CPU using %100 by nnn

[abdyek]

Hi,
I use nnn v2.3 on manjaro linux - i3.
It is running nnn at background when I close it.
https://postimg.cc/s11YZnQ4

[jarun]

Please share the exact steps to reproduce.

[abdyek]

Ohh.. sorry
Firstly, my english is not good so I am sorry for it
I use vim for programming. Folders of my projects are at /mnt/Depo/Project
I added export NNN_BMS='d:/mnt/Depo;p:/mnt/Depo/Projects;' to .bashrc file,
I prefer to go to my project folder using leader key + p and return shell with ! to open vim,
Sometimes I open nnn another terminal window and close it
What can I share info about this issue ?

[jarun]

What can I share info about this issue ?

I couldn't reproduce your issue. So I need definite steps - how did you start nnn, what's your terminal emulator and shell. What did you do after starting nnn, basically a way to reproduce it on my setup locally so I can analyze the issue.

nnn kills itself if the parent process has exited so I have to know the steps when I guess this is not happening.

Also, please try on master and see if you are seeing the issue.

[abdyek]

I use i3-wm, gnome-terminal, vim and manjaro linux than
I will explain it step by step

• I opened a new gnome terminal using $mod key + enter
• I started nnn with commant of "nnn"
• I went to my bookmarks with leader key + p (export NNN_BMS='d:/mnt/Depo;p:/mnt/Depo/Projects;')
• I returned shell with ! and started vim using "vim"
• I worked in the terminal for a while
• I opened new another terminal using $mod key + enter
• I started nnn with commant of "nnn"
• I used it and closed it

[jarun]

OK.

I worked in the terminal for a while

did you quit vim and nnn or left vim open?

I used it and closed it

what is it? Used the terminal and closed it directly? Did you quit nnn?

[jarun]

I have tried to reproduce it using your steps and directly closing the terminal (xfce4-terminal) at the points I noted above. However, I do not see the issue. In both the cases nnn quits when I close the terminal directly.

Can you try this on the latest release v2.4?

[jarun]

Please revert back when you have more info.

[cowabungadude69]

Here's a simple way to recreate it I think.

• open a terminal
• start nnn
• enter shell with !
• start nnn in that shell
• close the terminal

Tried this on two machines with simple terminal and bash.

[jarun]

I will look into it.

[jarun]

@cowabungadude69 thanks for the steps. I could reproduce the issue with st and terminator.

The issue happens due to the following deadlock:

nnn keeps checking if the parent has exited. However, when it spawns a child it waits (blocks) for the child to exit and can't check if its parent has exited. The child on the other hand, doesn't quit because it's parent hasn't exited.

I have fixed it. Please test and confirm the patch.

[cowabungadude69]

Yep, no problems here. Thank you.

[jarun]

@cowabungadude69 I believe I have to pull back patch 32dde33 and document as a known issue. The problem with polling on waitpid is whenever a child process is spawned, the parent nnn process uses 100% memory.

This is a serious problem. In case of the scenario you reported, the terminal is closed with a nested nnn instance and it can be easily avoided (by not closing the terminal directly without closing a running nnn instance). However the fix is going to affect every user who spawns a child process.

[borestad]

How bad of a fix would it be to spawn a helper process that looks if nnn is still running - but not in TTY-mode anymore - and then kill the main process and itself?

[borestad]

Some reference to ncdu that I think might have the same issue

rofl0r/ncdu@cbe24d6

[jarun]

Update: this issue is fixed now!

I will leave it as a known issue as documented currently. The time taken to confirm any elaborate mechanism on all supported platforms is significant and I would rather add a useful feature if I get the time instead.

[jarun]

@abdyek @cowabungadude69 @borestad this issue is now fixed.

[jcguu95]

Off topic.. but I appreciate watching you fixing problems! Thanks for great work!