Dired copy asynchronously

Question

Is there a way to modify/tell dired to copy files asynchronously? If you mark multiple files in dired and then use 'C' to copy them, emacs locks up until every file is copied. I instead want this copy to be started, and for me to continue editing as it goes on in the background. Is there a way to get this behaviour?

EDIT: Actually, C calls 'dired-do-copy' in dired-aux, not in dired itself. Sorry for any confusion.

Answer 1

I found this answer quite helpful: https://emacs.stackexchange.com/a/13802/10761. Reading that answer shows that you can make it so that dired will copy with the scp method instead of the ssh method (the latter initially encodes the file with gzip and that can be quite slow). The scp method will only copy with the scp program when the file is larger than tramp-copy-size-limit (which is 10240 by default). Using this scp method in conjunction with dired-async-mode is very nice, as it will not only copy quickly with scp, but it will also do it asynchronously and out of your way.

Also, I think this is useful: https://oremacs.com/2016/02/24/dired-rsync/. It provides this snippet of code to use rsync to copy files in dired:

;;;###autoload
(defun ora-dired-rsync (dest)
  (interactive
   (list
    (expand-file-name
     (read-file-name
      "Rsync to:"
      (dired-dwim-target-directory)))))
  ;; store all selected files into "files" list
  (let ((files (dired-get-marked-files
                nil current-prefix-arg))
        ;; the rsync command
        (tmtxt/rsync-command
         "rsync -arvz --progress "))
    ;; add all selected file names as arguments
    ;; to the rsync command
    (dolist (file files)
      (setq tmtxt/rsync-command
            (concat tmtxt/rsync-command
                    (shell-quote-argument file)
                    " ")))
    ;; append the destination
    (setq tmtxt/rsync-command
          (concat tmtxt/rsync-command
                  (shell-quote-argument dest)))
    ;; run the async shell command
    (async-shell-command tmtxt/rsync-command "*rsync*")
    ;; finally, switch to that window
    (other-window 1)))

(define-key dired-mode-map "Y" 'ora-dired-rsync)

Answer 2

See also the Emacs function dired-do-async-shell-command.

For an even more generic solution see https://github.com/jwiegley/emacs-async with which you also can evaluate arbitrary Emacs Lisp code through call to a separate Emacs process (which of course incurs a bit of extra latency). More specifically regard file operations see the file dired-async.el in this repo.

Also note that there is work on threading in Emacs under the working name Concurrent Emacs but it's not there yet. See http://www.emacswiki.org/emacs/ConcurrentEmacs for details.