mercurial/transaction.py

transaction: refactor transaction.abort and rollback to use the same code

This adds a change to the way that abort is processed, as it will not continue
truncating files beyond the first failure, otherwise the respective
functionality is maintained, i.e. abort will not unlink files, but rollback
will.

Co-contributor: Sune Foldager <[e-mail]>

# transaction.py - simple journalling 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, incorporated herein by reference.

from i18n import _
import os, errno
import error

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, unlink=True):
    for f, o, ignore in entries:
        if o or not unlink:
            try:
                opener(f, 'a').truncate(o)
            except:
                report(_("failed to truncate %s\n") % f)
                raise
        else:
            try:
                fn = opener(f).name
                os.unlink(fn)
            except OSError, inst:
                if inst.errno != errno.ENOENT:
                    raise
    os.unlink(journal)

class transaction(object):
    def __init__(self, report, opener, journal, after=None, createmode=None):
        self.journal = None

        self.count = 1
        self.report = report
        self.opener = opener
        self.after = after
        self.entries = []
        self.map = {}
        self.journal = journal

        self.file = open(self.journal, "w")
        if createmode is not None:
            os.chmod(self.journal, createmode & 0666)

    def __del__(self):
        if self.journal:
            if self.entries: self._abort()
            self.file.close()

    @active
    def add(self, file, offset, data=None):
        if file in self.map: 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 find(self, file):
        if file in self.map:
            return self.entries[self.map[file]]
        return None

    @active
    def replace(self, file, offset, data=None):
        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
        return self

    def running(self):
        return self.count > 0

    @active
    def close(self):
        self.count -= 1
        if self.count != 0:
            return
        self.file.close()
        self.entries = []
        if self.after:
            self.after()
        else:
            os.unlink(self.journal)
        self.journal = None

    @active
    def abort(self):
        self._abort()

    def _abort(self):
        self.count = 0
        self.file.close()

        if not self.entries: return

        self.report(_("transaction abort!\n"))

        try:
            try:
                _playback(self.journal, self.report, self.opener, self.entries, False)
                self.report(_("rollback completed\n"))
            except:
                self.report(_("rollback failed - please run hg recover\n"))
        finally:
            self.journal = None


def rollback(opener, file, report):
    entries = []

    for l in open(file).readlines():
        f, o = l.split('\0')
        entries.append((f, int(o), None))

    _playback(file, report, opener, entries)