task: improve threading

app/task/task.h

@@ -93,6 +93,7 @@ public slots:
   bool Start()
   {
     start_time_ = QDateTime::currentMSecsSinceEpoch();
+    emit Started(start_time_);
 
     bool ret = Run();
 
@@ -150,6 +151,8 @@ protected:
   }
 
 signals:
+  void Started(qint64 start_time);
+
   /**
    * @brief Signal emitted whenever progress is made
    *

app/task/taskmanager.cpp

@@ -29,6 +29,7 @@ TaskManager* TaskManager::instance_ = nullptr;
 
 TaskManager::TaskManager()
 {
+  thread_pool_.setMaxThreadCount(1);
 }
 
 TaskManager::~TaskManager()
@@ -95,9 +96,9 @@ void TaskManager::AddTask(Task* t)
   // Run task concurrently
   watcher->setFuture(
 #if QT_VERSION_MAJOR >= 6
-        QtConcurrent::run(&Task::Start, t)
+        QtConcurrent::run(&thread_pool_, &Task::Start, t)
 #else
-        QtConcurrent::run(t, &Task::Start)
+        QtConcurrent::run(&thread_pool_, t, &Task::Start)
 #endif
         );