine依然可以进行推理，后续将不需要转序列化/反序列化再次构建引擎engine了，但每次推理需构建引擎会很耗时间，教程将不会推荐，我也强烈建议

engine序列化方法。然我将说明无需序列化的推理，便于加深理解。具体细节如下图。

 为防止读者误解，我将贴出修改后的主函数，其所有方法函数将在下面代码里。

int main() {

    bool serialize = false;
    std::string engine_path = "./model.engine";

    if (serialize) {
        //将模型序列化
        IHostMemory* modelStream{ nullptr };
        modelStream = engine2serialize(); //构建引擎与保存

    }
    else {
        //加载引擎，预测图片
        std::string path = "./2.jpg";
        cv::Mat img = cv::imread(path);
        if (img.empty()) {
            std::cout << "input images error!" << std::endl;
            return 0;
        }
        cv::Mat imgInput;
        cv::resize(img, imgInput, cv::Size(INPUT_W, INPUT_H), 0, 0, cv::INTER_LINEAR);

        vector<cv::Mat> InputImage;

        InputImage.push_back(imgInput);
        InputImage.push_back(imgInput);

        float input[BatchSize * 3 * INPUT_H * INPUT_W];
        float output[BatchSize * 2 * INPUT_H * INPUT_W];

        ProcessImage(InputImage,input);
        
        //ICudaEngine* engine = inite_engine(engine_path);

        IBuilder* builder = createInferBuilder(gLogger);
        IBuilderConfig* config = builder->createBuilderConfig();
        ICudaEngine* engine = createEngine(BatchSize, builder, config, DataType::kFLOAT,  "./trynet.wts");

        IExecutionContext* context = engine->createExecutionContext();
        assert(context != nullptr);

        doInference(*context, input, output, 2);


        cout << "output_count:" << sizeof(output) / sizeof(output[0]) << endl;
        cout << "BatchSize:" << BatchSize << "INPUT_H:" << INPUT_H << "INPUT_W:" << INPUT_W << endl;
        
        //for (int i = 0; i < BatchSize * 2 * INPUT_H * INPUT_W; i++) {
        //    cout << i << *output << endl;
        //}

    }


}

③完成引擎构建，实际可以使用IExecutionContext* context = engine->createExecutionContext();进行推理，而使用CUDA推理需将输入输出转到cuda上，因此需要数据转换，此时可用模板doInference函数，也来源别人框架。

④ APIToMode/createEngine/doInference等函数，属于基本默认方法，APIToMode函数集成并将其序列化；createEngine主要搭建网络并将其转为engine，其中搭建网络很重要；doinference函数属于如何推理，并将输入输出在

host与cuda内存传输，主要稍微修改输入输出，其它可复制。

 ⑤ 我已验证，若构建引擎可使用batch为1，而推理可使用batch为n，构建好的引擎的序列化，推理宽高batch可任意修改。dt构建输入float32或half等数据。

以下为具体实习tensrrt C++API基本模板。 

#include "NvInferRuntimeCommon.h"
#include <cassert>
#include "NvInfer.h"    // TensorRT library
#include "iostream"     // Standard input/output library
#include <map>          // for weight maps
#include <fstream>      // for file-handling
#include <chrono>       // for timing the execution<br>
#include <assert.h>
#include "NvInfer.h"
#include "cuda_runtime_api.h"
#include<opencv2/core/core.hpp>
#include<opencv2/highgui/highgui.hpp>
#include <opencv2/opencv.hpp>
#include<vector>


using namespace nvinfer1;
using namespace std;



static const int INPUT_H = 32;
static const int INPUT_W = 32;
static const int INPUT_C = 3;


const char* INPUT_NAME = "data";
const char* OUTPUT_NAME = "pred";
static const int BatchSize = 2;












//载入权重函数
map<string, Weights> loadWeights(const string file) {
    /*
     * Parse the .wts file and store weights in dict format.
     * @param file path to .wts file
     * @return weight_map: dictionary containing weights and their values
     */

    std::cout << " Loading weights..." << file << std::endl;
    std::map<string, Weights> weightMap;  //定义声明

    // Open Weight file
    ifstream input(file);
    assert(input.is_open() && "[ERROR]: Unable to load weight file...");

    int32_t count;
    input >> count;//右移获得第一个数据，得到有多少个权重
    assert(count > 0 && "Invalid weight map file.");

    // Loop through number of line, actually the number of weights & biases
    while (count--) {
        // TensorRT weights
        Weights wt{ DataType::kFLOAT, nullptr, 0 };
        uint32_t size;
        // Read name and type of weights
        std::string w_name;
        input >> w_name >> std::dec >> size;
        wt.type = DataType::kFLOAT;

        uint32_t* val = reinterpret_cast<uint32_t*>(malloc(sizeof(uint32_t) * size));




        for (uint32_t x = 0, y = size; x < y; ++x) {
            // Change hex values to uint32 (for higher values)
            input >> std::hex >> val[x];  //hex为16进制
        }
        wt.values = val;
        wt.count = size;
        cout << "weigth:" << val << endl;
        // Add weight values against its name (key)
        weightMap[w_name] = wt;  //将权重结果保存此处
    }
    return weightMap;
}



//构建Logger
class Logger : public ILogger
{
    void log(Severity severity, const char* msg) noexcept override
    {
        // suppress info-level messages
        if (severity <= Severity::kWARNING)
            std::cout << msg << std::endl;
    }
} gLogger;

#define CHECK(status) \
    do\
    {\
        auto ret = (status);\
        if (ret != 0)\
        {\
            std::cerr << "Cuda failure: " << ret << std::endl;\
            abort();\
        }\
    } while (0)



















// 搭建网络 创造引擎
ICudaEngine* createEngine(unsigned int maxBatchSize, IBuilder* builder, IBuilderConfig* config, DataType dt,string wts_path= "./trynet.wts")
{

    INetworkDefinition* network = builder->createNetworkV2(0U);
    // Create input tensor of shape { 1, 32, 32 } with name INPUT_BLOB_NAME
    
    ITensor* data = network->addInput(INPUT_NAME, dt, Dims3{ 3, INPUT_H, INPUT_W });
    assert(data);

    std::map<std::string, Weights> weightMap = loadWeights(wts_path);

    IConvolutionLayer* conv1 = network->addConvolutionNd(*data, 64, DimsHW{ 3, 3 }, weightMap["cov1.weight"], weightMap["cov1.bias"]);
    assert(conv1);
    conv1->setName("cov1");//设置名字
    conv1->setPaddingNd(DimsHW{ 1, 1 });
    conv1 = network->addConvolutionNd(*conv1->getOutput(0), 2, DimsHW{ 3, 3 }, weightMap["cov2.weight"], weightMap["cov2.bias"]);
    conv1->setPaddingNd(DimsHW{ 1, 1 });
    conv1->setName("cov2");//设置名字

    conv1->getOutput(0)->setName(OUTPUT_NAME);
    network->markOutput(*conv1->getOutput(0));




    // 构建引擎，其它网络都可以使用这个
    builder->setMaxBatchSize(maxBatchSize);
    config->setMaxWorkspaceSize(1 << 20);
    ICudaEngine* engine = builder->buildEngineWithConfig(*network, *config);

    network->destroy();// Don't need the network any more 释放内存

    // Release host memory
    for (auto& mem : weightMap)
    {
        free((void*)(mem.second.values));
    }

    return engine;
}

//构建模型将其序列化
void APIToModel(unsigned int maxBatchSize, IHostMemory** modelStream, DataType dt,string wts_path = "./trynet.wts")
{
    // Create builder
    IBuilder* builder = createInferBuilder(gLogger);
    IBuilderConfig* config = builder->createBuilderConfig();

    // Create model to populate the network, then set the outputs and create an engine
    ICudaEngine* engine = createEngine(maxBatchSize, builder, config, dt,wts_path=wts_path);
    assert(engine != nullptr);

    // Serialize the engine
    (*modelStream) = engine->serialize();

    // Close everything down
    engine->destroy();
    builder->destroy();
}



//保存序列化的模型
IHostMemory* engine2serialize(std::string engine_path = "model.engine", DataType dt = DataType::kFLOAT)
{
   
    IHostMemory* modelStream{ nullptr };
    APIToModel(1, &modelStream, dt); //batchsize 
    assert(modelStream != nullptr);

    std::ofstream p(engine_path, std::ios::binary);
    if (!p)
    {
        std::cerr << "could not open plan output file" << std::endl;

    }
    p.write(reinterpret_cast<const char*>(modelStream->data()), modelStream->size());
    modelStream->destroy();
    return modelStream;

}




/*****************************************         推理               ***********************************************************/





//加工图片变成拥有batch的输入， tensorrt输入需要的格式，为一个维度
void ProcessImage(std::vector<cv::Mat> InputImage, float input_data[]) {

    int ImgCount = InputImage.size();
    assert(ImgCount == BatchSize);
    //float input_data[BatchSize * 3 * INPUT_H * INPUT_W];
    for (int b = 0; b < ImgCount; b++) {
        cv::Mat img = InputImage.at(b);
        int w = img.cols;
        int h = img.rows;
        int i = 0;
        for (int row = 0; row < h; ++row) {
            uchar* uc_pixel = img.data + row * img.step;
            for (int col = 0; col < INPUT_W; ++col) {
                input_data[b * 3 * INPUT_H * INPUT_W + i] = (float)uc_pixel[2] / 255.0;
                input_data[b * 3 * INPUT_H * INPUT_W + i + INPUT_H * INPUT_W] = (float)uc_pixel[1] / 255.0;
                input_data[b * 3 * INPUT_H * INPUT_W + i + 2 * INPUT_H * INPUT_W] = (float)uc_pixel[0] / 255.0;
                uc_pixel += 3;
                ++i;
            }
        }

    }

}


//读取engine文件，将其反序列化，构造engine结构，相当于网络初始化
ICudaEngine* inite_engine(std::string engine_path) {
    char* trtModelStream{ nullptr }; //指针函数,创建保存engine序列化文件结果
    size_t size{ 0 };
    // read model from the engine file
    std::ifstream file(engine_path, std::ios::binary);
    if (file.good()) {
        file.seekg(0, file.end);
        size = file.tellg();
        file.seekg(0, file.beg);
        trtModelStream = new char[size];
        assert(trtModelStream);
        file.read(trtModelStream, size);
        file.close();
    }
    // create a runtime (required for deserialization of model) with NVIDIA's logger
    IRuntime* runtime = createInferRuntime(gLogger); //反序列化方法
    assert(runtime != nullptr);
    // deserialize engine for using the char-stream
    ICudaEngine* engine = runtime->deserializeCudaEngine(trtModelStream, size, nullptr);
    assert(engine != nullptr);

    /*
    一个engine可以有多个execution context，并允许将同一套weights用于多个推理任务。
    可以在并行的CUDA streams流中按每个stream流一个engine和一个context来处理图像。
    每个context在engine相同的GPU上创建。
    */
    runtime->destroy();
    return engine;

};

//engine->createExecutionContext()加载engine后内容，该函数需要根据网络输入/输出略微修改
void doInference(IExecutionContext& context, float* input, float* output, int batchSize)
{
    const ICudaEngine& engine = context.getEngine();

    // Pointers to input and output device buffers to pass to engine.
    // Engine requires exactly IEngine::getNbBindings() number of buffers.
    assert(engine.getNbBindings() == 2);
    void* buffers[2];

    // In order to bind the buffers, we need to know the names of the input and output tensors.
    // Note that indices are guaranteed to be less than IEngine::getNbBindings()
    const int inputIndex = engine.getBindingIndex(INPUT_NAME);
    const int outputIndex = engine.getBindingIndex(OUTPUT_NAME);

    // Create GPU buffers on device
    CHECK(cudaMalloc(&buffers[inputIndex], batchSize * 3 * INPUT_H * INPUT_W * sizeof(float)));  //CHECK 核对校验  也可不使用
    cudaMalloc(&buffers[outputIndex], batchSize * 2 * INPUT_H * INPUT_W * sizeof(float));

    // Create stream
    cudaStream_t stream;
    cudaStreamCreate(&stream);

    // DMA input batch data to device, infer on the batch asynchronously, and DMA output back to host
    cudaMemcpyAsync(buffers[inputIndex], input, batchSize * 3 * INPUT_H * INPUT_W * sizeof(float), cudaMemcpyHostToDevice, stream);
    context.enqueue(batchSize, buffers, stream, nullptr);//通常TensorRT的执行是异步的，因此将kernels加入队列放在CUDA stream流上
    cudaMemcpyAsync(output, buffers[outputIndex], batchSize * 2 * INPUT_H * INPUT_W * sizeof(float), cudaMemcpyDeviceToHost, stream);
    cudaStreamSynchronize(stream);

    // Release stream and buffers
    cudaStreamDestroy(stream);
    cudaFree(buffers[inputIndex]);
    cudaFree(buffers[outputIndex]);
}

   

int main() {

    bool serialize = false;
    std::string engine_path = "./model.engine";

    if (serialize) {
        //将模型序列化
        IHostMemory* modelStream{ nullptr };
        modelStream = engine2serialize(); //构建引擎与保存

    }
    else {
        //加载引擎，预测图片
        std::string path = "./2.jpg";
        cv::Mat img = cv::imread(path);
        if (img.empty()) {
            std::cout << "input images error!" << std::endl;
            return 0;
        }
        cv::Mat imgInput;
        cv::resize(img, imgInput, cv::Size(INPUT_W, INPUT_H), 0, 0, cv::INTER_LINEAR);

        vector<cv::Mat> InputImage;

        InputImage.push_back(imgInput);
        InputImage.push_back(imgInput);

        float input[BatchSize * 3 * INPUT_H * INPUT_W];
        float output[BatchSize * 2 * INPUT_H * INPUT_W];

        ProcessImage(InputImage,input);
        ICudaEngine* engine = inite_engine(engine_path);

        IExecutionContext* context = engine->createExecutionContext();
        assert(context != nullptr);
 

        doInference(*context, input, output, 2);


        cout << "output_count:" << sizeof(output) / sizeof(output[0]) << endl;
        cout << "BatchSize:" << BatchSize << "INPUT_H:" << INPUT_H << "INPUT_W:" << INPUT_W << endl;
        
        //for (int i = 0; i < BatchSize * 2 * INPUT_H * INPUT_W; i++) {
        //    cout << i << *output << endl;
        //}

    }


}

结果展示：

以上为本次进一步理解和实现tensorrt的过程，若有问题，欢迎指正。

下次我将使用onnx搭建网络解析。

最后无需复制啥，只需按照以下配置(照猫画虎)即可完成windows10的visual tudio的环境配置:

电脑环境path配置：
E:\InstallPackage\TensorRT-8.4.0.6\lib
E:\InstallPackage\opencv\build\x64\vc15\bin

说明：engine无需电脑环境配置

包含目录：
C:\Program Files\NVIDIA GPU Computing Toolkit\CUDA\v11.1\include
E:\InstallPackage\eigen-3.4.0
E:\InstallPackage\opencv\build\include\opencv2
E:\InstallPackage\opencv\build\include
E:\InstallPackage\TensorRT-8.4.0.6\include

库目录：
C:\Program Files\NVIDIA GPU Computing Toolkit\CUDA\v11.1\lib\x64
E:\InstallPackage\opencv\build\x64\vc15\lib
E:\InstallPackage\TensorRT-8.4.0.6\lib

链接器-->附加依赖：
opencv_world455d.lib
nvinfer.lib
nvinfer_plugin.lib
nvonnxparser.lib
nvparsers.lib
cuda.lib
cudart.lib