我更改并获取矢量元素。 因此，当线程正在运行时，我使用互斥锁来更改矢量的元素。
但是如果我只想枚举向量的元素，我是否仍然必须锁定向量？
代码如下：
#include <napi.h>
#include "facedetect.h"
#include "opencv2/objdetect.hpp"
#include "opencv2/highgui.hpp"
#include "opencv2/imgproc.hpp"
#include <iostream>
#include <thread>
using namespace std;
using namespace cv;
std::mutex facesMutex;
string cascadeName = "/usr/local/share/opencv4/haarcascades/haarcascade_frontalface_alt.xml";;
bool running = true;
vector<Rect> faces;
class FaceDetectWorker : public Napi::AsyncWorker {
public:
FaceDetectWorker(Napi::Function& callback, string url)
: Napi::AsyncWorker(callback), url(url) {
}
~FaceDetectWorker() {
}
vector<Rect> detectAndDraw( Mat& img, CascadeClassifier& cascade)
{
double t = 0;
vector<Rect> faces;
Mat gray, smallImg;
cvtColor( img, gray, COLOR_BGR2GRAY );
//double scale = 1;
// scale = 1, fx = 1 / scale
double fx = 1;
resize( gray, smallImg, Size(), fx, fx, INTER_LINEAR_EXACT );
equalizeHist( smallImg, smallImg );
t = (double)getTickCount();
cascade.detectMultiScale( smallImg, faces,
1.1, 2, 0
//|CASCADE_FIND_BIGGEST_OBJECT
//|CASCADE_DO_ROUGH_SEARCH
|CASCADE_SCALE_IMAGE,
Size(30, 30) );
t = (double)getTickCount() - t;
printf( "detection time = %g ms\n", t*1000/getTickFrequency());
return faces;
}
// Executed inside the worker-thread.
// It is not safe to access JS engine data structure
// here, so everything we need for input and output
// should go on `this`.
void Execute () {
Mat frame, image;
VideoCapture capture;
CascadeClassifier cascade;
if (!cascade.load(samples::findFile(cascadeName)))
{
Napi::AsyncWorker::SetError("ERROR: Could not load classifier cascade");
return;
}
if (!capture.open(url))
{
Napi::AsyncWorker::SetError("ERROR: Error opening video stream " + url);
return;
}
if( capture.isOpened() )
{
cout << "Video capturing has been started ..." << endl;
try {
while(running) {
capture >> frame;
if( frame.empty()) {
continue;
}
Mat frame1 = frame.clone();
vector<Rect> facesResult = detectAndDraw( frame1, cascade);
facesMutex.lock();
faces = facesResult;
facesMutex.unlock();
std::this_thread::sleep_for(std::chrono::milliseconds(30));
}
} catch (std::exception &e) {
facesMutex.unlock();
Napi::AsyncWorker::SetError(e.what());
}
}
}
// Executed when the async work is complete
// this function will be run inside the main event loop
// so it is safe to use JS engine data again
void OnOK() {
Napi::HandleScope scope(Env());
Callback().Call({Env().Undefined(), Env().Undefined()});
}
private:
string url;
};
// Asynchronous access to the `Estimate()` function
Napi::Value FaceDetect(const Napi::CallbackInfo& info) {
Napi::String url = info[0].As<Napi::String>().ToString();
Napi::Function callback = info[1].As<Napi::Function>();
FaceDetectWorker* faceDetectWorker = new FaceDetectWorker(callback, url);
faceDetectWorker->Queue();
return info.Env().Undefined();
}
Napi::Array FaceDetectGet(const Napi::CallbackInfo &info) {
Napi::Array faceArray = Napi::Array::New(info.Env(), faces.size());
facesMutex.lock();
for(int i = 0; i < faces.size(); i++) {
Rect rect = faces[i];
Napi::Object obj = Napi::Object::New(info.Env());
obj.Set("x", rect.x);
obj.Set("y", rect.y);
obj.Set("width", rect.width);
obj.Set("height", rect.height);
faceArray[i] = obj;
}
facesMutex.unlock();
return faceArray;
}
所以问题是，如果我使用仅枚举向量的FaceDetectGet，我应该对其进行锁定和解锁吗？
答案 0 :(得分：0)
实际上，解决方案是使用共享互斥锁。
代码如下：
#include <napi.h>
#include "facedetect.h"
#include "opencv2/objdetect.hpp"
#include "opencv2/highgui.hpp"
#include "opencv2/imgproc.hpp"
#include <iostream>
#include <thread>
#include <mutex> // For std::unique_lock
#include <shared_mutex>
// https://stackoverflow.com/questions/55313194/do-i-have-to-lock-a-vectors-that-i-just-enumerate-or-i-only-do-it-when-i-change?noredirect=1#comment97357425_55313194
using namespace std;
using namespace cv;
std::shared_mutex _facesMutex;
string cascadeName = "/usr/local/share/opencv4/haarcascades/haarcascade_frontalface_alt.xml";;
bool running = true;
vector<Rect> faces;
class FaceDetectWorker : public Napi::AsyncWorker {
public:
FaceDetectWorker(Napi::Function& callback, string url, int skip, int sleep)
: Napi::AsyncWorker(callback), url(url), skip(skip), sleep(sleep) {
}
~FaceDetectWorker() {
}
vector<Rect> detectFaces(Mat &img, CascadeClassifier &cascade)
{
double t = 0;
vector<Rect> faces;
Mat gray, smallImg;
cvtColor( img, gray, COLOR_BGR2GRAY );
//double scale = 1;
// scale = 1, fx = 1 / scale
double fx = 1;
//resize( gray, smallImg, Size(), fx, fx, INTER_LINEAR_EXACT );
//equalizeHist( gray, smallImg );
//t = (double)getTickCount();
cascade.detectMultiScale( gray, faces,
1.1, 2, 0
//|CASCADE_FIND_BIGGEST_OBJECT
//|CASCADE_DO_ROUGH_SEARCH
|CASCADE_SCALE_IMAGE,
Size(30, 30) );
//t = (double)getTickCount() - t;
//printf( "detection time = %g ms\n", t*1000/getTickFrequency());
return faces;
}
// Executed inside the worker-thread.
// It is not safe to access JS engine data structure
// here, so everything we need for input and output
// should go on `this`.
void Execute () {
running = true;
Mat frame, image;
VideoCapture capture;
CascadeClassifier cascade;
if (!cascade.load(samples::findFile(cascadeName)))
{
Napi::AsyncWorker::SetError("ERROR: Could not load classifier cascade");
return;
}
if (!capture.open(url))
{
Napi::AsyncWorker::SetError("ERROR: Error opening video stream " + url);
return;
}
if( capture.isOpened() )
{
cout << "Video capturing has been started ..." << endl;
try {
int skipCount = 0;
while(running) {
//capture.read(frame);
capture >> frame;
if( frame.empty()) {
continue;
}
skipCount++;
//cout<< "sleep " << sleep << " skip " << skip << endl;
if (skipCount >= skip) {
//cout<< "calculation " << skipCount << endl;
skipCount = 0;
Mat frame1 = frame.clone();
vector<Rect> facesResult = detectFaces(frame1, cascade);
std::unique_lock lock(_facesMutex);
faces = facesResult;
lock.unlock();
}
//waitKey(250);
std::this_thread::sleep_for(std::chrono::milliseconds(sleep));
}
} catch (std::exception &e) {
Napi::AsyncWorker::SetError(e.what());
}
} else {
Napi::AsyncWorker::SetError("ERROR: Could not open video camera " + url);
}
}
// Executed when the async work is complete
// this function will be run inside the main event loop
// so it is safe to use JS engine data again
void OnOK() {
Napi::HandleScope scope(Env());
Callback().Call({Env().Undefined(), Env().Undefined()});
}
private:
string url;
int skip = 3;
int sleep = 30;
};
// Asynchronous access to the `Estimate()` function
Napi::Value FaceDetect(const Napi::CallbackInfo& info) {
Napi::String url = info[0].As<Napi::String>();
Napi::Number skip = info[1].As<Napi::Number>();
Napi::Number sleep = info[2].As<Napi::Number>();
Napi::Function callback = info[3].As<Napi::Function>();
FaceDetectWorker* faceDetectWorker = new FaceDetectWorker(callback, url, skip, sleep);
faceDetectWorker->Queue();
return info.Env().Undefined();
}
Napi::Array FaceDetectGet(const Napi::CallbackInfo &info) {
Napi::Array faceArray = Napi::Array::New(info.Env(), faces.size());
std::shared_lock lock(_facesMutex);
vector<Rect> faces2 = faces;
lock.unlock();
for(int i = 0; i < faces2.size(); i++) {
Rect rect = faces[i];
Napi::Object obj = Napi::Object::New(info.Env());
obj.Set("x", rect.x);
obj.Set("y", rect.y);
obj.Set("width", rect.width);
obj.Set("height", rect.height);
faceArray[i] = obj;
}
return faceArray;
}
void FaceDetectCancel(const Napi::CallbackInfo &info) {
running = false;
}