(gs-load-image): Use sleep-for.

From David.Kastrup@neuroinformatik.ruhr-uni-bochum.de.

diff --git a/lisp/gs.el b/lisp/gs.el
index 19d463de4ecd7dc9ed38f2b0b1abb8200fbf9751..9bcf289320583a18b32129054a052cf15534a4de 100644 (file)
--- a/lisp/gs.el
+++ b/lisp/gs.el
@@ -153,21 +153,44 @@ the form \"WINDOW-ID PIXMAP-ID\".  Value is non-nil if successful."
   (unwind-protect
       (let ((file (plist-get (cdr spec) :file))
            gs
-           (timeout 10))
-       ;; Wait while property gets freed from a previous ghostscript
-       ;; process
-       (while (and (not (zerop (length (x-window-property "GHOSTVIEW" 
-                                                          frame))))
-                   (not (zerop timeout)))
-         (sit-for 0 100 t)
-         (setq timeout (1- timeout)))
-       ;; No use waiting longer.  We might want to try killing off
-       ;; stuck processes, but there is no point in doing so: either
-       ;; they are stuck for good, in which case the user would
-       ;; probably be responsible for that, and killing them off will
-       ;; make debugging harder, or they are not.  In that case, they
-       ;; will cause incomplete displays.  But the same will happen
-       ;; if they are killed, anyway.
+           (timeout 40))
+       ;; Wait while property gets freed from a previous ghostscript process
+       ;; sit-for returns nil as soon as input starts being
+       ;; available, so if we want to give GhostScript a reasonable
+       ;; chance of starting up, we better use sleep-for.  We let
+       ;; sleep-for wait only half the time because if input is
+       ;; available, it is more likely that we don't care that much
+       ;; about garbled redisplay and are in a hurry.
+       (while (and
+               ;; Wait while the property is not yet available
+               (not (zerop (length (x-window-property "GHOSTVIEW"
+                                                      frame))))
+               ;; The following was an alternative condition: wait
+               ;; while there is still a process running.  The idea
+               ;; was to avoid contention between processes.  Turned
+               ;; out even more sluggish.
+               ;; (get-buffer-process "*GS*")
+               (not (zerop timeout)))
+         (unless (sit-for 0 100 t)
+           (sleep-for 0 50))
+         (setq timeout (1- timeout)))
+
+       ;; No use waiting longer.  We might want to try killing off
+       ;; stuck processes, but there is no point in doing so: either
+       ;; they are stuck for good, in which case the user would
+       ;; probably be responsible for that, and killing them off will
+       ;; make debugging harder, or they are not.  In that case, they
+       ;; will cause incomplete displays.  But the same will happen
+       ;; if they are killed, anyway. The whole is rather
+       ;; disconcerting, and fast scrolling through a dozen images
+       ;; will make Emacs freeze for a while.  The alternatives are a)
+       ;; proper implementation not waiting at all but creating
+       ;; appropriate queues, or b) permanently bad display due to
+       ;; bad cached images.  So remember that this
+       ;; is just a hack and if people don't like the behaviour, they
+       ;; will most likely like the easy alternatives even less.
+       ;; And at least the image cache will make the delay apparent
+       ;; just once.
        (gs-set-ghostview-window-prop frame spec img-width img-height)
        (gs-set-ghostview-colors-window-prop frame pixel-colors)
        (setenv "GHOSTVIEW" window-and-pixmap-id)