Passing a QProcess to a function

taraj

Hi,

How do I pass a new QProcess to a function? I can't get the pointers right... what */& goes where?

Thank you so much!

file.cpp (has qthreadpool to run ProcessThread, need to return value so using connect

QProcess *proc = new QProcess();
ProcessThread *pt = new ProcessThread(node->nodeName(), proc);
connect(proc, SIGNAL(finished(int, QProcess::ExitStatus)), this, SLOT(showAnswer()),Qt::QueuedConnection);
 pool->start(pt);

//showAnswer() function in file.cpp

ProcessThread.cpp

ProcessThread::ProcessThread(QString name, QProcess *proc) :  x(name), _proc(0)
{  
   _proc = proc;
}
void ProcessThread::run()
{
}

ProcessThread.h
class ProcessThread : public QRunnable
{
Q_OBJECT
public:
   ProcessThread(QString, QProcess *);
   void run();

jsulm

@taraj said in Passing a QProcess to a function:

I can't get the pointers right... what */& goes where?

I suggest you read a book about C++ as this is really very basic knowledge.
The code looks correct so far except I do not know how _proc is defined. Do you get any errors?

There is another big problem with your code: if you want to use QProcess instance in another thread then either create it in that thread (inside run()) or move it to that thread using https://doc.qt.io/qt-5/qobject.html#moveToThread

Christian Ehrlicher

And the next problem - you don't need a thread when you just want to run a QProcess.

taraj

@Christian-Ehrlicher yes, currently I have just qprocess but to run the script on a remote machine for at least 50 nodes takes too long and the rest of the GUI application 'sort of' freezes/blocks and can miss the monitoring messages it also receives separately so using threads was a way to try to speed it up
I believe can use signals and slots to communicate back with the main thread—(using QueuedConnection) but can't quite get it going.. didn't seem to like SIGNAL(finished)

jsulm

@taraj As I wrote before: create the QProcess instance inside the thread where you want to use it...

Christian Ehrlicher

@taraj said in Passing a QProcess to a function:

so using threads was a way to try to speed it up

No! QProcess is async.

and can miss the monitoring messages

No, this can not happen, all stdout/stderr is buffered.

taraj

I ended up doing it like this:
https://mayaposch.wordpress.com/2011/11/01/how-to-really-truly-use-qthreads-the-full-explanation/

QProcess was created in the thread and used signal/slot to get the return value from the QThread back to the main GUI thread using emit()

Thanks

Christian Ehrlicher

Still no thread needed for such a task...