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# Copyright (C) 2009 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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
"""Implementation of Graph algorithms when we have already loaded everything.
"""
from bzrlib import (
revision,
)
class _KnownGraphNode(object):
"""Represents a single object in the known graph."""
__slots__ = ('key', 'parent_keys', 'child_keys', 'gdfo')
def __init__(self, key, parent_keys):
self.key = key
self.parent_keys = parent_keys
self.child_keys = []
# Greatest distance from origin
self.gdfo = None
def __repr__(self):
return '%s(%s gdfo:%s par:%s child:%s)' % (
self.__class__.__name__, self.key, self.gdfo,
self.parent_keys, self.child_keys)
class KnownGraph(object):
"""This is a class which assumes we already know the full graph."""
def __init__(self, parent_map, do_cache=True):
"""Create a new KnownGraph instance.
:param parent_map: A dictionary mapping key => parent_keys
"""
self._nodes = {}
# Maps {sorted(revision_id, revision_id): heads}
self._known_heads = {}
self.do_cache = do_cache
self._initialize_nodes(parent_map)
self._find_gdfo()
def _initialize_nodes(self, parent_map):
"""Populate self._nodes.
After this has finished:
- self._nodes will have an entry for every entry in parent_map.
- ghosts will have a parent_keys = None,
- all nodes found will also have .child_keys populated with all known
child_keys,
- self._tails will list all the nodes without parents.
"""
tails = self._tails = set()
nodes = self._nodes
for key, parent_keys in parent_map.iteritems():
if key in nodes:
node = nodes[key]
node.parent_keys = parent_keys
if parent_keys:
# This node has been added before being seen in parent_map
# (see below)
tails.remove(node)
else:
node = _KnownGraphNode(key, parent_keys)
nodes[key] = node
for parent_key in parent_keys:
try:
parent_node = nodes[parent_key]
except KeyError:
parent_node = _KnownGraphNode(parent_key, None)
nodes[parent_key] = parent_node
# Potentially a tail, if we're wrong we'll remove it later
# (see above)
tails.add(parent_node)
parent_node.child_keys.append(key)
def _find_gdfo(self):
nodes = self._nodes
known_parent_gdfos = {}
pending = []
for node in self._tails:
node.gdfo = 1
pending.append(node)
while pending:
node = pending.pop()
for child_key in node.child_keys:
child = nodes[child_key]
try:
known_parent_gdfos[child_key] += 1
except KeyError:
known_parent_gdfos[child_key] = 1
if child.gdfo is None or node.gdfo + 1 > child.gdfo:
child.gdfo = node.gdfo + 1
if known_parent_gdfos[child_key] == len(child.parent_keys):
# We are the last parent updating that node, we can
# continue from there
pending.append(child)
def heads(self, keys):
"""Return the heads from amongst keys.
This is done by searching the ancestries of each key. Any key that is
reachable from another key is not returned; all the others are.
This operation scales with the relative depth between any two keys. It
uses gdfo to avoid walking all ancestry.
:param keys: An iterable of keys.
:return: A set of the heads. Note that as a set there is no ordering
information. Callers will need to filter their input to create
order if they need it.
"""
candidate_nodes = dict((key, self._nodes[key]) for key in keys)
if revision.NULL_REVISION in candidate_nodes:
# NULL_REVISION is only a head if it is the only entry
candidate_nodes.pop(revision.NULL_REVISION)
if not candidate_nodes:
return frozenset([revision.NULL_REVISION])
if len(candidate_nodes) < 2:
# No or only one candidate
return frozenset(candidate_nodes)
heads_key = frozenset(candidate_nodes)
if heads_key != frozenset(keys):
# Mention duplicates
note('%s != %s', heads_key, frozenset(keys))
# Do we have a cached result ?
try:
heads = self._known_heads[heads_key]
return heads
except KeyError:
pass
# Let's compute the heads
seen = set()
pending = []
min_gdfo = None
for node in candidate_nodes.values():
if node.parent_keys:
pending.extend(node.parent_keys)
if min_gdfo is None or node.gdfo < min_gdfo:
min_gdfo = node.gdfo
nodes = self._nodes
while pending:
node_key = pending.pop()
if node_key in seen:
# node already appears in some ancestry
continue
seen.add(node_key)
node = nodes[node_key]
if node.gdfo <= min_gdfo:
continue
if node.parent_keys:
pending.extend(node.parent_keys)
heads = heads_key.difference(seen)
if self.do_cache:
self._known_heads[heads_key] = heads
return heads
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