Remove resetGlobalScheduler calls from C API

check/TestHighsParallel.cpp

@@ -7,6 +7,7 @@
 #include <iostream>
 
 #include "catch.hpp"
+#include "interfaces/highs_c_api.h"
 #include "matrix_multiplication.hpp"
 #include "parallel/HighsParallel.h"
 
@@ -305,4 +306,52 @@ TEST_CASE("CancelNestedTasks", "[parallel]") {
   }
 
   HighsTaskExecutor::shutdown();
+}
+
+TEST_CASE("ParallelCApi", "[parallel]") {
+  // This test exposes a failure in the C api when creating and destroying Highs
+  // instances on separate threads.
+  // One thread solves a mip, while the other loses some time before destroying
+  // the instance. If this causes the scheduler to be terminated (i.e., if
+  // Highs_destroy calls resetGlobalScheduler) while the first thread is still
+  // using it, the first thread may crash, hang, or terminate with wrong
+  // results.
+
+  highs::parallel::initialize_scheduler();
+
+  std::string model = std::string(HIGHS_DIR) + "/check/instances/egout.mps";
+  const double expected_obj = 568.1007;
+  double actual_obj;
+  double total = 0;
+
+  {
+    highs::parallel::TaskGroup tg;
+
+    tg.spawn([&]() {
+      void* highs = Highs_create();
+      Highs_setBoolOptionValue(highs, "output_flag", dev_run);
+      Highs_setStringOptionValue(highs, "parallel", "on");
+      Highs_readModel(highs, model.c_str());
+      Highs_run(highs);
+      Highs_getDoubleInfoValue(highs, "objective_function_value", &actual_obj);
+      Highs_destroy(highs);
+    });
+
+    tg.spawn([&]() {
+      void* highs = Highs_create();
+      for (int i = 0; i < 1e6; ++i) {
+        total += (double)i * i * i;
+      }
+      Highs_destroy(highs);
+    });
+
+    tg.taskWait();
+
+    REQUIRE(total > 1e18);
+    REQUIRE(std::abs(actual_obj - expected_obj) / std::abs(expected_obj) <
+            1e-4);
+  }
+  // TaskGroup destructor must be called before scheduler is killed
+
+  HighsTaskExecutor::shutdown(true);
 }

examples/call_highs_from_c_minimal.c

@@ -655,5 +655,6 @@ int main() {
   minimal_api();
   minimal_api_qp();
   full_api();
+  Highs_resetGlobalScheduler(1);
   return 0;
 }

highs/interfaces/highs_c_api.cpp

@@ -61,9 +61,6 @@ HighsInt Highs_lpCall(const HighsInt num_col, const HighsInt num_row,
       if (copy_row_basis) row_basis_status[i] = (HighsInt)basis.row_status[i];
     }
   }
-
-  highs.resetGlobalScheduler(true);
-
   return (HighsInt)status;
 }
 
@@ -106,9 +103,6 @@ HighsInt Highs_mipCall(const HighsInt num_col, const HighsInt num_row,
         row_value[i] = solution.row_value[i];
     }
   }
-
-  highs.resetGlobalScheduler(true);
-
   return (HighsInt)status;
 }
 
@@ -165,16 +159,12 @@ HighsInt Highs_qpCall(
       if (copy_row_basis) row_basis_status[i] = (HighsInt)basis.row_status[i];
     }
   }
-
-  highs.resetGlobalScheduler(true);
-
   return (HighsInt)status;
 }
 
 void* Highs_create(void) { return new Highs(); }
 
 void Highs_destroy(void* highs) {
-  Highs::resetGlobalScheduler(true);
   delete (Highs*)highs;
 }