Write .installed.cfg only once, in safe way and only if there's any change

Previous attempt to fix possible corruption was reverted because it had severe
performance issues (both CPU & storage).

Also, updating a part does not put it anymore at the end of the list of
installed parts. It was breaking uninstall dependencies.

src/zc/buildout/buildout.py

@@ -26,6 +26,7 @@ from cStringIO import StringIO
 import copy
 import distutils.errors
 import glob
+import errno
 import itertools
 import logging
 import os
@@ -182,6 +183,12 @@ def _print_annotate(data):
                     line = '   '
     print
 
+def _remove_ignore_missing(path):
+    try:
+        os.remove(path)
+    except OSError, e:
+        if e.errno != errno.ENOENT:
+            raise
 
 def _unannotate_section(section):
     for key in section:
@@ -651,8 +658,9 @@ class Buildout(UserDict.DictMixin):
         self._maybe_upgrade()
 
         # load installed data
-        (installed_part_options, installed_exists
-         )= self._read_installed_part_options()
+        installed_part_options = self._read_installed_part_options()
+        installed_parts = installed_part_options['buildout']['parts']
+        installed_parts = installed_parts and installed_parts.split() or []
 
         # Remove old develop eggs
         self._uninstall(
@@ -665,22 +673,13 @@ class Buildout(UserDict.DictMixin):
         installed_part_options['buildout']['installed_develop_eggs'
                                            ] = installed_develop_eggs
 
-        if installed_exists:
-            self._update_installed(
-                installed_develop_eggs=installed_develop_eggs)
-
-        # get configured and installed part lists
-        conf_parts = self['buildout']['parts']
-        conf_parts = conf_parts and conf_parts.split() or []
-        installed_parts = installed_part_options['buildout']['parts']
-        installed_parts = installed_parts and installed_parts.split() or []
-
         try:
             if install_args:
                 install_parts = install_args
                 uninstall_missing = False
             else:
-                install_parts = conf_parts
+                install_parts = self['buildout']['parts']
+                install_parts = install_parts and install_parts.split() or ()
                 uninstall_missing = True
 
             # load and initialize recipes
@@ -697,7 +696,6 @@ class Buildout(UserDict.DictMixin):
                     _save_options(section, self[section], sys.stdout)
                 print
 
-
             # compute new part recipe signatures
             self._compute_part_signatures(install_parts)
 
@@ -741,9 +739,6 @@ class Buildout(UserDict.DictMixin):
                 self._uninstall_part(part, installed_part_options)
                 installed_parts = [p for p in installed_parts if p != part]
 
-                if installed_exists:
-                    self._update_installed(parts=' '.join(installed_parts))
-
             # Check for unused buildout options:
             _check_for_unused_options_in_section(self, 'buildout')
 
@@ -753,7 +748,6 @@ class Buildout(UserDict.DictMixin):
                 saved_options = self[part].copy()
                 recipe = self[part].recipe
                 if part in installed_parts: # update
-                    need_to_save_installed = False
                     __doing__ = 'Updating %s.', part
                     self._logger.info(*__doing__)
                     old_options = installed_part_options[part]
@@ -770,33 +764,15 @@ class Buildout(UserDict.DictMixin):
 
                     try:
                         installed_files = self[part]._call(update)
-                    except:
+                    except Exception:
                         installed_parts.remove(part)
                         self._uninstall(old_installed_files)
-                        if installed_exists:
-                            self._update_installed(
-                                parts=' '.join(installed_parts))
                         raise
 
-                    old_installed_files = old_installed_files.split('\n')
                     if installed_files is None:
                         installed_files = old_installed_files
-                    else:
-                        if isinstance(installed_files, str):
-                            installed_files = [installed_files]
-                        else:
-                            installed_files = list(installed_files)
-
-                        need_to_save_installed = [
-                            p for p in installed_files
-                            if p not in old_installed_files]
-
-                        if need_to_save_installed:
-                            installed_files = (old_installed_files
-                                               + need_to_save_installed)
 
                 else: # install
-                    need_to_save_installed = True
                     __doing__ = 'Installing %s.', part
                     self._logger.info(*__doing__)
                     installed_files = self[part]._call(recipe.install)
@@ -805,49 +781,51 @@ class Buildout(UserDict.DictMixin):
                             "The %s install returned None.  A path or "
                             "iterable of paths should be returned.",
                             part)
-                        installed_files = ()
-                    elif isinstance(installed_files, str):
-                        installed_files = [installed_files]
-                    else:
-                        installed_files = list(installed_files)
+                        installed_files = ""
 
-                installed_part_options[part] = saved_options
-                saved_options['__buildout_installed__'
-                              ] = '\n'.join(installed_files)
+                if not isinstance(installed_files, str):
+                    installed_files = '\n'.join(installed_files)
+                saved_options['__buildout_installed__'] = installed_files
                 saved_options['__buildout_signature__'] = signature
+                installed_part_options[part] = saved_options
+                part in installed_parts or installed_parts.append(part)
 
-                installed_parts = [p for p in installed_parts if p != part]
-                installed_parts.append(part)
                 _check_for_unused_options_in_section(self, part)
 
-                if need_to_save_installed:
-                    installed_part_options['buildout']['parts'] = (
-                        ' '.join(installed_parts))
-                    self._save_installed_options(installed_part_options)
-                    installed_exists = True
-                else:
-                    assert installed_exists  # nothing to tell the user here
-                    self._update_installed(parts=' '.join(installed_parts))
-
         finally:
-            pass
-
-        if installed_develop_eggs:
-            if not installed_exists:
-                self._save_installed_options(installed_part_options)
-        elif (not installed_parts) and installed_exists:
-            os.remove(self['buildout']['installed'])
+            installed_path = self['buildout']['installed']
+            if installed_parts:
+                new = StringIO()
+                buildout = installed_part_options['buildout']
+                buildout['parts'] = ' '.join(installed_parts)
+                _save_options('buildout', buildout, new)
+                for part in installed_parts:
+                    print >>new
+                    _save_options(part, installed_part_options[part], new)
+                new = new.getvalue()
+                try:
+                    with open(installed_path) as f:
+                        save = f.read(1+len(new)) != new
+                except IOError, e:
+                    if e.errno != errno.ENOENT:
+                        raise
+                    save = True
+                if save:
+                    self._logger.info("Writing %s", installed_path)
+                    installed_tmp = installed_path + ".tmp"
+                    try:
+                        with open(installed_tmp, "w") as f:
+                            f.write(new)
+                            f.flush()
+                            os.fsync(f.fileno())
+                        os.rename(installed_tmp, installed_path)
+                    finally:
+                        _remove_ignore_missing(installed_tmp)
+            else:
+                _remove_ignore_missing(installed_path)
 
         self._unload_extensions()
 
-    def _update_installed(self, **buildout_options):
-        installed = self['buildout']['installed']
-        f = open(installed, 'a')
-        f.write('\n[buildout]\n')
-        for option, value in buildout_options.items():
-            _save_option(option, value, f)
-        f.close()
-
     def _uninstall_part(self, part, installed_part_options):
         # uninstall part
         __doing__ = 'Uninstalling %s.', part
@@ -966,11 +944,9 @@ class Buildout(UserDict.DictMixin):
                     options[option] = value
                 result[section] = Options(self, section, options)
 
-            return result, True
+            return result
         else:
-            return ({'buildout': Options(self, 'buildout', {'parts': ''})},
-                    False,
-                    )
+            return {'buildout': Options(self, 'buildout', {'parts': ''})}
 
     def _uninstall(self, installed):
         for f in installed.split('\n'):
@@ -1011,17 +987,6 @@ class Buildout(UserDict.DictMixin):
         return ' '.join(installed)
 
 
-    def _save_installed_options(self, installed_options):
-        installed = self['buildout']['installed']
-        if not installed:
-            return
-        f = open(installed, 'w')
-        _save_options('buildout', installed_options['buildout'], f)
-        for part in installed_options['buildout']['parts'].split():
-            print >>f
-            _save_options(part, installed_options[part], f)
-        f.close()
-
     def _error(self, message, *args):
         raise zc.buildout.UserError(message % args)