[BUG] Hang in libcudf replace_multiple

[lithomas1]

Describe the bug
A clear and concise description of what the bug is.

libcudf hangs in replace multiple when the targets column contains an empty string.

Steps/Code to reproduce bug
Follow this guide http://matthewrocklin.com/blog/work/2018/02/28/minimal-bug-reports to craft a minimal bug report. This helps us reproduce the issue you're having and resolve the issue more quickly.

Using pylibcudf,

import pyarrow as pa
import cudf._lib.pylibcudf as plc

input_array = pa.array([
    "a",
    "b",
    "c",
    "d",
    "e",
    "f",
    "g",
    "h",
])

data = pa.array([
    "AbC",
    "de",
    "FGHI",
    "j",
    "kLm",
    "nOPq",
    "",
    "RsT",
])

print('hang starts now!')

plc.strings.replace.replace_multiple(
    plc.interop.from_arrow(input_array), plc.interop.from_arrow(data), plc.interop.from_arrow(input_array)
)

Expected behavior
A clear and concise description of what you expected to happen.

Environment overview (please complete the following information)

• Environment location: [Bare-metal, Docker, Cloud(specify cloud provider)]
• Method of cuDF install: [conda, Docker, or from source]
  • If method of install is [Docker], provide docker pull & docker run commands used

Environment details
Please run and paste the output of the cudf/print_env.sh script here, to gather any other relevant environment details

Additional context
Add any other context about the problem here.

Backtrace (sorry, I didn't have the time to figure out how to compile libcudf in debug mode, but hopefully this helps)

I got it by pressing ctrl+c in gdb after "hang starts now" is printed

#8  0x00007fff3ec70898 in cudaStreamSynchronize () from /home/coder/.conda/envs/rapids/lib/libcudart.so.12
#9  0x00007fff189a2a78 in cudf::detail::sizes_to_offsets_iterator<int*, long> thrust::cuda_cub::detail::exclusive_scan_n_impl<thrust::detail::execute_with_allocator<rmm::mr::thrust_allocator<char>, thrust::cuda_cub::execute_on_stream_base>, thrust::transform_iterator<cuda::__4::__detail::__return_type_wrapper<int, __nv_dl_wrapper_t<__nv_dl_tag<std::pair<std::unique_ptr<cudf::column, std::default_delete<cudf::column> >, long> (*)(int*, int*, rmm::cuda_stream_view, cuda::mr::__4::basic_resource_ref<(cuda::mr::__4::_AllocType)1, cuda::mr::__4::device_accessible>), &(std::pair<std::unique_ptr<cudf::column, std::default_delete<cudf::column> >, long> cudf::strings::detail::make_offsets_child_column<int*>(int*, int*, rmm::cuda_stream_view, cuda::mr::__4::basic_resource_ref<(cuda::mr::__4::_AllocType)1, cuda::mr::__4::device_accessible>)), 1u>, int*, int const> >, thrust::counting_iterator<int, thrust::use_default, thrust::use_default, thrust::use_default>, thrust::use_default, thrust::use_default>, long, cudf::detail::sizes_to_offsets_iterator<int*, long>, long, thrust::plus<void> >(thrust::cuda_cub::execution_policy<thrust::detail::execute_with_allocator<rmm::mr::thrust_allocator<char>, thrust::cuda_cub::execute_on_stream_base> >&, thrust::transform_iterator<cuda::__4::__detail::__return_type_wrapper<int, __nv_dl_wrapper_t<__nv_dl_tag<std::pair<std::unique_ptr<cudf::column, std::default_delete<cudf::column> >, long> (*)(int*, int*, rmm::cuda_stream_view, cuda::mr::__4::basic_resource_ref<(cuda::mr::__4::_AllocType)1, cuda::mr::__4::device_accessible>), &(std::pair<std::unique_ptr<cudf::column, std::default_delete<cudf::column> >, long> cudf::strings::detail::make_offsets_chil--Type <RET> for more, q to quit, c to continue without paging--
d_column<int*>(int*, int*, rmm::cuda_stream_view, cuda::mr::__4::basic_resource_ref<(cuda::mr::__4::_AllocType)1, cuda::mr::__4::device_accessible>)), 1u>, int*, int const> >, thrust::counting_iterator<int, thrust::use_default, thrust::use_default, thrust::use_default>, thrust::use_default, thrust::use_default>, long, cudf::detail::sizes_to_offsets_iterator<int*, long>, long, thrust::plus<void>) [clone .isra.0] () from /home/coder/cudf/cpp/build/conda/cuda-12.2/release/libcudf.so
#10 0x00007fff189a70d4 in auto cudf::detail::sizes_to_offsets<thrust::transform_iterator<cuda::__4::__detail::__return_type_wrapper<int, __nv_dl_wrapper_t<__nv_dl_tag<std::pair<std::unique_ptr<cudf::column, std::default_delete<cudf::column> >, long> (*)(int*, int*, rmm::cuda_stream_view, cuda::mr::__4::basic_resource_ref<(cuda::mr::__4::_AllocType)1, cuda::mr::__4::device_accessible>), &(std::pair<std::unique_ptr<cudf::column, std::default_delete<cudf::column> >, long> cudf::strings::detail::make_offsets_child_column<int*>(int*, int*, rmm::cuda_stream_view, cuda::mr::__4::basic_resource_ref<(cuda::mr::__4::_AllocType)1, cuda::mr::__4::device_accessible>)), 1u>, int*, int const> >, thrust::counting_iterator<int, thrust::use_default, thrust::use_default, thrust::use_default>, thrust::use_default, thrust::use_default>, int*>(thrust::transform_iterator<cuda::__4::__detail::__return_type_wrapper<int, __nv_dl_wrapper_t<__nv_dl_tag<std::pair<std::unique_ptr<cudf::column, std::default_delete<cudf::column> >, long> (*)(int*, int*, rmm::cuda_stream_view, cuda::mr::__4::basic_resource_ref<(cuda::mr::__4::_AllocType)1, cuda::mr::__4::device_accessible>), &(std::pair<std::unique_ptr<cudf::column, std::default_delete<cudf::column> >, long> cudf::strings::detail::make_offsets_child_column<int*>(int*, int*, rmm::cuda_stream_view, cuda::mr::__4::basic_resource_ref<(cuda::mr::__4::_AllocType)1, cuda::mr::__4::device_accessible>)), 1u>, int*, int const> >, thrust::counting_iterator<int, thrust::use_default, thrust::use_default, thrust::use_default>, thrust::use_default, thrust::use_default>, thrust::transform_iterator<cuda::__4::__detail::__return_type_wrapper<int, __nv_dl_wrapper_t<__nv_dl_tag<std::pair<std::unique_ptr<cudf::column, std::default_delete<cudf::column> >, long> (*)(int*, int*, rmm::cuda_stream_view, cuda::mr::__4::basic_resource_ref<(cuda::mr::__4::_AllocType)1, cuda::mr::__4::device_accessible>), &(std::pair<std::unique_ptr<cudf::column, std::default_delete<cudf::column> >, long> cudf::strings::detail::make_offsets_child_column<int*>(int*, int*, rmm::cuda_stream_view, cuda::mr::__4::basic_resource_ref<(cuda::mr::__4::_AllocType)1, cuda::mr::__4::device_accessible>)), 1u>, int*, int const> >, thrust::counting_iterator<int, thrust::use_default, thrust::use_default, thrust::use_default>, thrust::use_default, thrust::use_default>, int*, rmm::cuda_stream_view) () from /home/coder/cudf/cpp/build/conda/cuda-12.2/release/libcudf.so
#11 0x00007fff189abb9e in std::pair<std::unique_ptr<cudf::column, std::default_delete<cudf::column> >, long> cudf::strings::detail::make_offsets_child_column<int*>(int*, int*, rmm::cuda_stream_view, cuda::mr::__4::basic_resource_ref<(cuda::mr::__4::_AllocType)1, cuda::mr::__4::device_accessible>) () from /home/coder/cudf/cpp/build/conda/cuda-12.2/release/libcudf.so
#12 0x00007fff1a14d243 in auto cudf::strings::detail::make_strings_children<cudf::strings::detail::(anonymous namespace)::replace_multi_fn>(cudf::strings::detail::(anonymous namespace)::replace_multi_fn, int, int, rmm::cuda_stream_view, cuda::mr::__4::basic_resource_ref<(cuda::mr::__4::_AllocType)1, cuda::mr::__4::device_accessible>) () from /home/coder/cudf/cpp/build/conda/cuda-12.2/release/libcudf.so
--Type <RET> for more, q to quit, c to continue without paging--
#13 0x00007fff1a1418ef in cudf::strings::detail::(anonymous namespace)::replace_string_parallel(cudf::strings_column_view const&, cudf::strings_column_view const&, cudf::strings_column_view const&, rmm::cuda_stream_view, cuda::mr::__4::basic_resource_ref<(cuda::mr::__4::_AllocType)1, cuda::mr::__4::device_accessible>) () from /home/coder/cudf/cpp/build/conda/cuda-12.2/release/libcudf.so
#14 0x00007fff1a14536f in cudf::strings::detail::replace_multiple(cudf::strings_column_view const&, cudf::strings_column_view const&, cudf::strings_column_view const&, rmm::cuda_stream_view, cuda::mr::__4::basic_resource_ref<(cuda::mr::__4::_AllocType)1, cuda::mr::__4::device_accessible>) () from /home/coder/cudf/cpp/build/conda/cuda-12.2/release/libcudf.so
#15 0x00007fff1a14547a in cudf::strings::replace_multiple(cudf::strings_column_view const&, cudf::strings_column_view const&, cudf::strings_column_view const&, rmm::cuda_stream_view, cuda::mr::__4::basic_resource_ref<(cuda::mr::__4::_AllocType)1, cuda::mr::__4::device_accessible>)
    () from /home/coder/cudf/cpp/build/conda/cuda-12.2/release/libcudf.so

[davidwendt]

Empty targets for cudf::strings::replace_multiple are not supported.
I'll open a PR to fix the hang and update the doxygen.

[lithomas1]

Thanks for the quick fix!