vimproc_async.vim

let s:vimproc = vimproc#pgroup_open("sleep 10 | echo 'hello'")
call s:vimproc.stdin.close()
let s:result = ""

augroup vimproc_async_test
    execute "autocmd! CursorHold,CursorHoldI * call"
                \ "s:receive_vimproc_result()"
augroup END

function! s:receive_vimproc_result()
    if !has_key(s:, "vimproc")
        return
    endif

    let vimproc = s:vimproc

    try
        if !vimproc.stdout.eof
            let s:result .= vimproc.stdout.read(1000, 0)
        endif

        if !vimproc.stderr.eof
            let s:result .= vimproc.stderr.read(1000, 0)
        endif

        if !(vimproc.stdout.eof && vimproc.stderr.eof)
            return 0
        endif
    catch
        echom v:throwpoint
    endtry

    augroup vimproc_async_test
        autocmd!
    augroup END

    call vimproc.stdout.close()
    call vimproc.stderr.close()
    call vimproc.waitpid()
    echom s:result
    unlet s:vimproc
    unlet s:result
endfunction