Added stop_search method to CpSolverSolutionCallback - closes #46

Author: ankane

CHANGELOG.md

@@ -1,5 +1,6 @@
 ## 0.18.0 (unreleased)
 
+- Added `stop_search` method to `CpSolverSolutionCallback`
 - Fixed error with `apply_locks` and `set_allowed_vehicles_for_index` methods
 - Dropped support for Ruby < 3.3
 

ext/or-tools/constraint.cpp

@@ -432,13 +432,17 @@ void init_constraint(Rice::Module& m) {
           parameters.set_num_search_workers(1);
 
           m.Add(NewFeasibleSolutionObserver(
-            [&callback](const CpSolverResponse& r) {
+            [&](const CpSolverResponse& r) {
               if (!ruby_native_thread_p()) {
                 throw std::runtime_error{"Non-Ruby thread"};
               }
 
               callback.call("response=", r);
               callback.call("on_solution_callback");
+
+              if (callback.attr_get("@stopped")) {
+                StopSearch(&m);
+              }
             })
           );
         }

lib/or_tools/cp_solver_solution_callback.rb

@@ -16,5 +16,9 @@ def value(expr)
     def objective_value
       @response&.objective_value
     end
+
+    def stop_search
+      @stopped = true
+    end
   end
 end

test/constraint_test.rb

@@ -47,6 +47,20 @@ def on_solution_callback
   end
 end
 
+class StopSearchCallback < ORTools::CpSolverSolutionCallback
+   attr_reader :solution_count
+
+  def initialize
+    super()
+    @solution_count = 0
+  end
+
+  def on_solution_callback
+    @solution_count += 1
+    stop_search if @solution_count >= 3
+  end
+end
+
 class ConstraintTest < Minitest::Test
   # https://developers.google.com/optimization/cp/cp_solver
   def test_cp_sat_solver
@@ -156,6 +170,10 @@ def test_cryptoarithmetic
     assert_equal 182, solver.num_conflicts
     assert_equal 1777, solver.num_branches
     assert_equal 72, solution_printer.solution_count
+
+    stop_callback = StopSearchCallback.new
+    status = solver.solve(model, stop_callback)
+    assert_equal 3, stop_callback.solution_count
   end
 
   # https://developers.google.com/optimization/cp/queens