From patchwork Fri Mar 14 23:52:50 2014
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Subject: init: changed creation order of 00changelog and requires files
 (issue3960)
From: Lucas Moscovicz <lmoscovicz@fb.com>
X-Patchwork-Id: 3946
Message-Id: <6e4f55fbc42b4d06d1ef.1394841170@dev1037.prn2.facebook.com>
To: mercurial-devel@selenic.com
Date: Fri, 14 Mar 2014 16:52:50 -0700

# HG changeset patch
# User Lucas Moscovicz <lmoscovicz@fb.com>
# Date 1389639192 28800
#      Mon Jan 13 10:53:12 2014 -0800
# Node ID 6e4f55fbc42b4d06d1efd610d21851935dc90f26
# Parent  e87bd3485a07f4b231febef26c6797855a64af3d
init: changed creation order of 00changelog and requires files (issue3960)

When initializing a repo with hg init if another client cloned the repo after
the 00changelog file was created but before the requires file was created they
would get an error about unknown revlog format.  To fix it, I changed the
creation order of those files since the changelog file can be created at any
time during the initialization.

Also, to solve the race problem that came up where an old client commited
something to the repo before both the requires and the 00changelog file were
created and then the 00changelog file would overwrite that commit, the initial
name of the .hg folder was changed to .hgtmp, getting renamed back to .hg once
the requires and 00changelog files are created leaving no point in time where
an old client can commit to the new styled repo.

diff --git a/mercurial/localrepo.py b/mercurial/localrepo.py
--- a/mercurial/localrepo.py
+++ b/mercurial/localrepo.py
@@ -195,26 +195,37 @@ class localrepository(object):
 
         if not self.vfs.isdir():
             if create:
-                if not self.wvfs.exists():
-                    self.wvfs.makedirs()
-                self.vfs.makedir(notindexed=True)
-                requirements = self._baserequirements(create)
-                if self.ui.configbool('format', 'usestore', True):
-                    self.vfs.mkdir("store")
-                    requirements.append("store")
-                    if self.ui.configbool('format', 'usefncache', True):
-                        requirements.append("fncache")
-                        if self.ui.configbool('format', 'dotencode', True):
-                            requirements.append('dotencode')
-                    # create an invalid changelog
-                    self.vfs.append(
-                        "00changelog.i",
-                        '\0\0\0\2' # represents revlogv2
-                        ' dummy changelog to prevent using the old repo layout'
-                    )
-                if self.ui.configbool('format', 'generaldelta', False):
-                    requirements.append("generaldelta")
-                requirements = set(requirements)
+                oldvfs = self.vfs
+                try:
+                    self.vfs = scmutil.vfs(self.wvfs.join(".hgtmp"))
+                    self.opener = self.vfs
+                    if not self.wvfs.exists():
+                        self.wvfs.makedirs()
+                    self.vfs.makedir(notindexed=True)
+                    requirements = self._baserequirements(create)
+                    if self.ui.configbool('format', 'usestore', True):
+                        self.vfs.mkdir("store")
+                        requirements.append("store")
+                        if self.ui.configbool('format', 'usefncache', True):
+                            requirements.append("fncache")
+                            if self.ui.configbool('format', 'dotencode', True):
+                                requirements.append('dotencode')
+                    if self.ui.configbool('format', 'generaldelta', False):
+                        requirements.append("generaldelta")
+                    requirements = set(requirements)
+                    self._writerequirements(requirements)
+                    if self.ui.configbool('format', 'usestore', True):
+                        # create an invalid changelog
+                        self.vfs.append(
+                            "00changelog.i",
+                            '\0\0\0\2' # represents revlogv2
+                            ' dummy changelog to prevent using the old repo \
+                            layout'
+                        )
+                    self.wvfs.rename(".hgtmp", ".hg")
+                finally:
+                    self.vfs = oldvfs
+                    self.opener = oldvfs
             else:
                 raise error.RepoError(_("repository %s not found") % path)
         elif create:
@@ -247,9 +258,6 @@ class localrepository(object):
         self.sjoin = self.store.join
         self.vfs.createmode = self.store.createmode
         self._applyrequirements(requirements)
-        if create:
-            self._writerequirements()
-
 
         self._branchcaches = {}
         self.filterpats = {}
@@ -285,9 +293,11 @@ class localrepository(object):
         if chunkcachesize is not None:
             self.sopener.options['chunkcachesize'] = chunkcachesize
 
-    def _writerequirements(self):
+    def _writerequirements(self, requirements=None):
         reqfile = self.opener("requires", "w")
-        for r in sorted(self.requirements):
+        if requirements is None:
+            requirements = self.requirements
+        for r in sorted(requirements):
             reqfile.write("%s\n" % r)
         reqfile.close()