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.
# 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 <mpm@selenic.com>
#
# 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:
# 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)