Job_control

Nvim :help pages, generated from source using the tree-sitter-vimdoc parser.

Nvim job control job-control

Job control is a way to perform multitasking in Nvim, so scripts can spawn and control multiple processes without blocking the current Nvim instance.

Concepts

Job Id job-id

Each job is identified by an integer id, unique for the life of the current Nvim session. Each job-id is a valid channel-id: they share the same "key space". Functions like jobstart() return job ids; functions like jobstop(), chansend(), rpcnotify(), and rpcrequest() take job ids.

Job stdio streams form a channel which can send and receive raw bytes or msgpack-rpc messages.

Usage job-control-usage

To control jobs, use the "job…" family of functions: jobstart(), jobstop(), etc.

Example:

function! s:OnEvent(job_id, data, event) dict
  if a:event == 'stdout'
    let str = self.shell.' stdout: '.join(a:data)
  elseif a:event == 'stderr'
    let str = self.shell.' stderr: '.join(a:data)
  else
    let str = self.shell.' exited'
  endif
  call append(line('$'), str)
endfunction
let s:callbacks = {
\ 'on_stdout': function('s:OnEvent'),
\ 'on_stderr': function('s:OnEvent'),
\ 'on_exit': function('s:OnEvent')
\ }
let job1 = jobstart(['bash'], extend({'shell': 'shell 1'}, s:callbacks))
let job2 = jobstart(['bash', '-c', 'for i in {1..10}; do echo hello $i!; sleep 1; done'], extend({'shell': 'shell 2'}, s:callbacks))

To test the above script, copy it to a file ~/foo.vim and run it:

nvim -u ~/foo.vim

Description of what happens:

Two bash shells are spawned by jobstart() with their stdin/stdout/stderr streams connected to nvim.

The first shell is idle, waiting to read commands from its stdin.

The second shell is started with -c which executes the command (a for-loop printing 0 through 9) and then exits.

OnEvent() callback is passed to jobstart() to handle various job events. It displays stdout/stderr data received from the shells.

For on_stdout and on_stderr see channel-callback. on_exit
Arguments passed to on_exit callback: 0: job-id 1: Exit-code of the process, or 128+SIGNUM if by signal (e.g. 143 on SIGTERM). 2: Event type: "exit"

Note: Buffered stdout/stderr data which has not been flushed by the sender will not trigger the on_stdout/on_stderr callback (but if the process ends, the on_exit callback will be invoked). For example, "ruby -e" buffers output, so small strings will be buffered unless "auto-flushing" ($stdout.sync=true) is enabled.

function! Receive(job_id, data, event)
  echom printf('%s: %s',a:event,string(a:data))
endfunction
call jobstart(['ruby', '-e',
  \ '$stdout.sync = true; 5.times do sleep 1 and puts "Hello Ruby!" end'],
  \ {'on_stdout': 'Receive'})

https://github.com/neovim/neovim/issues/1592

Note 2: Job event handlers may receive partial (incomplete) lines. For a given invocation of on_stdout/on_stderr, a:data is not guaranteed to end with a newline.

abcdefg may arrive as ['abc'], ['defg'].

abc\nefg may arrive as ['abc', ''], ['efg'] or ['abc'], ['','efg'], or even ['ab'], ['c','efg']. Easy way to deal with this: initialize a list as [''], then append to it as follows:

let s:chunks = ['']
func! s:on_stdout(job_id, data, event) dict
  let s:chunks[-1] .= a:data[0]
  call extend(s:chunks, a:data[1:])
endf

The jobstart-options dictionary is passed as self to the callback. The above example could be written in this "object-oriented" style:

let Shell = {}
function Shell.on_stdout(_job_id, data, event)
  call append(line('$'),
        \ printf('[%s] %s: %s', a:event, self.name, join(a:data[:-2])))
endfunction
let Shell.on_stderr = function(Shell.on_stdout)
function Shell.on_exit(job_id, _data, event)
  let msg = printf('job %d ("%s") finished', a:job_id, self.name)
  call append(line('$'), printf('[%s] BOOM!', a:event))
  call append(line('$'), printf('[%s] %s!', a:event, msg))
endfunction
function Shell.new(name, cmd)
  let object = extend(copy(g:Shell), {'name': a:name})
  let object.cmd = ['sh', '-c', a:cmd]
  let object.id = jobstart(object.cmd, object)
  $
  return object
endfunction
let instance = Shell.new('bomb',
      \ 'for i in $(seq 9 -1 1); do echo $i 1>&$((i % 2 + 1)); sleep 1; done')

To send data to the job's stdin, use chansend():

:call chansend(job1, "ls\n")
:call chansend(job1, "invalid-command\n")
:call chansend(job1, "exit\n")

A job may be killed at any time with the jobstop() function:

:call jobstop(job1)

Individual streams can be closed without killing the job, see chanclose().