[Interest] Finished signal from QProcess!

[Mandeep Sandhu]

On Wed, Feb 29, 2012 at 10:09 AM, Lata Agrawal
<lata.agrawal at enrouteinc.com> wrote:
> Hi,
>
> I am running console application C1 in QProcess. I am starting this console
> application C1 from another console application C2. Problem is:
> I am only getting finished signal from C1 when I use waitforfinshed() else I
> am not getting finished signal from C1. Here is the code:

Does your console app C1 quit after completing its work? Or is the
event loop still running in C1?...have your called
QApplication::quit/exit in C1 after it's done with it work? If not
then C1 will continue to run untill explicitly exited (or killed from
outside).

>
>                 QString strProgram;
>                 strProgram = <Path to C1>;
>
> updateProc->setProcessChannelMode(QProcess::ForwardedChannels);
>                 connect(updateProc,
> SIGNAL(finished(int,QProcess::ExitStatus)),
> SLOT(procStarted(int,QProcess::ExitStatus)), Qt::DirectConnection);

'procStarted' seems to be strange name for a slot handling the
'finished' singla!! :)
>
> updateProc->setStandardOutputProcess(this->thread()->parent());
>                 updateProc->start(strProgram, arguments);

Why is this needed? Is C2 processing o/p of C1...or do you simply want
to print stdout of C1 in C2's stdout (if so, then you've already done
that by setting the channel mode above)?

>
>                 //Download is over, indicate through bool variable that next
> downlaod can be started
>                 if(updateProc->waitForFinished(-1))
>                 {
>                     qDebug("Update process finished!\n");
>                 }
>                 else
>                 {
>                     qDebug("Update process not yet finished!\n");
>                 }
>
> void FloDownloadManager::procStarted(int retVal ,QProcess::ExitStatus
> exitStat)
> {
>     qDebug("Update process finished automatically!\n");
>     if(currentExecutingPriority == AdsUpdate)
>     {
>         emit adUpdateDone();
>     }
>     blnStartNextUpdate = true;
>
>     updateProc->deleteLater();
> }
>
>
> If I comment the waitforfinished() code, I don't get the finished signal.
> But if I include the waitforfinished() signal, I don't get the finished
> signal. Code for C1 is as follows:
>
> #include <QtCore/QCoreApplication>
> #include "updater.h"
>
> int main(int argc, char *argv[])
> {
>     QCoreApplication a(argc, argv);
>
>     qDebug("Inside Updater\n");
>
>     QTimer::singleShot(5000, &a, SLOT(quit()));
>     qDebug("returning from Updater process!@@@@@@@@\n");
>
>     return 0;
> }

You have not started the apps event loop!!!...what do you expect it
do? This program will exit out immediately! You need to do a.exec()
for the timer signal to be processed.

>
> I read on other forums that if main process does not wait for child process
> to finish like using waitforfinished, then finished signal will not be sent
> to main process, rather child process after finishing will become defunct or
> zombie. In my code above, if I use waitforfinished, then main process does
> receive finished signal.

AFAIK, in linux, if the parent process dies before a child process
finishes, it is re-parented to init (process with pid 1). This is
called an 'orphaned' process. Not to be confused with a zombie/defunct
in which a process has exited, but it's entry has not been removed
from process table.

More:
http://en.wikipedia.org/wiki/Orphan_process
http://en.wikipedia.org/wiki/Zombie_process

>
> Is there any way by which main process can receive finished signal without
> waiting for child process to finish?

Yes, by connecting to the child QProcess's 'finished' signal. Thats
what the signal is there for! :) It tells the parent when a process
has exited and with what exit code.

HTH,
-mandeep

> Regards,
> Lata
>
>
> --
>
>
> Lata Agrawal
> Senior Developer
> 9699750643
> En Route Media Pvt. Ltd.
>
>
>
> _______________________________________________
> Interest mailing list
> Interest at qt-project.org
> http://lists.qt-project.org/mailman/listinfo/interest
>