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Top-down or bottom-up design?

- by Gabriel Šcerbák

There are basically those two approaches to designing a system. What are the advantages and disadvantages? When should I use which? Should I combine those approaches? How?

Qthread - trouble shutting down threads

For the last few days, I've been trying out the new preferred approach for using QThreads without subclassing QThread. The trouble I'm having is when I try to shutdown a set of threads that I created. I regularly get a "Destroyed while thread is still running" message (if I'm running in Debug mode, I also get a Segmentation Fault dialog). My code is very simple, and I've tried to follow the examples that I've been able to find on the internet. My basic setup is as follows: I've a simple class that I want to run in a separate thread; in fact, I want to run 5 instances of this class, each in a separate thread. I have a simple dialog with a button to start each thread, and a button to stop each thread (10 buttons). When I click one of the "start" buttons, a new instance of the test class is created, a new QThread is created, a movetothread is called to get the test class object to the thread...also, since I have a couple of other members in the test class that need to move to the thread, I call movetothread a few additional times with these other items. Note that one of these items is a QUdpSocket, and although this may not make sense, I wanted to make sure that sockets could be moved to a separate thread in this fashion...I haven't tested the use of the socket in the thread at this point. Starting of the threads all seem to work fine. When I use the linux top command to see if the threads are created and running, they show up as expected. The problem occurs when I begin stopping the threads. I randomly (or it appears to be random) get the error described above. Class that is to run in separate thread: // Declaration class TestClass : public QObject { Q_OBJECT public: explicit TestClass(QObject *parent = 0); QTimer m_workTimer; QUdpSocket m_socket; Q_SIGNALS: void finished(); public Q_SLOTS: void start(); void stop(); void doWork(); }; // Implementation TestClass::TestClass(QObject *parent) : QObject(parent) { } void TestClass::start() { connect(&m_workTimer, SIGNAL(timeout()),this,SLOT(doWork())); m_workTimer.start(50); } void TestClass::stop() { m_workTimer.stop(); emit finished(); } void TestClass::doWork() { int j; for(int i = 0; i<10000; i++) { j = i; } } Inside my main app, code called to start the first thread (similar code exists for each of the other threads): mp_thread1 = new QThread(); mp_testClass1 = new TestClass(); mp_testClass1->moveToThread(mp_thread1); mp_testClass1->m_socket.moveToThread(mp_thread1); mp_testClass1->m_workTimer.moveToThread(mp_thread1); connect(mp_thread1, SIGNAL(started()), mp_testClass1, SLOT(start())); connect(mp_testClass1, SIGNAL(finished()), mp_thread1, SLOT(quit())); connect(mp_testClass1, SIGNAL(finished()), mp_testClass1, SLOT(deleteLater())); connect(mp_testClass1, SIGNAL(finished()), mp_thread1, SLOT(deleteLater())); connect(this,SIGNAL(stop1()),mp_testClass1,SLOT(stop())); mp_thread1->start(); Also inside my main app, this code is called when a stop button is clicked for a specific thread (in this case thread 1): emit stop1(); Sometimes it appears that threads are stopped and destroyed without issue. Other times, I get the error described above. Any guidance would be greatly appreciated. Thanks, Bryan

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