transaction: trivial refactoring
Differential Revision: https://phab.mercurial-scm.org/D10714
# 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 Olivia Mackall <olivia@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 __future__ import absolute_import
import errno
from .i18n import _
from . import (
error,
pycompat,
util,
)
from .utils import stringutil
version = 2
# These are the file generators that should only be executed after the
# finalizers are done, since they rely on the output of the finalizers (like
# the changelog having been written).
postfinalizegenerators = {b'bookmarks', b'dirstate'}
GEN_GROUP_ALL = b'all'
GEN_GROUP_PRE_FINALIZE = b'prefinalize'
GEN_GROUP_POST_FINALIZE = b'postfinalize'
def active(func):
def _active(self, *args, **kwds):
if self._count == 0:
raise error.ProgrammingError(
b'cannot use transaction when it is already committed/aborted'
)
return func(self, *args, **kwds)
return _active
def _playback(
journal,
report,
opener,
vfsmap,
entries,
backupentries,
unlink=True,
checkambigfiles=None,
):
for f, o in sorted(dict(entries).items()):
if o or not unlink:
checkambig = checkambigfiles and (f, b'') in checkambigfiles
try:
fp = opener(f, b'a', checkambig=checkambig)
if fp.tell() < o:
raise error.Abort(
_(
b"attempted to truncate %s to %d bytes, but it was "
b"already %d bytes\n"
)
% (f, o, fp.tell())
)
fp.truncate(o)
fp.close()
except IOError:
report(_(b"failed to truncate %s\n") % f)
raise
else:
try:
opener.unlink(f)
except (IOError, OSError) as inst:
if inst.errno != errno.ENOENT:
raise
backupfiles = []
for l, f, b, c in backupentries:
if l not in vfsmap and c:
report(b"couldn't handle %s: unknown cache location %s\n" % (b, l))
vfs = vfsmap[l]
try:
if f and b:
filepath = vfs.join(f)
backuppath = vfs.join(b)
checkambig = checkambigfiles and (f, l) in checkambigfiles
try:
util.copyfile(backuppath, filepath, checkambig=checkambig)
backupfiles.append(b)
except IOError:
report(_(b"failed to recover %s\n") % f)
else:
target = f or b
try:
vfs.unlink(target)
except (IOError, OSError) as inst:
if inst.errno != errno.ENOENT:
raise
except (IOError, OSError, error.Abort):
if not c:
raise
backuppath = b"%s.backupfiles" % journal
if opener.exists(backuppath):
opener.unlink(backuppath)
opener.unlink(journal)
try:
for f in backupfiles:
if opener.exists(f):
opener.unlink(f)
except (IOError, OSError, error.Abort):
# only pure backup file remains, it is sage to ignore any error
pass
class transaction(util.transactional):
def __init__(
self,
report,
opener,
vfsmap,
journalname,
undoname=None,
after=None,
createmode=None,
validator=None,
releasefn=None,
checkambigfiles=None,
name='<unnamed>',
):
"""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
* `releasefn`: called after releasing (with transaction and result)
`checkambigfiles` is a set of (path, vfs-location) tuples,
which determine whether file stat ambiguity should be avoided
for corresponded files.
"""
self._count = 1
self._usages = 1
self._report = report
# a vfs to the store content
self._opener = opener
# a map to access file in various {location -> vfs}
vfsmap = vfsmap.copy()
vfsmap[b''] = opener # set default value
self._vfsmap = vfsmap
self._after = after
self._offsetmap = {}
self._newfiles = set()
self._journal = journalname
self._undoname = undoname
self._queue = []
# A callback to do something just after releasing transaction.
if releasefn is None:
releasefn = lambda tr, success: None
self._releasefn = releasefn
self._checkambigfiles = set()
if checkambigfiles:
self._checkambigfiles.update(checkambigfiles)
self._names = [name]
# A dict dedicated to precisely tracking the changes introduced in the
# transaction.
self.changes = {}
# a dict of arguments to be passed to hooks
self.hookargs = {}
self._file = opener.open(self._journal, b"w+")
# a list of ('location', 'path', 'backuppath', cache) entries.
# - if 'backuppath' is empty, no file existed at backup time
# - if 'path' is empty, this is a temporary transaction file
# - if 'location' is not empty, the path is outside main opener reach.
# use 'location' value as a key in a vfsmap to find the right 'vfs'
# (cache is currently unused)
self._backupentries = []
self._backupmap = {}
self._backupjournal = b"%s.backupfiles" % self._journal
self._backupsfile = opener.open(self._backupjournal, b'w')
self._backupsfile.write(b'%d\n' % version)
if createmode is not None:
opener.chmod(self._journal, createmode & 0o666)
opener.chmod(self._backupjournal, createmode & 0o666)
# hold file generations to be performed on commit
self._filegenerators = {}
# hold callback to write pending data for hooks
self._pendingcallback = {}
# True is any pending data have been written ever
self._anypending = False
# holds callback to call when writing the transaction
self._finalizecallback = {}
# holds callback to call when validating the transaction
# should raise exception if anything is wrong
self._validatecallback = {}
if validator is not None:
self._validatecallback[b'001-userhooks'] = validator
# hold callback for post transaction close
self._postclosecallback = {}
# holds callbacks to call during abort
self._abortcallback = {}
def __repr__(self):
name = '/'.join(self._names)
return '<transaction name=%s, count=%d, usages=%d>' % (
name,
self._count,
self._usages,
)
def __del__(self):
if self._journal:
self._abort()
@active
def startgroup(self):
"""delay registration of file entry
This is used by strip to delay vision of strip offset. The transaction
sees either none or all of the strip actions to be done."""
self._queue.append([])
@active
def endgroup(self):
"""apply delayed registration of file entry.
This is used by strip to delay vision of strip offset. The transaction
sees either none or all of the strip actions to be done."""
q = self._queue.pop()
for f, o in q:
self._addentry(f, o)
@active
def add(self, file, offset):
"""record the state of an append-only file before update"""
if (
file in self._newfiles
or file in self._offsetmap
or file in self._backupmap
):
return
if self._queue:
self._queue[-1].append((file, offset))
return
self._addentry(file, offset)
def _addentry(self, file, offset):
"""add a append-only entry to memory and on-disk state"""
if (
file in self._newfiles
or file in self._offsetmap
or file in self._backupmap
):
return
if offset:
self._offsetmap[file] = offset
else:
self._newfiles.add(file)
# add enough data to the journal to do the truncate
self._file.write(b"%s\0%d\n" % (file, offset))
self._file.flush()
@active
def addbackup(self, file, hardlink=True, location=b''):
"""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 self._queue:
msg = b'cannot use transaction.addbackup inside "group"'
raise error.ProgrammingError(msg)
if (
file in self._newfiles
or file in self._offsetmap
or file in self._backupmap
):
return
vfs = self._vfsmap[location]
dirname, filename = vfs.split(file)
backupfilename = b"%s.backup.%s" % (self._journal, filename)
backupfile = vfs.reljoin(dirname, backupfilename)
if vfs.exists(file):
filepath = vfs.join(file)
backuppath = vfs.join(backupfile)
util.copyfile(filepath, backuppath, hardlink=hardlink)
else:
backupfile = b''
self._addbackupentry((location, file, backupfile, False))
def _addbackupentry(self, entry):
"""register a new backup entry and write it to disk"""
self._backupentries.append(entry)
self._backupmap[entry[1]] = len(self._backupentries) - 1
self._backupsfile.write(b"%s\0%s\0%s\0%d\n" % entry)
self._backupsfile.flush()
@active
def registertmp(self, tmpfile, location=b''):
"""register a temporary transaction file
Such files will be deleted when the transaction exits (on both
failure and success).
"""
self._addbackupentry((location, b'', tmpfile, False))
@active
def addfilegenerator(
self, genid, filenames, genfunc, order=0, location=b''
):
"""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.
The `location` arguments may be used to indicate the files are located
outside of the the standard directory for transaction. It should match
one of the key of the `transaction.vfsmap` dictionary.
"""
# For now, we are unable to do proper backup and restore of custom vfs
# but for bookmarks that are handled outside this mechanism.
self._filegenerators[genid] = (order, filenames, genfunc, location)
@active
def removefilegenerator(self, genid):
"""reverse of addfilegenerator, remove a file generator function"""
if genid in self._filegenerators:
del self._filegenerators[genid]
def _generatefiles(self, suffix=b'', group=GEN_GROUP_ALL):
# write files registered for generation
any = False
if group == GEN_GROUP_ALL:
skip_post = skip_pre = False
else:
skip_pre = group == GEN_GROUP_POST_FINALIZE
skip_post = group == GEN_GROUP_PRE_FINALIZE
for id, entry in sorted(pycompat.iteritems(self._filegenerators)):
any = True
order, filenames, genfunc, location = entry
# for generation at closing, check if it's before or after finalize
is_post = id in postfinalizegenerators
if skip_post and is_post:
continue
elif skip_pre and not is_post:
continue
vfs = self._vfsmap[location]
files = []
try:
for name in filenames:
name += suffix
if suffix:
self.registertmp(name, location=location)
checkambig = False
else:
self.addbackup(name, location=location)
checkambig = (name, location) in self._checkambigfiles
files.append(
vfs(name, b'w', atomictemp=True, checkambig=checkambig)
)
genfunc(*files)
for f in files:
f.close()
# skip discard() loop since we're sure no open file remains
del files[:]
finally:
for f in files:
f.discard()
return any
@active
def findoffset(self, file):
if file in self._newfiles:
return 0
return self._offsetmap.get(file)
@active
def readjournal(self):
self._file.seek(0)
entries = []
for l in self._file.readlines():
file, troffset = l.split(b'\0')
entries.append((file, int(troffset)))
return entries
@active
def replace(self, file, offset):
"""
replace can only replace already committed entries
that are not pending in the queue
"""
if file in self._newfiles:
if not offset:
return
self._newfiles.remove(file)
self._offsetmap[file] = offset
elif file in self._offsetmap:
if not offset:
del self._offsetmap[file]
self._newfiles.add(file)
else:
self._offsetmap[file] = offset
else:
raise KeyError(file)
self._file.write(b"%s\0%d\n" % (file, offset))
self._file.flush()
@active
def nest(self, name='<unnamed>'):
self._count += 1
self._usages += 1
self._names.append(name)
return self
def release(self):
if self._count > 0:
self._usages -= 1
if self._names:
self._names.pop()
# 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
def addpending(self, category, callback):
"""add a callback to be called when the transaction is pending
The transaction will be given as callback's first argument.
Category is a unique identifier to allow overwriting an old callback
with a newer callback.
"""
self._pendingcallback[category] = callback
@active
def writepending(self):
"""write pending file to temporary version
This is used to allow hooks to view a transaction before commit"""
categories = sorted(self._pendingcallback)
for cat in categories:
# remove callback since the data will have been flushed
any = self._pendingcallback.pop(cat)(self)
self._anypending = self._anypending or any
self._anypending |= self._generatefiles(suffix=b'.pending')
return self._anypending
@active
def hasfinalize(self, category):
"""check is a callback already exist for a category"""
return category in self._finalizecallback
@active
def addfinalize(self, category, callback):
"""add a callback to be called when the transaction is closed
The transaction will be given as callback's first argument.
Category is a unique identifier to allow overwriting old callbacks with
newer callbacks.
"""
self._finalizecallback[category] = callback
@active
def addpostclose(self, category, callback):
"""add or replace a callback to be called after the transaction closed
The transaction will be given as callback's first argument.
Category is a unique identifier to allow overwriting an old callback
with a newer callback.
"""
self._postclosecallback[category] = callback
@active
def getpostclose(self, category):
"""return a postclose callback added before, or None"""
return self._postclosecallback.get(category, None)
@active
def addabort(self, category, callback):
"""add a callback to be called when the transaction is aborted.
The transaction will be given as the first argument to the callback.
Category is a unique identifier to allow overwriting an old callback
with a newer callback.
"""
self._abortcallback[category] = callback
@active
def addvalidator(self, category, callback):
"""adds a callback to be called when validating the transaction.
The transaction will be given as the first argument to the callback.
callback should raise exception if to abort transaction"""
self._validatecallback[category] = callback
@active
def close(self):
'''commit the transaction'''
if self._count == 1:
for category in sorted(self._validatecallback):
self._validatecallback[category](self)
self._validatecallback = None # Help prevent cycles.
self._generatefiles(group=GEN_GROUP_PRE_FINALIZE)
while self._finalizecallback:
callbacks = self._finalizecallback
self._finalizecallback = {}
categories = sorted(callbacks)
for cat in categories:
callbacks[cat](self)
# Prevent double usage and help clear cycles.
self._finalizecallback = None
self._generatefiles(group=GEN_GROUP_POST_FINALIZE)
self._count -= 1
if self._count != 0:
return
self._file.close()
self._backupsfile.close()
# cleanup temporary files
for l, f, b, c in self._backupentries:
if l not in self._vfsmap and c:
self._report(
b"couldn't remove %s: unknown cache location %s\n" % (b, l)
)
continue
vfs = self._vfsmap[l]
if not f and b and vfs.exists(b):
try:
vfs.unlink(b)
except (IOError, OSError, error.Abort) as inst:
if not c:
raise
# Abort may be raise by read only opener
self._report(
b"couldn't remove %s: %s\n" % (vfs.join(b), inst)
)
self._offsetmap = {}
self._newfiles = set()
self._writeundo()
if self._after:
self._after()
self._after = None # Help prevent cycles.
if self._opener.isfile(self._backupjournal):
self._opener.unlink(self._backupjournal)
if self._opener.isfile(self._journal):
self._opener.unlink(self._journal)
for l, _f, b, c in self._backupentries:
if l not in self._vfsmap and c:
self._report(
b"couldn't remove %s: unknown cache location"
b"%s\n" % (b, l)
)
continue
vfs = self._vfsmap[l]
if b and vfs.exists(b):
try:
vfs.unlink(b)
except (IOError, OSError, error.Abort) as inst:
if not c:
raise
# Abort may be raise by read only opener
self._report(
b"couldn't remove %s: %s\n" % (vfs.join(b), inst)
)
self._backupentries = []
self._journal = None
self._releasefn(self, True) # notify success of closing transaction
self._releasefn = None # Help prevent cycles.
# run post close action
categories = sorted(self._postclosecallback)
for cat in categories:
self._postclosecallback[cat](self)
# Prevent double usage and help clear cycles.
self._postclosecallback = 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 _writeundo(self):
"""write transaction data for possible future undo call"""
if self._undoname is None:
return
undobackupfile = self._opener.open(
b"%s.backupfiles" % self._undoname, b'w'
)
undobackupfile.write(b'%d\n' % version)
for l, f, b, c in self._backupentries:
if not f: # temporary file
continue
if not b:
u = b''
else:
if l not in self._vfsmap and c:
self._report(
b"couldn't remove %s: unknown cache location"
b"%s\n" % (b, l)
)
continue
vfs = self._vfsmap[l]
base, name = vfs.split(b)
assert name.startswith(self._journal), name
uname = name.replace(self._journal, self._undoname, 1)
u = vfs.reljoin(base, uname)
util.copyfile(vfs.join(b), vfs.join(u), hardlink=True)
undobackupfile.write(b"%s\0%s\0%s\0%d\n" % (l, f, u, c))
undobackupfile.close()
def _abort(self):
entries = self.readjournal()
self._count = 0
self._usages = 0
self._file.close()
self._backupsfile.close()
try:
if not entries and not self._backupentries:
if self._backupjournal:
self._opener.unlink(self._backupjournal)
if self._journal:
self._opener.unlink(self._journal)
return
self._report(_(b"transaction abort!\n"))
try:
for cat in sorted(self._abortcallback):
self._abortcallback[cat](self)
# Prevent double usage and help clear cycles.
self._abortcallback = None
_playback(
self._journal,
self._report,
self._opener,
self._vfsmap,
entries,
self._backupentries,
False,
checkambigfiles=self._checkambigfiles,
)
self._report(_(b"rollback completed\n"))
except BaseException as exc:
self._report(_(b"rollback failed - please run hg recover\n"))
self._report(
_(b"(failure reason: %s)\n") % stringutil.forcebytestr(exc)
)
finally:
self._journal = None
self._releasefn(self, False) # notify failure of transaction
self._releasefn = None # Help prevent cycles.
def rollback(opener, vfsmap, file, report, checkambigfiles=None):
"""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.
`checkambigfiles` is a set of (path, vfs-location) tuples,
which determine whether file stat ambiguity should be avoided at
restoring corresponded files.
"""
entries = []
backupentries = []
with opener.open(file) as fp:
lines = fp.readlines()
for l in lines:
try:
f, o = l.split(b'\0')
entries.append((f, int(o)))
except ValueError:
report(
_(b"couldn't read journal entry %r!\n") % pycompat.bytestr(l)
)
backupjournal = b"%s.backupfiles" % file
if opener.exists(backupjournal):
fp = opener.open(backupjournal)
lines = fp.readlines()
if lines:
ver = lines[0][:-1]
if ver == (b'%d' % version):
for line in lines[1:]:
if line:
# Shave off the trailing newline
line = line[:-1]
l, f, b, c = line.split(b'\0')
backupentries.append((l, f, b, bool(c)))
else:
report(
_(
b"journal was created by a different version of "
b"Mercurial\n"
)
)
_playback(
file,
report,
opener,
vfsmap,
entries,
backupentries,
checkambigfiles=checkambigfiles,
)