Hello everyone!

I am currently programming a GUI to display some results from a different C++ program using qwt plots. The results are transferred via 4 TCP links and are received in 4 QThreads. Each QThread sends the received data via a signal to a slot of the GUI to display the data in the plots. Each thread sends on average something like 5-10 signals per second. For a while everything is working fine (I am running the GUI under cygwin), but occasionally my GUI freezes. Sometimes this happens 5 minutes after starting the GUI and TCP data transfer, sometimes it happens after 2 hours. After some debugging it seems that the emit() calls block the QThreads. Interestingly, a very similar GUI programmed using exactly the same approach (but using only a single QThread) works absolutely fine. My (simplified) code looks as follows:

Qt Code: 
  1. int main(int argc, char *argv[])
  2. {
  3. 	QApplication a(argc, argv);
  4.  
  5. 	qRegisterMetaType<QSharedPointer<CPacket> >();
  6.  
  7. 	RodGui w;
  8. 	w.show();
  9. 	return a.exec();
  10. }
  11. Q_DECLARE_METATYPE(QSharedPointer<CPacket>)
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Qt Code: 
  1. class RodGui : public QMainWindow
  2. {
  3. 	Q_OBJECT
  4.  
  5. public:
  6. 	RodGui(QWidget *parent = 0);
  7. 	~RodGui();
  8.  
  9. private:
  10. 	void setupAndStartNetwork();
  11.  
  12. 	Network* networkThreadMi;
  13. 	Network* networkThreadBer;
  14. 	Network* networkThreadBuffer;
  15. 	Network* networkThreadQam;
  16.  
  17. 	//[qwt plot stuff and widgets]
  18.  
  19. private slots:
  20. 	void updatePlot(QSharedPointer<CPacket> packet);
  21. };
  22.  
  23.  
  24. RodGui::RodGui(QWidget *parent) : QMainWindow(parent)
  25. {
  26. 	// [create widgets and qwt plots]
  27. 	setupAndStartNetwork();
  28. }
  29.  
  30.  
  31. void RodGui::updatePlot(QSharedPointer<CPacket> packet) {
  32. 	// [do some calculations with packet and update qwt plots]
  33. }
  34.  
  35. void RodGui::setupAndStartNetwork() {
  36.  
  37. 	networkThreadMi = new Network(this, QString::number(20004));
  38. 	networkThreadBer = new Network(this, QString::number(20005));
  39. 	networkThreadBuffer = new Network(this, QString::number(20006));
  40. 	networkThreadQam = new Network(this, QString::number(20007));
  41.  
  42. 	QObject::connect(networkThreadMi, SIGNAL(processedDatagramsReady(QSharedPointer<CPacket>)),
  43. 						this, SLOT(updatePlot(QSharedPointer<CPacket>)), Qt::QueuedConnection);
  44. 	QObject::connect(networkThreadBer, SIGNAL(processedDatagramsReady(QSharedPointer<CPacket>)),
  45. 						this, SLOT(updatePlot(QSharedPointer<CPacket>)), Qt::QueuedConnection);
  46. 	QObject::connect(networkThreadBuffer, SIGNAL(processedDatagramsReady(QSharedPointer<CPacket>)),
  47. 						this, SLOT(updatePlot(QSharedPointer<CPacket>)), Qt::QueuedConnection);
  48. 	QObject::connect(networkThreadQam, SIGNAL(processedDatagramsReady(QSharedPointer<CPacket>)),
  49. 						this, SLOT(updatePlot(QSharedPointer<CPacket>)), Qt::QueuedConnection);
  50.  
  51. 	networkThreadMi->start();
  52. 	networkThreadBer->start();
  53. 	networkThreadBuffer->start();
  54. 	networkThreadQam->start();
  55. }
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Qt Code: 
  1. class Network : public QThread {
  2. 	Q_OBJECT
  3.  
  4. public:
  5. 	Network(QWidget *parent = 0, QString port = 0);
  6.  
  7. signals:
  8. 	void processedDatagramsReady(QSharedPointer<CPacket>);
  9.  
  10. private:
  11. 	QString port;
  12. 	//[TCP stuff (boost asio)]
  13.  
  14. protected:
  15. 	void run();
  16. };
  17.  
  18. void Network::run() {
  19.  
  20. 	while (true) {
  21. 		//[read some TCP packets via boost asio and deserialize to a class (derived from CPacket)]
  22. 		qDebug() << "emit: " << port;
  23. 		emit processedDatagramsReady(packet);
  24. 		qDebug() << "emit complete: " << port;
  25. 	}
  26. }
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When my GUI freezes the last debug output on my console looks like this:
[...]
emit: xx
emit complete: xx
emit: 20004
emit: 20005
emit: 20006
emit: 20007

So it seems that the event loop is freezing after some time, blocking the emit calls from all QThreads. Is there a problem with the approach itself? Or am I simply firing too many signals per second? Any idea what might cause this problem?

Thanks in advance!
Jan