Qprocess and mpi not finishing

[wysota]

Sounds more like QT signals are somehow hijacking the mpi functionality.

This is very unlikely. A parent process can't intercept its child's signals. Especially that QProcess is cross-platform so it is very unlikely it uses unix signals at all.

IF i manually kill mpiexec, the QProcess does send the finished() signal.

This also suggests mpiexec just doesn't want to die on its own. If Qt hijacked its signals, it would also have hijacked the one you had sent.

Since the QProcesses maintains a connection, it always thinks it needs to stay alive and therefore never exits.

No, because if that was true, mpiexec would never die when ran from a terminal as the shell maintains a similar connection to its file descriptors as Qt does. It's the parent process that creates descriptors for its child before calling execve() or equivalent and it usually "attaches" those descriptors to itself. mpiexec must be detecting it's not the owner of its own process group and doesn't terminate. It probably sends some signal to the group leader, at least that could be the case on Unix. I don't know how processes are groupped in Windows.

[vdwgeert]

Currently I'm facing the same problem with mpiexec, did you found a solution for this problem then?

[DjayDjay]

Exactly the same problem : still no solution (6 years after !)

Working with Qt 4.8, Windows

[ChrisW67]

Rather than post "Me too!" Perhaps you could put some effort in to write a small, self-contained example that demonstrates the problem. The problem almost certainly has nothing to do with Qt but you never know what the process of distilling and sharing the problem might show you.

You could also capture any standard output/error output from mpiexec, which I am sure could be useful in conjunction with other MPI log.

BTW: Mar 2009 to Jan 2014 is a long way short of 6 years.

[DjayDjay]

Ok i was a bit frustrated ... and you are right 2009 to 2014 is a bit less than 6 years !

The solution i found is to use the command "system" rather than qprocess

My first idea was to use QProcess like this :
QProcess process;
process.setWorkingDirectory( "xxxx" );
process.setProcessChannelMode(QProcess::MergedChan nels);
process.setStandardOutputFile("logfile");
process.start(commandProcess,argumentsProcess);
process.waitForFinished(-1);

But as i mentionned, the qprocess never sends a finish signal (why, this is the question and that's maybe mpiexec problem ??)

Solution i did is (using command system) :
QString command = commandProcess+" "+argumentsProcess.join(" ")+ " > "+logProcessFilePath;
command = QDir::toNativeSeparators(command);
command.replace(":\\",":\\\\");
int returnCode = system(command.toStdString().c_str());

[matpen]

I am sorry to post in a very old thread, but I figured that it might help others looking for an answer in a search engine...

I just had the very same problem, which might be due to this bug, at least according to my research.
According to that message, OpenMPI is catching the SIGCHLD signal, which is necessary for QProcess "finished" signal to work correctly (and thus for QProcess::waitForFinished()).

The message says that this was changed in OpenMPI series 1.6 and 1.7.
As of today, the latest Ubuntu 15.10 ships with OpenMPI 1.6.5, which apparently is still affected by this (mis-)behaviour.

Upgrading to a later OpenMPI version should therefore fix the problem.
I did this by installing OpenMPI 1.10.2 from source, which is very easily done by following these instructions, and I can confirm that the problem is solved.

Hope this helps...