support specific num_threads for data loading in c_api.

include/LightGBM/utils/openmp_wrapper.h

@@ -22,7 +22,6 @@ public:
   void ReThrow() {
     if (ex_ptr_ != nullptr) {
       std::rethrow_exception(ex_ptr_);
-      ex_ptr_ = nullptr;
     }
   }
   void CaptureException() {

src/c_api.cpp

@@ -323,9 +323,12 @@ int LGBM_DatasetCreateFromFile(const char* filename,
                                DatasetHandle* out) {
   API_BEGIN();
   auto param = ConfigBase::Str2Map(parameters);
-  IOConfig io_config;
-  io_config.Set(param);
-  DatasetLoader loader(io_config, nullptr, 1, filename);
+  OverallConfig config;
+  config.Set(param);
+  if (config.num_threads > 0) {
+    omp_set_num_threads(config.num_threads);
+  }
+  DatasetLoader loader(config.io_config, nullptr, 1, filename);
   if (reference == nullptr) {
     *out = loader.LoadFromFile(filename);
   } else {
@@ -346,9 +349,12 @@ int LGBM_DatasetCreateFromSampledColumn(double** sample_data,
                                         DatasetHandle* out) {
   API_BEGIN();
   auto param = ConfigBase::Str2Map(parameters);
-  IOConfig io_config;
-  io_config.Set(param);
-  DatasetLoader loader(io_config, nullptr, 1, nullptr);
+  OverallConfig config;
+  config.Set(param);
+  if (config.num_threads > 0) {
+    omp_set_num_threads(config.num_threads);
+  }
+  DatasetLoader loader(config.io_config, nullptr, 1, nullptr);
   *out = loader.CostructFromSampleData(sample_data, sample_indices, ncol, num_per_col,
                                        num_sample_row,
                                        static_cast<data_size_t>(num_total_row));
@@ -433,14 +439,17 @@ int LGBM_DatasetCreateFromMat(const void* data,
                               DatasetHandle* out) {
   API_BEGIN();
   auto param = ConfigBase::Str2Map(parameters);
-  IOConfig io_config;
-  io_config.Set(param);
+  OverallConfig config;
+  config.Set(param);
+  if (config.num_threads > 0) {
+    omp_set_num_threads(config.num_threads);
+  }
   std::unique_ptr<Dataset> ret;
   auto get_row_fun = RowFunctionFromDenseMatric(data, nrow, ncol, data_type, is_row_major);
   if (reference == nullptr) {
     // sample data first
-    Random rand(io_config.data_random_seed);
-    int sample_cnt = static_cast<int>(nrow < io_config.bin_construct_sample_cnt ? nrow : io_config.bin_construct_sample_cnt);
+    Random rand(config.io_config.data_random_seed);
+    int sample_cnt = static_cast<int>(nrow < config.io_config.bin_construct_sample_cnt ? nrow : config.io_config.bin_construct_sample_cnt);
     auto sample_indices = rand.Sample(nrow, sample_cnt);
     sample_cnt = static_cast<int>(sample_indices.size());
     std::vector<std::vector<double>> sample_values(ncol);
@@ -455,7 +464,7 @@ int LGBM_DatasetCreateFromMat(const void* data,
         }
       }
     }
-    DatasetLoader loader(io_config, nullptr, 1, nullptr);
+    DatasetLoader loader(config.io_config, nullptr, 1, nullptr);
     ret.reset(loader.CostructFromSampleData(Common::Vector2Ptr<double>(sample_values).data(),
                                             Common::Vector2Ptr<int>(sample_idx).data(),
                                             static_cast<int>(sample_values.size()),
@@ -494,15 +503,18 @@ int LGBM_DatasetCreateFromCSR(const void* indptr,
                               DatasetHandle* out) {
   API_BEGIN();
   auto param = ConfigBase::Str2Map(parameters);
-  IOConfig io_config;
-  io_config.Set(param);
+  OverallConfig config;
+  config.Set(param);
+  if (config.num_threads > 0) {
+    omp_set_num_threads(config.num_threads);
+  }
   std::unique_ptr<Dataset> ret;
   auto get_row_fun = RowFunctionFromCSR(indptr, indptr_type, indices, data, data_type, nindptr, nelem);
   int32_t nrow = static_cast<int32_t>(nindptr - 1);
   if (reference == nullptr) {
     // sample data first
-    Random rand(io_config.data_random_seed);
-    int sample_cnt = static_cast<int>(nrow < io_config.bin_construct_sample_cnt ? nrow : io_config.bin_construct_sample_cnt);
+    Random rand(config.io_config.data_random_seed);
+    int sample_cnt = static_cast<int>(nrow < config.io_config.bin_construct_sample_cnt ? nrow : config.io_config.bin_construct_sample_cnt);
     auto sample_indices = rand.Sample(nrow, sample_cnt);
     sample_cnt = static_cast<int>(sample_indices.size());
     std::vector<std::vector<double>> sample_values;
@@ -522,7 +534,7 @@ int LGBM_DatasetCreateFromCSR(const void* indptr,
       }
     }
     CHECK(num_col >= static_cast<int>(sample_values.size()));
-    DatasetLoader loader(io_config, nullptr, 1, nullptr);
+    DatasetLoader loader(config.io_config, nullptr, 1, nullptr);
     ret.reset(loader.CostructFromSampleData(Common::Vector2Ptr<double>(sample_values).data(),
                                             Common::Vector2Ptr<int>(sample_idx).data(),
                                             static_cast<int>(sample_values.size()),
@@ -561,14 +573,17 @@ int LGBM_DatasetCreateFromCSC(const void* col_ptr,
                               DatasetHandle* out) {
   API_BEGIN();
   auto param = ConfigBase::Str2Map(parameters);
-  IOConfig io_config;
-  io_config.Set(param);
+  OverallConfig config;
+  config.Set(param);
+  if (config.num_threads > 0) {
+    omp_set_num_threads(config.num_threads);
+  }
   std::unique_ptr<Dataset> ret;
   int32_t nrow = static_cast<int32_t>(num_row);
   if (reference == nullptr) {
     // sample data first
-    Random rand(io_config.data_random_seed);
-    int sample_cnt = static_cast<int>(nrow < io_config.bin_construct_sample_cnt ? nrow : io_config.bin_construct_sample_cnt);
+    Random rand(config.io_config.data_random_seed);
+    int sample_cnt = static_cast<int>(nrow < config.io_config.bin_construct_sample_cnt ? nrow : config.io_config.bin_construct_sample_cnt);
     auto sample_indices = rand.Sample(nrow, sample_cnt);
     sample_cnt = static_cast<int>(sample_indices.size());
     std::vector<std::vector<double>> sample_values(ncol_ptr - 1);
@@ -588,7 +603,7 @@ int LGBM_DatasetCreateFromCSC(const void* col_ptr,
       OMP_LOOP_EX_END();
     }
     OMP_THROW_EX();
-    DatasetLoader loader(io_config, nullptr, 1, nullptr);
+    DatasetLoader loader(config.io_config, nullptr, 1, nullptr);
     ret.reset(loader.CostructFromSampleData(Common::Vector2Ptr<double>(sample_values).data(),
                                             Common::Vector2Ptr<int>(sample_idx).data(),
                                             static_cast<int>(sample_values.size()),
@@ -633,8 +648,11 @@ int LGBM_DatasetGetSubset(
   DatasetHandle* out) {
   API_BEGIN();
   auto param = ConfigBase::Str2Map(parameters);
-  IOConfig io_config;
-  io_config.Set(param);
+  OverallConfig config;
+  config.Set(param);
+  if (config.num_threads > 0) {
+    omp_set_num_threads(config.num_threads);
+  }
   auto full_dataset = reinterpret_cast<const Dataset*>(handle);
   CHECK(num_used_row_indices > 0);
   auto ret = std::unique_ptr<Dataset>(new Dataset(num_used_row_indices));

src/io/dataset.cpp

@@ -227,7 +227,6 @@ void Dataset::Construct(
   auto features_in_group = NoGroup(used_features);
 
   if (io_config.enable_bundle) {
-    std::chrono::duration<double, std::milli> bundling_time_;
     features_in_group = FastFeatureBundling(bin_mappers,
                                             sample_non_zero_indices, num_per_col, total_sample_cnt,
                                             used_features, io_config.max_conflict_rate,