Qt library

• big multiplatform library
• helpful documentation
• quick development -> use newest version
• own type for everything

Threads

Why to use threads?

• you have to - GUI and worker thread
• simplicity - sometimes
• speed-up

Threads

Basic concepts

• memory - own stack, together heap and cache
• nondeterministic (race condition)
• low level synchronization: mutex, semaphore, wait condition
• atomic instructions (CAS)
• reentrant and thread safe

Threads

Advanced things

• more synchronization: busy wait, notify, signals and slots
• problems
  • deadlock
  • starving and livelock
• analysis and debugging
  • Valgrind and Hellgrind
  • IDE visualisation
  • luck (mainly you don't want to debug thread problems)
• threading may be big security threat

Qt Threads

Possibilities

• alternatives for simple things:
  • QEventLoop::processEvents()
  • QTimer
  • QIODevice::readyRead()
• from low-level to high-level
• lot of documentations (method have info about being reentrant or thread safe)

Qt Threads

QThread

• basic class for everything (no limitations)
• inheritance vs composition
  • if you don't know, then instantiate
  • inherit only if you really have to (NO!, still bad idea for thread)
• great for threads running all the time (working thread for GUI thread)

Qt Threads

QThreadPool and QRunnable

• reuse threads for performance
• great for multiple actions in separate threads

Qt Threads

Qt Concurrent

• high-level
• typical thread algorithms: map, filter and reduce...
• nice and simple if an can use it

Qt Threads

Synchronization

• locks and mutexes and other synchro primitives - low-level
• events - high-level
  • signal-slot connection
  • queued connection
  • default way of synchro GUI and worker thread

Synchronization - events

Qt Threads

Signals

• Q_OBJECT
• QObject::connect(&from, signal, &to, slot);
• sending data between threads from->signal == to->slot
• GUI event - clicked()

GUI

Possibilities

• Qt Designer
• manually
• QtQuick

GUI

Manual way

• QGuiApplication and QWindow
• QWidget

GUI

#include <QCoreApplication>

#include "client.h"

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    Client myClient;
    myClient.show();

    return app.exec();
}

Questions?