~bzr-pqm/bzr/bzr.dev

# Copyright (C) 2005 by Canonical Ltd

# 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

from trace import mutter

from bzrlib.store import ImmutableStore

class CachedStore:

    """A store that caches data locally, to avoid repeated downloads.

    The precacache method should be used to avoid server round-trips for

    every piece of data.

    """

    def __init__(self, store, cache_dir):

        self.source_store = store

        self.cache_store = ImmutableStore(cache_dir)

    def __getitem__(self, id):

        mutter("Cache add %s" % id)

        if id not in self.cache_store:

            self.cache_store.add(self.source_store[id], id)

        return self.cache_store[id]

    def prefetch(self, ids):

        """Copy a series of ids into the cache, before they are used.

        For remote stores that support pipelining or async downloads, this can

        increase speed considerably.

        Failures while prefetching are ignored.

        """

        mutter("Prefetch of ids %s" % ",".join(ids))

        self.cache_store.copy_multi(self.source_store, ids, 

                                    permit_failure=True)