/loggerhead/trunk

#

# Copyright (C) 2006  Robey Pointer <robey@lag.net>

#

# This program is free software; you can redistribute it and/or modify

# it under the terms of the GNU General Public License as published by

# the Free Software Foundation; either version 2 of the License, or

# (at your option) any later version.

#

# This program is distributed in the hope that it will be useful,

# but WITHOUT ANY WARRANTY; without even the implied warranty of

# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

# GNU General Public License for more details.

#

# You should have received a copy of the GNU General Public License

# along with this program; if not, write to the Free Software

# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

#

"""

a cache for chewed-up "change" data structures, which are basically just a

different way of storing a revision.  the cache improves lookup times 10x

over bazaar's xml revision structure, though, so currently still worth doing.

once a revision is committed in bazaar, it never changes, so once we have

cached a change, it's good forever.

"""

import cPickle

import os

from loggerhead import util

from loggerhead.lockfile import LockFile

with_lock = util.with_lock('_lock', 'ChangeCache')

SQLITE_INTERFACE = os.environ.get('SQLITE_INTERFACE', 'sqlite')

if SQLITE_INTERFACE == 'pysqlite2':

    from pysqlite2 import dbapi2

    _param_marker = '?'

elif SQLITE_INTERFACE == 'sqlite':

    import sqlite as dbapi2

    _param_marker = '%s'

_select_stmt = ("select data from revisiondata where revid = ?"

                ).replace('?', _param_marker)

_insert_stmt = ("insert into revisiondata (revid, data) "

                "values (?, ?)").replace('?', _param_marker)

class FakeShelf(object):

    def __init__(self, filename):

        create_table = not os.path.exists(filename)

        self.connection = dbapi2.connect(filename)

        self.cursor = self.connection.cursor()

        if create_table:

            self._create_table()

    def _create_table(self):

        self.cursor.execute(

            "create table RevisionData "

            "(revid binary primary key, data binary)")

        self.connection.commit()

    def _serialize(self, obj):

        r = dbapi2.Binary(cPickle.dumps(obj, protocol=2))

        return r

    def _unserialize(self, data):

        return cPickle.loads(str(data))

    def get(self, revid):

        self.cursor.execute(_select_stmt, (revid,))

        filechange = self.cursor.fetchone()

        if filechange is None:

            return None

        else:

            return self._unserialize(filechange[0])

    def add(self, revid_obj_pairs):

        for  (r, d) in revid_obj_pairs:

            self.cursor.execute(_insert_stmt, (r, self._serialize(d)))

        self.connection.commit()

class FileChangeCache(object):

    def __init__(self, history, cache_path):

        self.history = history

        if not os.path.exists(cache_path):

            os.mkdir(cache_path)

        self._changes_filename = os.path.join(cache_path, 'filechanges.sql')

        # use a lockfile since the cache folder could be shared across

        # different processes.

        self._lock = LockFile(os.path.join(cache_path, 'filechange-lock'))

    @with_lock

    def get_file_changes(self, entries):

        out = []

        missing_entries = []

        missing_entry_indices = []

        cache = FakeShelf(self._changes_filename)

        for entry in entries:

            changes = cache.get(entry.revid)

            if changes is not None:

                out.append(changes)

            else:

                missing_entries.append(entry)

                missing_entry_indices.append(len(out))

                out.append(None)

        if missing_entries:

            missing_changes = self.history.get_file_changes_uncached(missing_entries)

            revid_changes_pairs = []

            for i, entry, changes in zip(

                missing_entry_indices, missing_entries, missing_changes):

                revid_changes_pairs.append((entry.revid, changes))

                out[i] = changes

            cache.add(revid_changes_pairs)

        return out