Several bug fixes

[nguidotti]

• Fixed early termination in CMS750_4 due to an incorrect root objective from the PDLP. It provides an objective in user space and B&B expects the objective in the solver space.
• Fixed setting the number of threads to a fixed value when running cuopt_cli. Now the number of threads in the probing cache can be controlled by the bounds_update::settings_t.
• Inverted loop order in probing cache to avoid creating and deleting the OpenMP thread pool each iteration.
• PDLP/Barrier no longer set the root objective and solution when the B&B is already running.
• Improved the logs when solving the root relaxation using the concurrent mode.

Checklist

• I am familiar with the Contributing Guidelines.
• Testing
  • New or existing tests cover these changes
  • Added tests
  • Created an issue to follow-up
  • NA
• Documentation
  • The documentation is up to date with these changes
  • Added new documentation
  • NA

Summary by CodeRabbit

• New Features

  • Added per-instance thread count configuration for presolve operations, with automatic scaling to system capabilities when not explicitly set.

• Bug Fixes

  • Improved root relaxation solution handling for enhanced stability.
  • Refined logging output for clearer MIP solver operation reporting.

_{✏️ Tip: You can customize this high-level summary in your review settings.}

[coderabbitai]

📝 Walkthrough

Walkthrough

This pull request introduces bidirectional user-space to solver-space objective value conversion, configures dynamic threading for presolve operations, implements conditional logging to suppress verbose output during MIP solving, and adds idempotency guards to prevent overwriting cached root solutions.

Changes

Cohort / File(s)	Summary
Objective value handling cpp/src/mip/diversity/diversity_manager.cu, cpp/src/mip/problem/problem.cuh, cpp/src/mip/problem/problem.cu, cpp/src/dual_simplex/branch_and_bound.hpp, cpp/src/dual_simplex/branch_and_bound.cpp	Introduces user-space to solver-space objective conversion via new get_solver_obj_from_user_obj() method. Updates B&B callback to pass both solver-space and user-space objectives as separate parameters. Adds is_root_solution_set flag to guard against overwriting root solution data. Updates set_root_relaxation_solution_callback signature to accept additional objective parameter.
Threading configuration cpp/src/mip/presolve/bounds_presolve.cuh, cpp/src/mip/presolve/probing_cache.cu	Replaces hard-coded thread configuration with configurable num_threads field (defaults to -1, computed as 0.2 × omp_get_max_threads() or clamped to [1, 8]). Adds OpenMP support headers. Updates per-thread pool sizing and parallel region configuration to use computed thread count.
Conditional logging cpp/src/linear_programming/solve.cu, cpp/src/dual_simplex/phase2.cpp	Adds CUOPT_LOG_CONDITIONAL_INFO macro to suppress verbose logging inside MIP contexts. Removes duplicated root relaxation statistics logging from phase2. Updates copyright year to 2022-2026.

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~50 minutes

🚥 Pre-merge checks | ✅ 1 | ❌ 2

❌ Failed checks (1 warning, 1 inconclusive)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 10.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.
Title check	❓ Inconclusive	The title is vague and generic, using non-descriptive phrasing that doesn't convey specific information about the actual changes made.	Replace with a more specific title highlighting the primary fix, such as 'Fix root objective handling in PDLP to Branch & Bound conversion' or summarize the main bug being addressed.

✅ Passed checks (1 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

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✨ Finishing touches

• 📝 Generate docstrings

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[coderabbitai]

Actionable comments posted: 0

Caution

Some comments are outside the diff and can’t be posted inline due to platform limitations.

⚠️ Outside diff range comments (1)

cpp/src/mip/presolve/probing_cache.cu (1)

859-910: Add defensive validation for num_threads before pool sizing and parallel launch

The code assumes settings.num_threads is always positive, but since settings_t is a public struct, external code can set num_threads to 0 (or modify it between initialization and use). If 0 is assigned:

• modification_vector_pool and substitution_vector_pool would have size 0
• #pragma omp parallel num_threads(0) produces undefined behavior (OpenMP spec)
• If threads spawn despite 0, thread_idx from omp_get_thread_num() will exceed pool bounds, causing out-of-bounds access

Add a defensive clamp before sizing the pools:

Proposed fix

-  const size_t num_threads = bound_presolve.settings.num_threads;
+  const i_t requested_threads = bound_presolve.settings.num_threads;
+  size_t num_threads =
+    requested_threads > 0 ? static_cast<size_t>(requested_threads)
+                          : static_cast<size_t>(omp_get_max_threads());
+  if (num_threads == 0) { num_threads = 1; }

Aligns with multithreading safety guidelines to prevent resource exhaustion and thread safety violations.

[akifcorduk]

Can't we undef the previous macro and still use CUOPT_LOG_INFO here?

[nguidotti]

I think it is better to add another macro, since there are some methods where we do not pass the setting as argument, hence they need to use the old version.

[nguidotti]

Ideally, we should add logger_t to the settings rather than CUOPT_LOG_INFO or rapids::logger_t.

[chris-maes]

This is where we should indicate that PDLP/Barrier won. Can you use the is_pdlp_solution to determine which of them won and print it here?

[nguidotti]

I did not find a way to get the winner solver from the optimization_problem_solution_t unless we change the API (#787). This object is user-facing, so it needs to be reflect on the Python side as well.

[coderabbitai]

Actionable comments posted: 1

🤖 Fix all issues with AI agents

In `@cpp/src/dual_simplex/branch_and_bound.hpp`:
- Around line 87-97: The plain bool is_root_solution_set is accessed
concurrently (read in set_root_relaxation_solution and written in
solve_root_relaxation), causing a data race; change the declaration of
is_root_solution_set to std::atomic<bool> and update all reads/writes in
functions such as set_root_relaxation_solution and solve_root_relaxation to use
.load()/.store() with appropriate memory orders (e.g., memory_order_acquire for
reads and memory_order_release for writes) to match the existing
root_crossover_solution_set_ usage, ensuring thread-safe checks and updates.