[R-package] Use ALTREP system to return C++-allocated arrays (#6213)

R-package/src/lightgbm_R.cpp

@@ -11,6 +11,7 @@
 #include <LightGBM/utils/text_reader.h>
 
 #include <R_ext/Rdynload.h>
+#include <R_ext/Altrep.h>
 
 #define R_NO_REMAP
 #define R_USE_C99_IN_CXX
@@ -24,6 +25,150 @@
 #include <utility>
 #include <vector>
 #include <algorithm>
+#include <type_traits>
+
+R_altrep_class_t lgb_altrepped_char_vec;
+R_altrep_class_t lgb_altrepped_int_arr;
+R_altrep_class_t lgb_altrepped_dbl_arr;
+
+template <class T>
+void delete_cpp_array(SEXP R_ptr) {
+  T *ptr_to_cpp_obj = static_cast<T*>(R_ExternalPtrAddr(R_ptr));
+  delete[] ptr_to_cpp_obj;
+  R_ClearExternalPtr(R_ptr);
+}
+
+void delete_cpp_char_vec(SEXP R_ptr) {
+  std::vector<char> *ptr_to_cpp_obj = static_cast<std::vector<char>*>(R_ExternalPtrAddr(R_ptr));
+  delete ptr_to_cpp_obj;
+  R_ClearExternalPtr(R_ptr);
+}
+
+// Note: MSVC has issues with Altrep classes, so they are disabled for it.
+// See: https://github.com/microsoft/LightGBM/pull/6213#issuecomment-2111025768
+#ifdef _MSC_VER
+#  define LGB_NO_ALTREP
+#endif
+
+#ifndef LGB_NO_ALTREP
+SEXP make_altrepped_raw_vec(void *void_ptr) {
+  std::unique_ptr<std::vector<char>> *ptr_to_cpp_vec = static_cast<std::unique_ptr<std::vector<char>>*>(void_ptr);
+  SEXP R_ptr = PROTECT(R_MakeExternalPtr(nullptr, R_NilValue, R_NilValue));
+  SEXP R_raw = PROTECT(R_new_altrep(lgb_altrepped_char_vec, R_NilValue, R_NilValue));
+
+  R_SetExternalPtrAddr(R_ptr, ptr_to_cpp_vec->get());
+  R_RegisterCFinalizerEx(R_ptr, delete_cpp_char_vec, TRUE);
+  ptr_to_cpp_vec->release();
+
+  R_set_altrep_data1(R_raw, R_ptr);
+  UNPROTECT(2);
+  return R_raw;
+}
+#else
+SEXP make_r_raw_vec(void *void_ptr) {
+  std::unique_ptr<std::vector<char>> *ptr_to_cpp_vec = static_cast<std::unique_ptr<std::vector<char>>*>(void_ptr);
+  R_xlen_t len = ptr_to_cpp_vec->get()->size();
+  SEXP out = PROTECT(Rf_allocVector(RAWSXP, len));
+  std::copy(ptr_to_cpp_vec->get()->begin(), ptr_to_cpp_vec->get()->end(), reinterpret_cast<char*>(RAW(out)));
+  UNPROTECT(1);
+  return out;
+}
+#define make_altrepped_raw_vec make_r_raw_vec
+#endif
+
+std::vector<char>* get_ptr_from_altrepped_raw(SEXP R_raw) {
+  return static_cast<std::vector<char>*>(R_ExternalPtrAddr(R_altrep_data1(R_raw)));
+}
+
+R_xlen_t get_altrepped_raw_len(SEXP R_raw) {
+  return get_ptr_from_altrepped_raw(R_raw)->size();
+}
+
+const void* get_altrepped_raw_dataptr_or_null(SEXP R_raw) {
+  return get_ptr_from_altrepped_raw(R_raw)->data();
+}
+
+void* get_altrepped_raw_dataptr(SEXP R_raw, Rboolean writeable) {
+  return get_ptr_from_altrepped_raw(R_raw)->data();
+}
+
+#ifndef LGB_NO_ALTREP
+template <class T>
+R_altrep_class_t get_altrep_class_for_type() {
+  if (std::is_same<T, double>::value) {
+    return lgb_altrepped_dbl_arr;
+  } else {
+    return lgb_altrepped_int_arr;
+  }
+}
+#else
+template <class T>
+SEXPTYPE get_sexptype_class_for_type() {
+  if (std::is_same<T, double>::value) {
+    return REALSXP;
+  } else {
+    return INTSXP;
+  }
+}
+
+template <class T>
+T* get_r_vec_ptr(SEXP x) {
+  if (std::is_same<T, double>::value) {
+    return static_cast<T*>(static_cast<void*>(REAL(x)));
+  } else {
+    return static_cast<T*>(static_cast<void*>(INTEGER(x)));
+  }
+}
+#endif
+
+template <class T>
+struct arr_and_len {
+  T *arr;
+  int64_t len;
+};
+
+#ifndef LGB_NO_ALTREP
+template <class T>
+SEXP make_altrepped_vec_from_arr(void *void_ptr) {
+  T *arr = static_cast<arr_and_len<T>*>(void_ptr)->arr;
+  uint64_t len = static_cast<arr_and_len<T>*>(void_ptr)->len;
+  SEXP R_ptr = PROTECT(R_MakeExternalPtr(nullptr, R_NilValue, R_NilValue));
+  SEXP R_len = PROTECT(Rf_allocVector(REALSXP, 1));
+  SEXP R_vec = PROTECT(R_new_altrep(get_altrep_class_for_type<T>(), R_NilValue, R_NilValue));
+
+  REAL(R_len)[0] = static_cast<double>(len);
+  R_SetExternalPtrAddr(R_ptr, arr);
+  R_RegisterCFinalizerEx(R_ptr, delete_cpp_array<T>, TRUE);
+
+  R_set_altrep_data1(R_vec, R_ptr);
+  R_set_altrep_data2(R_vec, R_len);
+  UNPROTECT(3);
+  return R_vec;
+}
+#else
+template <class T>
+SEXP make_R_vec_from_arr(void *void_ptr) {
+  T *arr = static_cast<arr_and_len<T>*>(void_ptr)->arr;
+  uint64_t len = static_cast<arr_and_len<T>*>(void_ptr)->len;
+  SEXP out = PROTECT(Rf_allocVector(get_sexptype_class_for_type<T>(), len));
+  std::copy(arr, arr + len, get_r_vec_ptr<T>(out));
+  UNPROTECT(1);
+  return out;
+}
+#define make_altrepped_vec_from_arr make_R_vec_from_arr
+#endif
+
+R_xlen_t get_altrepped_vec_len(SEXP R_vec) {
+  return static_cast<R_xlen_t>(Rf_asReal(R_altrep_data2(R_vec)));
+}
+
+const void* get_altrepped_vec_dataptr_or_null(SEXP R_vec) {
+  return R_ExternalPtrAddr(R_altrep_data1(R_vec));
+}
+
+void* get_altrepped_vec_dataptr(SEXP R_vec, Rboolean writeable) {
+  return R_ExternalPtrAddr(R_altrep_data1(R_vec));
+}
 
 #define COL_MAJOR (0)
 
@@ -964,8 +1109,6 @@ struct SparseOutputPointers {
   void* indptr;
   int32_t* indices;
   void* data;
-  int indptr_type;
-  int data_type;
   SparseOutputPointers(void* indptr, int32_t* indices, void* data)
   : indptr(indptr), indices(indices), data(data) {}
 };
@@ -1015,15 +1158,26 @@ SEXP LGBM_BoosterPredictSparseOutput_R(SEXP handle,
     &delete_SparseOutputPointers
   };
 
-  SEXP out_indptr_R = safe_R_int(out_len[1], &cont_token);
+  arr_and_len<int> indptr_str{static_cast<int*>(out_indptr), out_len[1]};
-  SET_VECTOR_ELT(out, 0, out_indptr_R);
+  SET_VECTOR_ELT(
-  SEXP out_indices_R = safe_R_int(out_len[0], &cont_token);
+    out, 0,
-  SET_VECTOR_ELT(out, 1, out_indices_R);
+    R_UnwindProtect(make_altrepped_vec_from_arr<int>,
-  SEXP out_data_R = safe_R_real(out_len[0], &cont_token);
+      static_cast<void*>(&indptr_str), throw_R_memerr, &cont_token, cont_token));
-  SET_VECTOR_ELT(out, 2, out_data_R);
+  pointers_struct->indptr = nullptr;
-  std::memcpy(INTEGER(out_indptr_R), out_indptr, out_len[1]*sizeof(int));
+
-  std::memcpy(INTEGER(out_indices_R), out_indices, out_len[0]*sizeof(int));
+  arr_and_len<int> indices_str{static_cast<int*>(out_indices), out_len[0]};
-  std::memcpy(REAL(out_data_R), out_data, out_len[0]*sizeof(double));
+  SET_VECTOR_ELT(
+    out, 1,
+    R_UnwindProtect(make_altrepped_vec_from_arr<int>,
+      static_cast<void*>(&indices_str), throw_R_memerr, &cont_token, cont_token));
+  pointers_struct->indices = nullptr;
+
+  arr_and_len<double> data_str{static_cast<double*>(out_data), out_len[0]};
+  SET_VECTOR_ELT(
+    out, 2,
+    R_UnwindProtect(make_altrepped_vec_from_arr<double>,
+      static_cast<void*>(&data_str), throw_R_memerr, &cont_token, cont_token));
+  pointers_struct->data = nullptr;
 
   UNPROTECT(3);
   return out;
@@ -1104,6 +1258,34 @@ SEXP LGBM_BoosterSaveModel_R(SEXP handle,
   R_API_END();
 }
 
+// Note: for some reason, MSVC crashes when an error is thrown here
+// if the buffer variable is defined as 'std::unique_ptr<std::vector<char>>',
+// but not if it is defined as '<std::vector<char>'.
+#ifndef _MSC_VER
+SEXP LGBM_BoosterSaveModelToString_R(SEXP handle,
+  SEXP num_iteration,
+  SEXP feature_importance_type,
+  SEXP start_iteration) {
+  SEXP cont_token = PROTECT(R_MakeUnwindCont());
+  R_API_BEGIN();
+  _AssertBoosterHandleNotNull(handle);
+  int64_t out_len = 0;
+  int64_t buf_len = 1024 * 1024;
+  int num_iter = Rf_asInteger(num_iteration);
+  int start_iter = Rf_asInteger(start_iteration);
+  int importance_type = Rf_asInteger(feature_importance_type);
+  std::unique_ptr<std::vector<char>> inner_char_buf(new std::vector<char>(buf_len));
+  CHECK_CALL(LGBM_BoosterSaveModelToString(R_ExternalPtrAddr(handle), start_iter, num_iter, importance_type, buf_len, &out_len, inner_char_buf->data()));
+  inner_char_buf->resize(out_len);
+  if (out_len > buf_len) {
+    CHECK_CALL(LGBM_BoosterSaveModelToString(R_ExternalPtrAddr(handle), start_iter, num_iter, importance_type, out_len, &out_len, inner_char_buf->data()));
+  }
+  SEXP out = R_UnwindProtect(make_altrepped_raw_vec, &inner_char_buf, throw_R_memerr, &cont_token, cont_token);
+  UNPROTECT(1);
+  return out;
+  R_API_END();
+}
+#else
 SEXP LGBM_BoosterSaveModelToString_R(SEXP handle,
   SEXP num_iteration,
   SEXP feature_importance_type,
@@ -1129,6 +1311,7 @@ SEXP LGBM_BoosterSaveModelToString_R(SEXP handle,
   return model_str;
   R_API_END();
 }
+#endif
 
 SEXP LGBM_BoosterDumpModel_R(SEXP handle,
   SEXP num_iteration,
@@ -1281,4 +1464,21 @@ LIGHTGBM_C_EXPORT void R_init_lightgbm(DllInfo *dll);
 void R_init_lightgbm(DllInfo *dll) {
   R_registerRoutines(dll, NULL, CallEntries, NULL, NULL);
   R_useDynamicSymbols(dll, FALSE);
+
+#ifndef LGB_NO_ALTREP
+  lgb_altrepped_char_vec = R_make_altraw_class("lgb_altrepped_char_vec", "lightgbm", dll);
+  R_set_altrep_Length_method(lgb_altrepped_char_vec, get_altrepped_raw_len);
+  R_set_altvec_Dataptr_method(lgb_altrepped_char_vec, get_altrepped_raw_dataptr);
+  R_set_altvec_Dataptr_or_null_method(lgb_altrepped_char_vec, get_altrepped_raw_dataptr_or_null);
+
+  lgb_altrepped_int_arr = R_make_altinteger_class("lgb_altrepped_int_arr", "lightgbm", dll);
+  R_set_altrep_Length_method(lgb_altrepped_int_arr, get_altrepped_vec_len);
+  R_set_altvec_Dataptr_method(lgb_altrepped_int_arr, get_altrepped_vec_dataptr);
+  R_set_altvec_Dataptr_or_null_method(lgb_altrepped_int_arr, get_altrepped_vec_dataptr_or_null);
+
+  lgb_altrepped_dbl_arr = R_make_altreal_class("lgb_altrepped_dbl_arr", "lightgbm", dll);
+  R_set_altrep_Length_method(lgb_altrepped_dbl_arr, get_altrepped_vec_len);
+  R_set_altvec_Dataptr_method(lgb_altrepped_dbl_arr, get_altrepped_vec_dataptr);
+  R_set_altvec_Dataptr_or_null_method(lgb_altrepped_dbl_arr, get_altrepped_vec_dataptr_or_null);
+#endif
 }