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Fix root cut CPUFJ solutions being dropped by the GPU heuristics #1497

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Merged
rapids-bot merged 2 commits into from
Jul 2, 2026
Merged

Fix root cut CPUFJ solutions being dropped by the GPU heuristics #1497

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a7df065
fix B&B solutions being ignoredf if not transmitted in time to the gp…
aliceb-nv Jul 1, 2026
5906fc1
Merge branch 'main' into fix/issue-1488-cpufj-incumbent
aliceb-nv Jul 1, 2026
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3 changes: 3 additions & 0 deletions cpp/src/branch_and_bound/branch_and_bound.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2691,6 +2691,9 @@ mip_status_t branch_and_bound_t<i_t, f_t>::solve(mip_solution_t<i_t, f_t>& solut
if (settings_.deterministic) {
queue_external_solution_deterministic(user_assignment, work_units);
} else {
if (settings_.solution_callback != nullptr) {
settings_.solution_callback(user_assignment, obj);
}
Comment on lines +2694 to +2696

@coderabbitai coderabbitai Bot Jul 1, 2026

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🗄️ Data Integrity & Integration | 🟠 Major | ⚡ Quick win

Unconditional solution_callback invocation bypasses the incumbent-improvement/feasibility gate used elsewhere.

Every other call site (repair_heuristic_solutions, add_feasible_solution) only invokes settings_.solution_callback after confirming the solution actually improves the incumbent (improves_incumbent(...)) and is feasibility-checked. Here the callback fires unconditionally for any CPUFJ improvement, before set_solution_from_heuristics validates feasibility via check_guess. Since the callback drives dm->rins.new_best_incumbent_callback, which is documented/named to represent a genuine new best incumbent, this can report non-improving or not-yet-validated solutions to RINS/population, polluting downstream state.

🐛 Proposed fix to gate the callback on actual incumbent improvement 
       } else {
-        if (settings_.solution_callback != nullptr) {
-          settings_.solution_callback(user_assignment, obj);
-        }
+        if (settings_.solution_callback != nullptr && improves_incumbent(obj)) {
+          settings_.solution_callback(user_assignment, obj);
+        }
         set_solution_from_heuristics(user_assignment);
       }
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Suggested change
if (settings_.solution_callback != nullptr) {
settings_.solution_callback(user_assignment, obj);
}
if (settings_.solution_callback != nullptr && improves_incumbent(obj)) {
settings_.solution_callback(user_assignment, obj);
}
🤖 Prompt for AI Agents 
Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@cpp/src/branch_and_bound/branch_and_bound.cpp` around lines 2694 - 2696, The
`solution_callback` call in `branch_and_bound.cpp` is firing too early inside
the CPUFJ improvement path. Update this branch to mirror the gating used in
`repair_heuristic_solutions` and `add_feasible_solution`: only invoke
`settings_.solution_callback` after `improves_incumbent(...)` succeeds and the
candidate has passed feasibility validation through
`set_solution_from_heuristics`/`check_guess`. Keep the callback aligned with a
genuine new incumbent so `dm->rins.new_best_incumbent_callback` is only notified
for validated incumbent improvements.

set_solution_from_heuristics(user_assignment);
}
};
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11 changes: 11 additions & 0 deletions cpp/src/mip_heuristics/solver.cu
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Expand Up @@ -507,6 +507,17 @@ solution_t<i_t, f_t> mip_solver_t<i_t, f_t>::run_solver()
sol = dm.run_solver();
} // implicit barrier for all tasks created in B&B and heuristics

if (!context.settings.heuristics_only && branch_and_bound->has_solver_space_incumbent()) {

@akifcorduk akifcorduk Jul 1, 2026

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Why is this needed? The callback already registers it on the heuristic thread, right? Is it because of the different thread completion orders?

@aliceb-nv aliceb-nv Jul 1, 2026

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It's not, I added this to err on the safe side in case future additions neglect to run the gpu heuristic callback

solution_t<i_t, f_t> branch_and_bound_sol(*context.problem_ptr);
branch_and_bound_sol.copy_new_assignment(branch_and_bound_solution.x);
branch_and_bound_sol.compute_feasibility();

if (branch_and_bound_sol.get_feasible() &&
(!sol.get_feasible() || branch_and_bound_sol.get_objective() < sol.get_objective())) {
sol = std::move(branch_and_bound_sol);
}
}

if (!context.settings.heuristics_only) {
if (branch_and_bound_solution.lower_bound > -std::numeric_limits<f_t>::infinity()) {
context.stats.set_solution_bound(
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