Summary

The Thrust 2.0.0 major release adds a dependency on libcu++ and contains several breaking changes. These include new diagnostics when inspecting device-only lambdas from the host, removal of the cub symlink in the Thrust repository root, and removal of the deprecated THRUST_*_BACKEND macros. It also includes several minor bugfixes and cleanups.

Breaking Changes

• [#1605]: Add libcu++ dependency.
  • A suitable version of libcu++ is provided through the ${THRUST_ROOT}/dependencies/libcudacxx/ submodule.
  • Non-cmake users may need to add the libcu++ include path to their builds (-I ${THRUST_ROOT}/dependencies/libcudacxx/include/).
  • The Thrust CMake packages have been updated to add this include path.
• [#1605]: The following macros are no longer defined by default. They can be re-enabled by defining THRUST_PROVIDE_LEGACY_ARCH_MACROS. These will be removed completely in a future release.
  • THRUST_IS_HOST_CODE: Replace with NV_IF_TARGET.
  • THRUST_IS_DEVICE_CODE: Replace with NV_IF_TARGET.
  • THRUST_INCLUDE_HOST_CODE: Replace with NV_IF_TARGET.
  • THRUST_INCLUDE_DEVICE_CODE: Replace with NV_IF_TARGET.
  • THRUST_DEVICE_CODE: Replace with NV_IF_TARGET.
• [#1661]: Thrust’s CUDA Runtime support macros have been updated to support NV_IF_TARGET. They are now defined consistently across all host/device compilation passes. This should not affect most usages of these macros, but may require changes for some edge cases.
  • THRUST_RUNTIME_FUNCTION: Execution space annotations for functions that invoke CUDA Runtime APIs.
    • Old behavior:
      • RDC enabled: Defined to __host__ __device__
      • RDC not enabled:
        • NVCC host pass: Defined to __host__ __device__
        • NVCC device pass: Defined to __host__
    • New behavior:
      • RDC enabled: Defined to __host__ __device__
      • RDC not enabled: Defined to __host__
  • __THRUST_HAS_CUDART__: No change in behavior, but no longer used in Thrust. Provided for legacy support only. Legacy behavior:
    • RDC enabled: Defined to 1.
    • RDC not enabled:
      • NVCC host pass: Defined to 1.
      • NVCC device pass: Defined to 0.
  • THRUST_RDC_ENABLED: New macro, may be combined with NV_IF_TARGET to replace most usages of __THRUST_HAS_CUDART__. Behavior:
    • RDC enabled: Macro is defined.
    • RDC not enabled: Macro is not defined.
• [#1701]: Remove the cub symlink from the root of the Thrust repository.
  • This symlink caused issues in certain build environments (e.g. NVIDIA/thrust#1328).
  • Builds that relied on this symlink will need to add the full CUB include path (-I ${THRUST_ROOT}/dependencies/cub).
  • CMake builds that use the Thrust packages via CPM, add_subdirectory, or find_package are not affected.
• [#1760]: A compile-time error is now emitted when a __device__-only lambda’s return type is queried from host code (requires libcu++ ≥ 1.9.0).
  • Due to limitations in the CUDA programming model, the result of this query is unreliable, and will silently return an incorrect result. This leads to difficult to debug errors.
  • When using libcu++ 1.9.0, an error will be emitted with information about work-arounds:
    • Use a named function object with a __device__-only implementation of operator().
    • Use a __host__ __device__ lambda.
    • Use cuda::proclaim_return_type (Added in libcu++ 1.9.0)
• [#1761]: Removed support for deprecated THRUST_DEVICE_BACKEND and THRUST_HOST_BACKEND macros. The THRUST_DEVICE_SYSTEM and THRUST_HOST_SYSTEM macros should be used instead.

Bug Fixes

• [#1605]: Fix some execution space warnings in the allocator library.
• [#1683]: Fix bug in iterator_category_to_traversal metafunctions.
• [#1715]: Add missing __thrust_exec_check_disable__ annotation to thrust::make_zip_function. Thanks to @mfbalin for this contribution.
• [#1722]: Remove CUDA-specific error handler from code that may be executed on non-CUDA backends. Thanks to @dkolsen-pgi for this contribution.
• [#1756]: Fix copy_if for output iterators that don’t support copy assignment. Thanks for @mfbalin for this contribution.

Other Enhancements

• [#1605]: Removed special case code for unsupported CUDA architectures.
• [#1605]: Replace several usages of __CUDA_ARCH__ with <nv/target> to handle host/device code divergence.
• [#1752]: Remove a leftover merge conflict from a documentation file. Thanks to @tabedzki for this contribution.