~bzr-pqm/bzr/bzr.dev

# Copyright (C) 2008 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

"""A simple first-in-first-out (FIFO) cache."""

from collections import deque

class FIFOCache(dict):

    """A class which manages a cache of entries, removing old ones."""

    def __init__(self, max_cache=100, after_cleanup_count=None):

        dict.__init__(self)

        self._max_cache = max_cache

        if after_cleanup_count is None:

            self._after_cleanup_count = self._max_cache * 8 / 10

        else:

            self._after_cleanup_count = min(after_cleanup_count,

                                            self._max_cache)

        self._cleanup = {} # map to cleanup functions when items are removed

        self._queue = deque() # Track when things are accessed

    def __setitem__(self, key, value):

        """Add a value to the cache, there will be no cleanup function."""

        self.add(key, value, cleanup=None)

    def __delitem__(self, key):

        # Remove the key from an arbitrary location in the queue

        remove = getattr(self._queue, 'remove', None)

        # Python2.5's has deque.remove, but Python2.4 does not

        if remove is not None:

            remove(key)

        else:

            # TODO: It would probably be faster to pop()/popleft() until we get to the

            #       key, and then insert those back into the queue. We know

            #       the key should only be present in one position, and we

            #       wouldn't need to rebuild the whole queue.

            self._queue = deque([k for k in self._queue if k != key])

        self._remove(key)

    def add(self, key, value, cleanup=None):

        """Add a new value to the cache.

        Also, if the entry is ever removed from the queue, call cleanup.

        Passing it the key and value being removed.

        :param key: The key to store it under

        :param value: The object to store

        :param cleanup: None or a function taking (key, value) to indicate

                        'value' should be cleaned up

        """

        if key in self:

            # Remove the earlier reference to this key, adding it again bumps

            # it to the end of the queue

            del self[key]

        self._queue.append(key)

        dict.__setitem__(self, key, value)

        if cleanup is not None:

            self._cleanup[key] = cleanup

        if len(self) > self._max_cache:

            self.cleanup()

    def cleanup(self):

        """Clear the cache until it shrinks to the requested size.

        This does not completely wipe the cache, just makes sure it is under

        the after_cleanup_count.

        """

        # Make sure the cache is shrunk to the correct size

        while len(self) > self._after_cleanup_count:

            self._remove_oldest()

        if len(self._queue) != len(self):

            raise AssertionError('The length of the queue should always equal'

                ' the length of the dict. %s != %s'

                % (len(self._queue), len(self)))

    def clear(self):

        """Clear out all of the cache."""

        # Clean up in FIFO order

        while self:

            self._remove_oldest()

    def _remove(self, key):

        """Remove an entry, making sure to call any cleanup function."""

        cleanup = self._cleanup.pop(key, None)

        # We override self.pop() because it doesn't play well with cleanup

        # functions.

        val = dict.pop(self, key)

        if cleanup is not None:

            cleanup(key, val)

        return val

    def _remove_oldest(self):

        """Remove the oldest entry."""

        key = self._queue.popleft()

        self._remove(key)

    # raise NotImplementedError on dict functions that would mutate the cache

    # which have not been properly implemented yet.

    def copy(self):

        raise NotImplementedError(self.copy)

    def pop(self, key, default=None):

        # If there is a cleanup() function, than it is unclear what pop()

        # should do. Specifically, we would have to call the cleanup on the

        # value before we return it, which should cause whatever resources were

        # allocated to be removed, which makes the return value fairly useless.

        # So instead, we just don't implement it.

        raise NotImplementedError(self.pop)

    def popitem(self):

        # See pop()

        raise NotImplementedError(self.popitem)

    def setdefault(self, key, defaultval=None):

        """similar to dict.setdefault"""

        if key in self:

            return self[key]

        self[key] = defaultval

        return defaultval

    def update(self, *args, **kwargs):

        """Similar to dict.update()"""

        if len(args) == 1:

            arg = args[0]

            if isinstance(arg, dict):

                for key, val in arg.iteritems():

                    self.add(key, val)

            else:

                for key, val in args[0]:

                    self.add(key, val)

        elif len(args) > 1:

            raise TypeError('update expected at most 1 argument, got %d'

                            % len(args))

        if kwargs:

            for key, val in kwargs.iteritems():

                self.add(key, val)

class FIFOSizeCache(FIFOCache):

    """An FIFOCache that removes things based on the size of the values.

    This differs in that it doesn't care how many actual items there are,

    it restricts the cache to be cleaned based on the size of the data.

    """

    def __init__(self, max_size=1024*1024, after_cleanup_size=None,

                 compute_size=None):

        """Create a new FIFOSizeCache.

        :param max_size: The max number of bytes to store before we start

            clearing out entries.

        :param after_cleanup_size: After cleaning up, shrink everything to this

            size (defaults to 80% of max_size).

        :param compute_size: A function to compute the size of a value. If

            not supplied we default to 'len'.

        """

        # Arbitrary, we won't really be using the value anyway.

        FIFOCache.__init__(self, max_cache=max_size)

        self._max_size = max_size

        if after_cleanup_size is None:

            self._after_cleanup_size = self._max_size * 8 / 10

        else:

            self._after_cleanup_size = min(after_cleanup_size, self._max_size)

        self._value_size = 0

        self._compute_size = compute_size

        if compute_size is None:

            self._compute_size = len

    def add(self, key, value, cleanup=None):

        """Add a new value to the cache.

        Also, if the entry is ever removed from the queue, call cleanup.

        Passing it the key and value being removed.

        :param key: The key to store it under

        :param value: The object to store, this value by itself is >=

            after_cleanup_size, then we will not store it at all.

        :param cleanup: None or a function taking (key, value) to indicate

                        'value' sohuld be cleaned up.

        """

        # Even if the new value won't be stored, we need to remove the old

        # value

        if key in self:

            # Remove the earlier reference to this key, adding it again bumps

            # it to the end of the queue

            del self[key]

        value_len = self._compute_size(value)

        if value_len >= self._after_cleanup_size:

            return

        self._queue.append(key)

        dict.__setitem__(self, key, value)

        if cleanup is not None:

            self._cleanup[key] = cleanup

        self._value_size += value_len

        if self._value_size > self._max_size:

            # Time to cleanup

            self.cleanup()

    def cleanup(self):

        """Clear the cache until it shrinks to the requested size.

        This does not completely wipe the cache, just makes sure it is under

        the after_cleanup_size.

        """

        # Make sure the cache is shrunk to the correct size

        while self._value_size > self._after_cleanup_size:

            self._remove_oldest()

    def _remove(self, key):

        """Remove an entry, making sure to maintain the invariants."""

        val = FIFOCache._remove(self, key)

        self._value_size -= self._compute_size(val)

        return val