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z3/src/smt/smt_parallel.cpp
Nikolaj Bjorner 04ddade2dd remove stale comment
2025-09-22 04:43:41 +03:00

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/*++
Copyright (c) 2020 Microsoft Corporation
Module Name:
smt_parallel.cpp
Abstract:
Parallel SMT, portfolio loop specialized to SMT core.
Author:
nbjorner 2020-01-31
Ilana Shapiro 2025
--*/
#include "util/scoped_ptr_vector.h"
#include "ast/ast_util.h"
#include "ast/ast_pp.h"
#include "ast/ast_ll_pp.h"
#include "ast/ast_translation.h"
#include "ast/simplifiers/then_simplifier.h"
#include "smt/smt_parallel.h"
#include "smt/smt_lookahead.h"
#include "solver/solver_preprocess.h"
#include <cmath>
#include <mutex>
class bounded_pp_exprs {
expr_ref_vector const &es;
public:
bounded_pp_exprs(expr_ref_vector const &es) : es(es) {}
std::ostream &display(std::ostream &out) const {
for (auto e : es)
out << mk_bounded_pp(e, es.get_manager()) << "\n";
return out;
}
};
inline std::ostream &operator<<(std::ostream &out, bounded_pp_exprs const &pp) {
return pp.display(out);
}
#ifdef SINGLE_THREAD
namespace smt {
lbool parallel::operator()(expr_ref_vector const &asms) {
return l_undef;
}
} // namespace smt
#else
#include <thread>
#define LOG_WORKER(lvl, s) IF_VERBOSE(lvl, verbose_stream() << "Worker " << id << s)
namespace smt {
void parallel::worker::run() {
search_tree::node<cube_config> *node = nullptr;
expr_ref_vector cube(m);
while (true) {
if (!b.get_cube(m_g2l, id, cube, node)) {
LOG_WORKER(1, " no more cubes\n");
return;
}
collect_shared_clauses();
check_cube_start:
LOG_WORKER(1, " CUBE SIZE IN MAIN LOOP: " << cube.size() << "\n");
lbool r = check_cube(cube);
if (!m.inc()) {
b.set_exception("context cancelled");
return;
}
switch (r) {
case l_undef: {
update_max_thread_conflicts();
LOG_WORKER(1, " found undef cube\n");
if (m_config.m_max_cube_depth <= cube.size())
goto check_cube_start;
auto atom = get_split_atom();
if (!atom)
goto check_cube_start;
b.split(m_l2g, id, node, atom);
simplify();
break;
}
case l_true: {
LOG_WORKER(1, " found sat cube\n");
model_ref mdl;
ctx->get_model(mdl);
b.set_sat(m_l2g, *mdl);
return;
}
case l_false: {
expr_ref_vector const &unsat_core = ctx->unsat_core();
LOG_WORKER(2, " unsat core:\n";
for (auto c : unsat_core) verbose_stream() << mk_bounded_pp(c, m, 3) << "\n");
// If the unsat core only contains external assumptions,
// unsatisfiability does not depend on the current cube and the entire problem is unsat.
if (all_of(unsat_core, [&](expr *e) { return asms.contains(e); })) {
LOG_WORKER(1, " determined formula unsat\n");
b.set_unsat(m_l2g, unsat_core);
return;
}
// report assumptions used in unsat core, so they can be used in final core
for (expr *e : unsat_core)
if (asms.contains(e))
b.report_assumption_used(m_l2g, e);
LOG_WORKER(1, " found unsat cube\n");
b.backtrack(m_l2g, unsat_core, node);
break;
}
}
if (m_config.m_share_units)
share_units();
}
}
parallel::worker::worker(unsigned id, parallel &p, expr_ref_vector const &_asms)
: id(id), p(p), b(p.m_batch_manager), m_smt_params(p.ctx.get_fparams()), asms(m), m_g2l(p.ctx.m, m),
m_l2g(m, p.ctx.m) {
for (auto e : _asms)
asms.push_back(m_g2l(e));
LOG_WORKER(1, " created with " << asms.size() << " assumptions\n");
m_smt_params.m_preprocess = false;
ctx = alloc(context, m, m_smt_params, p.ctx.get_params());
context::copy(p.ctx, *ctx, true);
ctx->set_random_seed(id + m_smt_params.m_random_seed);
// don't share initial units
ctx->pop_to_base_lvl();
m_num_shared_units = ctx->assigned_literals().size();
m_num_initial_atoms = ctx->get_num_bool_vars();
}
void parallel::worker::share_units() {
// Collect new units learned locally by this worker and send to batch manager
ctx->pop_to_base_lvl();
unsigned sz = ctx->assigned_literals().size();
for (unsigned j = m_num_shared_units; j < sz; ++j) { // iterate only over new literals since last sync
literal lit = ctx->assigned_literals()[j];
if (!ctx->is_relevant(lit.var()) && m_config.m_share_units_relevant_only)
continue;
if (m_config.m_share_units_initial_only && lit.var() >= m_num_initial_atoms) {
LOG_WORKER(2, " Skipping non-initial unit: " << lit.var() << "\n");
continue; // skip non-iniial atoms if configured to do so
}
expr_ref e(ctx->bool_var2expr(lit.var()), ctx->m); // turn literal into a Boolean expression
if (m.is_and(e) || m.is_or(e))
continue;
if (lit.sign())
e = m.mk_not(e); // negate if literal is negative
b.collect_clause(m_l2g, id, e);
}
m_num_shared_units = sz;
}
void parallel::worker::simplify() {
if (!m.inc())
return;
// first attempt: one-shot simplification of the context.
// a precise schedule of repeated simplification is TBD.
// also, the in-processing simplifier should be applied to
// a current set of irredundant clauses that may be reduced by
// unit propagation. By including the units we are effectively
// repeating unit propagation, but potentially not subsumption or
// Boolean simplifications that a solver could perform (smt_context doesnt really)
// Integration of inprocssing simplifcation here or in sat/smt solver could
// be based on taking the current clause set instead of the asserted formulas.
if (!m_config.m_inprocessing)
return;
if (m_config.m_inprocessing_delay > 0) {
--m_config.m_inprocessing_delay;
return;
}
ctx->pop_to_base_lvl();
if (ctx->m_base_lvl > 0)
return; // simplification only at base level
m_config.m_inprocessing = false; // initial strategy is to immediately disable inprocessing for future calls.
dependent_expr_simplifier *s = ctx->m_simplifier.get();
if (!s) {
// create a simplifier if none exists
// initialize it to a default pre-processing simplifier.
ctx->m_fmls = alloc(base_dependent_expr_state, m);
auto then_s = alloc(then_simplifier, m, ctx->get_params(), *ctx->m_fmls);
s = then_s;
ctx->m_simplifier = s;
init_preprocess(m, ctx->get_params(), *then_s, *ctx->m_fmls);
}
dependent_expr_state &fmls = *ctx->m_fmls.get();
// extract assertions from ctx.
// it is possible to track proof objects here if wanted.
// feed them to the simplifier
ptr_vector<expr> assertions;
expr_ref_vector units(m);
ctx->get_assertions(assertions);
ctx->get_units(units);
for (expr *e : assertions)
fmls.add(dependent_expr(m, e, nullptr, nullptr));
for (expr *e : units)
fmls.add(dependent_expr(m, e, nullptr, nullptr));
// run in-processing on the assertions
s->reduce();
scoped_ptr<context> new_ctx = alloc(context, m, m_smt_params, p.ctx.get_params());
// extract simplified assertions from the simplifier
// create a new context with the simplified assertions
// update ctx with the new context.
for (unsigned i = 0; i < fmls.qtail(); ++i) {
auto const &de = fmls[i];
new_ctx->assert_expr(de.fml());
}
asserted_formulas &src_af = ctx->m_asserted_formulas;
asserted_formulas &dst_af = new_ctx->m_asserted_formulas;
src_af.get_macro_manager().copy_to(dst_af.get_macro_manager());
new_ctx->copy_user_propagator(*ctx, true);
ctx = new_ctx.detach();
ctx->setup_context(true);
ctx->internalize_assertions();
auto old_atoms = m_num_initial_atoms;
m_num_shared_units = ctx->assigned_literals().size();
m_num_initial_atoms = ctx->get_num_bool_vars();
LOG_WORKER(1, " inprocess " << old_atoms << " -> " << m_num_initial_atoms << "\n");
}
void parallel::worker::collect_statistics(::statistics &st) const {
ctx->collect_statistics(st);
}
void parallel::worker::cancel() {
LOG_WORKER(1, " canceling\n");
m.limit().cancel();
}
void parallel::batch_manager::backtrack(ast_translation &l2g, expr_ref_vector const &core,
search_tree::node<cube_config> *node) {
std::scoped_lock lock(mux);
IF_VERBOSE(1, verbose_stream() << "Batch manager backtracking.\n");
if (m_state != state::is_running)
return;
vector<cube_config::literal> g_core;
for (auto c : core) {
expr_ref g_c(l2g(c), m);
if (!is_assumption(g_c))
g_core.push_back(expr_ref(l2g(c), m));
}
m_search_tree.backtrack(node, g_core);
IF_VERBOSE(1, m_search_tree.display(verbose_stream() << bounded_pp_exprs(core) << "\n"););
if (m_search_tree.is_closed()) {
m_state = state::is_unsat;
cancel_workers();
}
}
void parallel::batch_manager::split(ast_translation &l2g, unsigned source_worker_id,
search_tree::node<cube_config> *node, expr *atom) {
std::scoped_lock lock(mux);
expr_ref lit(m), nlit(m);
lit = l2g(atom);
nlit = mk_not(m, lit);
IF_VERBOSE(1, verbose_stream() << "Batch manager splitting on literal: " << mk_bounded_pp(lit, m, 3) << "\n");
if (m_state != state::is_running)
return;
// optional heuristic:
// node->get_status() == status::active
// and depth is 'high' enough
// then ignore split, and instead set the status of node to open.
m_search_tree.split(node, lit, nlit);
}
void parallel::batch_manager::collect_clause(ast_translation &l2g, unsigned source_worker_id, expr *clause) {
std::scoped_lock lock(mux);
expr *g_clause = l2g(clause);
if (!shared_clause_set.contains(g_clause)) {
shared_clause_set.insert(g_clause);
shared_clause sc{source_worker_id, expr_ref(g_clause, m)};
shared_clause_trail.push_back(sc);
}
}
void parallel::worker::collect_shared_clauses() {
expr_ref_vector new_clauses = b.return_shared_clauses(m_g2l, m_shared_clause_limit, id);
// iterate over new clauses and assert them in the local context
for (expr *e : new_clauses) {
ctx->assert_expr(e);
LOG_WORKER(2, " asserting shared clause: " << mk_bounded_pp(e, m, 3) << "\n");
}
}
expr_ref_vector parallel::batch_manager::return_shared_clauses(ast_translation &g2l, unsigned &worker_limit,
unsigned worker_id) {
std::scoped_lock lock(mux);
expr_ref_vector result(g2l.to());
for (unsigned i = worker_limit; i < shared_clause_trail.size(); ++i) {
if (shared_clause_trail[i].source_worker_id != worker_id)
result.push_back(g2l(shared_clause_trail[i].clause.get()));
}
worker_limit = shared_clause_trail.size(); // update the worker limit to the end of the current trail
return result;
}
lbool parallel::worker::check_cube(expr_ref_vector const &cube) {
for (auto &atom : cube)
asms.push_back(atom);
lbool r = l_undef;
ctx->get_fparams().m_max_conflicts = std::min(m_config.m_threads_max_conflicts, m_config.m_max_conflicts);
IF_VERBOSE(1, verbose_stream() << " Checking cube\n"
<< bounded_pp_exprs(cube)
<< "with max_conflicts: " << ctx->get_fparams().m_max_conflicts << "\n";);
try {
r = ctx->check(asms.size(), asms.data());
} catch (z3_error &err) {
b.set_exception(err.error_code());
} catch (z3_exception &ex) {
b.set_exception(ex.what());
} catch (...) {
b.set_exception("unknown exception");
}
asms.shrink(asms.size() - cube.size());
LOG_WORKER(1, " DONE checking cube " << r << "\n";);
return r;
}
expr_ref parallel::worker::get_split_atom() {
expr_ref result(m);
double score = 0;
unsigned n = 0;
ctx->pop_to_search_lvl();
for (bool_var v = 0; v < ctx->get_num_bool_vars(); ++v) {
if (ctx->get_assignment(v) != l_undef)
continue;
expr *e = ctx->bool_var2expr(v);
if (!e)
continue;
double new_score = ctx->m_lit_scores[0][v] * ctx->m_lit_scores[1][v];
ctx->m_lit_scores[0][v] /= 2;
ctx->m_lit_scores[1][v] /= 2;
if (new_score > score || !result || (new_score == score && m_rand(++n) == 0)) {
score = new_score;
result = e;
}
}
return result;
}
void parallel::batch_manager::set_sat(ast_translation &l2g, model &m) {
std::scoped_lock lock(mux);
IF_VERBOSE(1, verbose_stream() << "Batch manager setting SAT.\n");
if (m_state != state::is_running)
return;
m_state = state::is_sat;
p.ctx.set_model(m.translate(l2g));
cancel_workers();
}
void parallel::batch_manager::set_unsat(ast_translation &l2g, expr_ref_vector const &unsat_core) {
std::scoped_lock lock(mux);
IF_VERBOSE(1, verbose_stream() << "Batch manager setting UNSAT.\n");
if (m_state != state::is_running)
return;
m_state = state::is_unsat;
// each call to check_sat needs to have a fresh unsat core
SASSERT(p.ctx.m_unsat_core.empty());
for (expr *e : unsat_core)
p.ctx.m_unsat_core.push_back(l2g(e));
cancel_workers();
}
void parallel::batch_manager::set_exception(unsigned error_code) {
std::scoped_lock lock(mux);
IF_VERBOSE(1, verbose_stream() << "Batch manager setting exception code: " << error_code << ".\n");
if (m_state != state::is_running)
return;
m_state = state::is_exception_code;
m_exception_code = error_code;
cancel_workers();
}
void parallel::batch_manager::set_exception(std::string const &msg) {
std::scoped_lock lock(mux);
IF_VERBOSE(1, verbose_stream() << "Batch manager setting exception msg: " << msg << ".\n");
if (m_state != state::is_running)
return;
m_state = state::is_exception_msg;
m_exception_msg = msg;
cancel_workers();
}
void parallel::batch_manager::report_assumption_used(ast_translation &l2g, expr *assumption) {
std::scoped_lock lock(mux);
p.m_assumptions_used.insert(l2g(assumption));
}
lbool parallel::batch_manager::get_result() const {
if (m.limit().is_canceled())
return l_undef; // the main context was cancelled, so we return undef.
switch (m_state) {
case state::is_running: // batch manager is still running, but all threads have processed their cubes, which
// means all cubes were unsat
if (!m_search_tree.is_closed())
throw default_exception("inconsistent end state");
if (!p.m_assumptions_used.empty()) {
// collect unsat core from assumptions used, if any --> case when all cubes were unsat, but depend on
// nonempty asms, so we need to add these asms to final unsat core
SASSERT(p.ctx.m_unsat_core.empty());
for (auto a : p.m_assumptions_used)
p.ctx.m_unsat_core.push_back(a);
}
return l_false;
case state::is_unsat:
return l_false;
case state::is_sat:
return l_true;
case state::is_exception_msg:
throw default_exception(m_exception_msg.c_str());
case state::is_exception_code:
throw z3_error(m_exception_code);
default:
UNREACHABLE();
return l_undef;
}
}
bool parallel::batch_manager::get_cube(ast_translation &g2l, unsigned id, expr_ref_vector &cube, node *&n) {
cube.reset();
std::unique_lock<std::mutex> lock(mux);
if (m_search_tree.is_closed()) {
IF_VERBOSE(1, verbose_stream() << "all done\n";);
return false;
}
if (m_state != state::is_running) {
IF_VERBOSE(1, verbose_stream() << "aborting get_cube\n";);
return false;
}
node *t = m_search_tree.activate_node(n);
if (!t)
t = m_search_tree.find_active_node();
if (!t)
return false;
IF_VERBOSE(1, m_search_tree.display(verbose_stream()); verbose_stream() << "\n";);
n = t;
while (t) {
if (cube_config::literal_is_null(t->get_literal()))
break;
expr_ref lit(g2l.to());
lit = g2l(t->get_literal().get());
cube.push_back(lit);
t = t->parent();
}
return true;
}
void parallel::batch_manager::initialize() {
m_state = state::is_running;
m_search_tree.reset();
}
void parallel::batch_manager::collect_statistics(::statistics &st) const {
st.update("parallel-num_cubes", m_stats.m_num_cubes);
st.update("parallel-max-cube-size", m_stats.m_max_cube_depth);
}
lbool parallel::operator()(expr_ref_vector const &asms) {
ast_manager &m = ctx.m;
if (m.has_trace_stream())
throw default_exception("trace streams have to be off in parallel mode");
struct scoped_clear {
parallel &p;
scoped_clear(parallel &p) : p(p) {}
~scoped_clear() {
p.m_workers.reset();
p.m_assumptions_used.reset();
p.m_assumptions.reset();
}
};
scoped_clear clear(*this);
m_batch_manager.initialize();
m_workers.reset();
for (auto e : asms)
m_assumptions.insert(e);
scoped_limits sl(m.limit());
flet<unsigned> _nt(ctx.m_fparams.m_threads, 1);
SASSERT(num_threads > 1);
for (unsigned i = 0; i < num_threads; ++i)
m_workers.push_back(alloc(worker, i, *this, asms));
for (auto w : m_workers)
sl.push_child(&(w->limit()));
// Launch threads
vector<std::thread> threads(num_threads);
for (unsigned i = 0; i < num_threads; ++i) {
threads[i] = std::thread([&, i]() { m_workers[i]->run(); });
}
// Wait for all threads to finish
for (auto &th : threads)
th.join();
for (auto w : m_workers)
w->collect_statistics(ctx.m_aux_stats);
m_batch_manager.collect_statistics(ctx.m_aux_stats);
return m_batch_manager.get_result();
}
} // namespace smt
#endif
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