Fix concurrent root halt on terminal LP status

Author: Rohithmatham12

cpp/src/branch_and_bound/branch_and_bound.cpp

@@ -1981,6 +1981,15 @@ lp_status_t branch_and_bound_t<i_t, f_t>::solve_root_relaxation(
   std::string solver_name = "";
 
   lp_status_t root_status;
+  auto request_root_concurrent_halt = [this](lp_status_t status) {
+    if (status == lp_status_t::OPTIMAL || status == lp_status_t::INFEASIBLE ||
+        status == lp_status_t::UNBOUNDED || status == lp_status_t::UNBOUNDED_OR_INFEASIBLE ||
+        status == lp_status_t::ITERATION_LIMIT || status == lp_status_t::TIME_LIMIT ||
+        status == lp_status_t::NUMERICAL_ISSUES || status == lp_status_t::CUTOFF ||
+        status == lp_status_t::WORK_LIMIT) {
+      set_root_concurrent_halt(1);
+    }
+  };
 
 // Launch a task for solving the root LP relaxation via dual simplex.
 #pragma omp task default(shared) depend(out : root_status) priority(CUOPT_CRITICAL_TASK_PRIORITY)
@@ -1995,6 +2004,7 @@ lp_status_t branch_and_bound_t<i_t, f_t>::solve_root_relaxation(
                                                            root_vstatus_,
                                                            edge_norms_,
                                                            nullptr);
+    request_root_concurrent_halt(root_status);
   }
 
   // Wait for the root relaxation solution to be sent by the diversity manager or dual simplex

python/libcuopt/libcuopt/tests/test_cli.sh

@@ -31,3 +31,38 @@ cuopt_cli "${RAPIDS_DATASET_ROOT_DIR}"/linear_programming/good-mps-1.lp.bz2 | gr
 # Add a for mixed integer programming test with options
 
 cuopt_cli "${RAPIDS_DATASET_ROOT_DIR}"/mip/sample.mps --mip-absolute-gap 0.01 --time-limit 10 | grep -q "Solution objective" || (echo "Expected solution objective not found" && exit 1)
+
+# Regression for opportunistic concurrent root LP solve on an infeasible MILP.
+# Default opportunistic mode should return Infeasible instead of aborting.
+tmp_mps="$(mktemp "${TMPDIR:-/tmp}/cuopt-infeasible-milp.XXXXXX.mps")"
+trap 'rm -f "${tmp_mps}"' EXIT
+python3 - "${tmp_mps}" <<'PY'
+import sys
+
+path = sys.argv[1]
+n = 120
+a_vals = [1.0 + ((i * 37) % 90) / 10.0 for i in range(n)]
+b_vals = [a + (((i * 17) % 11) - 5.0) / 20.0 for i, a in enumerate(a_vals)]
+need_a = 0.8 * sum(a_vals)
+cap_b = 0.3 * sum(b_vals)
+
+with open(path, "w", encoding="utf-8") as f:
+    f.write("NAME          INFEAS_MILP\n")
+    f.write("ROWS\n")
+    f.write(" N  COST\n")
+    f.write(" G  NEED_A\n")
+    f.write(" L  CAP_B\n")
+    f.write("COLUMNS\n")
+    f.write("    M1        'MARKER'                 'INTORG'\n")
+    for i, (a, b) in enumerate(zip(a_vals, b_vals)):
+        f.write(f"    x{i:<8} COST      1                      NEED_A    {a:.17g}\n")
+        f.write(f"    x{i:<8} CAP_B     {b:.17g}\n")
+    f.write("    M2        'MARKER'                 'INTEND'\n")
+    f.write("RHS\n")
+    f.write(f"    RHS       NEED_A    {need_a:.17g}       CAP_B     {cap_b:.17g}\n")
+    f.write("BOUNDS\n")
+    for i in range(n):
+        f.write(f" UP BND       x{i:<8} 1\n")
+    f.write("ENDATA\n")
+PY
+cuopt_cli "${tmp_mps}" --time-limit 30 | grep -q "Infeasible" || (echo "Expected infeasible status for opportunistic MILP" && exit 1)