Merge lp:~vila/bzr-svn/525571-minimal-atomic-write-bazaar-conf-files-2.1 into lp:bzr-svn/1.0

[Vincent Ladeuil]

Use atomic writes to protect config files against concurrent writers.

This patch should fix bug #525571 for lp.

https://code.edge.launchpad.net/~vila/bzr/525571-lock-bazaar-conf-files/+merge/28898
won't land soon but https://code.edge.launchpad.net/~vila/bzr/525571-minimal-atomic-write-bazaar-conf-files-2.1/+merge/29086 has already landed for bzr-2.1

The later is a minimal fix but needs to be done too in bzr-svn (which this patch does).

The former is a more correct/robust/whatever solution but lp:bzr-svn@3323 is not enough to use it.
The discussion I had with Jelmer that led to 3323 was based on a flawed design that didn't
require to use @needs_write_lock on set_user_option() methods (the correct design will break the backward compatibility for the 3323 fix :-/).

See the mp discussions mentioned above for the details, but in summary *this* patch:
- mimics the minimal fix landed in bzr-2.1,
- will fix the issue encountered on lp,
- doesn't require deploying a new bzr on lp,
- requires that a new bzr-svn is deployed on lp.

=== modified file 'NEWS'
--- NEWS	2010-06-29 17:30:48 +0000
+++ NEWS	2010-07-08 07:21:42 +0000
@@ -55,6 +55,9 @@
   * Cope with concurrent access to ~/.bazaar/subversion.conf. 
     (Vincent Ladeuil, Jelmer Vernooij, #525571)
 
+  * Concurrent processes don't mix up writes in config files (interim
+    fix for lp).  (Vincent Ladeuil, #525571)
+
  FEATURES
 
   * Support fetching a limited number of revisions. (Michael Hudson)

=== modified file 'config.py'
--- config.py	2010-06-29 17:30:48 +0000
+++ config.py	2010-07-08 07:21:42 +0000
@@ -1,4 +1,4 @@
-# Copyright (C) 2007-2009 Jelmer Vernooij <[e-mail]>
+# Copyright (C) 2007-2010 Jelmer Vernooij <[e-mail]>
 
 # This program is free software; you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
@@ -107,12 +107,13 @@
         :param name: Name of the option.
         :param value: Value of the option.
         """
-        conf_dir = os.path.dirname(self._get_filename())
-        ensure_config_dir_exists(conf_dir)
+        file_name = self._get_filename()
+        ensure_config_dir_exists(os.path.dirname(file_name))
+        atomic_file = atomicfile.AtomicFile(file_name)
         self[name] = value
-        f = open(self._get_filename(), 'wb')
-        self._get_parser().write(f)
-        f.close()
+        self._get_parser().write(atomic_file)
+        atomic_file.commit()
+        atomic_file.close()
 
 
 class SvnRepositoryConfig(Config):