qt check QProcess state regularly - c++

Question

I´m starting multiple QProcesses from a textfile (for example different programs like notepad.exe and so on) and want to regularly check if they are still running.
A while loop isn´t the solution, since it is blocking the ui-thread.
How can this be achieved? In Java (Android) I would do this with a asynctask
connected to a ScheduldExecutorService. Is something similar available for qt?
This is where I start my processes:
void mywidget::startprocesses(QString &text)
{
QProcess *process = new QProcess(this);
this->myprocess.append(process);
process->start(text);
int state = process->state();
addlabelstatus(state);
}
And here the method is called:
while(!stream->atEnd()) //check stream until empty and assign line as a caption to a new QLabel
{
this->fileread = stream->readLine();
if(!this->fileread.isEmpty())
{
central->addlabel(this->fileread);
central->startprocesses(this->fileread);
}
}
void mywidget::addlabelstatus(QProcess::ProcessState newstate)
{
QString sstring;
if(newstate == 0)
{
QString sstring = "Wird nicht ausgeführt";
QLabel *label = new QLabel(sstring);
this->processstatus.append(label);
this->vrarea->addWidget(label);
}
else if (newstate == 1)
{
QString sstring = "Wird gestartet!";
QLabel *label = new QLabel(sstring);
this->processstatus.append(label);
this->vrarea->addWidget(label);
}
else if (newstate == 2)
{
QString sstring = "Wird ausgeführt!";
QLabel *label = new QLabel(sstring);
this->processstatus.append(label);
this->vrarea->addWidget(label);
}
else
{
QString sstring = "kein Status vorhanden!";
QLabel *label = new QLabel(sstring);
this->processstatus.append(label);
this->vrarea->addWidget(label);
}
}

Answer 1

Each QProcess has finished(int exitCode, QProcess::ExitStatus exitStatus) and stateChanged(QProcess::ProcessState newState) signals, that emits when some process has been terminated or changed (by type of). So your code can be:
.H side:
public slots:
void processFinished(int exitCode, QProcess::ExitStatus exitStatus);
void addlabelstatus(QProcess::ProcessState newState);
.CPP side:
void mywidget::processFinished(int exitCode, QProcess::ExitStatus exitStatus)
{
<...>
}
void mywidget::addlabelstatus(QProcess::ProcessState newState)
{
switch(newState) {
<...>
};
}
// Your code change
QProcess *process = new QProcess(this);
this->myprocess.append(process);
connect(process, &QProcess::finished, this, &mywidget::processFinished);
connect(process, &QProcess::stateChanged, this, &mywidget::addlabelstatus);
process->start(text);
UPDATE FOR COMMENT QUESTION
You can try this way:
.H side
public slots:
void processFinished(QLabel *label, int exitCode, QProcess::ExitStatus exitStatus);
void addlabelstatus(QLabel *label, QProcess::ProcessState newState);
.CPP side
void mywidget::processFinished(QLabel *label, int exitCode, QProcess::ExitStatus exitStatus)
{
<...>
}
void mywidget::addlabelstatus(QLabel *label, QProcess::ProcessState newState)
{
switch(newState) {
<...>
};
}
while(!stream->atEnd()) {
this->fileread = stream->readLine();
if(!this->fileread.isEmpty()) {
QLabel *label = new QLabel(this->fileread);
QProcess *process = new QProcess(this);
this->myprocess.append(process);
connect(process, &QProcess::finished, [=]
(int exitCode, QProcess::ExitStatus exitStatus)
{ processFinished(label, exitCode, exitStatus); });
connect(process, &QProcess::stateChanged, [=]
(QProcess::ProcessState newState)
{ addlabelstatus(label, newState); });
process->start(text);
}
}

Answer 2

A while loop isn´t the solution, since it is blocking the ui-thread.
Correct. However, since Qt is an event-driven framework, you could use a timer:-
// Assuming we have a list of processes QList<QProcess*> called timerList
QTimer* pTimer = new QTimer;
connect(pTimer, &QTimer::timeout, [=](){
foreach(QProcess* proc, timerList)
{
// get state
int state = process->state();
// update UI
addlabelstatus(state);
}
});
pTimer->start(1000); // every second
Or alternatively, as #someoneinthebox answered, connect to each QProcess's stateChanged signal to notify you when it occurs and react to that.