Adding string row size iterator for row to column and column to row conversion

java/src/main/native/src/row_conversion.cu

@@ -23,6 +23,7 @@
 #include <cudf/detail/utilities/vector_factories.hpp>
 #include <cudf/lists/lists_column_device_view.cuh>
 #include <cudf/scalar/scalar_factories.hpp>
+#include <cudf/strings/strings_column_view.hpp>
 #include <cudf/table/table.hpp>
 #include <cudf/types.hpp>
 #include <cudf/utilities/bit.hpp>
@@ -34,6 +35,7 @@
 #include <rmm/exec_policy.hpp>
 #include <thrust/binary_search.h>
 #include <thrust/iterator/counting_iterator.h>
+#include <thrust/iterator/discard_iterator.h>
 #include <thrust/iterator/transform_iterator.h>
 #include <thrust/scan.h>
 #include <type_traits>
@@ -187,8 +189,82 @@ struct batch_data {
   std::vector<row_batch> row_batches; // information about each batch such as byte count
 };
 
-struct row_offset_functor {
-  row_offset_functor(size_type fixed_width_only_row_size)
+/**
+ * @brief builds row size information for tables that contain strings
+ *
+ * @param tbl table from which to compute row size information
+ * @param fixed_width_and_validity_size size of fixed-width and validity data in this table
+ * @param stream cuda stream on which to operate
+ * @return device vector of size_types of the row sizes of the table
+ */
+rmm::device_uvector<size_type> build_string_row_sizes(table_view const &tbl,
+                                                      size_type fixed_width_and_validity_size,
+                                                      rmm::cuda_stream_view stream) {
+  auto const num_rows = tbl.num_rows();
+  rmm::device_uvector<size_type> d_row_sizes(num_rows, stream);
+  thrust::uninitialized_fill(rmm::exec_policy(stream), d_row_sizes.begin(), d_row_sizes.end(), 0);
+
+  auto d_offsets_iterators = [&]() {
+    std::vector<strings_column_view::offset_iterator> offsets_iterators;
+    auto offsets_iter = thrust::make_transform_iterator(
+        tbl.begin(), [](auto const &col) -> strings_column_view::offset_iterator {
+          if (!is_fixed_width(col.type())) {
+            CUDF_EXPECTS(col.type().id() == type_id::STRING, "only string columns are supported!");
+            return strings_column_view(col).offsets_begin();
+          } else {
+            return nullptr;
+          }
+        });
+    std::copy_if(offsets_iter, offsets_iter + tbl.num_columns(),
+                 std::back_inserter(offsets_iterators),
+                 [](auto const &offset_ptr) { return offset_ptr != nullptr; });
+    return make_device_uvector_async(offsets_iterators, stream);
+  }();
+
+  auto const num_columns = static_cast<size_type>(d_offsets_iterators.size());
+
+  thrust::for_each(rmm::exec_policy(stream), thrust::make_counting_iterator(0),
+                   thrust::make_counting_iterator(num_columns * num_rows),
+                   [d_offsets_iterators = d_offsets_iterators.data(), num_columns, num_rows,
+                    d_row_sizes = d_row_sizes.data()] __device__(auto element_idx) {
+                     auto const row = element_idx % num_rows;
+                     auto const col = element_idx / num_rows;
+                     auto const val =
+                         d_offsets_iterators[col][row + 1] - d_offsets_iterators[col][row];
+                     atomicAdd(&d_row_sizes[row], val);
+                   });
+
+  // transform the row sizes to include fixed width size and alignment
+  thrust::transform(rmm::exec_policy(stream), d_row_sizes.begin(), d_row_sizes.end(),
+                    d_row_sizes.begin(), [fixed_width_and_validity_size] __device__(auto row_size) {
+                      return util::round_up_unsafe(fixed_width_and_validity_size + row_size,
+                                                   JCUDF_ROW_ALIGNMENT);
+                    });
+
+  return d_row_sizes;
+}
+
+/**
+ * @brief functor to return the offset of a row in a table with string columns
+ *
+ */
+struct string_row_offset_functor {
+  string_row_offset_functor(device_span<size_type> _d_row_offsets)
+      : d_row_offsets(_d_row_offsets){};
+
+  __device__ inline size_type operator()(int row_number, int) const {
+    return d_row_offsets[row_number];
+  }
+
+  device_span<size_type> d_row_offsets;
+};
+
+/**
+ * @brief functor to return the offset of a row in a table with only fixed-width columns
+ *
+ */
+struct fixed_width_row_offset_functor {
+  fixed_width_row_offset_functor(size_type fixed_width_only_row_size)
       : _fixed_width_only_row_size(fixed_width_only_row_size){};
 
   __device__ inline size_type operator()(int row_number, int tile_row_start) const {
@@ -542,6 +618,10 @@ __global__ void copy_to_rows(const size_type num_rows, const size_type num_colum
         auto const relative_col = el / num_fetch_rows;
         auto const relative_row = el % num_fetch_rows;
         auto const absolute_col = relative_col + fetch_tile.start_col;
+        if (input_data[absolute_col] == nullptr) {
+          // variable-width data
+          continue;
+        }
         auto const absolute_row = relative_row + fetch_tile.start_row;
         auto const col_size = col_sizes[absolute_col];
         auto const col_offset = col_offsets[absolute_col];
@@ -1194,10 +1274,8 @@ static size_type compute_column_information(iterator begin, iterator end,
   auto validity_offset = fixed_width_size_per_row;
   column_starts.push_back(validity_offset);
 
-  return util::round_up_unsafe(
-      fixed_width_size_per_row +
-          util::div_rounding_up_safe(static_cast<size_type>(std::distance(begin, end)), CHAR_BIT),
-      JCUDF_ROW_ALIGNMENT);
+  return fixed_width_size_per_row +
+         util::div_rounding_up_safe(static_cast<size_type>(std::distance(begin, end)), CHAR_BIT);
 }
 
 /**
@@ -1512,20 +1590,27 @@ void determine_tiles(std::vector<size_type> const &column_sizes,
   }
 }
 
-#endif // #if !defined(__CUDA_ARCH__) || __CUDA_ARCH__ >= 700
-
-} // namespace detail
-
-std::vector<std::unique_ptr<column>> convert_to_rows(table_view const &tbl,
-                                                     rmm::cuda_stream_view stream,
-                                                     rmm::mr::device_memory_resource *mr) {
-#if !defined(__CUDA_ARCH__) || __CUDA_ARCH__ >= 700
-  auto const num_columns = tbl.num_columns();
-  auto const num_rows = tbl.num_rows();
-
-  auto const fixed_width_only = std::all_of(
-      tbl.begin(), tbl.end(), [](column_view const &c) { return is_fixed_width(c.type()); });
-
+/**
+ * @brief convert cudf table into JCUDF row format
+ *
+ * @tparam offsetFunctor functor type for offset functor
+ * @param tbl table to convert to JCUDF row format
+ * @param batch_info information about the batches of data
+ * @param offset_functor functor that returns the starting offset of each row
+ * @param column_starts starting offset of a column in a row
+ * @param column_sizes size of each element in a column
+ * @param fixed_width_size_per_row size of fixed-width data in a row of this table
+ * @param stream stream used
+ * @param mr selected memory resource for returned data
+ * @return vector of list columns containing byte columns of the JCUDF row data
+ */
+template <typename offsetFunctor>
+std::vector<std::unique_ptr<column>>
+convert_to_rows(table_view const &tbl, batch_data &batch_info, offsetFunctor offset_functor,
+                std::vector<size_type> const &column_starts,
+                std::vector<size_type> const &column_sizes,
+                size_type const fixed_width_size_per_row, rmm::cuda_stream_view stream,
+                rmm::mr::device_memory_resource *mr) {
   int device_id;
   CUDA_TRY(cudaGetDevice(&device_id));
   int total_shmem_in_bytes;
@@ -1537,23 +1622,12 @@ std::vector<std::unique_ptr<column>> convert_to_rows(table_view const &tbl,
       sizeof(cuda::barrier<cuda::thread_scope_block>) * NUM_TILES_PER_KERNEL_LOADED;
   auto const shmem_limit_per_tile = total_shmem_in_bytes / NUM_TILES_PER_KERNEL_LOADED;
 
-  // break up the work into tiles, which are a starting and ending row/col #.
-  // this tile size is calculated based on the shared memory size available
-  // we want a single tile to fill up the entire shared memory space available
-  // for the transpose-like conversion.
-
-  // There are two different processes going on here. The GPU conversion of the data
-  // and the writing of the data into the list of byte columns that are a maximum of
-  // 2 gigs each due to offset maximum size. The GPU conversion portion has to understand
-  // this limitation because the column must own the data inside and as a result it must be
-  // a distinct allocation for that column. Copying the data into these final buffers would
-  // be prohibitively expensive, so care is taken to ensure the GPU writes to the proper buffer.
-  // The tiles are broken at the boundaries of specific rows based on the row sizes up
-  // to that point. These are row batches and they are decided first before building the
-  // tiles so the tiles can be properly cut around them.
+  auto const num_rows = tbl.num_rows();
+  auto const num_columns = tbl.num_columns();
+  auto dev_col_sizes = make_device_uvector_async(column_sizes, stream, mr);
+  auto dev_col_starts = make_device_uvector_async(column_starts, stream, mr);
 
   // Get the pointers to the input columnar data ready
-
   auto data_begin = thrust::make_transform_iterator(
       tbl.begin(), [](auto const &c) { return c.template data<int8_t>(); });
   std::vector<int8_t const *> input_data(data_begin, data_begin + tbl.num_columns());
@@ -1565,27 +1639,6 @@ std::vector<std::unique_ptr<column>> convert_to_rows(table_view const &tbl,
   auto dev_input_data = make_device_uvector_async(input_data, stream, mr);
   auto dev_input_nm = make_device_uvector_async(input_nm, stream, mr);
 
-  std::vector<size_type> column_sizes;  // byte size of each column
-  std::vector<size_type> column_starts; // offset of column inside a row including alignment
-  column_sizes.reserve(num_columns);
-  column_starts.reserve(num_columns + 1); // we add a final offset for validity data start
-
-  auto schema_column_iter =
-      thrust::make_transform_iterator(thrust::make_counting_iterator(0),
-                                      [&tbl](auto i) -> std::tuple<data_type, column_view const> {
-                                        return {tbl.column(i).type(), tbl.column(i)};
-                                      });
-
-  auto const fixed_width_size_per_row = detail::compute_column_information(
-      schema_column_iter, schema_column_iter + num_columns, column_starts, column_sizes);
-
-  auto dev_col_sizes = make_device_uvector_async(column_sizes, stream, mr);
-  auto dev_col_starts = make_device_uvector_async(column_starts, stream, mr);
-
-  // total encoded row size. This includes fixed-width data, validity, and variable-width data.
-  auto row_size_iter = thrust::make_constant_iterator<uint64_t>(fixed_width_size_per_row);
-  auto batch_info = detail::build_batches(num_rows, row_size_iter, fixed_width_only, stream, mr);
-
   // the first batch always exists unless we were sent an empty table
   auto const first_batch_size = batch_info.row_batches[0].row_count;
 
@@ -1636,8 +1689,6 @@ std::vector<std::unique_ptr<column>> convert_to_rows(table_view const &tbl,
       util::div_rounding_up_unsafe(validity_tile_infos.size(), NUM_VALIDITY_TILES_PER_KERNEL));
   dim3 validity_threads(std::min(validity_tile_infos.size() * 32, 128lu));
 
-  detail::row_offset_functor offset_functor(fixed_width_size_per_row);
-
   detail::copy_to_rows<<<blocks, threads, total_shmem_in_bytes, stream.value()>>>(
       num_rows, num_columns, shmem_limit_per_tile, gpu_tile_infos, dev_input_data.data(),
       dev_col_sizes.data(), dev_col_starts.data(), offset_functor,
@@ -1670,6 +1721,76 @@ std::vector<std::unique_ptr<column>> convert_to_rows(table_view const &tbl,
                  });
 
   return ret;
+}
+#endif // #if !defined(__CUDA_ARCH__) || __CUDA_ARCH__ >= 700
+
+} // namespace detail
+
+std::vector<std::unique_ptr<column>> convert_to_rows(table_view const &tbl,
+                                                     rmm::cuda_stream_view stream,
+                                                     rmm::mr::device_memory_resource *mr) {
+#if !defined(__CUDA_ARCH__) || __CUDA_ARCH__ >= 700
+  auto const num_columns = tbl.num_columns();
+  auto const num_rows = tbl.num_rows();
+
+  auto const fixed_width_only = std::all_of(
+      tbl.begin(), tbl.end(), [](column_view const &c) { return is_fixed_width(c.type()); });
+
+  // break up the work into tiles, which are a starting and ending row/col #.
+  // this tile size is calculated based on the shared memory size available
+  // we want a single tile to fill up the entire shared memory space available
+  // for the transpose-like conversion.
+
+  // There are two different processes going on here. The GPU conversion of the data
+  // and the writing of the data into the list of byte columns that are a maximum of
+  // 2 gigs each due to offset maximum size. The GPU conversion portion has to understand
+  // this limitation because the column must own the data inside and as a result it must be
+  // a distinct allocation for that column. Copying the data into these final buffers would
+  // be prohibitively expensive, so care is taken to ensure the GPU writes to the proper buffer.
+  // The tiles are broken at the boundaries of specific rows based on the row sizes up
+  // to that point. These are row batches and they are decided first before building the
+  // tiles so the tiles can be properly cut around them.
+
+  std::vector<size_type> column_sizes;  // byte size of each column
+  std::vector<size_type> column_starts; // offset of column inside a row including alignment
+  column_sizes.reserve(num_columns);
+  column_starts.reserve(num_columns + 1); // we add a final offset for validity data start
+
+  auto schema_column_iter =
+      thrust::make_transform_iterator(thrust::make_counting_iterator(0),
+                                      [&tbl](auto i) -> std::tuple<data_type, column_view const> {
+                                        return {tbl.column(i).type(), tbl.column(i)};
+                                      });
+
+  auto const fixed_width_size_per_row = detail::compute_column_information(
+      schema_column_iter, schema_column_iter + num_columns, column_starts, column_sizes);
+  if (fixed_width_only) {
+    // total encoded row size. This includes fixed-width data and validity only. It does not include
+    // variable-width data since it isn't copied with the fixed-width and validity kernel.
+    auto row_size_iter = thrust::make_constant_iterator<uint64_t>(
+        util::round_up_unsafe(fixed_width_size_per_row, JCUDF_ROW_ALIGNMENT));
+
+    auto batch_info = detail::build_batches(num_rows, row_size_iter, fixed_width_only, stream, mr);
+
+    detail::fixed_width_row_offset_functor offset_functor(
+        util::round_up_unsafe(fixed_width_size_per_row, JCUDF_ROW_ALIGNMENT));
+
+    return detail::convert_to_rows(tbl, batch_info, offset_functor, column_starts, column_sizes,
+                                   fixed_width_size_per_row, stream, mr);
+  } else {
+    auto row_sizes = detail::build_string_row_sizes(tbl, fixed_width_size_per_row, stream);
+
+    auto row_size_iter = cudf::detail::make_counting_transform_iterator(
+        0, detail::row_size_functor(num_rows, row_sizes.data(), 0));
+
+    auto batch_info = detail::build_batches(num_rows, row_size_iter, fixed_width_only, stream, mr);
+
+    detail::string_row_offset_functor offset_functor(batch_info.batch_row_offsets);
+
+    return detail::convert_to_rows(tbl, batch_info, offset_functor, column_starts, column_sizes,
+                                   fixed_width_size_per_row, stream, mr);
+  }
+
 #else
   CUDF_FAIL("Column to row conversion optimization requires volta or later hardware.");
   return {};
@@ -1768,8 +1889,9 @@ std::unique_ptr<table> convert_from_rows(lists_column_view const &input,
   auto iter = thrust::make_transform_iterator(thrust::make_counting_iterator(0), [&schema](auto i) {
     return std::make_tuple(schema[i], nullptr);
   });
-  auto const fixed_width_size_per_row =
-      detail::compute_column_information(iter, iter + num_columns, column_starts, column_sizes);
+  auto const fixed_width_size_per_row = util::round_up_unsafe(
+      detail::compute_column_information(iter, iter + num_columns, column_starts, column_sizes),
+      JCUDF_ROW_ALIGNMENT);
 
   // Ideally we would check that the offsets are all the same, etc. but for now
   // this is probably fine
@@ -1842,7 +1964,7 @@ std::unique_ptr<table> convert_from_rows(lists_column_view const &input,
 
   dim3 validity_threads(std::min(validity_tile_infos.size() * 32, 128lu));
 
-  detail::row_offset_functor offset_functor(fixed_width_size_per_row);
+  detail::fixed_width_row_offset_functor offset_functor(fixed_width_size_per_row);
 
   detail::copy_from_rows<<<blocks, threads, total_shmem_in_bytes, stream.value()>>>(
       num_rows, num_columns, shmem_limit_per_tile, offset_functor, gpu_batch_row_boundaries.data(),