Unable to resume backgrounded Neovim-terminal-emulator-process using `kill -CONT`

Question

So, I'm trying to find an actual solution to another question on here that doesn't really have one. However, I'm running into a problem with backgrounding/foregrounding behaviour.

I need to background any processes spawned from the shell inside the terminal. So far, I have the following assembled:

function! s:terminal_clear()
   let l:scrollback = &scrollback
   set scrollback=1

   " Background any child-process. (No idea why <C-z> doesn't work.)
   let l:children = systemlist('pgrep -P '.b:terminal_job_pid)
   for pid in l:children[1:]
      call jobstart(['kill', '-STOP', pid])
   endfor

   " Space at the start of the command, plus additional space-return, prevents this from being added
   " to shell history. Requires `setopt histignorespace`.
   call chansend(&channel, " printf '\\n%.0s' {1..200}\<CR> \<CR>")
   call feedkeys("i\<C-l>")

   sleep 1000m

   for pid in l:children
      call jobstart(['kill', '-CONT', pid])
   endfor

   exec "set scrollback=".l:scrollback
endfunction

Unfortunately, the for-loop at the end, calling kill -CONT ... on each backgrounded PID, isn't functioning.

I can resume the suspended processes manually, using fg; but that's a bit of a nonstarter (doing so in the terminal-emulator-in-question, almost no matter what I do, leaves an fg entry in the shell-history — completely defeating all the work I've been doing here in the first place to prevent precisely that.)

Does anybody know why kill -CONT might not work on a process inside Vim's terminal emulator? What am I doing incorrectly, here?

Answer 1

Note that job control in a shell is different from just sending a SIGSTOP signal to the process. It's actually much more about setting terminal settings, such as the controlling process group. So you can't really just foreground a suspended job in the shell by sending the processes in that job a SIGCONT (or, for that matter, any other signal.)

See also:

• What makes Ctrl-Z different from kill -STOP
• Job Control in bash documentation
• What is the purpose of the controlling terminal?