view mercurial/transaction.py @ 18063:34a1a639d835

revset.children: ignore rev numbers that are too low

This replaces unnecessary parentrevs() calls with calculating min(parentset).
Even though the min operation is O(size of parentset), since parentrevs is
relatively expensive, this tradeoff almost always works in our favour. In a
repository with over 400,000 changesets, hg perfrevset "children(X)" takes:

       Set X       Before    After
       -1           0.51s    0.06s
    -1000:          0.55s    0.08s
   -10000:          0.56s    0.10s
  -100000:          0.60s    0.25s
  -100000:-99000    0.55s    0.19s
        0:100000    0.60s    0.61s
      all()         0.72s    0.74s

The relative performance is similar for Mercurial's own repository -- several
times faster in most cases, slightly slower for revisions close to 0 and
all().

# 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 os, 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, 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:
                fp = opener(f)
                fn = fp.name
                fp.close()
                util.unlink(fn)
            except (IOError, OSError), inst:
                if inst.errno != errno.ENOENT:
                    raise
    util.unlink(journal)

class transaction(object):
    def __init__(self, report, opener, journal, after=None, createmode=None):
        self.count = 1
        self.usages = 1
        self.report = report
        self.opener = opener
        self.after = after
        self.entries = []
        self.map = {}
        self.journal = journal
        self._queue = []

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

    def __del__(self):
        if self.journal:
            self._abort()

    @active
    def startgroup(self):
        self._queue.append([])

    @active
    def endgroup(self):
        q = self._queue.pop()
        d = ''.join(['%s\0%d\n' % (x[0], x[1]) for x in q])
        self.entries.extend(q)
        self.file.write(d)
        self.file.flush()

    @active
    def add(self, file, offset, data=None):
        if file in self.map:
            return
        if self._queue:
            self._queue[-1].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 find(self, file):
        if file in self.map:
            return self.entries[self.map[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'''
        self.count -= 1
        if self.count != 0:
            return
        self.file.close()
        self.entries = []
        if self.after:
            self.after()
        if os.path.isfile(self.journal):
            util.unlink(self.journal)
        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()

        try:
            if not self.entries:
                if self.journal:
                    util.unlink(self.journal)
                return

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

            try:
                _playback(self.journal, self.report, self.opener,
                          self.entries, 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):
    entries = []

    fp = util.posixfile(file)
    lines = fp.readlines()
    fp.close()
    for l in lines:
        f, o = l.split('\0')
        entries.append((f, int(o), None))

    _playback(file, report, opener, entries)