QProcess object not emitting finished(int) signal

[Tiansen]

Hello,

I have a weird trouble. I have created a QProcess object and started an external program. But... when program finishes, object is not emitting finished signal. How is this possible? What can I do to workaround this?

My code example:

launcher::launcher(QWidget *parent, Qt::WFlags flags)
	: QDialog(parent, flags)
{
       QProcess program;
	Sleep(3000);
	program.start("/path/to/my/program.exe");
	connect(&program, SIGNAL(finished(int)), this, SLOT(OnExit())); 
}
 
 
void launcher::OnExit()
{
	QMessageBox::information(this,"","Izhod");
}

launcher::launcher(QWidget *parent, Qt::WFlags flags)
	: QDialog(parent, flags)
{
       QProcess program;
	Sleep(3000);
	program.start("/path/to/my/program.exe");
	connect(&program, SIGNAL(finished(int)), this, SLOT(OnExit())); 
}


void launcher::OnExit()
{
	QMessageBox::information(this,"","Izhod");
}

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[wysota]

Your program doesn't even start. The QProcess object that controls it gets destroyed when you leave the constructor. Create it on heap instead.

[spirit]

this slot works, but your programm terminated immediately. create QProcess in a heap.
wysota, you was first

[Tiansen]

Well, actually my program does not end. I did not paste the whole constructor code .
After connect.... line I have this:

while (true)
{
Sleep(1000)
}

So I stay in constructor and my program keeps running. It stays in constructor because I don't want it to open GUI. It's ugly I know but it works and runs hidden. With Sleep I prevent 100% CPU utilization.

[spirit]

create console app and run process.

[Tiansen]

I don't want to open any window, not even console. I want it to run as services do (completely hidden), but don't know how to program real service.

Now it seems like signal-slots communication does not work until execution leaves constructor??

[spirit]

if you need a service you can use QtService from Qt Solutions.

[Tiansen]

I never programmed a service and I want to be sure that I cannot achieve my goal any other way before diving into this.

I still do not understand why it does not work as it is now.

[Tiansen]

If I comment out while loop so that it opens GUI then object indeed emits signal. So it seems that with that loop I blocked processing of signals. Any other idea to create a "hidden" launcher without programming a service?

[Tiansen]

Hmmm, now I figured out something. I can leave constructor as in first post (without while loop), but just comment out following line in main.cpp:

//w.show();

and it works as intended (launches program, shows dialog box when program exits and stays completely hidden). Does this have any side effect?

[spirit]

what do you want to achive? do you use any GUI in your app or you need only start another process, so you don't need GUI?

[Tiansen]

Okay, I wil try to explain:

1. I DON'T want ANY window (NO GUI, no console either)

2. I just want to first run 2 other processes and then restart them if one of them dies/exits.

This is all I want. And it seems I can achieve that if i comment out w.show().


P.S.: I only had that QMessageBox because I tested behaviour. Application must stay completely silent normally.

[spirit]

there is some "magic" to hidding your app (i.e. that it don't appear in task bar), but for this "magic" you need to use platform dependent code.
so, I suggest to use QtService or take a look at QSystemTrayIcon

[Tiansen]

I think I "invented" such magic too