function! s:handler(job_id, data, event_type)
    echo a:job_id . ' ' . a:event_type
    echo join(a:data, "\n")
endfunction

if has('win32') || has('win64')
    let argv = ['cmd', '/c', 'dir c:\ /b']
else
    let argv = ['bash', '-c', 'ls']
endif

let jobid = async#job#start(argv, {
    \ 'on_stdout': function('s:handler'),
    \ 'on_stderr': function('s:handler'),
    \ 'on_exit': function('s:handler'),
\ })

if jobid > 0
    echom 'job started'
else
    echom 'job failed to start'
endif

" If you want to get the process id of the job
let pid = async#job#pid(jobid)

" If you want to wait the job:
call async#job#wait([jobid], 5000)  " timeout: 5 sec

" If you want to stop the job:
call async#job#stop(jobid)

APIs

APIs are based on neovim's job control APIs.

Embedding

Async.vim can be either embedded with other plugins or be used as an external plugin. If you want to embed all you need is to change these 5 function names async#job# to what ever you want. E.g.:

" public apis {{{
function! yourplugin#job#start(cmd, opts) abort
    return s:job_start(a:cmd, a:opts)
endfunction

function! yourplugin#job#stop(jobid) abort
    call s:job_stop(a:jobid)
endfunction

function! yourplugin#job#send(jobid, data) abort
    call s:job_send(a:jobid, a:data)
endfunction

function! yourplugin#job#wait(jobids, ...) abort
    let l:timeout = get(a:000, 0, -1)
    return s:job_wait(a:jobids, l:timeout)
endfunction

function! yourplugin#job#pid(jobid) abort
    return s:job_pid(a:jobid)
endfunction
" }}}

Todos

Fallback to sync system() calls in vim that doesn't support job
job_stop and job_send is treated as noop when using system()
on_stderr doesn't work when using system()
Fallback to python/ruby threads and vimproc instead of using system() for better compatibility (PRs welcome!!!)