Kill a process and its children

hbatalha

I am using a command line program that I started using QProcess and that program uses ffmpeg to complete its task.
The problem I am having is that I can't kill ffmpeg, I can kill the program that started it but that doesn't kill it.
I've tried to get the process id and I used it to taskill it but it still doesn't kill ffmpeg.

In this answer he used wmic on windows, but couldn't figure out how exactly that is done/

SGaist

Hi,

Can you interrupt somehow that program cleanly rather than killing it ?

JonB

@hbatalha
First it's much preferable if you exit processes cleanly like @SGaist says. Why are you in a position when you need to kill ffmpeg?

But if you do have to, I suggest you first confirm that you can bring up Task Manager and find and successfully terminate it from there? If you can do that manually we can talk about doing it programatically.

hbatalha

@SGaist I looked for a way to interrupt it with Qt but found none

hbatalha

@JonB said in Kill a process and its children:

First it's much preferable if you exit processes cleanly like @SGaist says.

There's no way to exit cleanly with QProcess, I have to kill.

Why are you in a position when you need to kill ffmpeg?

Because ffmpeg is a child process of the command line program I am using, when I kill the program with QProcess::kill it will not kill ffmpeg wich is what I wish it could happen.
For example if I am using that program directly in cmd, when it starts ffmpeg I just need ctrl+c to kill the program along with ffmpeg instance it started. That 's what I am trying figure out how to do with Qt.

JonB

@hbatalha said in Kill a process and its children:

There's no way to exit cleanly with QProcess, I have to kill.

Nothing to do with QProcess. The question was why ffmpeg has to be killed at all. Why does it not exit normally after doing whatever it is you ask it to do?

when it starts ffmpeg I just need ctrl+c to kill the program along with ffmpeg instance it started.

Ctrl+C is a different matter. It is probably sent to ffmpeg when run from command prompt, or something similar. In any case, you are not running it interactively from a command prompt and you say killing the command line parent program does not terminate the ffmpeg, so that is where we are. You can read the discussion in the https://forum.qt.io/topic/86762/can-t-stop-a-process to which you referred.

I told you that if you can confirm that you are able to run Task Manager, find the ffmpeg process by name and kill it from there, then we could look at doing that from code. But you chose not to answer.

deleted471

@hbatalha Try Detach

JonB

@APM0X400
Why do you think that will help? Worth a try I guess, but I would not have thought so.

SGaist

@hbatalha beside the good points of @JonB, what exactly are you using to pilot ffmpeg ?

hbatalha

@JonB said in Kill a process and its children:

Why does it not exit normally after doing whatever it is you ask it to do?

It does exit normally after completing its task. But I want to give the user the option to cancel whatever it is doing any time. I can't stop ffmpeg with QProcess because it is a child process of the process QProcess

But you chose not to answer.

Sorry, I must have missed it. Yes I can go in the task manager and kill with no problem, that's what I have been doing.

@SGaist said in Kill a process and its children:

what exactly are you using to pilot ffmpeg ?

I am using yt-dlp which in turn uses ffmpeg to do some file conversions. Those conversion usually takes a long time, that's why I want to give the user the ability to cancel it anytime.

jsulm

@hbatalha What about https://doc.qt.io/qt-5/qprocess.html#kill ?

SGaist

If the QProcess::kill suggested by @jsulm does not work as expected (which I think should), then try sending the SIGINT signal to the process.

JonB

@hbatalha said in Kill a process and its children:

Yes I can go in the task manager and kill with no problem, that's what I have been doing

You can try @SGaist's attempt to send the parent process a SIGINT and hope that might interrupt its child, I don't know how that all works on Windows.

To get at the ffmpeg process to kill it: you should be able to use EnumProcesses function (psapi.h) to enumerate all running processes and look at their names, and kill the desired one. I came across https://social.msdn.microsoft.com/Forums/en-US/67331e20-a30b-417d-85e5-f9350fef908d/do-we-need-to-use-enumprocesses-and-enumprocessmodules-when-terminating-the-process-in-c?forum=vcgeneral or https://stackoverflow.com/questions/1916574/how-to-effectively-kill-a-process-in-c-win32 you might want to read through. Or Google windows enumprocesses kill process to get going.

JoeCFD

@JonB said in Kill a process and its children:

ffmpeg

https://stackoverflow.com/questions/9722624/how-to-stop-ffmpeg-remotely

JoeCFD

You send out ctrl + C to exit cleanly
kill( m_process->processId(), SIGINT );

hbatalha

I thank everyone's reply here, I was able to find a solution for windows by, as suggested in the replies, sending SIGNT signal to the parent process.

I found the solution in @JonB referenced SO post in this answer and translated it into Qt code:

QProcess::execute("taskkill", {"/pid", QString::number(process->processId()), "/t", "/f"});

I am yet to test the QProcess::kill behavior in Linux. It would be a bonus if someone who knows telling me.

JoeCFD

@hbatalha kill( m_process->processId(), SIGINT ); is same as Ctrl + C.
will work on both Windows and Linux. kill() is c code. You do not need taskkill pid on Windows and kill -9 pid on Linux.

hbatalha

@JoeCFD in which header will I find the kill function?

JoeCFD

@hbatalha #include <signal.h>

hbatalha

@JoeCFD said in Kill a process and its children:

@hbatalha #include <signal.h>

I am still getting undeclared identifier 'kill' error after including <signal.h>