Kill a process and its children
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@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.
@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
QProcessbecause it is a child process of the processQProcessBut 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.
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@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
QProcessbecause it is a child process of the processQProcessBut 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.
@hbatalha What about https://doc.qt.io/qt-5/qprocess.html#kill ?
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If the QProcess::kill suggested by @jsulm does not work as expected (which I think should), then try sending the
SIGINTsignal to the process. -
@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
QProcessbecause it is a child process of the processQProcessBut 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.
@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
SIGINTand 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 processto get going. -
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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::killbehavior in Linux. It would be a bonus if someone who knows telling me. -
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::killbehavior in Linux. It would be a bonus if someone who knows telling me. -
@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. -
@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> -
@hbatalha Sorry. My bad. It is not for Windows. I thought it is standard C code.
You may try kill -9 pid on MingW. -
@hbatalha if it works, it should be ok. Ctrl+C is cleaner, I believe.
https://stackoverflow.com/questions/813086/can-i-send-a-ctrl-c-sigint-to-an-application-on-windows
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What you want is
QProcess::terminate, which does the right thing™, and the right thing is to traverse the threads of the process and post theWM_QUITmessage to each one that runs an event loop. If the process doesn't run an event loop, then the program you're trying to run was never (ever) intended to be controlled from the outside and you should open a feature request for its developers. Coincidentally if it doesn't integrate into the windows event queue, then don't run it, or at least don't expect to (semi)magically be able to control it from another process.Don't kill processes, just as you don't (assumedly) go around killing kittens. It's called
killfor a good reason and it's bad and ugly, and you shan't do it unless you've exhausted every other means, which you haven't. -
What you want is
QProcess::terminate, which does the right thing™, and the right thing is to traverse the threads of the process and post theWM_QUITmessage to each one that runs an event loop. If the process doesn't run an event loop, then the program you're trying to run was never (ever) intended to be controlled from the outside and you should open a feature request for its developers. Coincidentally if it doesn't integrate into the windows event queue, then don't run it, or at least don't expect to (semi)magically be able to control it from another process.Don't kill processes, just as you don't (assumedly) go around killing kittens. It's called
killfor a good reason and it's bad and ugly, and you shan't do it unless you've exhausted every other means, which you haven't.@kshegunov said in Kill a process and its children:
What you want is
QProcess::terminateQProcess::terminatedoesn't do anything when I call it on Windowsand the right thing is to traverse the threads of the process and post the WM_QUIT message to each one that runs an event loop.
How do you propose to do that?
then the program you're trying to run was never (ever) intended to be controlled from the outside and you should open a feature request for its developers.
Could you elaborate?
