tracker: avoiding segmentation faults

src/contents/ui/Tracker.qml

@@ -92,6 +92,7 @@ Kirigami.ScrollablePage {
  Component.onCompleted: {
  EoSTrackerBackend.videoSink = videoOutput.videoSink;
  }
+ Component.onDestruction: EoSTrackerBackend.stop() // So we do not write to an invalid videoSink
 
  MouseArea {
  id: mouseArea

src/tracker.cpp

@@ -36,6 +36,7 @@
 #include <ios>
 #include <iterator>
 #include <memory>
+#include <mutex>
 #include <opencv2/core/cvstd_wrapper.hpp>
 #include <opencv2/core/mat.hpp>
 #include <opencv2/core/types.hpp>
@@ -208,16 +209,30 @@ Backend::Backend(QObject* parent)
  connect(this, &Backend::videoSinkChanged, [this]() { draw_offline_image(); });
 
  connect(camera_video_sink.get(), &QVideoSink::videoFrameChanged, [this](const QVideoFrame& frame) {
+ std::lock_guard<std::mutex> trackers_lock_guard(trackers_mutex);
+
  if (!pause_preview && !exiting) {
- input_video_frame = frame;
- process_frame();
+ QMetaObject::invokeMethod(
+ this,
+ [this, frame] {
+ input_video_frame = frame;
+ process_frame();
+ },
+ Qt::QueuedConnection);
  }
  });
 
  connect(media_player_video_sink.get(), &QVideoSink::videoFrameChanged, [this](const QVideoFrame& frame) {
+ std::lock_guard<std::mutex> trackers_lock_guard(trackers_mutex);
+
  if (!pause_preview && !exiting) {
- input_video_frame = frame;
- process_frame();
+ QMetaObject::invokeMethod(
+ this,
+ [this, frame] {
+ input_video_frame = frame;
+ process_frame();
+ },
+ Qt::QueuedConnection);
  }
  });
 
@@ -246,9 +261,14 @@ Backend::Backend(QObject* parent)
 }
 
 Backend::~Backend() {
- exiting = true;
  camera->stop();
  media_player->stop();
+
+ std::lock_guard<std::mutex> trackers_lock_guard(trackers_mutex);
+
+ util::debug("Tracker backend exiting...");
+
+ exiting = true;
 }
 
 void Backend::start() {
@@ -416,6 +436,8 @@ void Backend::drawRoiSelection(const bool& state) {
 }
 
 void Backend::createNewRoi(double x, double y, double width, double height) {
+ std::lock_guard<std::mutex> trackers_lock_guard(trackers_mutex);
+
  cv::Rect2d roi = {x, y, width, height}; // region of interest that is being created
 
  cv::Ptr<cv::legacy::Tracker> tracker;
@@ -462,6 +484,8 @@ void Backend::newRoiSelection(double x, double y, double width, double height) {
 }
 
 int Backend::removeRoi(double x, double y) {
+ std::lock_guard<std::mutex> trackers_lock_guard(trackers_mutex);
+
  initial_time = 0;
 
  for (size_t n = 0; n < trackers.size(); n++) {
@@ -480,6 +504,8 @@ int Backend::removeRoi(double x, double y) {
 }
 
 void Backend::removeAllTrackers() {
+ std::lock_guard<std::mutex> trackers_lock_guard(trackers_mutex);
+
  trackers.clear();
 }
 

src/tracker.hpp

@@ -13,6 +13,7 @@
 #include <QMediaPlayer>
 #include <QVideoSink>
 #include <memory>
+#include <mutex>
 #include <opencv2/core/cvstd_wrapper.hpp>
 #include <opencv2/core/types.hpp>
 #include <opencv2/tracking.hpp>
@@ -152,6 +153,8 @@ class Backend : public QObject {
 
  std::vector<std::tuple<cv::Ptr<cv::legacy::Tracker>, cv::Rect2d, bool, QList<QPointF>, QList<QPointF>>> trackers;
 
+ std::mutex trackers_mutex;
+
  void find_best_camera_resolution();
  void draw_offline_image();
  void process_frame();

src/util.cpp

@@ -14,7 +14,10 @@
 #include <cstring>
 #include <ext/string_conversions.h>
 #include <filesystem>
+#include <format>
+#include <sstream>
 #include <string>
+#include <thread>
 
 namespace util {
 
@@ -46,6 +49,14 @@ void info(const std::string& s, source_location location) {
  qInfo().noquote() << prepare_debug_message(s, location);
 }
 
+void print_thread_id() {
+ std::ostringstream oss;
+
+ oss << std::this_thread::get_id() << '\n';
+
+ warning(std::format("thread id: {0}", oss.str()));
+}
+
 auto v4l2_find_device(const std::string& description) -> std::string {
  for (const auto& entry : std::filesystem::directory_iterator("/dev/")) {
  auto child_path = std::filesystem::path(entry);

src/util.hpp

@@ -22,6 +22,8 @@ void warning(const std::string& s, source_location location = source_location::c
 
 void info(const std::string& s, source_location location = source_location::current());
 
+void print_thread_id();
+
 auto v4l2_find_device(const std::string& description) -> std::string;
 
 void v4l2_disable_dynamic_fps(const std::string& device_path);