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Simple library for asynchronous processing in Emacs
Emacs Lisp

License GPL 3 MELPA MELPA Stable


async.el is a module for doing asynchronous processing in Emacs.


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.

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.


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\\)-")
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