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
- async-package
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.
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.
Users of Debian 9 or later or Ubuntu 16.04 or later may simply apt-get install elpa-async.
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
or
machine xxxxx port xxx login xxx password xxxxxxx
for more specific hosts (smtp, mails etc...)
See auth-sources manual for more infos.
However, when choosing the destination with completion (e.g. helm) and you have no ".authinfo" file or just no entry for this host, tramp will prompt for password and offer you to save it, if you answer 'yes' you will be able to achieve you async operation as the child Emacs will use this just created ".authinfo" file, if you say 'no', your dired-async process will hang forever because child emacs is waiting for password.
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.
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.
When using async-bytecomp-package-mode only compilation is done
async. To do all async (download and (re)install) the function
async-package-do-action is provided, it is used by Helm packages UI.
To enable this feature, ensure smtpmail-async.el is loaded and use
(setq message-send-mail-function 'async-smtpmail-send-it).
WARNINGS:
-
When using recent emacs (25+) the network security manager maybe called interactively in child emacs and make
async-smtpmail-send-itfail, so be sure to send email once synchronously before usingasync-smtpmail-send-itas yourmessage-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.
The interface is intended to be very easy to use:
async-start START-FUNC FINISH-FUNC
Execute START-FUNC (often a lambda) in a subordinate Emacs process. When done, the return value is passed to FINISH-FUNC. Example:
(async-start
;; What to do in the child process
(lambda ()
(message "This is a test")
(sleep-for 3)
222)
;; 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)
222))))
(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):
(async-start
(lambda ()
(delete-file "a remote file on a slow link" nil))
'ignore)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.
async-start-process NAME PROGRAM FINISH-FUNC &rest PROGRAM-ARGS
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:
(async-start
`(lambda ()
(require 'smtpmail)
(with-temp-buffer
(insert ,(buffer-substring-no-properties (point-min) (point-max)))
;; Pass in the variable environment for smtpmail
,(async-inject-variables "\\`\\(smtpmail\\|\\(user-\\)?mail\\)-")
(smtpmail-send-it)))
'ignore)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.
Examples:
(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")
z)
(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.