~bzr-pqm/bzr/bzr.dev : contents of bzrlib/lru

~bzr-pqm/bzr/bzr.dev : (revision 2993.1.1)

# Copyright (C) 2006 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 least-recently-used (LRU) cache."""

from collections import deque
import gc


class LRUCache(object):
    """A class which manages a cache of entries, removing unused ones."""

    def __init__(self, max_cache=100, after_cleanup_size=None):
        self._max_cache = max_cache
        if after_cleanup_size is None:
            self._after_cleanup_size = self._max_cache
        else:
            self._after_cleanup_size = min(after_cleanup_size, self._max_cache)

        self._compact_queue_length = 4*self._max_cache

        self._cache = {}
        self._cleanup = {}
        self._queue = deque() # Track when things are accessed
        self._refcount = {} # number of entries in self._queue for each key

    def __contains__(self, key):
        return key in self._cache

    def __getitem__(self, key):
        val = self._cache[key]
        self._record_access(key)
        return val

    def __len__(self):
        return len(self._cache)

    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' sohuld be cleaned up.
        """
        if key in self._cache:
            self._remove(key)
        self._cache[key] = value
        self._cleanup[key] = cleanup
        self._record_access(key)

        if len(self._cache) > self._max_cache:
            # Trigger the 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 len(self._cache) > self._after_cleanup_size:
            self._remove_lru()

    def __setitem__(self, key, value):
        """Add a value to the cache, there will be no cleanup function."""
        self.add(key, value, cleanup=None)

    def _record_access(self, key):
        """Record that key was accessed."""
        self._queue.append(key)
        # Can't use setdefault because you can't += 1 the result
        self._refcount[key] = self._refcount.get(key, 0) + 1

        # If our access queue is too large, clean it up too
        if len(self._queue) > self._compact_queue_length:
            self._compact_queue()

    def _compact_queue(self):
        """Compact the queue, leaving things in sorted last appended order."""
        new_queue = deque()
        for item in self._queue:
            if self._refcount[item] == 1:
                new_queue.append(item)
            else:
                self._refcount[item] -= 1
        self._queue = new_queue
        # All entries should be of the same size. There should be one entry in
        # queue for each entry in cache, and all refcounts should == 1
        assert (len(self._queue) == len(self._cache) ==
                len(self._refcount) == sum(self._refcount.itervalues()))

    def _remove(self, key):
        """Remove an entry, making sure to maintain the invariants."""
        cleanup = self._cleanup.pop(key)
        val = self._cache.pop(key)
        if cleanup is not None:
            cleanup(key, val)
        return val

    def _remove_lru(self):
        """Remove one entry from the lru, and handle consequences.

        If there are no more references to the lru, then this entry should be
        removed from the cache.
        """
        key = self._queue.popleft()
        self._refcount[key] -= 1
        if not self._refcount[key]:
            del self._refcount[key]
            self._remove(key)

    def clear(self):
        """Clear out all of the cache."""
        # Clean up in LRU order
        while self._cache:
            self._remove_lru()


class LRUSizeCache(LRUCache):
    """An LRUCache 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 just restricts the cache to be cleaned up after so much data is stored.

    The values that are added must support len(value).
    """

    def __init__(self, max_size=1024*1024, after_cleanup_size=None,
                 compute_size=None):
        """Create a new LRUSizeCache.

        :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.
        :param compute_size: A function to compute the size of the values. We
            use a function here, so that you can pass 'len' if you are just
            using simple strings, or a more complex function if you are using
            something like a list of strings, or even a custom object.
            The function should take the form "compute_size(value) => integer".
            If not supplied, it defaults to 'len()'
        """
        # This approximates that texts are > 0.5k in size. It only really
        # effects when we clean up the queue, so we don't want it to be too
        # large.
        LRUCache.__init__(self, max_cache=int(max_size/512))
        self._max_size = max_size
        if after_cleanup_size is None:
            self._after_cleanup_size = self._max_size
        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
        :param cleanup: None or a function taking (key, value) to indicate
                        'value' sohuld be cleaned up.
        """
        if key in self._cache:
            self._remove(key)
        value_len = self._compute_size(value)
        if value_len >= self._after_cleanup_size:
            return
        self._value_size += value_len
        self._cache[key] = value
        self._cleanup[key] = cleanup
        self._record_access(key)

        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_lru()

    def _remove(self, key):
        """Remove an entry, making sure to maintain the invariants."""
        val = LRUCache._remove(self, key)
        self._value_size -= self._compute_size(val)

2993.1.1 by Robert Collins * New module ``lru_cache`` providing a cache for use by tasks that need	1	# Copyright (C) 2006 Canonical Ltd
	2	#
	3	# This program is free software; you can redistribute it and/or modify
	4	# it under the terms of the GNU General Public License as published by
	5	# the Free Software Foundation; either version 2 of the License, or
	6	# (at your option) any later version.
	7	#
	8	# This program is distributed in the hope that it will be useful,
	9	# but WITHOUT ANY WARRANTY; without even the implied warranty of
	10	# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	11	# GNU General Public License for more details.
	12	#
	13	# You should have received a copy of the GNU General Public License
	14	# along with this program; if not, write to the Free Software
	15	# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
	16
	17	"""A simple least-recently-used (LRU) cache."""
	18
	19	from collections import deque
	20	import gc
	21
	22
	23	class LRUCache(object):
	24	"""A class which manages a cache of entries, removing unused ones."""
	25
	26	def __init__(self, max_cache=100, after_cleanup_size=None):
	27	self._max_cache = max_cache
	28	if after_cleanup_size is None:
	29	self._after_cleanup_size = self._max_cache
	30	else:
	31	self._after_cleanup_size = min(after_cleanup_size, self._max_cache)
	32
	33	self._compact_queue_length = 4*self._max_cache
	34
	35	self._cache = {}
	36	self._cleanup = {}
	37	self._queue = deque() # Track when things are accessed
	38	self._refcount = {} # number of entries in self._queue for each key
	39
	40	def __contains__(self, key):
	41	return key in self._cache
	42
	43	def __getitem__(self, key):
	44	val = self._cache[key]
	45	self._record_access(key)
	46	return val
	47
	48	def __len__(self):
	49	return len(self._cache)
	50
	51	def add(self, key, value, cleanup=None):
	52	"""Add a new value to the cache.
	53
	54	Also, if the entry is ever removed from the queue, call cleanup.
	55	Passing it the key and value being removed.
	56
	57	:param key: The key to store it under
	58	:param value: The object to store
	59	:param cleanup: None or a function taking (key, value) to indicate
	60	'value' sohuld be cleaned up.
	61	"""
	62	if key in self._cache:
	63	self._remove(key)
	64	self._cache[key] = value
65	self._cleanup[key] = cleanup
66	self._record_access(key)
67
68	if len(self._cache) > self._max_cache:
69	# Trigger the cleanup
70	self.cleanup()
71
72	def cleanup(self):
73	"""Clear the cache until it shrinks to the requested size.
74
75	This does not completely wipe the cache, just makes sure it is under
76	the after_cleanup_size.
77	"""
78	# Make sure the cache is shrunk to the correct size
79	while len(self._cache) > self._after_cleanup_size:
80	self._remove_lru()
81
82	def __setitem__(self, key, value):
83	"""Add a value to the cache, there will be no cleanup function."""
84	self.add(key, value, cleanup=None)
85
86	def _record_access(self, key):
87	"""Record that key was accessed."""
88	self._queue.append(key)
89	# Can't use setdefault because you can't += 1 the result
90	self._refcount[key] = self._refcount.get(key, 0) + 1
91
92	# If our access queue is too large, clean it up too
93	if len(self._queue) > self._compact_queue_length:
94	self._compact_queue()
95
96	def _compact_queue(self):
97	"""Compact the queue, leaving things in sorted last appended order."""
98	new_queue = deque()
99	for item in self._queue:
100	if self._refcount[item] == 1:
101	new_queue.append(item)
102	else:
103	self._refcount[item] -= 1
104	self._queue = new_queue
105	# All entries should be of the same size. There should be one entry in
106	# queue for each entry in cache, and all refcounts should == 1
107	assert (len(self._queue) == len(self._cache) ==
108	len(self._refcount) == sum(self._refcount.itervalues()))
109
110	def _remove(self, key):
111	"""Remove an entry, making sure to maintain the invariants."""
112	cleanup = self._cleanup.pop(key)
113	val = self._cache.pop(key)
114	if cleanup is not None:
115	cleanup(key, val)
116	return val
117
118	def _remove_lru(self):
119	"""Remove one entry from the lru, and handle consequences.
120
121	If there are no more references to the lru, then this entry should be
122	removed from the cache.
123	"""
124	key = self._queue.popleft()
125	self._refcount[key] -= 1
126	if not self._refcount[key]:
127	del self._refcount[key]
128	self._remove(key)
129
130	def clear(self):
131	"""Clear out all of the cache."""
132	# Clean up in LRU order
133	while self._cache:
134	self._remove_lru()
135
136
137	class LRUSizeCache(LRUCache):
138	"""An LRUCache that removes things based on the size of the values.
139
140	This differs in that it doesn't care how many actual items there are,
141	it just restricts the cache to be cleaned up after so much data is stored.
142
143	The values that are added must support len(value).
144	"""
145
146	def __init__(self, max_size=1024*1024, after_cleanup_size=None,
147	compute_size=None):
148	"""Create a new LRUSizeCache.
149
150	:param max_size: The max number of bytes to store before we start
151	clearing out entries.
152	:param after_cleanup_size: After cleaning up, shrink everything to this
153	size.
154	:param compute_size: A function to compute the size of the values. We
155	use a function here, so that you can pass 'len' if you are just
156	using simple strings, or a more complex function if you are using
157	something like a list of strings, or even a custom object.
158	The function should take the form "compute_size(value) => integer".
159	If not supplied, it defaults to 'len()'
160	"""
161	# This approximates that texts are > 0.5k in size. It only really
162	# effects when we clean up the queue, so we don't want it to be too
163	# large.
164	LRUCache.__init__(self, max_cache=int(max_size/512))
165	self._max_size = max_size
166	if after_cleanup_size is None:
167	self._after_cleanup_size = self._max_size
168	else:
169	self._after_cleanup_size = min(after_cleanup_size, self._max_size)
170
171	self._value_size = 0
172	self._compute_size = compute_size
173	if compute_size is None:
174	self._compute_size = len
175
176	def add(self, key, value, cleanup=None):
177	"""Add a new value to the cache.
178
179	Also, if the entry is ever removed from the queue, call cleanup.
180	Passing it the key and value being removed.
181
182	:param key: The key to store it under
183	:param value: The object to store
184	:param cleanup: None or a function taking (key, value) to indicate
185	'value' sohuld be cleaned up.
186	"""
187	if key in self._cache:
188	self._remove(key)
189	value_len = self._compute_size(value)
190	if value_len >= self._after_cleanup_size:
191	return
192	self._value_size += value_len
193	self._cache[key] = value
194	self._cleanup[key] = cleanup
195	self._record_access(key)
196
197	if self._value_size > self._max_size:
198	# Time to cleanup
199	self.cleanup()
200
201	def cleanup(self):
202	"""Clear the cache until it shrinks to the requested size.
203
204	This does not completely wipe the cache, just makes sure it is under
205	the after_cleanup_size.
206	"""
207	# Make sure the cache is shrunk to the correct size
208	while self._value_size > self._after_cleanup_size:
209	self._remove_lru()
210
211	def _remove(self, key):
212	"""Remove an entry, making sure to maintain the invariants."""
213	val = LRUCache._remove(self, key)
214	self._value_size -= self._compute_size(val)