andishgar commented on issue #46578:
URL: https://github.com/apache/arrow/issues/46578#issuecomment-2915664149
@kou, the example below demonstrates a practical case where one buffer is
viewed and the other is copied (when cpu_memory_manager_ is passed). I will
send a pull request soon to clarify this further
```c++
TEST_F(TestArrayDataStatisticsViewOrCopyTO,
CudaBufferAndCudaBufferPointToCpuMemory) {
ASSERT_OK_AND_ASSIGN(auto bitmap_buffer,
GenerateGPUBitmapBufferPointToCpuMemory(10));
ASSERT_OK_AND_ASSIGN(auto data_buffer, GenerateGPUtDataBuffer(
{1, 2, 3, 4, 5, 6, 7, 8, 9,
10}));
auto array_data = ArrayData::Make(int32(), 10, {bitmap_buffer,
data_buffer});
auto statistics = std::make_shared<ArrayStatistics>();
statistics->max = 10;
array_data->statistics = statistics;
array_data->null_count = 4;
// Why does the assertion below fail?
// ASSERT_TRUE(is_valid_as_array(array_data));
{
// Since it's not possible to get a host pointer from data_buffer,
//data_buffer is copied. (bitmap_buffer is viewed)
ASSERT_OK_AND_ASSIGN(auto copied_array_data,
array_data->ViewOrCopyTo(cpu_memory_manager_));
ASSERT_FALSE(is_statistics_viewed(array_data, copied_array_data));
}
{
// Despite using the same memory manager, data_buffer is still being
copied.
// Should we consider this a bug?
ASSERT_OK_AND_ASSIGN(auto copied_array_data,
array_data->ViewOrCopyTo(cuda_memory_manager_));
ASSERT_FALSE(is_statistics_viewed(array_data, copied_array_data));
}
{
// Since neither the buffer nor the 'to' memory manager belong to the
CPU,
// the buffers are copied.
ASSERT_OK_AND_ASSIGN(auto copied_array_data,
array_data->ViewOrCopyTo(my_cuda_memory_manager));
ASSERT_FALSE(is_statistics_viewed(array_data, copied_array_data));
}
}
```
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