Skip to content


Switch branches/tags

Name already in use

A tag already exists with the provided branch name. Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. Are you sure you want to create this branch?

Latest commit


Git stats


Failed to load latest commit information.
Latest commit message
Commit time



async.el is a module for doing asynchronous processing in Emacs. Some async applications are provided as well with this package:

  • Dired-async
  • smtp-mail-async
  • async-bytecomp


You can install emacs-async package from MELPA using package.el.

You can also install from sources, in this case you should install using make and make install to ensure emacs-async is installed in a standard load-path destination where other packages can find it easily when compiling.

Install dired-async

Add to your .emacs.el:

(autoload 'dired-async-mode "dired-async.el" nil t)
(dired-async-mode 1)

This will allow you to run asynchronously the dired commands for copying, renaming and symlinking. If you are a helm user, this will allow you to copy, rename etc... asynchronously from helm. Note that with helm you can disable this by running the copy, rename etc... commands with a prefix argument.

If you don't want to make dired/helm asynchronous disable it with dired-async-mode.

Debian and Ubuntu

Users of Debian 9 or later or Ubuntu 16.04 or later may simply apt-get install elpa-async.

Authentication and user interaction

Some authentications require user interaction, for example answering to a prompt, entering a passwords etc. Your async implementation should avoid any such user interaction, to avoid being stuck with a prompt you will not be able to answer to in the child emacs. For all what is remote (mails, tramp etc...) you have to let emacs manage your identification with auth-sources, so that you do not have to enter a password.

Basically all you need is something like this in your init file:

(use-package auth-source
  :no-require t
  :config (setq auth-sources '("~/.authinfo.gpg" "~/.netrc")))

And a "~/.authinfo.gpg" file containing entries such as

default port sudo login root password xxxxxxxx


machine xxxxx port xxx login xxx password xxxxxxx

for more specific hosts (smtp, mails etc...)

See auth-sources manual for more infos.

NOTE: For all your async implementations in emacs-26+ versions that handle remote files (tramp), you will have to let-bind async-quiet-switch to -q to workaround a tramp bug that prevent emacs -Q to use auth-sources mechanism.

Enable asynchronous compilation of your (M)elpa packages

By default emacs package.el compile packages in its running emacs session. This is not a problem when installing a new package (which is not actually loaded in current emacs) but it may create errors and bad compilation when upgrading a package (old version of package is already loaded and running in current emacs). You can remedy to this by allowing async to compile your packages asynchronously, (helm and magit actually do this by default, so if you are using these packages they will compile asynchronously) to do this, add to your init file:

(async-bytecomp-package-mode 1)

You can control which packages will compile async with async-bytecomp-allowed-packages. Set it to '(all) to be sure you will compile all packages asynchronously.

Send mails asynchronously with smtp mail async

To enable this feature, ensure smtp-mail-async.el is loaded and use

(setq message-send-mail-function 'async-smtpmail-send-it).


  • When using recent emacs (25+) the network security manager maybe called interactively in child emacs and make async-smtpmail-send-it fail, so be sure to send email once synchronously before using async-smtpmail-send-it as your message-send-mail-function.

  • You may loose your sent mail if your network is down, so ensure to queue your mails if so. you can do this automatically, see issue #64.

Async usage

The interface is intended to be very easy to use:



Execute START-FUNC (often a lambda) in a subordinate Emacs process. When done, the return value is passed to FINISH-FUNC. Example:

   ;; What to do in the child process
   (lambda ()
     (message "This is a test")
     (sleep-for 3)

   ;; What to do when it finishes
   (lambda (result)
     (message "Async process done, result should be 222: %s" result)))

If FINISH-FUNC is nil or missing, a future is returned that can be inspected using async-get, blocking until the value is ready. Example:

(let ((proc (async-start
               ;; What to do in the child process
               (lambda ()
                 (message "This is a test")
                 (sleep-for 3)

    (message "I'm going to do some work here") ;; ....

    (message "Waiting on async process, result should be 222: %s"
             (async-get proc)))

If you don't want to use a callback, and you don't care about any return value from the child process, pass the 'ignore symbol as the second argument (if you don't, and never call async-get, it will leave *emacs* process buffers hanging around):

 (lambda ()
   (delete-file "a remote file on a slow link" nil))

Note: Even when FINISH-FUNC is present, a future is still returned except that it yields no value (since the value is passed to FINISH-FUNC). Calling async-get on such a future always returns nil. It can still be useful, however, as an argument to async-ready or async-wait.



Start the executable PROGRAM asynchronously. See async-start. PROGRAM is passed PROGRAM-ARGS, calling FINISH-FUNC with the process object when done. If FINISH-FUNC is nil, the future object will return the process object when the program is finished. Set DEFAULT-DIRECTORY to change PROGRAM's current working directory.


async-get FUTURE

Get the value from an asynchronously called function when it is ready. FUTURE is returned by async-start or async-start-process when its FINISH-FUNC is nil.


async-ready FUTURE

Query a FUTURE to see if its function's value is ready -- i.e., if no blocking would result from a call to async-get on that FUTURE.


async-wait FUTURE

Wait for FUTURE to become ready.


async-inject-variables INCLUDE-REGEXP &optional PREDICATE EXCLUDE-REGEXP

Return a setq form that replicates part of the calling environment. It sets the value for every variable matching INCLUDE-REGEXP and also PREDICATE. It will not perform injection for any variable matching EXCLUDE-REGEXP (if present). It is intended to be used as follows:

   `(lambda ()
      (require 'smtpmail)
        (insert ,(buffer-substring-no-properties (point-min) (point-max)))
        ;; Pass in the variable environment for smtpmail
        ,(async-inject-variables "\\`\\(smtpmail\\|\\(user-\\)?mail\\)-")


async-let BINDINGS &rest FORMS

Allow to establish let bindings asynchronously. Each value of binding can refer to the symbols already bound in BINDINGS (like let*). FORMS are executed once BINDINGS have been evaluated, but without blocking emacs.


(async-let ((x "hello")
            (y "world"))
  (message "%s %s" x y))
(async-let ((x (* 5 2))
            (y (+ x 4))
            (z (+ x y)))
  (message "%d + %d = %d" x y z))

Note that if you bind something to nil and set it afterward in body, the evaluation of this binding will NOT be asynchronous, but will happen in you current emacs, blocking it if the evaluation of this value is sufficiently important, e.g:

(async-let ((x "hello")
            (y "world")
  (setq z (+ 1 2)) ;; Huge calculation of Z will block emacs.
  (message "%s %s %d" x y z))

IOW if the calculation of Z is huge and you want it asynchronous evaluate it in BINDINGS but not in FORMS.