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britney2-ubuntu/britney2/installability/solver.py

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# -*- coding: utf-8 -*-
# Copyright (C) 2012 Niels Thykier <niels@thykier.net>
# - Includes code by Paul Harrison
# (http://www.logarithmic.net/pfh-files/blog/01208083168/sort.py)
# 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.
import logging
from collections import deque
from britney2.utils import (ifilter_only, iter_except)
from britney2.installability.tester import InstallabilityTester
def compute_scc(graph):
"""Iterative algorithm for strongly-connected components
Iterative variant of Tarjan's algorithm for finding strongly-connected
components.
:param graph: Table of all nodes along which their edges (in "before" and "after")
:return: List of components (each component is a list of items)
"""
result = []
low = {}
node_stack = []
def _handle_succ(parent, parent_num, successors_remaining):
while successors_remaining:
succ = successors_remaining.pop()
succ_num = low.get(succ, None)
if succ_num is not None:
if succ_num < parent_num:
# These two nodes are part of the probably
# same SSC (or succ is isolated
low[parent] = parent_num = succ_num
continue
# It cannot be a part of a SCC if it does not have depends
# or reverse depends.
if not graph[succ]['before'] or not graph[succ]['after']:
# Short-cut obviously isolated component
result.append((succ,))
# Set the item number so high that no other item might
# mistakenly assume that they can form a component via
# this item.
# (Replaces the "is w on the stack check" for us from
# the original algorithm)
low[succ] = len(graph) + 1
continue
succ_num = len(low)
low[succ] = succ_num
work_stack.append((succ, len(node_stack), succ_num, graph[succ]['before']))
node_stack.append(succ)
# "Recurse" into the child node first
return True
return False
for n in graph:
if n in low:
continue
# It cannot be a part of a SCC if it does not have depends
# or reverse depends.
if not graph[n]['before'] or not graph[n]['after']:
# Short-cut obviously isolated component
result.append((n,))
# Set the item number so high that no other item might
# mistakenly assume that they can form a component via
# this item.
# (Replaces the "is w on the stack check" for us from
# the original algorithm)
low[n] = len(graph) + 1
continue
root_num = len(low)
low[n] = root_num
# DFS work-stack needed to avoid call recursion. It (more or less)
# replaces the variables on the call stack in Tarjan's algorithm
work_stack = [(n, len(node_stack), root_num, graph[n]['before'])]
node_stack.append(n)
while work_stack:
node, stack_idx, orig_node_num, successors = work_stack[-1]
if successors and _handle_succ(node, low[node], successors):
# _handle_succ has pushed a new node on to work_stack
# and we need to "restart" the loop to handle that first
continue
# This node is done; remove it from the work stack
work_stack.pop()
# This node is out of successor. Push up the "low" value
# (Exception: root node has no parent)
node_num = low[node]
if work_stack:
parent = work_stack[-1][0]
parent_num = low[parent]
if node_num <= parent_num:
# This node is a part of a component with its parent.
# We update the parent's node number and push the
# responsibility of building the component unto the
# parent.
low[parent] = node_num
continue
if node_num != orig_node_num:
# The node is a part of an SCC with a ancestor (and parent)
continue
# We got a component
component = tuple(node_stack[stack_idx:])
del node_stack[stack_idx:]
result.append(component)
# Re-number all items, so no other item might
# mistakenly assume that they can form a component via
# one of these items.
# (Replaces the "is w on the stack check" for us from
# the original algorithm)
new_num = len(graph) + 1
for item in component:
low[item] = new_num
assert not node_stack
return result
class InstallabilitySolver(InstallabilityTester):
def __init__(self, universe, revuniverse, testing, broken, essentials,
eqv_table):
"""Create a new installability solver
universe is a dict mapping package tuples to their
dependencies and conflicts.
revuniverse is a dict mapping package tuples to their reverse
dependencies and reverse conflicts.
testing is a (mutable) set of package tuples that determines
which of the packages in universe are currently in testing.
broken is a (mutable) set of package tuples that are known to
be uninstallable.
Package tuple: (pkg_name, pkg_version, pkg_arch)
- NB: arch:all packages are "re-mapped" to given architecture.
(simplifies caches and dependency checking)
"""
super().__init__(universe, revuniverse, testing,
broken, essentials, eqv_table)
def solve_groups(self, groups):
sat_in_testing = self._testing.isdisjoint
universe = self._universe
revuniverse = self._revuniverse
result = []
emitted = set()
queue = deque()
order = {}
ptable = {}
key2item = {}
going_out = set()
going_in = set()
debug_solver = self.logger.isEnabledFor(logging.DEBUG)
# Build the tables
for (item, adds, rms) in groups:
key = str(item)
key2item[key] = item
order[key] = {'before': set(), 'after': set()}
going_in.update(adds)
going_out.update(rms)
for a in adds:
ptable[a] = key
for r in rms:
ptable[r] = key
if debug_solver: # pragma: no cover
self._dump_groups(groups)
# This large loop will add ordering constrains on each "item"
# that migrates based on various rules.
for (item, adds, rms) in groups:
key = str(item)
oldcons = set()
newcons = set()
for r in rms:
oldcons.update(universe[r][1])
for a in adds:
newcons.update(universe[a][1])
current = newcons & oldcons
oldcons -= current
newcons -= current
if oldcons:
# Some of the old binaries have "conflicts" that will
# be removed.
for o in ifilter_only(ptable, oldcons):
# "key" removes a conflict with one of
# "other"'s binaries, so it is probably a good
# idea to migrate "key" before "other"
other = ptable[o]
if other == key:
# "Self-conflicts" => ignore
continue
if debug_solver and other not in order[key]['before']: # pragma: no cover
self.logger.debug("Conflict induced order: %s before %s", key, other)
order[key]['before'].add(other)
order[other]['after'].add(key)
for r in ifilter_only(revuniverse, rms):
# The binaries have reverse dependencies in testing;
# check if we can/should migrate them first.
for rdep in revuniverse[r][0]:
for depgroup in universe[rdep][0]:
rigid = depgroup - going_out
if not sat_in_testing(rigid):
# (partly) satisfied by testing, assume it is okay
continue
if rdep in ptable:
other = ptable[rdep]
if other == key:
# "Self-dependency" => ignore
continue
if debug_solver and other not in order[key]['after']: # pragma: no cover
self.logger.debug("Removal induced order: %s before %s", key, other)
order[key]['after'].add(other)
order[other]['before'].add(key)
for a in adds:
# Check if this item should migrate before others
# (e.g. because they depend on a new [version of a]
# binary provided by this item).
for depgroup in universe[a][0]:
rigid = depgroup - going_out
if not sat_in_testing(rigid):
# (partly) satisfied by testing, assume it is okay
continue
# okay - we got three cases now.
# - "swap" (replace existing binary with a newer version)
# - "addition" (add new binary without removing any)
# - "removal" (remove binary without providing a new)
#
# The problem is that only the two latter requires
# an ordering. A "swap" (in itself) should not
# affect us.
other_adds = set()
other_rms = set()
for d in ifilter_only(ptable, depgroup):
if d in going_in:
# "other" provides something "key" needs,
# schedule accordingly.
other = ptable[d]
other_adds.add(other)
else:
# "other" removes something "key" needs,
# schedule accordingly.
other = ptable[d]
other_rms.add(other)
for other in (other_adds - other_rms):
if debug_solver and other != key and other not in order[key]['after']: # pragma: no cover
self.logger.debug("Dependency induced order (add): %s before %s", key, other)
order[key]['after'].add(other)
order[other]['before'].add(key)
for other in (other_rms - other_adds):
if debug_solver and other != key and other not in order[key]['before']: # pragma: no cover
self.logger.debug("Dependency induced order (remove): %s before %s", key, other)
order[key]['before'].add(other)
order[other]['after'].add(key)
# === MILESTONE: Partial-order constrains computed ===
# At this point, we have computed all the partial-order
# constrains needed. Some of these may have created strongly
# connected components (SSC) [of size 2 or greater], which
# represents a group of items that (we believe) must migrate
# together.
#
# Each one of those components will become an "easy" hint.
comps = compute_scc(order)
merged = {}
scc = {}
# Now that we got the SSCs (in comps), we select on item from
# each SSC to represent the group and become an ID for that
# SSC.
# * ssc[ssc_id] => All the items in that SSC
# * merged[item] => The ID of the SSC to which the item belongs.
#
# We also "repair" the ordering, so we know in which order the
# hints should be emitted.
for com in comps:
scc_id = com[0]
scc[scc_id] = com
merged[scc_id] = scc_id
if len(com) > 1:
so_before = order[scc_id]['before']
so_after = order[scc_id]['after']
for n in com:
if n == scc_id:
continue
so_before.update(order[n]['before'])
so_after.update(order[n]['after'])
merged[n] = scc_id
del order[n]
if debug_solver: # pragma: no cover
self.logger.debug("SCC: %s -- %s", scc_id, str(sorted(com)))
for com in comps:
node = com[0]
nbefore = set(merged[b] for b in order[node]['before'])
nafter = set(merged[b] for b in order[node]['after'])
# Drop self-relations (usually caused by the merging)
nbefore.discard(node)
nafter.discard(node)
order[node]['before'] = nbefore
order[node]['after'] = nafter
for com in comps:
scc_id = com[0]
for other_scc_id in order[scc_id]['before']:
order[other_scc_id]['after'].add(scc_id)
for other_scc_id in order[scc_id]['after']:
order[other_scc_id]['before'].add(scc_id)
if debug_solver: # pragma: no cover
self.logger.debug("-- PARTIAL ORDER --")
initial_round = []
for com in sorted(order):
if debug_solver and order[com]['before']: # pragma: no cover
self.logger.debug("N: %s <= %s", com, str(sorted(order[com]['before'])))
if not order[com]['after']:
# This component can be scheduled immediately, add it
# to the queue
initial_round.append(com)
elif debug_solver: # pragma: no cover
self.logger.debug("N: %s >= %s", com, str(sorted(order[com]['after'])))
queue.extend(sorted(initial_round, key=len))
del initial_round
if debug_solver: # pragma: no cover
self.logger.debug("-- END PARTIAL ORDER --")
self.logger.debug("-- LINEARIZED ORDER --")
for cur in iter_except(queue.popleft, IndexError):
if order[cur]['after'] <= emitted and cur not in emitted:
# This item is ready to be emitted right now
if debug_solver: # pragma: no cover
self.logger.debug("%s -- %s", cur, sorted(scc[cur]))
emitted.add(cur)
result.append([key2item[x] for x in scc[cur]])
if order[cur]['before']:
# There are components that come after this one.
# Add it to queue:
# - if it is ready, it will be emitted.
# - else, it will be dropped and re-added later.
queue.extend(sorted(order[cur]['before'] - emitted, key=len))
if debug_solver: # pragma: no cover
self.logger.debug("-- END LINEARIZED ORDER --")
return result
def _dump_groups(self, groups): # pragma: no cover
self.logger.debug("=== Groups ===")
for (item, adds, rms) in groups:
self.logger.debug("%s => A: %s, R: %s", str(item), str(adds), str(rms))
self.logger.debug("=== END Groups ===")