mercurial/exchange.py

bundle2: feed a binary stream to `peer.unbundle`

This input will have to travel over the wire anyway, so we feed the peer method
with a simple binary stream and rely on the server side to use `readbundle`
to create the python object.

The test output changes because the bundle is created marginally sooner and the
debug output interleaves in a different way.

# exchange.py - utility to exchange data between repos.
#
# Copyright 2005-2007 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 _
from node import hex, nullid
import errno
import util, scmutil, changegroup, base85
import discovery, phases, obsolete, bookmarks, bundle2

def readbundle(ui, fh, fname, vfs=None):
    header = changegroup.readexactly(fh, 4)

    alg = None
    if not fname:
        fname = "stream"
        if not header.startswith('HG') and header.startswith('\0'):
            fh = changegroup.headerlessfixup(fh, header)
            header = "HG10"
            alg = 'UN'
    elif vfs:
        fname = vfs.join(fname)

    magic, version = header[0:2], header[2:4]

    if magic != 'HG':
        raise util.Abort(_('%s: not a Mercurial bundle') % fname)
    if version == '10':
        if alg is None:
            alg = changegroup.readexactly(fh, 2)
        return changegroup.unbundle10(fh, alg)
    elif version == '20':
        return bundle2.unbundle20(ui, fh, header=magic + version)
    else:
        raise util.Abort(_('%s: unknown bundle version %s') % (fname, version))


class pushoperation(object):
    """A object that represent a single push operation

    It purpose is to carry push related state and very common operation.

    A new should be created at the beginning of each push and discarded
    afterward.
    """

    def __init__(self, repo, remote, force=False, revs=None, newbranch=False):
        # repo we push from
        self.repo = repo
        self.ui = repo.ui
        # repo we push to
        self.remote = remote
        # force option provided
        self.force = force
        # revs to be pushed (None is "all")
        self.revs = revs
        # allow push of new branch
        self.newbranch = newbranch
        # did a local lock get acquired?
        self.locallocked = None
        # Integer version of the push result
        # - None means nothing to push
        # - 0 means HTTP error
        # - 1 means we pushed and remote head count is unchanged *or*
        #   we have outgoing changesets but refused to push
        # - other values as described by addchangegroup()
        self.ret = None
        # discover.outgoing object (contains common and outgoing data)
        self.outgoing = None
        # all remote heads before the push
        self.remoteheads = None
        # testable as a boolean indicating if any nodes are missing locally.
        self.incoming = None
        # set of all heads common after changeset bundle push
        self.commonheads = None

def push(repo, remote, force=False, revs=None, newbranch=False):
    '''Push outgoing changesets (limited by revs) from a local
    repository to remote. Return an integer:
      - None means nothing to push
      - 0 means HTTP error
      - 1 means we pushed and remote head count is unchanged *or*
        we have outgoing changesets but refused to push
      - other values as described by addchangegroup()
    '''
    pushop = pushoperation(repo, remote, force, revs, newbranch)
    if pushop.remote.local():
        missing = (set(pushop.repo.requirements)
                   - pushop.remote.local().supported)
        if missing:
            msg = _("required features are not"
                    " supported in the destination:"
                    " %s") % (', '.join(sorted(missing)))
            raise util.Abort(msg)

    # there are two ways to push to remote repo:
    #
    # addchangegroup assumes local user can lock remote
    # repo (local filesystem, old ssh servers).
    #
    # unbundle assumes local user cannot lock remote repo (new ssh
    # servers, http servers).

    if not pushop.remote.canpush():
        raise util.Abort(_("destination does not support push"))
    # get local lock as we might write phase data
    locallock = None
    try:
        locallock = pushop.repo.lock()
        pushop.locallocked = True
    except IOError, err:
        pushop.locallocked = False
        if err.errno != errno.EACCES:
            raise
        # source repo cannot be locked.
        # We do not abort the push, but just disable the local phase
        # synchronisation.
        msg = 'cannot lock source repository: %s\n' % err
        pushop.ui.debug(msg)
    try:
        pushop.repo.checkpush(pushop)
        lock = None
        unbundle = pushop.remote.capable('unbundle')
        if not unbundle:
            lock = pushop.remote.lock()
        try:
            _pushdiscovery(pushop)
            if _pushcheckoutgoing(pushop):
                pushop.repo.prepushoutgoinghooks(pushop.repo,
                                                 pushop.remote,
                                                 pushop.outgoing)
                if pushop.remote.capable('bundle2'):
                    _pushbundle2(pushop)
                else:
                    _pushchangeset(pushop)
            _pushcomputecommonheads(pushop)
            _pushsyncphase(pushop)
            _pushobsolete(pushop)
        finally:
            if lock is not None:
                lock.release()
    finally:
        if locallock is not None:
            locallock.release()

    _pushbookmark(pushop)
    return pushop.ret

def _pushdiscovery(pushop):
    # discovery
    unfi = pushop.repo.unfiltered()
    fci = discovery.findcommonincoming
    commoninc = fci(unfi, pushop.remote, force=pushop.force)
    common, inc, remoteheads = commoninc
    fco = discovery.findcommonoutgoing
    outgoing = fco(unfi, pushop.remote, onlyheads=pushop.revs,
                   commoninc=commoninc, force=pushop.force)
    pushop.outgoing = outgoing
    pushop.remoteheads = remoteheads
    pushop.incoming = inc

def _pushcheckoutgoing(pushop):
    outgoing = pushop.outgoing
    unfi = pushop.repo.unfiltered()
    if not outgoing.missing:
        # nothing to push
        scmutil.nochangesfound(unfi.ui, unfi, outgoing.excluded)
        return False
    # something to push
    if not pushop.force:
        # if repo.obsstore == False --> no obsolete
        # then, save the iteration
        if unfi.obsstore:
            # this message are here for 80 char limit reason
            mso = _("push includes obsolete changeset: %s!")
            mst = "push includes %s changeset: %s!"
            # plain versions for i18n tool to detect them
            _("push includes unstable changeset: %s!")
            _("push includes bumped changeset: %s!")
            _("push includes divergent changeset: %s!")
            # If we are to push if there is at least one
            # obsolete or unstable changeset in missing, at
            # least one of the missinghead will be obsolete or
            # unstable. So checking heads only is ok
            for node in outgoing.missingheads:
                ctx = unfi[node]
                if ctx.obsolete():
                    raise util.Abort(mso % ctx)
                elif ctx.troubled():
                    raise util.Abort(_(mst)
                                     % (ctx.troubles()[0],
                                        ctx))
        newbm = pushop.ui.configlist('bookmarks', 'pushing')
        discovery.checkheads(unfi, pushop.remote, outgoing,
                             pushop.remoteheads,
                             pushop.newbranch,
                             bool(pushop.incoming),
                             newbm)
    return True

def _pushbundle2(pushop):
    """push data to the remote using bundle2

    The only currently supported type of data is changegroup but this will
    evolve in the future."""
    # Send known head to the server for race detection.
    bundler = bundle2.bundle20(pushop.ui)
    if not pushop.force:
        part = bundle2.bundlepart('CHECK:HEADS', data=iter(pushop.remoteheads))
        bundler.addpart(part)
    # add the changegroup bundle
    cg = changegroup.getlocalbundle(pushop.repo, 'push', pushop.outgoing)
    cgpart = bundle2.bundlepart('CHANGEGROUP', data=cg.getchunks())
    bundler.addpart(cgpart)
    stream = util.chunkbuffer(bundler.getchunks())
    reply = pushop.remote.unbundle(stream, ['force'], 'push')
    try:
        op = bundle2.processbundle(pushop.repo, reply)
    except KeyError, exc:
        raise util.Abort('missing support for %s' % exc)
    cgreplies = op.records.getreplies(cgpart.id)
    assert len(cgreplies['changegroup']) == 1
    pushop.ret = cgreplies['changegroup'][0]['return']

def _pushchangeset(pushop):
    """Make the actual push of changeset bundle to remote repo"""
    outgoing = pushop.outgoing
    unbundle = pushop.remote.capable('unbundle')
    # TODO: get bundlecaps from remote
    bundlecaps = None
    # create a changegroup from local
    if pushop.revs is None and not (outgoing.excluded
                            or pushop.repo.changelog.filteredrevs):
        # push everything,
        # use the fast path, no race possible on push
        bundler = changegroup.bundle10(pushop.repo, bundlecaps)
        cg = changegroup.getsubset(pushop.repo,
                                   outgoing,
                                   bundler,
                                   'push',
                                   fastpath=True)
    else:
        cg = changegroup.getlocalbundle(pushop.repo, 'push', outgoing,
                                        bundlecaps)

    # apply changegroup to remote
    if unbundle:
        # local repo finds heads on server, finds out what
        # revs it must push. once revs transferred, if server
        # finds it has different heads (someone else won
        # commit/push race), server aborts.
        if pushop.force:
            remoteheads = ['force']
        else:
            remoteheads = pushop.remoteheads
        # ssh: return remote's addchangegroup()
        # http: return remote's addchangegroup() or 0 for error
        pushop.ret = pushop.remote.unbundle(cg, remoteheads,
                                            'push')
    else:
        # we return an integer indicating remote head count
        # change
        pushop.ret = pushop.remote.addchangegroup(cg, 'push', pushop.repo.url())

def _pushcomputecommonheads(pushop):
    unfi = pushop.repo.unfiltered()
    if pushop.ret:
        # push succeed, synchronize target of the push
        cheads = pushop.outgoing.missingheads
    elif pushop.revs is None:
        # All out push fails. synchronize all common
        cheads = pushop.outgoing.commonheads
    else:
        # I want cheads = heads(::missingheads and ::commonheads)
        # (missingheads is revs with secret changeset filtered out)
        #
        # This can be expressed as:
        #     cheads = ( (missingheads and ::commonheads)
        #              + (commonheads and ::missingheads))"
        #              )
        #
        # while trying to push we already computed the following:
        #     common = (::commonheads)
        #     missing = ((commonheads::missingheads) - commonheads)
        #
        # We can pick:
        # * missingheads part of common (::commonheads)
        common = set(pushop.outgoing.common)
        nm = pushop.repo.changelog.nodemap
        cheads = [node for node in pushop.revs if nm[node] in common]
        # and
        # * commonheads parents on missing
        revset = unfi.set('%ln and parents(roots(%ln))',
                         pushop.outgoing.commonheads,
                         pushop.outgoing.missing)
        cheads.extend(c.node() for c in revset)
    pushop.commonheads = cheads

def _pushsyncphase(pushop):
    """synchronise phase information locally and remotely"""
    unfi = pushop.repo.unfiltered()
    cheads = pushop.commonheads
    if pushop.ret:
        # push succeed, synchronize target of the push
        cheads = pushop.outgoing.missingheads
    elif pushop.revs is None:
        # All out push fails. synchronize all common
        cheads = pushop.outgoing.commonheads
    else:
        # I want cheads = heads(::missingheads and ::commonheads)
        # (missingheads is revs with secret changeset filtered out)
        #
        # This can be expressed as:
        #     cheads = ( (missingheads and ::commonheads)
        #              + (commonheads and ::missingheads))"
        #              )
        #
        # while trying to push we already computed the following:
        #     common = (::commonheads)
        #     missing = ((commonheads::missingheads) - commonheads)
        #
        # We can pick:
        # * missingheads part of common (::commonheads)
        common = set(pushop.outgoing.common)
        nm = pushop.repo.changelog.nodemap
        cheads = [node for node in pushop.revs if nm[node] in common]
        # and
        # * commonheads parents on missing
        revset = unfi.set('%ln and parents(roots(%ln))',
                         pushop.outgoing.commonheads,
                         pushop.outgoing.missing)
        cheads.extend(c.node() for c in revset)
    pushop.commonheads = cheads
    # even when we don't push, exchanging phase data is useful
    remotephases = pushop.remote.listkeys('phases')
    if (pushop.ui.configbool('ui', '_usedassubrepo', False)
        and remotephases    # server supports phases
        and pushop.ret is None # nothing was pushed
        and remotephases.get('publishing', False)):
        # When:
        # - this is a subrepo push
        # - and remote support phase
        # - and no changeset was pushed
        # - and remote is publishing
        # We may be in issue 3871 case!
        # We drop the possible phase synchronisation done by
        # courtesy to publish changesets possibly locally draft
        # on the remote.
        remotephases = {'publishing': 'True'}
    if not remotephases: # old server or public only reply from non-publishing
        _localphasemove(pushop, cheads)
        # don't push any phase data as there is nothing to push
    else:
        ana = phases.analyzeremotephases(pushop.repo, cheads,
                                         remotephases)
        pheads, droots = ana
        ### Apply remote phase on local
        if remotephases.get('publishing', False):
            _localphasemove(pushop, cheads)
        else: # publish = False
            _localphasemove(pushop, pheads)
            _localphasemove(pushop, cheads, phases.draft)
        ### Apply local phase on remote

        # Get the list of all revs draft on remote by public here.
        # XXX Beware that revset break if droots is not strictly
        # XXX root we may want to ensure it is but it is costly
        outdated =  unfi.set('heads((%ln::%ln) and public())',
                             droots, cheads)
        for newremotehead in outdated:
            r = pushop.remote.pushkey('phases',
                                      newremotehead.hex(),
                                      str(phases.draft),
                                      str(phases.public))
            if not r:
                pushop.ui.warn(_('updating %s to public failed!\n')
                                       % newremotehead)

def _localphasemove(pushop, nodes, phase=phases.public):
    """move <nodes> to <phase> in the local source repo"""
    if pushop.locallocked:
        phases.advanceboundary(pushop.repo, phase, nodes)
    else:
        # repo is not locked, do not change any phases!
        # Informs the user that phases should have been moved when
        # applicable.
        actualmoves = [n for n in nodes if phase < pushop.repo[n].phase()]
        phasestr = phases.phasenames[phase]
        if actualmoves:
            pushop.ui.status(_('cannot lock source repo, skipping '
                               'local %s phase update\n') % phasestr)

def _pushobsolete(pushop):
    """utility function to push obsolete markers to a remote"""
    pushop.ui.debug('try to push obsolete markers to remote\n')
    repo = pushop.repo
    remote = pushop.remote
    if (obsolete._enabled and repo.obsstore and
        'obsolete' in remote.listkeys('namespaces')):
        rslts = []
        remotedata = repo.listkeys('obsolete')
        for key in sorted(remotedata, reverse=True):
            # reverse sort to ensure we end with dump0
            data = remotedata[key]
            rslts.append(remote.pushkey('obsolete', key, '', data))
        if [r for r in rslts if not r]:
            msg = _('failed to push some obsolete markers!\n')
            repo.ui.warn(msg)

def _pushbookmark(pushop):
    """Update bookmark position on remote"""
    ui = pushop.ui
    repo = pushop.repo.unfiltered()
    remote = pushop.remote
    ui.debug("checking for updated bookmarks\n")
    revnums = map(repo.changelog.rev, pushop.revs or [])
    ancestors = [a for a in repo.changelog.ancestors(revnums, inclusive=True)]
    (addsrc, adddst, advsrc, advdst, diverge, differ, invalid
     ) = bookmarks.compare(repo, repo._bookmarks, remote.listkeys('bookmarks'),
                           srchex=hex)

    for b, scid, dcid in advsrc:
        if ancestors and repo[scid].rev() not in ancestors:
            continue
        if remote.pushkey('bookmarks', b, dcid, scid):
            ui.status(_("updating bookmark %s\n") % b)
        else:
            ui.warn(_('updating bookmark %s failed!\n') % b)

class pulloperation(object):
    """A object that represent a single pull operation

    It purpose is to carry push related state and very common operation.

    A new should be created at the beginning of each pull and discarded
    afterward.
    """

    def __init__(self, repo, remote, heads=None, force=False):
        # repo we pull into
        self.repo = repo
        # repo we pull from
        self.remote = remote
        # revision we try to pull (None is "all")
        self.heads = heads
        # do we force pull?
        self.force = force
        # the name the pull transaction
        self._trname = 'pull\n' + util.hidepassword(remote.url())
        # hold the transaction once created
        self._tr = None
        # set of common changeset between local and remote before pull
        self.common = None
        # set of pulled head
        self.rheads = None
        # list of missing changeset to fetch remotely
        self.fetch = None
        # result of changegroup pulling (used as return code by pull)
        self.cgresult = None
        # list of step remaining todo (related to future bundle2 usage)
        self.todosteps = set(['changegroup', 'phases', 'obsmarkers'])

    @util.propertycache
    def pulledsubset(self):
        """heads of the set of changeset target by the pull"""
        # compute target subset
        if self.heads is None:
            # We pulled every thing possible
            # sync on everything common
            c = set(self.common)
            ret = list(self.common)
            for n in self.rheads:
                if n not in c:
                    ret.append(n)
            return ret
        else:
            # We pulled a specific subset
            # sync on this subset
            return self.heads

    def gettransaction(self):
        """get appropriate pull transaction, creating it if needed"""
        if self._tr is None:
            self._tr = self.repo.transaction(self._trname)
        return self._tr

    def closetransaction(self):
        """close transaction if created"""
        if self._tr is not None:
            self._tr.close()

    def releasetransaction(self):
        """release transaction if created"""
        if self._tr is not None:
            self._tr.release()

def pull(repo, remote, heads=None, force=False):
    pullop = pulloperation(repo, remote, heads, force)
    if pullop.remote.local():
        missing = set(pullop.remote.requirements) - pullop.repo.supported
        if missing:
            msg = _("required features are not"
                    " supported in the destination:"
                    " %s") % (', '.join(sorted(missing)))
            raise util.Abort(msg)

    lock = pullop.repo.lock()
    try:
        _pulldiscovery(pullop)
        if pullop.remote.capable('bundle2'):
            _pullbundle2(pullop)
        if 'changegroup' in pullop.todosteps:
            _pullchangeset(pullop)
        if 'phases' in pullop.todosteps:
            _pullphase(pullop)
        if 'obsmarkers' in pullop.todosteps:
            _pullobsolete(pullop)
        pullop.closetransaction()
    finally:
        pullop.releasetransaction()
        lock.release()

    return pullop.cgresult

def _pulldiscovery(pullop):
    """discovery phase for the pull

    Current handle changeset discovery only, will change handle all discovery
    at some point."""
    tmp = discovery.findcommonincoming(pullop.repo.unfiltered(),
                                       pullop.remote,
                                       heads=pullop.heads,
                                       force=pullop.force)
    pullop.common, pullop.fetch, pullop.rheads = tmp

def _pullbundle2(pullop):
    """pull data using bundle2

    For now, the only supported data are changegroup."""
    kwargs = {'bundlecaps': set(['HG20'])}
    # pulling changegroup
    pullop.todosteps.remove('changegroup')
    if not pullop.fetch:
            pullop.repo.ui.status(_("no changes found\n"))
            pullop.cgresult = 0
    else:
        kwargs['common'] = pullop.common
        kwargs['heads'] = pullop.heads or pullop.rheads
        if pullop.heads is None and list(pullop.common) == [nullid]:
            pullop.repo.ui.status(_("requesting all changes\n"))
    if kwargs.keys() == ['format']:
        return # nothing to pull
    bundle = pullop.remote.getbundle('pull', **kwargs)
    try:
        op = bundle2.processbundle(pullop.repo, bundle, pullop.gettransaction)
    except KeyError, exc:
        raise util.Abort('missing support for %s' % exc)
    assert len(op.records['changegroup']) == 1
    pullop.cgresult = op.records['changegroup'][0]['return']

def _pullchangeset(pullop):
    """pull changeset from unbundle into the local repo"""
    # We delay the open of the transaction as late as possible so we
    # don't open transaction for nothing or you break future useful
    # rollback call
    pullop.todosteps.remove('changegroup')
    if not pullop.fetch:
            pullop.repo.ui.status(_("no changes found\n"))
            pullop.cgresult = 0
            return
    pullop.gettransaction()
    if pullop.heads is None and list(pullop.common) == [nullid]:
        pullop.repo.ui.status(_("requesting all changes\n"))
    elif pullop.heads is None and pullop.remote.capable('changegroupsubset'):
        # issue1320, avoid a race if remote changed after discovery
        pullop.heads = pullop.rheads

    if pullop.remote.capable('getbundle'):
        # TODO: get bundlecaps from remote
        cg = pullop.remote.getbundle('pull', common=pullop.common,
                                     heads=pullop.heads or pullop.rheads)
    elif pullop.heads is None:
        cg = pullop.remote.changegroup(pullop.fetch, 'pull')
    elif not pullop.remote.capable('changegroupsubset'):
        raise util.Abort(_("partial pull cannot be done because "
                                   "other repository doesn't support "
                                   "changegroupsubset."))
    else:
        cg = pullop.remote.changegroupsubset(pullop.fetch, pullop.heads, 'pull')
    pullop.cgresult = changegroup.addchangegroup(pullop.repo, cg, 'pull',
                                                 pullop.remote.url())

def _pullphase(pullop):
    # Get remote phases data from remote
    pullop.todosteps.remove('phases')
    remotephases = pullop.remote.listkeys('phases')
    publishing = bool(remotephases.get('publishing', False))
    if remotephases and not publishing:
        # remote is new and unpublishing
        pheads, _dr = phases.analyzeremotephases(pullop.repo,
                                                 pullop.pulledsubset,
                                                 remotephases)
        phases.advanceboundary(pullop.repo, phases.public, pheads)
        phases.advanceboundary(pullop.repo, phases.draft,
                               pullop.pulledsubset)
    else:
        # Remote is old or publishing all common changesets
        # should be seen as public
        phases.advanceboundary(pullop.repo, phases.public,
                               pullop.pulledsubset)

def _pullobsolete(pullop):
    """utility function to pull obsolete markers from a remote

    The `gettransaction` is function that return the pull transaction, creating
    one if necessary. We return the transaction to inform the calling code that
    a new transaction have been created (when applicable).

    Exists mostly to allow overriding for experimentation purpose"""
    pullop.todosteps.remove('obsmarkers')
    tr = None
    if obsolete._enabled:
        pullop.repo.ui.debug('fetching remote obsolete markers\n')
        remoteobs = pullop.remote.listkeys('obsolete')
        if 'dump0' in remoteobs:
            tr = pullop.gettransaction()
            for key in sorted(remoteobs, reverse=True):
                if key.startswith('dump'):
                    data = base85.b85decode(remoteobs[key])
                    pullop.repo.obsstore.mergemarkers(tr, data)
            pullop.repo.invalidatevolatilesets()
    return tr

def getbundle(repo, source, heads=None, common=None, bundlecaps=None):
    """return a full bundle (with potentially multiple kind of parts)

    Could be a bundle HG10 or a bundle HG20 depending on bundlecaps
    passed. For now, the bundle can contain only changegroup, but this will
    changes when more part type will be available for bundle2.

    This is different from changegroup.getbundle that only returns an HG10
    changegroup bundle. They may eventually get reunited in the future when we
    have a clearer idea of the API we what to query different data.

    The implementation is at a very early stage and will get massive rework
    when the API of bundle is refined.
    """
    # build bundle here.
    cg = changegroup.getbundle(repo, source, heads=heads,
                               common=common, bundlecaps=bundlecaps)
    if bundlecaps is None or 'HG20' not in bundlecaps:
        return cg
    # very crude first implementation,
    # the bundle API will change and the generation will be done lazily.
    bundler = bundle2.bundle20(repo.ui)
    part = bundle2.bundlepart('changegroup', data=cg.getchunks())
    bundler.addpart(part)
    return util.chunkbuffer(bundler.getchunks())

class PushRaced(RuntimeError):
    """An exception raised during unbundling that indicate a push race"""

def check_heads(repo, their_heads, context):
    """check if the heads of a repo have been modified

    Used by peer for unbundling.
    """
    heads = repo.heads()
    heads_hash = util.sha1(''.join(sorted(heads))).digest()
    if not (their_heads == ['force'] or their_heads == heads or
            their_heads == ['hashed', heads_hash]):
        # someone else committed/pushed/unbundled while we
        # were transferring data
        raise PushRaced('repository changed while %s - '
                        'please try again' % context)

def unbundle(repo, cg, heads, source, url):
    """Apply a bundle to a repo.

    this function makes sure the repo is locked during the application and have
    mechanism to check that no push race occurred between the creation of the
    bundle and its application.

    If the push was raced as PushRaced exception is raised."""
    r = 0
    # need a transaction when processing a bundle2 stream
    tr = None
    lock = repo.lock()
    try:
        check_heads(repo, heads, 'uploading changes')
        # push can proceed
        if util.safehasattr(cg, 'params'):
            tr = repo.transaction('unbundle')
            ret = bundle2.processbundle(repo, cg, lambda: tr)
            tr.close()
            stream = util.chunkbuffer(ret.reply.getchunks())
            r = bundle2.unbundle20(repo.ui, stream)
        else:
            r = changegroup.addchangegroup(repo, cg, source, url)
    finally:
        if tr is not None:
            tr.release()
        lock.release()
    return r