gtags-cscope.vim from gnu global https://www.gnu.org/software/global/manual/global.html
Ported auto update from gtags.vim to gtags-cscope.vim. When a file is modified
and saved, global -u --single-update is called to update tags.

Add following line to .vimrc use VimPlug to install:
Plug 'multilobyte/gtags-cscope'

Configure following variables in $HOME/.vimrc.
" To use the default key/mouse mapping:
" let GtagsCscope_Auto_Map = 1
" To ignore letter case when searching:
" let GtagsCscope_Ignore_Case = 1
" To use absolute path name:
" let GtagsCscope_Absolute_Path = 1
" To deterring interruption:
" let GtagsCscope_Keep_Alive = 1
" If you hope auto loading:
" let GtagsCscope_Auto_Load = 1
" To use 'vim -t ', ':tag' and '<C-]>'
" set cscopetag
" To auto update tags when a file is saved " let GtagsCscope_Auto_Update = 1

then run the following in Vim:
:source %
:PlugInstall