Row accessor

The row_accessor class provides a read-only access to the rows of the table as contiguous homogeneous array.

Usage example

#include <CL/sycl.hpp>
#include <iostream>

#include "oneapi/dal/table/homogen.hpp"
#include "oneapi/dal/table/row_accessor.hpp"

using namespace oneapi;

int main() {
   sycl::queue queue { sycl::default_selector() };

   constexpr float host_data[] = {
      1.0f, 1.5f, 2.0f,
      2.1f, 3.2f, 3.7f,
      4.0f, 4.9f, 5.0f,
      5.2f, 6.1f, 6.2f
   };

   constexpr std::int64_t row_count = 4;
   constexpr std::int64_t column_count = 3;

   auto shared_data = sycl::malloc_shared<float>(row_count * column_count, queue);
   auto event = queue.memcpy(shared_data, host_data, sizeof(float) * row_count * column_count);
   auto t = dal::homogen_table::wrap(queue, data, row_count, column_count, { event });

   // Accessing second and third rows of the table
   dal::row_accessor<const float> acc { t };

   auto block = acc.pull(queue, {1, 3});
   for(std::int64_t i = 0; i < block.get_count(); i++) {
      std::cout << block[i] << ", ";
   }
   std::cout << std::endl;

   sycl::free(shared_data, queue);
   return 0;
}

Programming interface

All types and functions in this section shall be declared in the oneapi::dal namespace and be available via inclusion of the oneapi/dal/table/row_accessor.hpp header file.

template <typename Data>
class row_accessor {
public:
    using data_t = std::remove_const_t<Data>;

public:
    row_accessor(const table& obj);

    array<data_t> pull(sycl::queue& queue,
                       const range& rows             = { 0, -1 },
                       const sycl::usm::alloc& alloc = sycl::usm::alloc::shared) const;

    Data* pull(sycl::queue& queue,
            array<data_t>& block,
            const range& rows             = { 0, -1 },
            const sycl::usm::alloc& alloc = sycl::usm::alloc::shared) const;
};

template<typename Data>
class row_accessor

Template Parameters

Data – The type of data values in blocks returned by the accessor. Shall be const-qualified for read-only access. An accessor shall support at least float, double, and std::int32_t types of \(Data\).

Constructors

row_accessor(const table &obj)

Creates a new read-only accessor object from the table. The check that the accessor supports the table kind of \(obj\) shall be performed. The reference to the \(obj\) table shall be stored within the accessor to obtain data from the table.

Public Methods

array<data_t> pull(sycl::queue &queue, const range &rows = {0, -1}, const sycl::usm::alloc &alloc = sycl::usm::alloc::shared) const

Provides access to the rows of the table. The method shall return an array that directly points to the memory within the table if it is possible. In that case, the array shall refer to the memory as to immutable data. Otherwise, the new memory block shall be allocated, the data from the table rows shall be converted and copied into this block. The array shall refer to the block as to mutable data.

Parameters

• queue – The SYCL* queue object.

• rows – The range of rows that data shall be returned from the accessor.

• alloc – The requested kind of USM in the returned block.

Preconditions

rows are within the range of [0, obj.row_count).

Data *pull(sycl::queue &queue, array<data_t> &block, const range &rows = {0, -1}, const sycl::usm::alloc &alloc = sycl::usm::alloc::shared) const

Provides access to the rows of the table. The method shall return the block.data pointer.

Parameters

• queue – The SYCL* queue object.

• block – The block which memory is reused (if it is possible) to obtain the data from the table. The block memory shall be reset either when its size is not big enough, or when it contains immutable data, or when direct memory from the table can be used. If the block is reset to use a direct memory pointer from the object, it shall refer to this pointer as to immutable memory block.

• rows – The range of rows that data shall be returned from the accessor.

• alloc – The requested kind of USM in the returned block.

Preconditions

rows are within the range of [0, obj.row_count).