Re: auto-revert-mode and tramp file handlers

[Michael Albinus <michael.albinus@gmx.de>]

Kai Grossjohann <kai@emptydomain.de> writes:

> Luc Teirlinck <teirllm@dms.auburn.edu> writes:
>
>> Is there no way that tramp could detect that the user is off line in a
>> fraction of a second (as ssh apparently can) and if so, return nil for
>> file-exists-p and other functions that expect a return value of nil in
>> this case?
>
> I see what you're talking about.  The problem is that Tramp invokes
> ssh to connect the remote host, then waits 60 seconds for the shell
> prompt.  Additionally, it could check whether the process is still
> alive and stop waiting when the process dies.  I completely forgot to
> put this in.

The following patch might do the job:

magdalene:~/src> diff -u emacs/lisp/net/tramp.el tramp/lisp/tramp.el
--- emacs/lisp/net/tramp.el     2004-05-08 22:43:20.000000000 +0200
+++ tramp/lisp/tramp.el 2004-05-13 22:27:19.000000000 +0200
@@ -5025,6 +5025,8 @@
     (with-timeout (60 (throw 'tramp-action 'timeout))
       (while (not found)
        (accept-process-output p 1)
+       (unless (memq (process-status p) '(run open))
+         (throw 'tramp-action 'process-died))
        (goto-char (point-min))
        (setq todo actions)
        (while todo
@@ -5062,6 +5064,8 @@
     (with-timeout (60 (throw 'tramp-action 'timeout))
       (while (not found)
        (accept-process-output p 1)
+       (unless (memq (process-status p) '(run open))
+         (throw 'tramp-action 'process-died))
        (setq todo actions)
        (goto-char (point-min))
        (while todo
@@ -5466,12 +5470,16 @@
              (with-timeout (timeout)
                (while (not found)
                  (accept-process-output proc 1)
+                (unless (memq (process-status proc) '(run open))
+                  (error "Process has died"))
                  (goto-char (point-min))
                  (setq found (when (re-search-forward regexp nil t)
                                (tramp-match-string-list)))))))
           (t
            (while (not found)
              (accept-process-output proc 1)
+            (unless (memq (process-status proc) '(run open))
+              (error "Process has died"))
              (goto-char (point-min))
              (setq found (when (re-search-forward regexp nil t)
                            (tramp-match-string-list))))))
@@ -6079,12 +6087,16 @@
                (with-timeout (timeout)
                  (while (not found)
                    (accept-process-output proc 1)
+                  (unless (memq (process-status proc) '(run open))
+                    (error "Process has died"))
                    (goto-char (point-max))
                    (forward-line -1)
                    (setq found (looking-at end-of-output))))))
             (t
              (while (not found)
                (accept-process-output proc 1)
+              (unless (memq (process-status proc) '(run open))
+                (error "Process has died"))
                (goto-char (point-max))
                (forward-line -1)
                (setq found (looking-at end-of-output))))))

It's not "a fraction of a second", and it just returns with an error
in case a connection is broken, but it is better than waiting 60".
Silently returning for `file-exists-p' and friends is outstanding.

It is really a design question, whether Tramp shall report a broken
connection, or whether it should just return. Don't know what's
better.

Also available in Tramp CVS, together with the recent patch provided
by Kai.

Best regards, Michael.