CODEWITHSUNDEEP
c++qt
user1265478
user1265478

Reputation: 109

How to properly shutdown QProcess which I have created?

In my Qt C++ program I created a process as follows:

myProcess = new QProcess();
myProcess->start(programpath, arguments);

Terminating the process is handled as follows: 

myProcess->terminate();

Terminating the child process with QProcess::kill(),terminate() or close() works, but I don't want to use it because it doesn't give the child process a chance to clean up before exiting.

Is there any other way to exit the process? Thanks!

Upvotes: 1

Views: 4017

Answers (2)

JustMaximumPower
JustMaximumPower

Reputation: 1277

terminate actually gives the process an chance to clean up. The program being terminated just has to take that chance i.e. the system sents a SIGTERM and the application and it can ignore that and exit cleanly on its own. If this is still not nice enough then you have to implement your own way of asking the application to quit. Jeremy Friesner made some good successions. If the application code is not written by yourself you'll have to read the documentation for that program closer, maybe its documented how to do that.

Upvotes: 2

Jeremy Friesner
Jeremy Friesner

Reputation: 73041

The polite way would be for the parent process to politely ask the child process to go away. Then when the child process exits (of its own volition), the QProcess object will emit a finished(int, QProcess::ExitStatus) signal, and you can have a slot connected to that signal that will continue your process (e.g. by deleting the QProcess object at that time). (Or if you don't mind blocking your Qt event loop for a little while, you could just call waitForFinished() on the QProcess object after asking it to exit, and waitForFinished() won't return until the process has gone away or the timeout period has elapsed)

Of course for the above to work you need some way to ask the child process to exit. How you go about doing that will depend on what the child process is running. If you're lucky, you are in control of the child process's code, in which case you can modify it to exit in response to some action of the parent process -- for example, you could code the child process to exit when its stdin descriptor is closed, and have the parent process call closeWriteChannel() on the QProcess object to cause that to happen. Or if you're running under Linux/Unix you could send a SIGINT signal to the child process and the child process could set up a handler that would catch the signal and start an orderly shutdown. Or if you want something really stupid-quick and dirty, have the child process periodically check for the presence of a file at a well-known location (e.g. "/tmp/hey-child-process-PIDNUMBERHERE-go-away.txt" or something) and the parent process would create such a file when it wants the child to go away. Not that I'd recommend that last method as I don't think it would be very robust, except maybe as a proof of concept.

Upvotes: 2

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