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britney2-ubuntu/britney2/installability/tester.py
Niels Thykier 42be17ad26 inst-tester: Correctly handle unresolved essential choices 
Britney has a special case for essential packages to ensure that any
package that with essential packages are not installable.  This check
did not account for a case, where a package is not co-installable with
two or more pseudo-essential package part of the same OR dependency.
A contrived example based on real world data:

  Package: foo
  # Conflict with all providers of "awk"
  Conflicts: mawk | gawk | original-awk

This alone is actually not sufficient to trigger the bug, as
_get_min_pseudo_ess_set is in theory some times smart enough to pick
an "obvious" solution between the pseudo-essential option.
  When it does, one of the above ends up in the (de-facto) essential set
and then the installability tester correctly rejects "foo".

Though, even with the fix above, the handling for this is probably not
correct if the essential set is not (fully co-)installable.  However,
that basically only happens if we are bootstrapping an architecture
(or testing is royally broken, in which case this is the least of our
worries).

Signed-off-by: Niels Thykier <niels@thykier.net>
2017-02-11 11:08:52 +00:00

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# -*- coding: utf-8 -*-
# Copyright (C) 2012 Niels Thykier <niels@thykier.net>
# 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.
from collections import defaultdict
from functools import partial
from itertools import chain, filterfalse
from britney2.utils import iter_except
class InstallabilityTester(object):
def __init__(self, universe, revuniverse, testing, broken, essentials,
safe_set, eqv_table):
"""Create a new installability tester
universe is a dict mapping package ids to their
dependencies and conflicts.
revuniverse is a table containing all packages with reverse
relations mapping them to their reverse relations.
testing is a (mutable) set of package ids that determines
which of the packages in universe are currently in testing.
broken is a (mutable) set of package ids that are known to
be uninstallable.
essentials is a set of packages with "Essential: yes".
safe_set is a set of all packages which have no conflicts and
either have no dependencies or only depends on other "safe"
packages.
Package id: (pkg_name, pkg_version, pkg_arch)
- NB: arch:all packages are "re-mapped" to given architecture.
(simplifies caches and dependency checking)
"""
self._universe = universe
self._testing = testing
self._broken = broken
self._essentials = essentials
self._revuniverse = revuniverse
self._safe_set = safe_set
self._eqv_table = eqv_table
self._stats = InstallabilityStats()
# Cache of packages known to be broken - we deliberately do not
# include "broken" in it. See _optimize for more info.
self._cache_broken = set()
# Cache of packages known to be installable
self._cache_inst = set()
# Per "arch" cache of the "minimal" (possibly incomplete)
# pseudo-essential set. This includes all the packages that
# are essential and packages that will always follow.
#
# It may not be a complete essential set, since alternatives
# are not always resolved. Noticably cases like "awk" may be
# left out (since it could be either gawk, mawk or
# original-awk) unless something in this sets depends strictly
# on one of them
self._cache_ess = {}
def compute_testing_installability(self):
"""Computes the installability of packages in testing
This method computes the installability of all packages in
testing and caches the result. This has the advantage of
making "is_installable" queries very fast for all packages
in testing.
"""
check_inst = self._check_inst
cbroken = self._cache_broken
cache_inst = self._cache_inst
eqv_table = self._eqv_table
testing = self._testing
tcopy = [x for x in testing]
for t in filterfalse(cache_inst.__contains__, tcopy):
if t in cbroken:
continue
res = check_inst(t)
if t in eqv_table:
eqv = (x for x in eqv_table[t] if x in testing)
if res:
cache_inst.update(eqv)
else:
eqv_set = frozenset(eqv)
testing -= eqv_set
cbroken |= eqv_set
@property
def stats(self):
return self._stats
def are_equivalent(self, pkg_id1, pkg_id2):
"""Test if pkg_id1 and pkg_id2 are equivalent
:param pkg_id1 The id of the first package
:param pkg_id2 The id of the second package
:return: True if pkg_id1 and pkg_id2 have the same "signature" in
the package dependency graph (i.e. relations can not tell
them apart semantically except for their name). Otherwise False
"""
eqv_table = self._eqv_table
return pkg_id1 in eqv_table and pkg_id2 in eqv_table[pkg_id1]
def reverse_dependencies_of(self, pkg_id):
"""Returns the set of reverse dependencies of a given package
:param pkg_id: The package id as defined in the constructor.
:return: A set containing the package ids all of the reverse
dependencies of the input package. The result is suite agnostic.
"""
revuniverse = self._revuniverse
if pkg_id not in revuniverse:
return frozenset()
return revuniverse[pkg_id][0]
def negative_dependencies_of(self, pkg_id):
"""Returns the set of negative dependencies of a given package
Note that there is no "reverse_negative_dependencies_of" method,
since negative dependencies have no "direction" unlike positive
dependencies.
:param pkg_id: The package id as defined in the constructor.
:return: A set containing the package ids all of the negative
dependencies of the input package. The result is suite agnostic.
"""
return self._universe[pkg_id][1]
def dependencies_of(self, pkg_id):
"""Returns the set of dependencies of a given package
:param pkg_id: The package id as defined in the constructor.
:return: A set containing the package ids all of the dependencies
of the input package. The result is suite agnostic.
"""
return self._universe[pkg_id][0]
def any_of_these_are_in_testing(self, pkgs):
"""Test if at least one package of a given set is in testing
:param pkgs: A set of package ids (as defined in the constructor)
:return: True if any of the packages in pkgs are currently in testing
"""
return not self._testing.isdisjoint(pkgs)
def add_testing_binary(self, pkg_id):
"""Add a binary package to "testing"
If the package is not known, this method will throw an
KeyError.
:param pkg_id The id of the package
"""
if pkg_id not in self._universe: # pragma: no cover
raise KeyError(str(pkg_id))
if pkg_id in self._broken:
self._testing.add(pkg_id)
elif pkg_id not in self._testing:
self._testing.add(pkg_id)
if self._cache_inst:
self._stats.cache_drops += 1
self._cache_inst = set()
if self._cache_broken:
# Re-add broken packages as some of them may now be installable
self._testing |= self._cache_broken
self._cache_broken = set()
if pkg_id in self._essentials and pkg_id.architecture in self._cache_ess:
# Adds new essential => "pseudo-essential" set needs to be
# recomputed
del self._cache_ess[pkg_id.architecture]
return True
def remove_testing_binary(self, pkg_id):
"""Remove a binary from "testing"
:param pkg_id The id of the package
If the package is not known, this method will throw an
KeyError.
"""
if pkg_id not in self._universe: # pragma: no cover
raise KeyError(str(pkg_id))
self._cache_broken.discard(pkg_id)
if pkg_id in self._testing:
self._testing.remove(pkg_id)
if pkg_id.architecture in self._cache_ess and pkg_id in self._cache_ess[pkg_id.architecture][0]:
# Removes a package from the "pseudo-essential set"
del self._cache_ess[pkg_id.architecture]
if pkg_id not in self._revuniverse:
# no reverse relations - safe
return True
if pkg_id not in self._broken and pkg_id in self._cache_inst:
# It is in our cache (and not guaranteed to be broken) - throw out the cache
self._cache_inst = set()
self._stats.cache_drops += 1
return True
def is_installable(self, pkg_id):
"""Test if a package is installable in this package set
The package is assumed to be in "testing" and only packages in
"testing" can be used to satisfy relations.
:param pkg_id The id of the package
Returns True iff the package is installable.
Returns False otherwise.
"""
self._stats.is_installable_calls += 1
if pkg_id not in self._universe: # pragma: no cover
raise KeyError(str(pkg_id))
if pkg_id not in self._testing or pkg_id in self._broken:
self._stats.cache_hits += 1
return False
if pkg_id in self._cache_inst:
self._stats.cache_hits += 1
return True
self._stats.cache_misses += 1
return self._check_inst(pkg_id)
def _check_inst(self, t, musts=None, never=None, choices=None):
# See the explanation of musts, never and choices below.
cache_inst = self._cache_inst
stats = self._stats
if musts and t in cache_inst and not never:
# use the inst cache only for direct queries/simple queries.
cache = True
if choices:
# This is a recursive call, where there is no "never" so far.
# We know t satisfies at least one of the remaining choices.
# If it satisfies all remaining choices, we can use the cache
# in this case (since never is empty).
#
# Otherwise, a later choice may be incompatible with t.
for choice in choices:
if t in choice:
continue
cache = False
break
if cache:
return True
universe = self._universe
testing = self._testing
cbroken = self._cache_broken
safe_set = self._safe_set
eqv_table = self._eqv_table
# Our installability verdict - start with "yes" and change if
# prove otherwise.
verdict = True
# set of packages that must be installed with this package
if musts is None:
musts = set()
musts.add(t)
# set of packages we can *never* choose (e.g. due to conflicts)
if never is None:
never = set()
# set of relations were we have a choice, but where we have not
# committed ourselves yet. Hopefully some choices may be taken
# for us (if one of the alternatives appear in "musts")
if choices is None:
choices = set()
# The subset of musts we haven't checked yet.
check = {t}
if len(musts) == 1:
# Include the essential packages in testing as a starting point.
if t.architecture not in self._cache_ess:
# The minimal essential set cache is not present -
# compute it now.
(start, ess_never, ess_choices) = self._get_min_pseudo_ess_set(t.architecture)
else:
(start, ess_never, ess_choices) = self._cache_ess[t.architecture]
if t in ess_never:
# t conflicts with something in the essential set or the essential
# set conflicts with t - either way, t is f***ed
cbroken.add(t)
testing.remove(t)
stats.conflicts_essential += 1
return False
musts.update(start)
never.update(ess_never)
choices.update(ess_choices)
# curry check_loop
check_loop = partial(self._check_loop, universe, testing,
eqv_table, stats, musts, never, cbroken)
# Useful things to remember:
#
# * musts and never are disjointed at all times
# - if not, t cannot be installable. Either t, or one of
# its dependencies conflict with t or one of its (other)
# dependencies.
#
# * choices should generally be avoided as much as possible.
# - picking a bad choice requires backtracking
# - sometimes musts/never will eventually "solve" the choice.
#
# * check never includes choices (these are always in choices)
#
# * A package is installable if never and musts are disjointed
# and both check and choices are empty.
# - exception: resolve_choices may determine the installability
# of t via recursion (calls _check_inst). In this case
# check and choices are not (always) empty.
def _prune_choices(rebuild, len=len):
"""Picks a choice from choices and updates rebuild.
Prunes the choices and updates "rebuild" to reflect the
pruned choices.
Returns True if t is installable (determined via recursion).
Returns False if a choice was picked and added to check.
Returns None if t is uninstallable (no choice can be picked).
NB: If this returns False, choices should be replaced by
rebuild.
"""
# We already satisfied/chosen at least one of the literals
# in the choice, so the choice is gone
for choice in filter(musts.isdisjoint, choices):
# cbroken is needed here because (in theory) it could
# have changed since the choice was discovered and it
# is smaller than testing (so presumably faster)
remain = choice - never - cbroken
if len(remain) > 1 and not remain.isdisjoint(safe_set):
first = None
for r in filter(safe_set.__contains__, remain):
# don't bother giving extra arguments to _check_inst. "safe" packages are
# usually trivial to satisfy on their own and will not involve conflicts
# (so never will not help)
if r in cache_inst or self._check_inst(r):
first = r
break
if first:
musts.add(first)
check.add(first)
stats.choice_resolved_using_safe_set += 1
continue
# None of the safe set choices are installable, so drop them
remain -= safe_set
if len(remain) == 1:
# the choice was reduced to one package we haven't checked - check that
check.update(remain)
musts.update(remain)
stats.choice_presolved += 1
continue
if not remain:
# all alternatives would violate the conflicts or are uninstallable
# => package is not installable
stats.choice_presolved += 1
return False
# The choice is still deferred
rebuild.add(frozenset(remain))
return True
# END _prune_choices
while check:
if not check_loop(choices, check):
verdict = False
break
if choices:
rebuild = set()
if not _prune_choices(rebuild):
verdict = False
break
if not check and rebuild:
# We have to "guess" now, which is always fun, but not cheap. We
# stop guessing:
# - once we run out of choices to make (obviously), OR
# - if one of the choices exhaust all but one option
if self.resolve_choices(check, musts, never, rebuild):
# The recursive call have already updated the
# cache so there is not point in doing it again.
return True
choices = rebuild
if verdict:
# if t is installable, then so are all packages in musts
self._cache_inst.update(musts)
stats.solved_installable += 1
else:
stats.solved_uninstallable += 1
return verdict
def resolve_choices(self, check, musts, never, choices):
universe = self._universe
testing = self._testing
eqv_table = self._eqv_table
stats = self._stats
cbroken = self._cache_broken
while choices:
choice_options = choices.pop()
choice = iter(choice_options)
last = next(choice) # pick one to go last
solved = False
for p in choice:
musts_copy = musts.copy()
never_tmp = set()
choices_tmp = set()
check_tmp = {p}
if not self._check_loop(universe, testing, eqv_table,
stats, musts_copy, never_tmp,
cbroken, choices_tmp,
check_tmp):
# p cannot be chosen/is broken (unlikely, but ...)
continue
# Test if we can pick p without any consequences.
# - when we can, we avoid a backtrack point.
if never_tmp <= never and choices_tmp <= choices:
# we can pick p without picking up new conflicts
# or unresolved choices. Therefore we commit to
# using p.
musts.update(musts_copy)
stats.choice_resolved_without_restore_point += 1
solved = True
break
if not musts.isdisjoint(never_tmp):
# If we pick p, we will definitely end up making
# t uninstallable, so p is a no-go.
continue
stats.backtrace_restore_point_created += 1
# We are not sure that p is safe, setup a backtrack
# point and recurse.
never_tmp |= never
choices_tmp |= choices
if self._check_inst(p, musts_copy, never_tmp,
choices_tmp):
# Success, p was a valid choice and made it all
# installable
return True
# If we get here, we failed to find something that
# would satisfy choice (without breaking the
# installability of t). This means p cannot be used
# to satisfy the dependencies, so pretend to conflict
# with it - hopefully it will reduce future choices.
never.add(p)
stats.backtrace_restore_point_used += 1
if not solved:
# Optimization for the last case; avoid the recursive call
# and just assume the last will lead to a solution. If it
# doesn't there is no solution and if it does, we don't
# have to back-track anyway.
check.add(last)
musts.add(last)
stats.backtrace_last_option += 1
return False
def _check_loop(self, universe, testing, eqv_table, stats, musts, never,
cbroken, choices, check, len=len,
frozenset=frozenset):
"""Finds all guaranteed dependencies via "check".
If it returns False, t is not installable. If it returns True
then "check" is exhausted. If "choices" are empty and this
returns True, then t is installable.
"""
# Local variables for faster access...
not_satisfied = partial(filter, musts.isdisjoint)
# While we have guaranteed dependencies (in check), examine all
# of them.
for cur in iter_except(check.pop, KeyError):
(deps, cons) = universe[cur]
if cons:
# Conflicts?
if cur in never:
# cur adds a (reverse) conflict, so check if cur
# is in never.
#
# - there is a window where two conflicting
# packages can be in check. Example "A" depends
# on "B" and "C". If "B" conflicts with "C",
# then both "B" and "C" could end in "check".
return False
# We must install cur for the package to be installable,
# so "obviously" we can never choose any of its conflicts
never.update(cons & testing)
# depgroup can be satisfied by picking something that is
# already in musts - lets pick that (again). :)
for depgroup in not_satisfied(deps):
# Of all the packages listed in the relation remove those that
# are either:
# - not in testing
# - known to be broken (by cache)
# - in never
candidates = (depgroup & testing) - never
if not candidates:
# We got no candidates to satisfy it - this
# package cannot be installed with the current
# testing
if cur not in cbroken and depgroup.isdisjoint(never):
# cur's dependency cannot be satisfied even if never was empty.
# This means that cur itself is broken (as well).
cbroken.add(cur)
testing.remove(cur)
return False
if len(candidates) == 1:
# only one possible solution to this choice and we
# haven't seen it before
check.update(candidates)
musts.update(candidates)
else:
possible_eqv = set(x for x in candidates if x in eqv_table)
if len(possible_eqv) > 1:
# Exploit equivalency to reduce the number of
# candidates if possible. Basically, this
# code maps "similar" candidates into a single
# candidate that will give a identical result
# to any other candidate it eliminates.
#
# See InstallabilityTesterBuilder's
# _build_eqv_packages_table method for more
# information on how this works.
new_cand = set(x for x in candidates if x not in possible_eqv)
stats.eqv_table_times_used += 1
for chosen in iter_except(possible_eqv.pop, KeyError):
new_cand.add(chosen)
possible_eqv -= eqv_table[chosen]
stats.eqv_table_total_number_of_alternatives_eliminated += len(candidates) - len(new_cand)
if len(new_cand) == 1:
check.update(new_cand)
musts.update(new_cand)
stats.eqv_table_reduced_to_one += 1
continue
elif len(candidates) == len(new_cand):
stats.eqv_table_reduced_by_zero += 1
candidates = frozenset(new_cand)
else:
# Candidates have to be a frozenset to be added to choices
candidates = frozenset(candidates)
# defer this choice till later
choices.add(candidates)
return True
def _get_min_pseudo_ess_set(self, arch):
if arch not in self._cache_ess:
# The minimal essential set cache is not present -
# compute it now.
testing = self._testing
eqv_table = self._eqv_table
cbroken = self._cache_broken
universe = self._universe
stats = self._stats
ess_base = set(x for x in self._essentials if x.architecture == arch and x in testing)
start = set(ess_base)
ess_never = set()
ess_choices = set()
not_satisfied = partial(filter, start.isdisjoint)
while ess_base:
self._check_loop(universe, testing, eqv_table, stats,
start, ess_never, cbroken,
ess_choices, ess_base)
if ess_choices:
# Try to break choices where possible
nchoice = set()
for choice in not_satisfied(ess_choices):
b = False
for c in choice:
if universe[c][1] <= ess_never and \
not any(not_satisfied(universe[c][0])):
ess_base.add(c)
b = True
break
if not b:
nchoice.add(choice)
ess_choices = nchoice
else:
break
for x in start:
ess_never.update(universe[x][1])
self._cache_ess[arch] = (frozenset(start), frozenset(ess_never), frozenset(ess_choices))
return self._cache_ess[arch]
def compute_stats(self):
universe = self._universe
eqv_table = self._eqv_table
graph_stats = defaultdict(ArchStats)
seen_eqv = defaultdict(set)
for pkg in universe:
(pkg_name, pkg_version, pkg_arch) = pkg
deps, con = universe[pkg]
arch_stats = graph_stats[pkg_arch]
arch_stats.nodes += 1
if pkg in eqv_table and pkg not in seen_eqv[pkg_arch]:
eqv = [e for e in eqv_table[pkg] if e.architecture == pkg_arch]
arch_stats.eqv_nodes += len(eqv)
arch_stats.add_dep_edges(deps)
arch_stats.add_con_edges(con)
for stat in graph_stats.values():
stat.compute_all()
return graph_stats
class InstallabilityStats(object):
def __init__(self):
self.cache_hits = 0
self.cache_misses = 0
self.cache_drops = 0
self.backtrace_restore_point_created = 0
self.backtrace_restore_point_used = 0
self.backtrace_last_option = 0
self.choice_presolved = 0
self.choice_resolved_using_safe_set = 0
self.choice_resolved_without_restore_point = 0
self.is_installable_calls = 0
self.solved_installable = 0
self.solved_uninstallable = 0
self.conflicts_essential = 0
self.eqv_table_times_used = 0
self.eqv_table_reduced_to_one = 0
self.eqv_table_reduced_by_zero = 0
self.eqv_table_total_number_of_alternatives_eliminated = 0
def stats(self):
formats = [
"Requests - is_installable: {is_installable_calls}",
"Cache - hits: {cache_hits}, misses: {cache_misses}, drops: {cache_drops}",
"Choices - pre-solved: {choice_presolved}, safe-set: {choice_resolved_using_safe_set}, No RP: {choice_resolved_without_restore_point}",
"Backtrace - RP created: {backtrace_restore_point_created}, RP used: {backtrace_restore_point_used}, reached last option: {backtrace_last_option}",
"Solved - installable: {solved_installable}, uninstallable: {solved_uninstallable}, conflicts essential: {conflicts_essential}",
"Eqv - times used: {eqv_table_times_used}, perfect reductions: {eqv_table_reduced_to_one}, failed reductions: {eqv_table_reduced_by_zero}, total no. of alternatives pruned: {eqv_table_total_number_of_alternatives_eliminated}",
]
return [x.format(**self.__dict__) for x in formats]
class ArchStats(object):
def __init__(self):
self.nodes = 0
self.eqv_nodes = 0
self.dep_edges = []
self.con_edges = []
self.stats = defaultdict(lambda: defaultdict(int))
def stat(self, statname):
return self.stats[statname]
def stat_summary(self):
text = []
for statname in ['nodes', 'dependency-clauses', 'dependency-clause-alternatives', 'negative-dependency-clauses']:
stat = self.stats[statname]
if statname != 'nodes':
format_str = "%s, max: %d, min: %d, median: %d, average: %f (%d/%d)"
values = [statname, stat['max'], stat['min'], stat['median'], stat['average'], stat['sum'], stat['size']]
if 'average-per-node' in stat:
format_str += ", average-per-node: %f"
values.append(stat['average-per-node'])
else:
format_str = "nodes: %d, eqv-nodes: %d"
values = (self.nodes, self.eqv_nodes)
text.append(format_str % tuple(values))
return text
def add_dep_edges(self, edges):
self.dep_edges.append(edges)
def add_con_edges(self, edges):
self.con_edges.append(edges)
def _list_stats(self, stat_name, sorted_list, average_per_node=False):
if sorted_list:
stats = self.stats[stat_name]
stats['max'] = sorted_list[-1]
stats['min'] = sorted_list[0]
stats['sum'] = sum(sorted_list)
stats['size'] = len(sorted_list)
stats['average'] = float(stats['sum'])/len(sorted_list)
stats['median'] = sorted_list[len(sorted_list)//2]
if average_per_node:
stats['average-per-node'] = float(stats['sum'])/self.nodes
def compute_all(self):
dep_edges = self.dep_edges
con_edges = self.con_edges
sorted_no_dep_edges = sorted(len(x) for x in dep_edges)
sorted_size_dep_edges = sorted(len(x) for x in chain.from_iterable(dep_edges))
sorted_no_con_edges = sorted(len(x) for x in con_edges)
self._list_stats('dependency-clauses', sorted_no_dep_edges)
self._list_stats('dependency-clause-alternatives', sorted_size_dep_edges, average_per_node=True)
self._list_stats('negative-dependency-clauses', sorted_no_con_edges)
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