Implement asynchronous thumbnail generation in image-dired

Additionally, all FOO-options defcustoms that were in fact shell command
strings have been converted to argument lists.  Another method for
shrinking PNG thumbs with optipng(1) has been added.
* lisp/image-dired.el: Remove TODO item in commentary.
(image-dired-cmd-create-thumbnail-options):
(image-dired-cmd-create-temp-image-options):
(image-dired-cmd-rotate-thumbnail-options):
(image-dired-cmd-rotate-original-options):
(image-dired-cmd-write-exif-data-options):
(image-dired-cmd-read-exif-data-options): Convert to argument lists.
(image-dired-cmd-pngnq-program, image-dired-cmd-pngcrush-program):
Change string type to file.
(image-dired-cmd-create-standard-thumbnail-command): Remove.
(image-dired-cmd-pngnq-options):
(image-dired-cmd-create-standard-thumbnail-options):
(image-dired-cmd-optipng-program, image-dired-cmd-optipng-options):
New defcustoms.
(image-dired-queue, image-dired-queue-active-jobs):
(image-dired-queue-active-limit): New variables.
(image-dired-pngnq-thumb, image-dired-pngcrush-thumb):
(image-dired-optipng-thumb): New functions.
(image-dired-create-thumb-1): Renamed from image-dired-create-thumb.
Use start-process instead of call-process.  Set file modes.  Trigger
PNG file optimization in process sentinel.
(image-dired-thumb-queue-run, image-dired-create-thumb): New functions.
(image-dired-display-thumbs):
(image-dired-create-thumbs): Don't expect call-process return value.
(image-dired-display-image, image-dired-rotate-thumbnail): Use
start-process instead of call-process.
(image-dired-rotate-original, image-dired-set-exif-data):
(image-dired-get-exif-data): Adapt to arguments being an arg list.

1 files changed, 285 insertions, 140 deletions

diff --git a/lisp/image-dired.el b/lisp/image-dired.el
index 6902d742dbb..560cadbe75b 100644
--- a/lisp/image-dired.el
+++ b/lisp/image-dired.el
@@ -118,8 +118,6 @@
 ;; * From thumbs.el: Add the "modify" commands (emboss, negate,
 ;;   monochrome etc).
 ;;
-;; * Asynchronous creation of thumbnails.
-;;
 ;; * Add `image-dired-display-thumbs-ring' and functions to cycle that.  Find
 ;; out which is best, saving old batch just before inserting new, or
 ;; saving the current batch in the ring when inserting it.  Adding it
@@ -230,14 +228,15 @@ Used together with `image-dired-cmd-create-thumbnail-options'."
   :group 'image-dired)
 
 (defcustom image-dired-cmd-create-thumbnail-options
-  "%p -size %wx%h \"%f\" -resize \"%wx%h>\" -strip jpeg:\"%t\""
-  "Format of command used to create thumbnail image.
-Available options are %p which is replaced by
-`image-dired-cmd-create-thumbnail-program', %w which is replaced by
+  '("-size" "%wx%h" "%f" "-resize" "%wx%h>" "-strip" "jpeg:%t")
+  "Options of command used to create thumbnail image.
+Used with `image-dired-cmd-create-thumbnail-program'.
+Available format specifiers are: %w which is replaced by
 `image-dired-thumb-width', %h which is replaced by `image-dired-thumb-height',
 %f which is replaced by the file name of the original image and %t
 which is replaced by the file name of the thumbnail file."
-  :type 'string
+  :version "26.1"
+  :type '(repeat (string :tag "Argument"))
   :group 'image-dired)
 
 (defcustom image-dired-cmd-create-temp-image-program "convert"
@@ -247,14 +246,15 @@ Used together with `image-dired-cmd-create-temp-image-options'."
   :group 'image-dired)
 
 (defcustom image-dired-cmd-create-temp-image-options
-  "%p -size %wx%h \"%f\" -resize \"%wx%h>\" -strip jpeg:\"%t\""
-  "Format of command used to create temporary image for display window.
-Available options are %p which is replaced by
-`image-dired-cmd-create-temp-image-program', %w and %h which is replaced by
+  '("-size" "%wx%h" "%f" "-resize" "%wx%h>" "-strip" "jpeg:%t")
+  "Options of command used to create temporary image for display window.
+Used together with `image-dired-cmd-create-temp-image-program',
+Available format specifiers are: %w and %h which are replaced by
 the calculated max size for width and height in the image display window,
 %f which is replaced by the file name of the original image and %t which
 is replaced by the file name of the temporary file."
-  :type 'string
+  :version "26.1"
+  :type '(repeat (string :tag "Argument"))
   :group 'image-dired)
 
 (defcustom image-dired-cmd-pngnq-program
@@ -264,49 +264,72 @@ is replaced by the file name of the temporary file."
 It quantizes colors of PNG images down to 256 colors or fewer
 using the Neuquant procedure."
   :version "26.1"
-  :type '(choice (const :tag "Not Set" nil) string)
+  :type '(choice (const :tag "Not Set" nil) file)
+  :group 'image-dired)
+
+(defcustom image-dired-cmd-pngnq-options
+  '("-f" "%t")
+  "Arguments to pass `image-dired-cmd-pngnq-program'.
+Available format specifiers are the same as in
+`image-dired-cmd-create-thumbnail-options'."
+  :version "26.1"
+  :type '(repeat (string :tag "Argument"))
   :group 'image-dired)
 
 (defcustom image-dired-cmd-pngcrush-program (executable-find "pngcrush")
   "The file name of the `pngcrush' program.
 It optimizes the compression of PNG images.  Also it adds PNG textual chunks
 with the information required by the Thumbnail Managing Standard."
-  :type '(choice (const :tag "Not Set" nil) string)
+  :type '(choice (const :tag "Not Set" nil) file)
   :group 'image-dired)
 
-(defcustom image-dired-cmd-create-standard-thumbnail-command
-  (concat
-   "%p -size %wx%h \"%f\" "
-   (unless (or image-dired-cmd-pngcrush-program image-dired-cmd-pngnq-program)
-     (concat
-      "-set \"Thumb::MTime\" \"%m\" "
-      "-set \"Thumb::URI\" \"file://%f\" "
-      "-set \"Description\" \"Thumbnail of file://%f\" "
-      "-set \"Software\" \"" (emacs-version) "\" "))
-   "-thumbnail \"%wx%h>\" png:\"%t\""
-   (if image-dired-cmd-pngnq-program
-       (concat
-        " ; " image-dired-cmd-pngnq-program " -f \"%t\""
-        (unless image-dired-cmd-pngcrush-program
-          " ; mv %q %t")))
-   (if image-dired-cmd-pngcrush-program
-       (concat
-        (unless image-dired-cmd-pngcrush-program
-          " ; cp %t %q")
-        " ; " image-dired-cmd-pngcrush-program " -q "
-        "-text b \"Description\" \"Thumbnail of file://%f\" "
-        "-text b \"Software\" \"" (emacs-version) "\" "
-        ;; "-text b \"Thumb::Image::Height\" \"%oh\" "
-        ;; "-text b \"Thumb::Image::Mimetype\" \"%mime\" "
-        ;; "-text b \"Thumb::Image::Width\" \"%ow\" "
-        "-text b \"Thumb::MTime\" \"%m\" "
-        ;; "-text b \"Thumb::Size\" \"%b\" "
-        "-text b \"Thumb::URI\" \"file://%f\" "
-        "%q %t"
-        " ; rm %q")))
-  "Command to create thumbnails according to the Thumbnail Managing Standard."
+(defcustom image-dired-cmd-pngcrush-options
+  `("-q"
+    "-text" "b" "Description" "Thumbnail of file://%f"
+    "-text" "b" "Software" ,(emacs-version)
+    ;; "-text b \"Thumb::Image::Height\" \"%oh\" "
+    ;; "-text b \"Thumb::Image::Mimetype\" \"%mime\" "
+    ;; "-text b \"Thumb::Image::Width\" \"%ow\" "
+    "-text" "b" "Thumb::MTime" "%m"
+    ;; "-text b \"Thumb::Size\" \"%b\" "
+    "-text" "b" "Thumb::URI" "file://%f"
+    "%q" "%t")
+  "Arguments for `image-dired-cmd-pngcrush-program'.
+Available format specifiers are the same as in
+`image-dired-cmd-create-thumbnail-options', with %q for a
+temporary file name (typically generated by pnqnq)"
   :version "26.1"
-  :type 'string
+  :type '(repeat (string :tag "Argument"))
+  :group 'image-dired)
+
+(defcustom image-dired-cmd-optipng-program (executable-find "optipng")
+  "The file name of the `optipng' program."
+  :type '(choice (const :tag "Not Set" nil) file)
+  :group 'image-dired)
+
+(defcustom image-dired-cmd-optipng-options '("-o5" "%t")
+  "Arguments passed to `image-dired-optipng-program'.
+Available format specifiers are described in
+`image-dired-cmd-create-thumbnail-options'."
+  :type '(repeat (string :tag "Argument"))
+  :link '(url-link "man:optipng(1)")
+  :group 'image-dired)
+
+(defcustom image-dired-cmd-create-standard-thumbnail-options
+  (append '("-size" "%wx%h" "%f")
+          (unless (or image-dired-cmd-pngcrush-program
+                      image-dired-cmd-pngnq-program)
+            (list
+             "-set" "Thumb::MTime" "%m"
+             "-set" "Thumb::URI" "file://%f"
+             "-set" "Description" "Thumbnail of file://%f"
+             "-set" "Software" (emacs-version)))
+          '("-thumbnail" "%wx%h>" "png:%t"))
+  "Options for creating thumbnails according to the Thumbnail Managing Standard.
+Available format specifiers are the same as in
+`image-dired-cmd-create-thumbnail-options', with %m for file modification time."
+  :version "26.1"
+  :type '(repeat (string :tag "Argument"))
   :group 'image-dired)
 
 (defcustom image-dired-cmd-rotate-thumbnail-program
@@ -317,14 +340,15 @@ Used together with `image-dired-cmd-rotate-thumbnail-options'."
   :group 'image-dired)
 
 (defcustom image-dired-cmd-rotate-thumbnail-options
-  "%p -rotate %d \"%t\""
-  "Format of command used to rotate thumbnail image.
-Available options are %p which is replaced by
-`image-dired-cmd-rotate-thumbnail-program', %d which is replaced by the
+  '("-rotate" "%d" "%t")
+  "Arguments of command used to rotate thumbnail image.
+Used with `image-dired-cmd-rotate-thumbnail-program'.
+Available format specifiers are: %d which is replaced by the
 number of (positive) degrees to rotate the image, normally 90 or 270
 \(for 90 degrees right and left), %t which is replaced by the file name
 of the thumbnail file."
-  :type 'string
+  :version "26.1"
+  :type '(repeat (string :tag "Argument"))
   :group 'image-dired)
 
 (defcustom image-dired-cmd-rotate-original-program
@@ -335,15 +359,16 @@ Used together with `image-dired-cmd-rotate-original-options'."
   :group 'image-dired)
 
 (defcustom image-dired-cmd-rotate-original-options
-  "%p -rotate %d -copy all -outfile %t \"%o\""
-  "Format of command used to rotate original image.
-Available options are %p which is replaced by
-`image-dired-cmd-rotate-original-program', %d which is replaced by the
+  '("-rotate" "%d" "-copy" "all" "-outfile" "%t" "%o")
+  "Arguments of command used to rotate original image.
+Used with `image-dired-cmd-rotate-original-program'.
+Available format specifiers are: %d which is replaced by the
 number of (positive) degrees to rotate the image, normally 90 or
 270 \(for 90 degrees right and left), %o which is replaced by the
 original image file name and %t which is replaced by
 `image-dired-temp-image-file'."
-  :type 'string
+  :version "26.1"
+  :type '(repeat (string :tag "Argument"))
   :group 'image-dired)
 
 (defcustom image-dired-temp-rotate-image-file
@@ -367,13 +392,14 @@ Used together with `image-dired-cmd-write-exif-data-options'."
   :group 'image-dired)
 
 (defcustom image-dired-cmd-write-exif-data-options
-  "%p -%t=\"%v\" \"%f\""
-  "Format of command used to write EXIF data.
-Available options are %p which is replaced by
-`image-dired-cmd-write-exif-data-program', %f which is replaced by
+  '("-%t=%v" "%f")
+  "Arguments of command used to write EXIF data.
+Used with `image-dired-cmd-write-exif-data-program'.
+Available format specifiers are: %f which is replaced by
 the image file name, %t which is replaced by the tag name and %v
 which is replaced by the tag value."
-  :type 'string
+  :version "26.1"
+  :type '(repeat (string :tag "Argument"))
   :group 'image-dired)
 
 (defcustom image-dired-cmd-read-exif-data-program
@@ -384,12 +410,13 @@ Used together with `image-dired-cmd-read-exif-data-options'."
   :group 'image-dired)
 
 (defcustom image-dired-cmd-read-exif-data-options
-  "%p -s -s -s -%t \"%f\""
-  "Format of command used to read EXIF data.
-Available options are %p which is replaced by
-`image-dired-cmd-write-exif-data-program', %f which is replaced
+  '("-s" "-s" "-s" "-%t" "%f")
+  "Arguments of command used to read EXIF data.
+Used with `image-dired-cmd-read-exif-data-program'.
+Available format specifiers are: %f which is replaced
 by the image file name and %t which is replaced by the tag name."
-  :type 'string
+  :version "26.1"
+  :type '(repeat (string :tag "Argument"))
   :group 'image-dired)
 
 (defcustom image-dired-gallery-hidden-tags
@@ -640,7 +667,81 @@ DIMENSION should be either the symbol 'width or 'height."
         (width image-dired-thumb-width)
         (height image-dired-thumb-height)))))
 
-(defun image-dired-create-thumb (original-file thumbnail-file)
+(defvar image-dired-queue nil
+  "List of items in the queue.
+Each item has the form (ORIGINAL-FILE TARGET-FILE).")
+
+(defvar image-dired-queue-active-jobs 0
+  "Number of active jobs in `image-dired-queue'.")
+
+(defvar image-dired-queue-active-limit 2
+  "Maximum number of concurrent jobs permitted for generating images.
+Increase at own risk.")
+
+(defun image-dired-pngnq-thumb (spec)
+  "Quantize thumbnail described by format SPEC with pngnq(1)."
+  (let ((process
+         (apply #'start-process "image-dired-pngnq" nil
+                image-dired-cmd-pngnq-program
+                (mapcar (lambda (arg) (format-spec arg spec))
+                        image-dired-cmd-pngnq-options))))
+    (setf (process-sentinel process)
+          (lambda (process status)
+            (if (and (eq (process-status process) 'exit)
+                     (zerop (process-exit-status process)))
+                ;; Pass off to pngcrush, or just rename the
+                ;; THUMB-nq8.png file back to THUMB.png
+                (if (and image-dired-cmd-pngcrush-program
+                         (executable-find image-dired-cmd-pngcrush-program))
+                    (image-dired-pngcrush-thumb spec)
+                  (let ((nq8 (cdr (assq ?q spec)))
+                        (thumb (cdr (assq ?t spec))))
+                    (rename-file nq8 thumb t)))
+              (message "command %S %s" (process-command process)
+                       (replace-regexp-in-string "\n" "" status)))))
+    process))
+
+(defun image-dired-pngcrush-thumb (spec)
+  "Optimize thumbnail decsribed by format SPEC with pngcrush(1)."
+  ;; If pngnq wasn't run, then the THUMB-nq8.png file does not exist.
+  ;; pngcrush needs an infile and outfile, so we just copy THUMB to
+  ;; THUMB-nq8.png and use the latter as a temp file.
+  (when (not image-dired-cmd-pngnq-program)
+    (let ((temp (cdr (assq ?q spec)))
+          (thumb (cdr (assq ?t spec))))
+      (copy-file thumb temp)))
+  (let ((process
+         (apply #'start-process "image-dired-pngcrush" nil
+                image-dired-cmd-pngcrush-program
+                (mapcar (lambda (arg) (format-spec arg spec))
+                        image-dired-cmd-pngcrush-options))))
+    (setf (process-sentinel process)
+          (lambda (process status)
+            (unless (and (eq (process-status process) 'exit)
+                         (zerop (process-exit-status process)))
+              (message "command %S %s" (process-command process)
+                       (replace-regexp-in-string "\n" "" status)))
+            (when (memq (process-status process) '(exit signal))
+              (let ((temp (cdr (assq ?q spec))))
+                (delete-file temp)))))
+    process))
+
+(defun image-dired-optipng-thumb (spec)
+  "Optimize thumbnail decsribed by format SPEC with optipng(1)."
+  (let ((process
+         (apply #'start-process "image-dired-optipng" nil
+                image-dired-cmd-optipng-program
+                (mapcar (lambda (arg) (format-spec arg spec))
+                        image-dired-cmd-optipng-options))))
+    (setf (process-sentinel process)
+          (lambda (process status)
+            (unless (and (eq (process-status process) 'exit)
+                         (zerop (process-exit-status process)))
+              (message "command %S %s" (process-command process)
+                       (replace-regexp-in-string "\n" "" status)))))
+    process))
+
+(defun image-dired-create-thumb-1 (original-file thumbnail-file)
   "For ORIGINAL-FILE, create thumbnail image named THUMBNAIL-FILE."
   (image-dired--check-executable-exists
    'image-dired-cmd-create-thumbnail-program)
@@ -649,25 +750,76 @@ DIMENSION should be either the symbol 'width or 'height."
          (modif-time (floor (float-time (nth 5 (file-attributes original-file)))))
          (thumbnail-nq8-file (replace-regexp-in-string ".png\\'" "-nq8.png"
                                                        thumbnail-file))
-         (command
-          (format-spec
-           (if (memq image-dired-thumbnail-storage '(standard standard-large))
-               image-dired-cmd-create-standard-thumbnail-command
-             image-dired-cmd-create-thumbnail-options)
-           (list
-            (cons ?p image-dired-cmd-create-thumbnail-program)
-            (cons ?w width)
-            (cons ?h height)
-            (cons ?m modif-time)
-            (cons ?f original-file)
-            (cons ?q thumbnail-nq8-file)
-            (cons ?t thumbnail-file))))
-         thumbnail-dir)
-    (when (not (file-exists-p
-                (setq thumbnail-dir (file-name-directory thumbnail-file))))
-      (message "Creating thumbnail directory.")
-      (make-directory thumbnail-dir t))
-    (call-process shell-file-name nil nil nil shell-command-switch command)))
+         (spec
+          (list
+           (cons ?w width)
+           (cons ?h height)
+           (cons ?m modif-time)
+           (cons ?f original-file)
+           (cons ?q thumbnail-nq8-file)
+           (cons ?t thumbnail-file)))
+         (thumbnail-dir (file-name-directory thumbnail-file))
+         process)
+    (when (not (file-exists-p thumbnail-dir))
+      (message "Creating thumbnail directory")
+      (make-directory thumbnail-dir t)
+      (set-file-modes thumbnail-dir #o700))
+
+    ;; Thumbnail file creation processes begin here and are marshalled
+    ;; in a queue by `image-dired-create-thumb'.
+    (setq process
+          (apply #'start-process "image-dired-create-thumbnail" nil
+                 image-dired-cmd-create-thumbnail-program
+                 (mapcar
+                  (lambda (arg) (format-spec arg spec))
+                  (if (memq image-dired-thumbnail-storage
+                            '(standard standard-large))
+                      image-dired-cmd-create-standard-thumbnail-options
+                    image-dired-cmd-create-thumbnail-options))))
+
+    (setf (process-sentinel process)
+          (lambda (process status)
+            ;; Trigger next in queue once a thumbnail has been created
+            (cl-decf image-dired-queue-active-jobs)
+            (image-dired-thumb-queue-run)
+            (if (not (and (eq (process-status process) 'exit)
+                          (zerop (process-exit-status process))))
+                (message "Thumb could not be created for %s: %s"
+                         (abbreviate-file-name original-file)
+                         (replace-regexp-in-string "\n" "" status))
+              (set-file-modes thumbnail-file #o600)
+              (clear-image-cache thumbnail-file)
+              ;; PNG thumbnail has been created since we are
+              ;; following the XDG thumbnail spec, so try to optimize
+              (when (memq image-dired-thumbnail-storage
+                          '(standard standard-large))
+                (cond
+                 ((and image-dired-cmd-pngnq-program
+                       (executable-find image-dired-cmd-pngnq-program))
+                  (image-dired-pngnq-thumb spec))
+                 ((and image-dired-cmd-pngcrush-program
+                       (executable-find image-dired-cmd-pngcrush-program))
+                  (image-dired-pngcrush-thumb spec))
+                 ((and image-dired-cmd-optipng-program
+                       (executable-find image-dired-cmd-optipng-program))
+                  (image-dired-optipng-thumb spec)))))))
+    process))
+
+(defun image-dired-thumb-queue-run ()
+  "Run a queued job if one exists and not too many jobs are running.
+Queued items live in `image-dired-queue'."
+  (while (and image-dired-queue
+              (< image-dired-queue-active-jobs
+                 image-dired-queue-active-limit))
+    (cl-incf image-dired-queue-active-jobs)
+    (apply #'image-dired-create-thumb-1 (pop image-dired-queue))))
+
+(defun image-dired-create-thumb (original-file thumbnail-file)
+  "Add a job for generating thumbnail to `image-dired-queue'."
+  (setq image-dired-queue
+        (nconc image-dired-queue
+               (list (list original-file thumbnail-file))))
+  (run-at-time 0 nil #'image-dired-thumb-queue-run))
 
 ;;;###autoload
 (defun image-dired-dired-toggle-marked-thumbs (&optional arg)
@@ -867,10 +1019,9 @@ thumbnail buffer to be selected."
           (goto-char (point-max)))
         (dolist (curr-file files)
           (setq thumb-name (image-dired-thumb-name curr-file))
-          (if (and (not (file-exists-p thumb-name))
-                   (not (= 0 (image-dired-create-thumb curr-file thumb-name))))
-              (message "Thumb could not be created for file %s" curr-file)
-            (image-dired-insert-thumbnail thumb-name curr-file dired-buf))))
+          (when (not (file-exists-p thumb-name))
+            (image-dired-create-thumb curr-file thumb-name))
+          (image-dired-insert-thumbnail thumb-name curr-file dired-buf)))
       (if do-not-pop
           (display-buffer buf)
         (pop-to-buffer buf))
@@ -1554,8 +1705,7 @@ With prefix argument ARG, create thumbnails even if they already exist
         (clear-image-cache (expand-file-name thumb-name)))
       (when (or (not (file-exists-p thumb-name))
                 arg)
-        (when (not (= 0 (image-dired-create-thumb curr-file thumb-name)))
-          (error "Thumb could not be created"))))))
+        (image-dired-create-thumb curr-file thumb-name)))))
 
 (defvar image-dired-slideshow-timer nil
   "Slideshow timer.")
@@ -1747,17 +1897,19 @@ original size."
         (image-type 'jpeg))
     (setq file (expand-file-name file))
     (if (not original-size)
-        (let* ((command
-                (format-spec
-                 image-dired-cmd-create-temp-image-options
-                 (list
-                  (cons ?p image-dired-cmd-create-temp-image-program)
-                  (cons ?w (image-dired-display-window-width window))
-                  (cons ?h (image-dired-display-window-height window))
-                  (cons ?f file)
-                  (cons ?t new-file))))
-               (ret (call-process shell-file-name nil nil nil
-                                  shell-command-switch command)))
+        (let* ((spec
+                (list
+                 (cons ?p image-dired-cmd-create-temp-image-program)
+                 (cons ?w (image-dired-display-window-width window))
+                 (cons ?h (image-dired-display-window-height window))
+                 (cons ?f file)
+                 (cons ?t new-file)))
+               (ret
+                (apply #'call-process
+                       image-dired-cmd-create-temp-image-program nil nil nil
+                       (mapcar
+                        (lambda (arg) (format-spec arg spec))
+                        image-dired-cmd-create-temp-image-options))))
           (when (not (zerop ret))
             (error "Could not resize image")))
       (setq image-type (image-type-from-file-name file))
@@ -1811,14 +1963,10 @@ With prefix argument ARG, display image in its original size."
       (message "No thumbnail at point")
     (let* ((file (image-dired-thumb-name (image-dired-original-file-name)))
            (thumb (expand-file-name file))
-           command)
-      (setq command (format-spec
-                     image-dired-cmd-rotate-thumbnail-options
-                     (list
-                      (cons ?p image-dired-cmd-rotate-thumbnail-program)
-                      (cons ?d degrees)
-                      (cons ?t thumb))))
-      (call-process shell-file-name nil nil nil shell-command-switch command)
+           (spec (list (cons ?d degrees) (cons ?t thumb))))
+      (apply #'call-process image-dired-cmd-rotate-thumbnail-program nil nil nil
+             (mapcar (lambda (arg) (format-spec arg spec))
+                     image-dired-cmd-rotate-thumbnail-options))
       (clear-image-cache thumb))))
 
 (defun image-dired-rotate-thumbnail-left ()
@@ -1853,19 +2001,18 @@ overwritten.  This confirmation can be turned off using
    'image-dired-cmd-rotate-original-program)
   (if (not (image-dired-image-at-point-p))
       (message "No image at point")
-    (let ((file (image-dired-original-file-name))
-          command)
+    (let* ((file (image-dired-original-file-name))
+           (spec
+            (list
+             (cons ?d degrees)
+             (cons ?o (expand-file-name file))
+             (cons ?t image-dired-temp-rotate-image-file))))
       (unless (eq 'jpeg (image-type file))
         (error "Only JPEG images can be rotated!"))
-      (setq command (format-spec
-                     image-dired-cmd-rotate-original-options
-                     (list
-                      (cons ?p image-dired-cmd-rotate-original-program)
-                      (cons ?d degrees)
-                      (cons ?o (expand-file-name file))
-                      (cons ?t image-dired-temp-rotate-image-file))))
-      (if (not (= 0 (call-process shell-file-name nil nil nil
-                                  shell-command-switch command)))
+      (if (not (= 0 (apply #'call-process image-dired-cmd-rotate-original-program
+                           nil nil nil
+                           (mapcar (lambda (arg) (format-spec arg spec))
+                                   image-dired-cmd-rotate-original-options))))
           (error "Could not rotate image")
         (image-dired-display-image image-dired-temp-rotate-image-file)
         (if (or (and image-dired-rotate-original-ask-before-overwrite
@@ -1931,32 +2078,30 @@ default value at the prompt."
   "In FILE, set EXIF tag TAG-NAME to value TAG-VALUE."
   (image-dired--check-executable-exists
    'image-dired-cmd-write-exif-data-program)
-  (let (command)
-    (setq command (format-spec
-                   image-dired-cmd-write-exif-data-options
-                   (list
-                    (cons ?p image-dired-cmd-write-exif-data-program)
-                    (cons ?f (expand-file-name file))
-                    (cons ?t tag-name)
-                    (cons ?v tag-value))))
-    (call-process shell-file-name nil nil nil shell-command-switch command)))
+  (let ((spec
+         (list
+          (cons ?f (expand-file-name file))
+          (cons ?t tag-name)
+          (cons ?v tag-value))))
+    (apply #'call-process image-dired-cmd-write-exif-data-program nil nil nil
+           (mapcar (lambda (arg) (format-spec arg spec))
+                   image-dired-cmd-write-exif-data-options))))
 
 (defun image-dired-get-exif-data (file tag-name)
   "From FILE, return EXIF tag TAG-NAME."
   (image-dired--check-executable-exists
    'image-dired-cmd-read-exif-data-program)
   (let ((buf (get-buffer-create "*image-dired-get-exif-data*"))
-        command tag-value)
-    (setq command (format-spec
-                   image-dired-cmd-read-exif-data-options
-                   (list
-                    (cons ?p image-dired-cmd-read-exif-data-program)
-                    (cons ?f file)
-                    (cons ?t tag-name))))
+        (spec (list (cons ?f file) (cons ?t tag-name)))
+        tag-value)
     (with-current-buffer buf
       (delete-region (point-min) (point-max))
-      (if (not (eq (call-process shell-file-name nil t nil
-                                 shell-command-switch command) 0))
+      (if (not (eq (apply #'call-process image-dired-cmd-read-exif-data-program
+                          nil t nil
+                          (mapcar
+                           (lambda (arg) (format-spec arg spec))
+                           image-dired-cmd-read-exif-data-options))
+                   0))
           (error "Could not get EXIF tag")
         (goto-char (point-min))
         ;; Clean buffer from newlines and carriage returns before