[C API] Add OpenMP support validation in ThreadPoolBuilder

bindings/c/CMakeLists.txt

@@ -67,16 +67,17 @@ target_include_directories(${TARGET_NAME}
     PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/src
 )
 
-find_package(OpenMP REQUIRED)
-# PRIVATE: OpenMP is an implementation detail linked into the shared library.
-# Exporting it would force consumers of the C ABI to resolve a C++ OpenMP
-# target they never asked for.
-target_link_libraries(${TARGET_NAME} PRIVATE OpenMP::OpenMP_CXX)
+# Set default visibility to hidden for all symbols in the shared library.
+target_compile_options(${TARGET_NAME} PRIVATE -fvisibility=hidden)
 
-target_compile_options(${TARGET_NAME} PRIVATE
-    -DSVS_ENABLE_OMP=1
-    -fvisibility=hidden
-)
+find_package(OpenMP)
+if (OpenMP_CXX_FOUND)
+    # PRIVATE: OpenMP is an implementation detail linked into the shared library.
+    # Exporting it would force consumers of the C ABI to resolve a C++ OpenMP
+    # target they never asked for.
+    target_link_libraries(${TARGET_NAME} PRIVATE OpenMP::OpenMP_CXX)
+    target_compile_definitions(${TARGET_NAME} PRIVATE SVS_ENABLE_OMP=1)
+endif() # OpenMP_CXX_FOUND
 
 if(UNIX AND NOT APPLE)
     # Don't export 3rd-party symbols from the lib

bindings/c/docs/C_API_Design.md

@@ -358,7 +358,7 @@ Controls parallelization strategy for index operations.
 | Type | Configuration | Use Case |
 |------|---------------|----------|
 | **Native** | Thread count | Default SVS thread pool (recommended) |
-| **OpenMP** | Uses OMP_NUM_THREADS | Integration with OpenMP applications |
+| **OpenMP** | Thread count | Integration with OpenMP applications; requires a build with OpenMP support, otherwise `SVS_ERROR_NOT_IMPLEMENTED` |
 | **Single Thread** | No parallelization | Debugging or minimal overhead |
 | **Custom** | User-defined interface | Custom scheduling/work-stealing |
 

bindings/c/include/svs/c/svs_c.h

@@ -117,6 +117,8 @@ enum svs_storage_kind {
 };
 
 /// @brief Thread pool implementation used for parallel operations.
+/// @remarks SVS_THREADPOOL_KIND_OMP is available only if the library was built with
+/// OpenMP support; otherwise selecting it fails with SVS_ERROR_NOT_IMPLEMENTED.
 enum svs_threadpool_kind {
     SVS_THREADPOOL_KIND_NATIVE = 0,
     SVS_THREADPOOL_KIND_OMP = 1,
@@ -853,9 +855,15 @@ SVS_API bool svs_index_builder_set_storage(
 /// @brief Set the thread pool configuration for the index builder
 /// @param builder The index builder handle
 /// @param kind The kind of thread pool to use
-/// @param num_threads The number of threads to use (if applicable)
+/// @param num_threads The number of threads to use; must be greater than zero (ignored
+/// for SVS_THREADPOOL_KIND_SINGLE_THREAD)
 /// @param out_err An optional error handle to capture errors
 /// @return true on success, false on failure
+/// @error On failure, if out_err is provided, it will contain:
+/// - SVS_ERROR_INVALID_ARGUMENT if builder is NULL, num_threads is zero, or @p kind is
+///   SVS_THREADPOOL_KIND_CUSTOM (use svs_index_builder_set_threadpool_custom() instead)
+/// - SVS_ERROR_NOT_IMPLEMENTED if @p kind is SVS_THREADPOOL_KIND_OMP and the library was
+///   built without OpenMP support
 SVS_API bool svs_index_builder_set_threadpool(
     svs_index_builder_h builder,
     svs_threadpool_kind_t kind,
@@ -1336,9 +1344,10 @@ SVS_API bool svs_index_get_num_threads(
 /// @param out_err An optional error handle to capture errors
 /// @return true on success, false on failure
 /// @remarks This function is only supported for indices built with threadpool kinds
-/// SVS_THREADPOOL_KIND_NATIVE or SVS_THREADPOOL_KIND_OMP. Attempting to call this
-/// function on indices built with SVS_THREADPOOL_KIND_CUSTOM or
-/// SVS_THREADPOOL_KIND_SINGLE_THREAD will fail and return false.
+/// SVS_THREADPOOL_KIND_NATIVE or SVS_THREADPOOL_KIND_OMP (when built with OpenMP
+/// support). Attempting to call this function on indices built with
+/// SVS_THREADPOOL_KIND_CUSTOM or SVS_THREADPOOL_KIND_SINGLE_THREAD will fail and return
+/// false.
 /// @error On failure, if out_err is provided, it will contain:
 /// - SVS_ERROR_INVALID_OPERATION if the index's threadpool kind is unresizable
 /// - SVS_ERROR_INVALID_ARGUMENT if num_threads is invalid or zero

bindings/c/src/threadpool.hpp

@@ -112,6 +112,13 @@ class ThreadPoolBuilder {
                 "SVS_THREADPOOL_KIND_CUSTOM cannot be built automatically."
             );
         }
+
+        // Validate that SVS_OMP macro is properly defined.
+        SVS_VALIDATE_BOOL_ENV(SVS_OMP)
+
+        if (!SVS_OMP && kind == SVS_THREADPOOL_KIND_OMP) {
+            throw svs::c_runtime::not_implemented("OpenMP support is not enabled.");
+        }
     }
 
     ThreadPoolBuilder(svs_threadpool_i pool)
@@ -158,7 +165,12 @@ class ThreadPoolBuilder {
             case SVS_THREADPOOL_KIND_NATIVE:
                 return ThreadPoolHandle(NativeThreadPool(num_threads));
             case SVS_THREADPOOL_KIND_OMP:
+#if SVS_OMP
+                // OMPThreadPool is only available if OpenMP support is enabled.
                 return ThreadPoolHandle(OMPThreadPool(num_threads));
+#else
+                throw svs::c_runtime::not_implemented("OpenMP support is not enabled.");
+#endif
             case SVS_THREADPOOL_KIND_SINGLE_THREAD:
                 return ThreadPoolHandle(SequentialThreadPool());
             case SVS_THREADPOOL_KIND_CUSTOM:

bindings/c/tests/c_api_index.cpp

@@ -692,31 +692,38 @@ CATCH_TEST_CASE("C API Threadpool Management", "[c_api][index][threadpool]") {
         // Set OMP threadpool
         bool success =
             svs_index_builder_set_threadpool(builder, SVS_THREADPOOL_KIND_OMP, 3, error);
-        CATCH_REQUIRE(success);
-        CATCH_REQUIRE(svs_error_ok(error));
+        // If OMP is not implemented, success will be false and the error code will be
+        // SVS_ERROR_NOT_IMPLEMENTED. Otherwise, success should be true and the error should
+        // be OK.
+        if (!success) {
+            CATCH_REQUIRE(svs_error_get_code(error) == SVS_ERROR_NOT_IMPLEMENTED);
+        } else {
+            CATCH_REQUIRE(svs_error_ok(error));
 
-        svs_index_h index = svs_index_build(builder, data.data(), NUM_VECTORS, error);
-        CATCH_REQUIRE(index != nullptr);
-        CATCH_REQUIRE(svs_error_ok(error));
+            svs_index_h index = svs_index_build(builder, data.data(), NUM_VECTORS, error);
+            CATCH_REQUIRE(index != nullptr);
+            CATCH_REQUIRE(svs_error_ok(error));
 
-        // Get current number of threads
-        size_t num_threads = 0;
-        success = svs_index_get_num_threads(index, &num_threads, error);
-        CATCH_REQUIRE(success);
-        CATCH_REQUIRE(svs_error_ok(error));
-        CATCH_REQUIRE(num_threads == 3);
+            // Get current number of threads
+            size_t num_threads = 0;
+            success = svs_index_get_num_threads(index, &num_threads, error);
+            CATCH_REQUIRE(success);
+            CATCH_REQUIRE(svs_error_ok(error));
+            CATCH_REQUIRE(num_threads == 3);
 
-        // Set to different number of threads
-        success = svs_index_set_num_threads(index, 5, error);
-        CATCH_REQUIRE(success);
-        CATCH_REQUIRE(svs_error_ok(error));
+            // Set to different number of threads
+            success = svs_index_set_num_threads(index, 5, error);
+            CATCH_REQUIRE(success);
+            CATCH_REQUIRE(svs_error_ok(error));
 
-        // Verify the change
-        success = svs_index_get_num_threads(index, &num_threads, error);
-        CATCH_REQUIRE(success);
-        CATCH_REQUIRE(num_threads == 5);
+            // Verify the change
+            success = svs_index_get_num_threads(index, &num_threads, error);
+            CATCH_REQUIRE(success);
+            CATCH_REQUIRE(num_threads == 5);
+
+            svs_index_free(index);
+        }
 
-        svs_index_free(index);
         svs_index_builder_free(builder);
         svs_algorithm_free(algorithm);
         svs_error_free(error);

bindings/c/tests/c_api_index_builder.cpp

@@ -125,8 +125,14 @@ CATCH_TEST_CASE("C API Index Builder", "[c_api][index_builder]") {
 
         bool success =
             svs_index_builder_set_threadpool(builder, SVS_THREADPOOL_KIND_OMP, 2, error);
-        CATCH_REQUIRE(success == true);
-        CATCH_REQUIRE(svs_error_ok(error) == true);
+        // If OMP is not implemented, success will be false and the error code will be
+        // SVS_ERROR_NOT_IMPLEMENTED. Otherwise, success should be true and the error should
+        // be OK.
+        if (!success) {
+            CATCH_REQUIRE(svs_error_get_code(error) == SVS_ERROR_NOT_IMPLEMENTED);
+        } else {
+            CATCH_REQUIRE(svs_error_ok(error) == true);
+        }
 
         svs_index_builder_free(builder);
         svs_algorithm_free(algorithm);