paused timers consume CPU

[andymass]

• nvim --version: NVIM v0.2.2
• Vim (version: ) behaves differently? Cannot reproduce in vim 8.1542
• Operating system/version: Arch linux/recent
• Terminal name/version: konsole/17.12.3
• $TERM: xterm-256color

Steps to reproduce:

Here is an example init.vim:

set nocompatible

if 0     " toggle to enable vim-airline
	let &rtp  = '~/.config/nvim/bundle/vim-airline,' . &rtp
endif

filetype plugin indent on
syntax on 

function! CallBack(tid)
	echo 'callback'
endfunction

let g:timer = timer_start(10, 'Callback',
            \ {'repeat': -1})

call timer_pause(g:timer, 1)

nnoremap <space> :<c-u>call timer_stop(g:timer)<cr>

run:

nvim -u init.vim init.vim

and htop or similar.

This is probably related to: #7871, though that was primarily about a memory leak.

Actual behavior

• Without vim-airline, neovim consumes 1%--2% CPU. Pressing space to stop the timer makes the CPU go to 0%.

• With vim-airline, neovim consumes 10%--12% CPU. Again, pressing space makes the CPU go to 0%.

To emphasize, I am not claiming this is any bug in vim-airline, but the presence of vim-airline exacerbates the issue many-fold, which may help in determining the cause.

Expected behaviour

There should be no CPU activity when timers are paused. In vim, there is apparently no cost to having timers paused.

[bfredl]

probably time_watcher_stop or time_watcher_start should be called in f_timer_paused (conditional on that the state actually changed).