23.0.50; Tramp blocks Emacs when unconnected to server

23.0.50; Tramp blocks Emacs when unconnected to server

[Martin Lüthi]

Hi

A major annoyance of Tramp is that it blocks Emacs when the server is
not reachable. The symptoms are

o open file on remote host with Tramp, edit, save
o disconnect from network (like: get laptop sleeping, reconnect
  somewhere else)
o close buffer visiting the remote file

The last action (closing the buffer) is not possible, and Emacs blocks
for a long time. C-g stops the unsuccessful communication
attempt. However it should be possible to close the buffer without
interaction with the remote server.


In GNU Emacs 23.0.50.1 (i686-pc-linux-gnu, GTK+ Version 2.11.6)
 of 2007-09-16 on yak
Windowing system distributor `The X.Org Foundation', version 11.0.10300000
Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: en_US
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: en_US.iso-8859-1
  locale-coding-system: iso-8859-1
  default-enable-multibyte-characters: t

Major mode: Text

Minor modes in effect:
  shell-dirtrack-mode: t
  which-function-mode: t
  show-paren-mode: t
  display-time-mode: t
  display-battery-mode: t
  tooltip-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  unify-8859-on-encoding-mode: t
  utf-translate-cjk-mode: t
  auto-compression-mode: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t
  abbrev-mode: t

Recent input:
M-x v m <return> g q M-x m e n u <tab> b <tab> m <tab> 
<return> <help-echo> <help-echo> <help-echo> <help-echo> 
<help-echo> <help-echo> <help-echo> <help-echo> <help-echo> 
<help-echo> <help-echo> <help-echo> <help-echo> <help-echo> 
<help-echo> <help-echo> <help-echo> <help-echo> <help-echo> 
<help-echo> <help-echo> <help-echo> <help-echo> <help-echo> 
<help-echo> <help-echo> <help-echo> <help-echo> <help-echo> 
<help-echo> <help-echo> <help-echo> <help-echo> <help-echo> 
<help-echo> <menu-bar> <help-menu> <report-emacs-b
ug>

Recent messages:
Decoding MIME message... done
Mark set
Parsing BBDB... (frobnicating...done)
79 messages, 0 new, 0 unread, 0 deleted
Checking for new mail for /home/tinu/projects/mail/INBOX...
Loading vm-crypto...done
No new mail for /home/tinu/projects/mail/INBOX
Quitting...
Menu-Bar mode enabled
Loading emacsbug...done

Re: 23.0.50; Tramp blocks Emacs when unconnected to server

[Michael Albinus]

"Martin Lüthi" <luethi@vaw.baug.ethz.ch> writes:

> Hi

Hi,

> A major annoyance of Tramp is that it blocks Emacs when the server is
> not reachable. The symptoms are
>
> o open file on remote host with Tramp, edit, save
> o disconnect from network (like: get laptop sleeping, reconnect
>   somewhere else)
> o close buffer visiting the remote file
>
> The last action (closing the buffer) is not possible, and Emacs blocks
> for a long time. C-g stops the unsuccessful communication
> attempt. However it should be possible to close the buffer without
> interaction with the remote server.

It is not clear to me what Tramp attempts to write when the buffer has
been saved.

Could you, please, set debug-on-quit to t? Next time you interrupt
Tramp in such a situation, there shall be a backtrace. Please provide this.

Best regards, Michael.

Re: 23.0.50; Tramp blocks Emacs when unconnected to server

[Stefan Monnier]

> o close buffer visiting the remote file

I do not know what you mean by "close the buffer".  Do you mean to kill it
with C-x k ?


        Stefan

Re: 23.0.50; Tramp blocks Emacs when unconnected to server

[Michael Albinus]

"Martin Lüthi" <luethi@vaw.baug.ethz.ch> writes:

> Hallo Michael

Hi,

> I started Emacs with the -q option and set debug-on-quit to t. Then I
> loaded a remote file, unplugged the network cable, and Emacs hangs on
> any edit of the buffer, and also when I try to kill the buffer. Looks
> like the "modification time" checks below are to blame.

Has the buffer been saved before unplugging the cable (you said this
in your initial posting)? Locally, when I call kill-buffer on a saved
buffer, verify-visited-file-modtime isn't invoked.

Could you, please, provide also the full backtrace? The one you've
sent starts with

tramp-file-name-handler(verify-visited-file-modtime #<buffer visco3d.C>)

But I would need to know where it has been called from.

> Best, Martin

Best regards, Michael.

Re: 23.0.50; Tramp blocks Emacs when unconnected to server

[Michael Albinus]

"Martin Lüthi" <luethi@vaw.baug.ethz.ch> writes:

> Michael

Hi Martin,

[I still keep emacs-devel CC, for traceability]

> Here is the full backtrace (sorry, if it got truncated). Interestingly
> enough I cannot reproduce the error now. Maybe sleeping is involved, too.

I cannot find anything in the backtrace which helps. Locally (I'm @home
meanwhile) I cannot reproduce the problem either. When I disable WLAN, I
can kill a buffer containing a remote file without problems, given the
buffer is not marked "modified".

When the buffer is not saved yet, Tramp runs indeed into a loop during
write operations when the network connection is broken. I'll try to find
a way that Tramp detects it (it must be performant). This will not be so
easy, because ssh tends to keep the connection for a while. And it is
not predictable what kind of timer inside Emacs we could set; it depends
on the length of the string being sent to the remote host, and on the
quality (throughput) of the connection.

However, this is different from the problem you did report.

Best regards, Michael.

Re: 23.0.50; Tramp blocks Emacs when unconnected to server

[Martin Lüthi]

Hi

Michael Albinus writes:
 > "Martin L