Deleting QProcess

[user_mail07]

I have problem when I am deleting QProcesses and I dont get any output. If I comment out deleteLater() method to delete processes I get right output in the form of string as expected. I have tried to use delete and deleteLater to delete processes. But something is still going wrong. I have created two seperate process to read data from external scripts. I am using QT3.

//Declared member Functions globally.
QString strFirstProcess;
QString strSecondProcess;
QProcess process1;
QProcess process2;
 
QString CMainTemplate::CreateControls()
 
{
lineEdit->setText(GetFirstProcess());
lineEdit2->setText(GetSecondProcess());
}
 
//...FIRST PROCESS
QString CMainTemplate::GetFirstProcess()	
 
{	
 
	process= new QProcess(this);
 
	//Add the arguments
	process1->addArgument( "/bash" );
	process->addArgument("GetFirstScript");
 
 
	if ( !process->start() )
		{
			qDebug("ERROR: First Process Never Started");
			process->deleteLater();
		}
 
	connect(process, SIGNAL(readyReadStdout()), this, SLOT(readFirstProcess()));
 
	return strFirstProcess;
 
}
//...SECOND PROCESS
QString CMainTemplate::GetSecondProcess()	
 
{	
 
	process1= new QProcess(this);
 
	//Add the arguments
	process1->addArgument( "/bash" );
	process1->addArgument("GetSecondScript");
 
 
	if ( !process1->start() )
		{
			qDebug("ERROR: Second Process Never Started");
			process1->deleteLater();
		}
 
	connect(process1, SIGNAL(readyReadStdout()), this, SLOT(readSecondProcess()));
 
	return strSecondProcess;
 
}
//=====================SLOTS TO READ STD OUT ===================================================
 
void CMainTemplate::readFirstProcess()
{
	QString str =  process->readStdout() ;
	strFirstProcess = str;
	process->deleteLater();
} 
void CMainTemplate::readSecondProcess()
 
{
	QString str =  process1->readStdout() ;
	strSecondProcess = str;
	process1->deleteLater();
}

//Declared member Functions globally.
QString strFirstProcess;
QString strSecondProcess;
QProcess process1;
QProcess process2;

QString CMainTemplate::CreateControls()

{
lineEdit->setText(GetFirstProcess());
lineEdit2->setText(GetSecondProcess());
}

//...FIRST PROCESS
QString CMainTemplate::GetFirstProcess()	

{	
	
	process= new QProcess(this);

	//Add the arguments
	process1->addArgument( "/bash" );
	process->addArgument("GetFirstScript");

	
	if ( !process->start() )
		{
			qDebug("ERROR: First Process Never Started");
			process->deleteLater();
		}

	connect(process, SIGNAL(readyReadStdout()), this, SLOT(readFirstProcess()));

	return strFirstProcess;

}
//...SECOND PROCESS
QString CMainTemplate::GetSecondProcess()	

{	
	
	process1= new QProcess(this);

	//Add the arguments
	process1->addArgument( "/bash" );
	process1->addArgument("GetSecondScript");

	
	if ( !process1->start() )
		{
			qDebug("ERROR: Second Process Never Started");
			process1->deleteLater();
		}

	connect(process1, SIGNAL(readyReadStdout()), this, SLOT(readSecondProcess()));

	return strSecondProcess;

}
//=====================SLOTS TO READ STD OUT ===================================================

void CMainTemplate::readFirstProcess()
{
	QString str =  process->readStdout() ;
	strFirstProcess = str;
	process->deleteLater();
} 
void CMainTemplate::readSecondProcess()

{
	QString str =  process1->readStdout() ;
	strSecondProcess = str;
	process1->deleteLater();
}

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[wysota]

You probably kill the process before all output is generated. The signal you connect to is emited when there is any data to read (like 1 character) and not when all data is pending. I suggest you delete the process object only when it tells you the process it controls has ended.

[user_mail07]

how do i know that particular process has ended its loop or should I delete only once after returning the string I mean data.

[wysota]

Look at the signals QProcess offers.

[user_mail07]

Well my application still crash and I get segmentation fault always. I tried processExited and launchedfinished signals too. It is just the matter of deleting qprocessed when I am running sequentially.

I tried few things such as

connect( process, SIGNAL(processExited()),this, SLOT(deleteLater()) );
OR
connect( process, SIGNAL(processExited()),this, SLOT(stopProces()) );

QString CMainTemplate::GetFirstProcess()   
{   
 
    process= new QProcess(this);
 
   //Add the arguments
 
    process->addArgument( "/bash" );
 
    process->addArgument("GetFirstScript");
if ( !process->start() )
    {
 
            qDebug("ERROR: First Process Never Started");
 
            process->deleteLater();
      	}
 
 
	 connect(process, SIGNAL(readyReadStdout()), this, SLOT(readFirstProcess()));
 
 	return strFirstProcess;
 
 
 
}
 
 
QString CMainTemplate::stopProces()
{
const QObject *sen=sender();
	delete sen;
}

QString CMainTemplate::GetFirstProcess()   
{   

    process= new QProcess(this);

   //Add the arguments

    process->addArgument( "/bash" );

    process->addArgument("GetFirstScript");
if ( !process->start() )
    {

            qDebug("ERROR: First Process Never Started");

            process->deleteLater();
      	}

 
	 connect(process, SIGNAL(readyReadStdout()), this, SLOT(readFirstProcess()));

 	return strFirstProcess;

 

}


QString CMainTemplate::stopProces()
{
const QObject *sen=sender();
	delete sen;
}

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[wysota]

Have you tried debugging to see where and why it crashes?

[user_mail07]

I tried to put some debug statements to see where it exactly crash. The segmentaion fault does not provide me any information. As soon as I call CreateContorls( ) to call two sequential process my application crash. It never prints any thing else . It looks like Slots readFirstProcess and readSecondProcess never get called otherwise it should print debug statements from slots such as "Print ReadOut Process1".

The output I receive after calling CreateControls() method is :-

Print Statement 1
Print Statement 2
Print Statement 3
Print Statement 4
Print Statement 5
Print Statement 6

But if executes only one process with GetFirstProcess( ) while commenting out second GetSecondProcess() then there is no problem.

QString CMainTemplate::CreateControls()
{
 
lineEdit->setText(GetFirstProcess());
//lineEdit2->setText(GetSecondProcess());
}

QString CMainTemplate::CreateControls()
{

lineEdit->setText(GetFirstProcess());
//lineEdit2->setText(GetSecondProcess());
}

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QString CMainTemplate::CreateControls()
{
 
lineEdit->setText(GetFirstProcess());
lineEdit2->setText(GetSecondProcess());
}
 
QString CMainTemplate::GetFirstProcess()   
{   
process= new QProcess(this);
//Add the arguments
process1->addArgument( "/bash" );
process->addArgument("GetFirstScript");
 
qDebug("Print Statement 1");
connect(process, SIGNAL(readyReadStdout()), this, SLOT(readFirstProcess()));
 
qDebug("Print Statement 2");
if ( !process->start() )
 {
	 qDebug("ERROR: First Process Never Started");
	process->deleteLater();
 }
 
qDebug("Print Statement 3");
 
return strFirstProcess;
}
 
//...SECOND PROCESS
 
QString CMainTemplate::GetSecondProcess()   
{   
process1= new QProcess(this);
//Add the arguments
process1->addArgument( "/bash" );
process1->addArgument("GetSecondScript");
 
qDebug("Print Statement 4");
 
connect(process1, SIGNAL(readyReadStdout()), this, SLOT(readSecondProcess()));
 
qDebug("Print Statement 5");
 
if ( !process1->start() )
 {
	 qDebug("ERROR: Second Process Never Started");
	 process->deleteLater();
 }
 
qDebug("Print Statement 6");
 
return strSecondProcess;
}
 
//=====================SLOTS TO READ STD OUT ===================================================
 
void CMainTemplate::readFirstProcess()
{
 
    QString str =  process->readStdout() ;
	strFirstProcess = str;
	qDebug("Print ReadOut Process1);
	process->deleteLater();
 
}
 
void CMainTemplate::readSecondProcess()
{
	QString str =  process1->readStdout() ;
	strSecondProcess = str;
	qDebug("Print ReadOut Process2);
	process1->deleteLater();
 
}

QString CMainTemplate::CreateControls()
{

lineEdit->setText(GetFirstProcess());
lineEdit2->setText(GetSecondProcess());
}

QString CMainTemplate::GetFirstProcess()   
{   
process= new QProcess(this);
//Add the arguments
process1->addArgument( "/bash" );
process->addArgument("GetFirstScript");

qDebug("Print Statement 1");
connect(process, SIGNAL(readyReadStdout()), this, SLOT(readFirstProcess()));

qDebug("Print Statement 2");
if ( !process->start() )
 {
	 qDebug("ERROR: First Process Never Started");
	process->deleteLater();
 }

qDebug("Print Statement 3");

return strFirstProcess;
}

//...SECOND PROCESS

QString CMainTemplate::GetSecondProcess()   
{   
process1= new QProcess(this);
//Add the arguments
process1->addArgument( "/bash" );
process1->addArgument("GetSecondScript");

qDebug("Print Statement 4");
 
connect(process1, SIGNAL(readyReadStdout()), this, SLOT(readSecondProcess()));

qDebug("Print Statement 5");

if ( !process1->start() )
 {
	 qDebug("ERROR: Second Process Never Started");
	 process->deleteLater();
 }

qDebug("Print Statement 6");

return strSecondProcess;
}

//=====================SLOTS TO READ STD OUT ===================================================

void CMainTemplate::readFirstProcess()
{

    QString str =  process->readStdout() ;
	strFirstProcess = str;
	qDebug("Print ReadOut Process1);
	process->deleteLater();

}

void CMainTemplate::readSecondProcess()
{
	QString str =  process1->readStdout() ;
	strSecondProcess = str;
	qDebug("Print ReadOut Process2);
	process1->deleteLater();

}

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[wysota]

I tried to put some debug statements to see where it exactly crash.

I meant using a debugger and its stack tracing abilities.