c++ - QT OpenCV multi threading to fetch images and display in GUI Main thread -


the basic idea

i developing application 4 usb cameras, frames must fetched these cameras , displayed in qlabel @ best possible fps.

fetching frames cameras sequentially results in low frame rate, though processor has 20% utilization.

how think frame rate can improved?

with use of multiple threads cpu utilization can increased, , there 4 threads each fetching images individual cameras, signaling , sending images gui thread(main thread) in turn display images appropriate label.

current design: based on https://mayaposch.wordpress.com/2011/11/01/how-to-really-truly-use-qthreads-the-full-explanation/

the thread class inherits qobject methods:

class fetchcam1 : public qobject {     q_object  public:     fetchcam1(cv::videocapture cap);     ~fetchcam1();  public slots:     void process();     cv::mat returncamframe();  signals:     void finished(); };

its implementation:

fetchcam1::fetchcam1(cv::videocapture cap) {     this->cap = cap; }  cv::mat fetchcam1::returncam1frame() {     return src; }  void fetchcam1::process() {     // allocate resources using new here     cap.read(src);     emit finished(); }

initiating threads , worker roles in main(gui) thread:

    captures1..s4, videocapture object, fetchcam1* worker1-4,      qthread* thread1-4; defined global variables.  thread1 = new qthread; worker1 = new fetchcam1(captures1); worker1->movetothread(thread1); connect(thread1, signal(started()), worker1, slot(process())); connect(worker1, signal(finished()), this, slot(updatecam1())); connect(worker1, signal(finished()), worker1, slot(process())); thread1->start();  thread2 = new qthread; worker2 = new fetchcam1(captures2); worker2->movetothread(thread2); connect(thread2, signal(started()), worker2, slot(process())); connect(worker2, signal(finished()), this, slot(updatecam2())); connect(worker2, signal(finished()), worker2, slot(process())); thread2->start();  thread3 = new qthread; worker3 = new fetchcam1(captures3); worker3->movetothread(thread3); connect(thread3, signal(started()), worker3, slot(process())); connect(worker3, signal(finished()), this, slot(updatecam3())); connect(worker3, signal(finished()), worker3, slot(process())); thread3->start();  thread4 = new qthread; worker4 = new fetchcam1(captures4); worker4->movetothread(thread4); connect(thread4, signal(started()), worker4, slot(process())); connect(worker4, signal(finished()), this, slot(updatecam4())); connect(worker4, signal(finished()), worker4, slot(process())); thread4->start();

each of invoke:

void mainwindow::updatecam1() {     cv::mat src = worker1->returncamframe();     qpixmap pixg = convertfrommat(src);     ui->label_4s1->setpixmap(pixg); } void mainwindow::updatecam2() {     cv::mat src = worker1->returncamframe();     qpixmap pixg = convertfrommat(src);     ui->label_4s2->setpixmap(pixg); } void mainwindow::updatecam3() {     cv::mat src = worker1->returncamframe();     qpixmap pixg = convertfrommat(src);     ui->label_4s3->setpixmap(pixg); } void mainwindow::updatecam4() {     cv::mat src = worker1->returncamframe();     qpixmap pixg = convertfrommat(src);     ui->label_4s4->setpixmap(pixg); }

please me identify doing wrong? above code start , load first few frames, after program crashes no errors whatsoever.

also if 1 thread used fetch images 1 camera, above code works great.

what right approach implement this? thank you.

update crash:

i believe frames 4 cameras being fetched quite fast, , that's generating way many signals main thread handle, causes overflow causing crash. believe kind of synchronization can how can go it?


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