transaction: work around and document issue with file backup

The backup restoration is actually hard-coded for the main file. And this
hard-coded list is the only one used when repairing an interrupted transaction
from another process.

Solving this problem is out of the scope of this series so we document it and
work around its implications.

mercurial/transaction.py

@@ -1,344 +1,348 b''
 # transaction.py - simple journaling scheme for mercurial
 #
 # This transaction scheme is intended to gracefully handle program
 # errors and interruptions. More serious failures like system crashes
 # can be recovered with an fsck-like tool. As the whole repository is
 # effectively log-structured, this should amount to simply truncating
 # anything that isn't referenced in the changelog.
 #
 # Copyright 2005, 2006 Matt Mackall <[e-mail]>
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 from i18n import _
 import errno
 import error, util
 
 def active(func):
     def _active(self, *args, **kwds):
         if self.count == 0:
             raise error.Abort(_(
                 'cannot use transaction when it is already committed/aborted'))
         return func(self, *args, **kwds)
     return _active
 
 def _playback(journal, report, opener, entries, backupentries, unlink=True):
     for f, o, _ignore in entries:
         if o or not unlink:
             try:
                 fp = opener(f, 'a')
                 fp.truncate(o)
                 fp.close()
             except IOError:
                 report(_("failed to truncate %s\n") % f)
                 raise
         else:
             try:
                 opener.unlink(f)
             except (IOError, OSError), inst:
                 if inst.errno != errno.ENOENT:
                     raise
 
     backupfiles = []
     for f, b, _ignore in backupentries:
         filepath = opener.join(f)
         backuppath = opener.join(b)
         try:
             util.copyfile(backuppath, filepath)
             backupfiles.append(b)
         except IOError:
             report(_("failed to recover %s\n") % f)
             raise
 
     opener.unlink(journal)
     backuppath = "%s.backupfiles" % journal
     if opener.exists(backuppath):
         opener.unlink(backuppath)
     for f in backupfiles:
         opener.unlink(f)
 
 class transaction(object):
     def __init__(self, report, opener, journal, after=None, createmode=None,
             onclose=None, onabort=None):
         """Begin a new transaction
 
         Begins a new transaction that allows rolling back writes in the event of
         an exception.
 
         * `after`: called after the transaction has been committed
         * `createmode`: the mode of the journal file that will be created
         * `onclose`: called as the transaction is closing, but before it is
         closed
         * `onabort`: called as the transaction is aborting, but before any files
         have been truncated
         """
         self.count = 1
         self.usages = 1
         self.report = report
         self.opener = opener
         self.after = after
         self.onclose = onclose
         self.onabort = onabort
         self.entries = []
         self.backupentries = []
         self.map = {}
         self.backupmap = {}
         self.journal = journal
         self._queue = []
         # a dict of arguments to be passed to hooks
         self.hookargs = {}
 
         self.backupjournal = "%s.backupfiles" % journal
         self.file = opener.open(self.journal, "w")
         self.backupsfile = opener.open(self.backupjournal, 'w')
         if createmode is not None:
             opener.chmod(self.journal, createmode & 0666)
             opener.chmod(self.backupjournal, createmode & 0666)
 
         # hold file generations to be performed on commit
         self._filegenerators = {}
 
     def __del__(self):
         if self.journal:
             self._abort()
 
     @active
     def startgroup(self):
         self._queue.append(([], []))
 
     @active
     def endgroup(self):
         q = self._queue.pop()
         self.entries.extend(q[0])
         self.backupentries.extend(q[1])
 
         offsets = []
         backups = []
         for f, o, _data in q[0]:
             offsets.append((f, o))
 
         for f, b, _data in q[1]:
             backups.append((f, b))
 
         d = ''.join(['%s\0%d\n' % (f, o) for f, o in offsets])
         self.file.write(d)
         self.file.flush()
 
         d = ''.join(['%s\0%s\0' % (f, b) for f, b in backups])
         self.backupsfile.write(d)
         self.backupsfile.flush()
 
     @active
     def add(self, file, offset, data=None):
         if file in self.map or file in self.backupmap:
             return
         if self._queue:
             self._queue[-1][0].append((file, offset, data))
             return
 
         self.entries.append((file, offset, data))
         self.map[file] = len(self.entries) - 1
         # add enough data to the journal to do the truncate
         self.file.write("%s\0%d\n" % (file, offset))
         self.file.flush()
 
     @active
     def addbackup(self, file, hardlink=True):
         """Adds a backup of the file to the transaction
 
         Calling addbackup() creates a hardlink backup of the specified file
         that is used to recover the file in the event of the transaction
         aborting.
 
         * `file`: the file path, relative to .hg/store
         * `hardlink`: use a hardlink to quickly create the backup
         """
 
         if file in self.map or file in self.backupmap:
             return
         backupfile = "%s.backup.%s" % (self.journal, file)
         if self.opener.exists(file):
             filepath = self.opener.join(file)
             backuppath = self.opener.join(backupfile)
             util.copyfiles(filepath, backuppath, hardlink=hardlink)
         else:
             self.add(file, 0)
             return
 
         if self._queue:
             self._queue[-1][1].append((file, backupfile))
             return
 
         self.backupentries.append((file, backupfile, None))
         self.backupmap[file] = len(self.backupentries) - 1
         self.backupsfile.write("%s\0%s\0" % (file, backupfile))
         self.backupsfile.flush()
 
     @active
     def addfilegenerator(self, genid, filenames, genfunc, order=0):
         """add a function to generates some files at transaction commit
 
         The `genfunc` argument is a function capable of generating proper
         content of each entry in the `filename` tuple.
 
         At transaction close time, `genfunc` will be called with one file
         object argument per entries in `filenames`.
 
         The transaction itself is responsible for the backup, creation and
         final write of such file.
 
         The `genid` argument is used to ensure the same set of file is only
         generated once. Call to `addfilegenerator` for a `genid` already
         present will overwrite the old entry.
 
         The `order` argument may be used to control the order in which multiple
         generator will be executed.
         """
         self._filegenerators[genid] = (order, filenames, genfunc)
 
     @active
     def find(self, file):
         if file in self.map:
             return self.entries[self.map[file]]
         if file in self.backupmap:
             return self.backupentries[self.backupmap[file]]
         return None
 
     @active
     def replace(self, file, offset, data=None):
         '''
         replace can only replace already committed entries
         that are not pending in the queue
         '''
 
         if file not in self.map:
             raise KeyError(file)
         index = self.map[file]
         self.entries[index] = (file, offset, data)
         self.file.write("%s\0%d\n" % (file, offset))
         self.file.flush()
 
     @active
     def nest(self):
         self.count += 1
         self.usages += 1
         return self
 
     def release(self):
         if self.count > 0:
             self.usages -= 1
         # if the transaction scopes are left without being closed, fail
         if self.count > 0 and self.usages == 0:
             self._abort()
 
     def running(self):
         return self.count > 0
 
     @active
     def close(self):
         '''commit the transaction'''
         # write files registered for generation
         for order, filenames, genfunc in sorted(self._filegenerators.values()):
             files = []
             try:
                 for name in filenames:
-                    self.addbackup(name)
+                    # Some files are already backed up when creating the
+                    # localrepo. Until this is properly fixed we disable the
+                    # backup for them.
+                    if name not in ('phaseroots',):
+                        self.addbackup(name)
                     files.append(self.opener(name, 'w', atomictemp=True))
                 genfunc(*files)
             finally:
                 for f in files:
                     f.close()
 
         if self.count == 1 and self.onclose is not None:
             self.onclose()
 
         self.count -= 1
         if self.count != 0:
             return
         self.file.close()
         self.backupsfile.close()
         self.entries = []
         if self.after:
             self.after()
         if self.opener.isfile(self.journal):
             self.opener.unlink(self.journal)
         if self.opener.isfile(self.backupjournal):
             self.opener.unlink(self.backupjournal)
             for _f, b, _ignore in self.backupentries:
                 self.opener.unlink(b)
         self.backupentries = []
         self.journal = None
 
     @active
     def abort(self):
         '''abort the transaction (generally called on error, or when the
         transaction is not explicitly committed before going out of
         scope)'''
         self._abort()
 
     def _abort(self):
         self.count = 0
         self.usages = 0
         self.file.close()
         self.backupsfile.close()
 
         if self.onabort is not None:
             self.onabort()
 
         try:
             if not self.entries and not self.backupentries:
                 if self.journal:
                     self.opener.unlink(self.journal)
                 if self.backupjournal:
                     self.opener.unlink(self.backupjournal)
                 return
 
             self.report(_("transaction abort!\n"))
 
             try:
                 _playback(self.journal, self.report, self.opener,
                           self.entries, self.backupentries, False)
                 self.report(_("rollback completed\n"))
             except Exception:
                 self.report(_("rollback failed - please run hg recover\n"))
         finally:
             self.journal = None
 
 
 def rollback(opener, file, report):
     """Rolls back the transaction contained in the given file
 
     Reads the entries in the specified file, and the corresponding
     '*.backupfiles' file, to recover from an incomplete transaction.
 
     * `file`: a file containing a list of entries, specifying where
     to truncate each file.  The file should contain a list of
     file\0offset pairs, delimited by newlines. The corresponding
     '*.backupfiles' file should contain a list of file\0backupfile
     pairs, delimited by \0.
     """
     entries = []
     backupentries = []
 
     fp = opener.open(file)
     lines = fp.readlines()
     fp.close()
     for l in lines:
         try:
             f, o = l.split('\0')
             entries.append((f, int(o), None))
         except ValueError:
             report(_("couldn't read journal entry %r!\n") % l)
 
     backupjournal = "%s.backupfiles" % file
     if opener.exists(backupjournal):
         fp = opener.open(backupjournal)
         data = fp.read()
         if len(data) > 0:
             parts = data.split('\0')
             for i in xrange(0, len(parts), 2):
                 f, b = parts[i:i + 1]
                 backupentries.append((f, b, None))
 
     _playback(file, report, opener, entries, backupentries)