switch to C++20 only

- remove support for C++17 - increase required CMake version to 3.25+ - remove `boost::atomic_ref usage` - update documention
psychocoderHPC · Sep 30, 2024 · bbf6271 · bbf6271
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diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
@@ -61,7 +61,7 @@ env:
   ALPAKA_CI_ONEAPI_VERSION: 2024.0
   ALPAKA_CI_TBB_VERSION: 2021.10.0
   ALPAKA_CI_RUN_TESTS: ON
-  alpaka_CXX_STANDARD: 17
+  alpaka_CXX_STANDARD: 20
   alpaka_ACC_CPU_B_SEQ_T_SEQ_ENABLE: ON
   alpaka_ACC_CPU_B_SEQ_T_THREADS_ENABLE: ON
   alpaka_ACC_CPU_B_TBB_T_SEQ_ENABLE: ON

diff --git a/.zenodo.json b/.zenodo.json
@@ -1,6 +1,6 @@
 {
   "title": "alpaka: Abstraction Library for Parallel Kernel Acceleration",
-  "description": "The alpaka library is a header-only C++17 abstraction library for accelerator development. Its aim is to provide performance portability across accelerators through the abstraction (not hiding!) of the underlying levels of parallelism.",
+  "description": "The alpaka library is a header-only C++20 abstraction library for accelerator development. Its aim is to provide performance portability across accelerators through the abstraction (not hiding!) of the underlying levels of parallelism.",
   "creators": [
     {
       "name": "Bocci, Andrea",

diff --git a/CMakeLists.txt b/CMakeLists.txt
@@ -6,7 +6,7 @@
 ################################################################################
 # Required CMake version
 
-cmake_minimum_required(VERSION 3.22)
+cmake_minimum_required(VERSION 3.25)
 
 cmake_policy(SET CMP0091 NEW)
 
@@ -25,7 +25,7 @@ string(REGEX MATCH "([0-9]+)" alpaka_VERSION_PATCH  ${alpaka_VERSION_PATCH_HPP})
 set(PACKAGE_VERSION "${alpaka_VERSION_MAJOR}.${alpaka_VERSION_MINOR}.${alpaka_VERSION_PATCH}")
 
 project(alpaka VERSION      ${alpaka_VERSION_MAJOR}.${alpaka_VERSION_MINOR}.${alpaka_VERSION_PATCH}
-               DESCRIPTION  "The alpaka library is a header-only C++17 abstraction library for accelerator development."
+               DESCRIPTION  "The alpaka library is a header-only C++20 abstraction library for accelerator development."
                HOMEPAGE_URL "https://github.com/alpaka-group/alpaka"
                LANGUAGES    CXX)
 

diff --git a/README.md b/README.md
@@ -11,7 +11,7 @@
 
 ![alpaka](docs/logo/alpaka_401x135.png)
 
-The **alpaka** library is a header-only C++17 abstraction library for accelerator development.
+The **alpaka** library is a header-only C++20 abstraction library for accelerator development.
 
 Its aim is to provide performance portability across accelerators through the abstraction (not hiding!) of the underlying levels of parallelism.
 
@@ -49,21 +49,21 @@ The [source code documentation](https://alpaka-group.github.io/alpaka/) is gener
 Accelerator Back-ends
 ---------------------
 
-| Accelerator Back-end   | Lib/API                                                 | Devices                | Execution strategy grid-blocks     | Execution strategy block-threads     |
-|------------------------|---------------------------------------------------------|------------------------|------------------------------------|--------------------------------------|
+| Accelerator Back-end   | Lib/API                                                 | Devices               | Execution strategy grid-blocks     | Execution strategy block-threads     |
+|------------------------|---------------------------------------------------------|-----------------------|------------------------------------|--------------------------------------|
 | Serial                 | n/a                                                     | Host CPU (single core) | sequential                         | sequential (only 1 thread per block) |
-| OpenMP 2.0+ blocks     | OpenMP 2.0+                                             | Host CPU (multi core)  | parallel (preemptive multitasking) | sequential (only 1 thread per block) |
-| OpenMP 2.0+ threads    | OpenMP 2.0+                                             | Host CPU (multi core)  | sequential                         | parallel (preemptive multitasking)   |
-| std::thread            | std::thread                                             | Host CPU (multi core)  | sequential                         | parallel (preemptive multitasking)   |
-| TBB                    | TBB 2.2+                                                | Host CPU (multi core)  | parallel (preemptive multitasking) | sequential (only 1 thread per block) |
-| CUDA                   | CUDA 9.0+                                               | NVIDIA GPUs            | parallel (undefined)               | parallel (lock-step within warps)    |
-| HIP(clang)             | [HIP 5.1+](https://github.com/ROCm-Developer-Tools/HIP) | AMD GPUs               | parallel (undefined)               | parallel (lock-step within warps)    |
+| OpenMP 2.0+ blocks     | OpenMP 2.0+                                             | Host CPU (multi core) | parallel (preemptive multitasking) | sequential (only 1 thread per block) |
+| OpenMP 2.0+ threads    | OpenMP 2.0+                                             | Host CPU (multi core) | sequential                         | parallel (preemptive multitasking)   |
+| std::thread            | std::thread                                             | Host CPU (multi core) | sequential                         | parallel (preemptive multitasking)   |
+| TBB                    | TBB 2.2+                                                | Host CPU (multi core) | parallel (preemptive multitasking) | sequential (only 1 thread per block) |
+| CUDA                   | CUDA 12.0+                                              | NVIDIA GPUs           | parallel (undefined)               | parallel (lock-step within warps)    |
+| HIP(clang)             | [HIP 6.0+](https://github.com/ROCm-Developer-Tools/HIP) | AMD GPUs              | parallel (undefined)               | parallel (lock-step within warps)    |
 
 
 Supported Compilers
 -------------------
 
-This library uses C++17 (or newer when available).
+This library uses C++20 (or newer when available).
 
 | Accelerator Back-end | gcc 9.5 (Linux)                           | gcc 10.4 / 11.1 (Linux)                   | gcc 12.3 (Linux)                      | gcc 13.1 (Linux)                      | clang 9 (Linux)                           | clang 10/11 (Linux)                             | clang 12 (Linux)                          | clang 13 (Linux)                      | clang 14 (Linux)                      | clang 15 (Linux)                      | clang 16 (Linux)                      | clang 17 (Linux)                      | clang 18 (Linux)                      | clang 19 (Linux)   | icpx 2024.2 (Linux)     | Xcode 13.2.1 / 14.2 / 14.3.1 (macOS) | Visual Studio 2022 (Windows) |
 |----------------------|-------------------------------------------|-------------------------------------------|---------------------------------------|---------------------------------------|-------------------------------------------|-------------------------------------------------|-------------------------------------------|---------------------------------------|---------------------------------------|---------------------------------------|---------------------------------------|---------------------------------------|---------------------------------------|--------------------|-------------------------|--------------------------------------|------------------------------|

diff --git a/benchmarks/CMakeLists.txt b/benchmarks/CMakeLists.txt
@@ -7,7 +7,7 @@
 # Required CMake version.
 ################################################################################
 
-cmake_minimum_required(VERSION 3.22)
+cmake_minimum_required(VERSION 3.25)
 
 project("alpakaBenchmarks" LANGUAGES CXX)
 

diff --git a/benchmarks/babelstream/CMakeLists.txt b/benchmarks/babelstream/CMakeLists.txt
@@ -3,7 +3,7 @@
 # SPDX-License-Identifier: ISC
 #
 
-cmake_minimum_required(VERSION 3.22)
+cmake_minimum_required(VERSION 3.25)
 set_property(GLOBAL PROPERTY USE_FOLDERS ON)
 
 project(babelstream LANGUAGES CXX)

diff --git a/cmake/alpakaCommon.cmake b/cmake/alpakaCommon.cmake
@@ -114,14 +114,14 @@ endif()
 set(alpaka_DEBUG "0" CACHE STRING "Debug level")
 set_property(CACHE alpaka_DEBUG PROPERTY STRINGS "0;1;2")
 
-set(alpaka_CXX_STANDARD_DEFAULT "17")
+set(alpaka_CXX_STANDARD_DEFAULT "20")
 # Check whether alpaka_CXX_STANDARD has already been defined as a non-cached variable.
 if(DEFINED alpaka_CXX_STANDARD)
     set(alpaka_CXX_STANDARD_DEFAULT ${alpaka_CXX_STANDARD})
 endif()
 
 set(alpaka_CXX_STANDARD ${alpaka_CXX_STANDARD_DEFAULT} CACHE STRING "C++ standard version")
-set_property(CACHE alpaka_CXX_STANDARD PROPERTY STRINGS "17;20")
+set_property(CACHE alpaka_CXX_STANDARD PROPERTY STRINGS "20")
 
 if(NOT TARGET alpaka)
     add_library(alpaka INTERFACE)
@@ -219,41 +219,6 @@ find_package(Boost ${_alpaka_BOOST_MIN_VER} REQUIRED
 
 target_link_libraries(alpaka INTERFACE Boost::headers)
 
-if(alpaka_ACC_CPU_B_SEQ_T_SEQ_ENABLE OR
-   alpaka_ACC_CPU_B_SEQ_T_THREADS_ENABLE OR
-   alpaka_ACC_CPU_B_TBB_T_SEQ_ENABLE OR
-   alpaka_ACC_CPU_B_OMP2_T_SEQ_ENABLE OR
-   alpaka_ACC_CPU_B_SEQ_T_OMP2_ENABLE)
-
-    if(NOT alpaka_ACC_CPU_DISABLE_ATOMIC_REF)
-        # Check for C++20 std::atomic_ref first
-        if(${alpaka_CXX_STANDARD} VERSION_GREATER_EQUAL "20")
-            try_compile(alpaka_HAS_STD_ATOMIC_REF # Result stored here
-                        "${PROJECT_BINARY_DIR}/alpakaFeatureTests" # Binary directory for output file
-                        SOURCES "${_alpaka_FEATURE_TESTS_DIR}/StdAtomicRef.cpp" # Source file
-                        CXX_STANDARD 20
-                        CXX_STANDARD_REQUIRED TRUE
-                        CXX_EXTENSIONS FALSE)
-            if(alpaka_HAS_STD_ATOMIC_REF AND (NOT alpaka_ACC_CPU_DISABLE_ATOMIC_REF))
-                message(STATUS "std::atomic_ref<T> found")
-                target_compile_definitions(alpaka INTERFACE ALPAKA_HAS_STD_ATOMIC_REF)
-            else()
-                message(STATUS "std::atomic_ref<T> NOT found")
-            endif()
-        endif()
-
-        if(Boost_ATOMIC_FOUND AND (NOT alpaka_HAS_STD_ATOMIC_REF))
-            message(STATUS "boost::atomic_ref<T> found")
-            target_link_libraries(alpaka INTERFACE Boost::atomic)
-        endif()
-    endif()
-
-    if(alpaka_ACC_CPU_DISABLE_ATOMIC_REF OR ((NOT alpaka_HAS_STD_ATOMIC_REF) AND (NOT Boost_ATOMIC_FOUND)))
-        message(STATUS "atomic_ref<T> was not found or manually disabled. Falling back to lock-based CPU atomics.")
-        target_compile_definitions(alpaka INTERFACE ALPAKA_DISABLE_ATOMIC_ATOMICREF)
-    endif()
-endif()
-
 if(${alpaka_DEBUG} GREATER 1)
     message(STATUS "Boost in:")
     cmake_print_variables(BOOST_ROOT)
@@ -468,10 +433,6 @@ if(alpaka_ACC_GPU_CUDA_ENABLE)
         elseif(CMAKE_CUDA_COMPILER_ID STREQUAL "NVIDIA")
             message(STATUS "nvcc is used as CUDA compiler")
 
-            if(alpaka_CXX_STANDARD GREATER_EQUAL 20 AND CMAKE_VERSION VERSION_LESS "3.25.0")
-                message(FATAL_ERROR "CMake 3.24 and older does not support C++20 for nvcc")
-            endif()
-
             # nvcc sets no linux/__linux macros on OpenPOWER linux
             # nvidia bug id: 2448610
             if(CMAKE_SYSTEM_NAME STREQUAL "Linux")
@@ -483,7 +444,7 @@ if(alpaka_ACC_GPU_CUDA_ENABLE)
             if(alpaka_CUDA_EXPT_EXTENDED_LAMBDA STREQUAL ON)
                 alpaka_set_compiler_options(DEVICE target alpaka "$<$<COMPILE_LANGUAGE:CUDA>:SHELL:--extended-lambda>")
             endif()
-            # This is mandatory because with C++17 many standard library functions we rely on are constexpr (std::min, std::multiplies, ...)
+            # This is mandatory because with C++20 many standard library functions we rely on are constexpr (std::min, std::multiplies, ...)
             alpaka_set_compiler_options(DEVICE target alpaka "$<$<COMPILE_LANGUAGE:CUDA>:SHELL:--expt-relaxed-constexpr>")
 
             # CMake automatically sets '-g' in debug mode

diff --git a/docs/source/basic/example.rst b/docs/source/basic/example.rst
@@ -26,7 +26,7 @@ The following example shows a minimal example of a ``CMakeLists.txt`` that uses
 .. code-block:: cmake
    :caption: CMakeLists.txt
 
-   cmake_minimum_required(VERSION 3.22)
+   cmake_minimum_required(VERSION 3.25)
    project("myexample" CXX)
 
    find_package(alpaka REQUIRED)
@@ -55,7 +55,7 @@ The ``add_subdirectory`` method does not require alpaka to be installed. Instead
 .. code-block:: cmake
    :caption: CMakeLists.txt
 
-   cmake_minimum_required(VERSION 3.22)
+   cmake_minimum_required(VERSION 3.25)
    project("myexample" CXX)
 
    add_subdirectory(thirdParty/alpaka)

diff --git a/docs/source/basic/install.rst b/docs/source/basic/install.rst
@@ -108,7 +108,7 @@ If user is going to create her/his own project/example outside the source tree a
 .. code-block::
 
   # Clone alpaka from github.com
-  git clone --branch 1.1.0 https://github.com/alpaka-group/alpaka.git
+  git clone --branch 1.2.0 https://github.com/alpaka-group/alpaka.git
   cd alpaka
   mkdir build && cd build
   cmake -DCMAKE_INSTALL_PREFIX=/install/ ..

diff --git a/docs/source/basic/library.rst b/docs/source/basic/library.rst
@@ -4,7 +4,7 @@ Library Interface
 As described in the chapter about the :doc:`Abstraction </basic/abstraction>`, the general design of the library is very similar to *CUDA* and *OpenCL* but extends both by some points, while not requiring any language extensions.
 General interface design as well as interface implementation decisions differentiating *alpaka* from those libraries are described in the Rationale section.
 It uses C++ because it is one of the most performant languages available on nearly all systems.
-Furthermore, C++17 allows to describe the concepts in a very abstract way that is not possible with many other languages.
+Furthermore, C++20 allows to describe the concepts in a very abstract way that is not possible with many other languages.
 The *alpaka* library extensively makes use of advanced functional C++ template meta-programming techniques.
 The Implementation Details section discusses the C++ library and the way it provides extensibility and optimizability.
 

diff --git a/docs/source/conf.py b/docs/source/conf.py
@@ -123,7 +123,7 @@
         "alpaka",
         "Abstraction Library for Parallel Kernel Acceleration",
         """
-     The alpaka library is a header-only C++17 abstraction library for
+     The alpaka library is a header-only C++20 abstraction library for
      accelerator development. Its aim is to provide performance portability
      across accelerators through the abstraction (not hiding!) of the underlying
      levels of parallelism.

diff --git a/docs/source/dev/details.rst b/docs/source/dev/details.rst
@@ -181,7 +181,7 @@ This functionality can be accessed by the corresponding ``alpaka::enqueue`` and
 
 Currently there is no native language support for describing and checking concepts in C++ at compile time.
 A study group (SG8) is working on the ISO `specification for concepts <http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/n4377.pdf>`_ and compiler forks implementing them do exist.
-For usage in current C++ there are libraries like `Boost.ConceptCheck <https://www.boost.org/doc/libs/1_58_0/libs/concept_check/concept_check.htm>`_ which try to emulate requirement checking of concept types.
+For usage in current C++ there are libraries like `Boost.ConceptCheck <https://www.boost.org/doc/libs/1_74_0/libs/concept_check/concept_check.htm>`_ which try to emulate requirement checking of concept types.
 Those libraries often exploit the preprocessor and require non-trivial changes to the function declaration syntax.
 Therefore the *alpaka* library does not currently make use of *Boost.ConceptCheck*.
 Neither does it facilitate the proposed concept specification due to its dependency on non-standard compilers.

diff --git a/docs/source/index.rst b/docs/source/index.rst
@@ -10,7 +10,7 @@
 
 *alpaka - An Abstraction Library for Parallel Kernel Acceleration*
 
-The alpaka library is a header-only C++17 abstraction library for accelerator development.
+The alpaka library is a header-only C++20 abstraction library for accelerator development.
 Its aim is to provide performance portability across accelerators through the abstraction (not hiding!) of the underlying levels of parallelism.
 
 .. CAUTION::

diff --git a/example/CMakeLists.txt b/example/CMakeLists.txt
@@ -7,7 +7,7 @@
 # Required CMake version.
 ################################################################################
 
-cmake_minimum_required(VERSION 3.22)
+cmake_minimum_required(VERSION 3.25)
 
 project("alpakaExamples" LANGUAGES CXX)
 

diff --git a/example/bufferCopy/CMakeLists.txt b/example/bufferCopy/CMakeLists.txt
@@ -6,7 +6,7 @@
 ################################################################################
 # Required CMake version.
 
-cmake_minimum_required(VERSION 3.22)
+cmake_minimum_required(VERSION 3.25)
 
 set_property(GLOBAL PROPERTY USE_FOLDERS ON)
 

diff --git a/example/complex/CMakeLists.txt b/example/complex/CMakeLists.txt
@@ -6,7 +6,7 @@
 ################################################################################
 # Required CMake version.
 
-cmake_minimum_required(VERSION 3.22)
+cmake_minimum_required(VERSION 3.25)
 
 set_property(GLOBAL PROPERTY USE_FOLDERS ON)
 

diff --git a/example/conv2DWithMdspan/CMakeLists.txt b/example/conv2DWithMdspan/CMakeLists.txt
@@ -6,7 +6,7 @@
 ################################################################################
 # Required CMake version.
 
-cmake_minimum_required(VERSION 3.22)
+cmake_minimum_required(VERSION 3.25)
 
 set_property(GLOBAL PROPERTY USE_FOLDERS ON)
 

diff --git a/example/convolution1D/CMakeLists.txt b/example/convolution1D/CMakeLists.txt
@@ -6,7 +6,7 @@
 ################################################################################
 # Required CMake version.
 
-cmake_minimum_required(VERSION 3.22)
+cmake_minimum_required(VERSION 3.25)
 
 set_property(GLOBAL PROPERTY USE_FOLDERS ON)
 

diff --git a/example/convolution2D/CMakeLists.txt b/example/convolution2D/CMakeLists.txt
@@ -6,7 +6,7 @@
 ################################################################################
 # Required CMake version.
 
-cmake_minimum_required(VERSION 3.22)
+cmake_minimum_required(VERSION 3.25)
 
 set_property(GLOBAL PROPERTY USE_FOLDERS ON)
 

diff --git a/example/counterBasedRng/CMakeLists.txt b/example/counterBasedRng/CMakeLists.txt
@@ -6,7 +6,7 @@
 ################################################################################
 # Required CMake version.
 
-cmake_minimum_required(VERSION 3.22)
+cmake_minimum_required(VERSION 3.25)
 
 set_property(GLOBAL PROPERTY USE_FOLDERS ON)
 

diff --git a/example/heatEquation/CMakeLists.txt b/example/heatEquation/CMakeLists.txt
@@ -6,7 +6,7 @@
 ################################################################################
 # Required CMake version.
 
-cmake_minimum_required(VERSION 3.22)
+cmake_minimum_required(VERSION 3.25)
 
 set_property(GLOBAL PROPERTY USE_FOLDERS ON)
 

diff --git a/example/heatEquation2D/CMakeLists.txt b/example/heatEquation2D/CMakeLists.txt
@@ -6,7 +6,7 @@
 ################################################################################
 # Required CMake version.
 
-cmake_minimum_required(VERSION 3.22)
+cmake_minimum_required(VERSION 3.25)
 
 set_property(GLOBAL PROPERTY USE_FOLDERS ON)
 

diff --git a/example/helloWorld/CMakeLists.txt b/example/helloWorld/CMakeLists.txt
@@ -6,7 +6,7 @@
 ################################################################################
 # Required CMake version.
 
-cmake_minimum_required(VERSION 3.22)
+cmake_minimum_required(VERSION 3.25)
 
 set_property(GLOBAL PROPERTY USE_FOLDERS ON)
 

diff --git a/example/helloWorldLambda/CMakeLists.txt b/example/helloWorldLambda/CMakeLists.txt
@@ -6,7 +6,7 @@
 ################################################################################
 # Required CMake version.
 
-cmake_minimum_required(VERSION 3.22)
+cmake_minimum_required(VERSION 3.25)
 
 set_property(GLOBAL PROPERTY USE_FOLDERS ON)
 

diff --git a/example/kernelSpecialization/CMakeLists.txt b/example/kernelSpecialization/CMakeLists.txt
@@ -6,7 +6,7 @@
 ################################################################################
 # Required CMake version.
 
-cmake_minimum_required(VERSION 3.22)
+cmake_minimum_required(VERSION 3.25)
 
 set_property(GLOBAL PROPERTY USE_FOLDERS ON)
 

diff --git a/example/ls/CMakeLists.txt b/example/ls/CMakeLists.txt
@@ -1,7 +1,7 @@
 # Copyright 2023 Bernhard Manfred Gruber
 # SPDX-License-Identifier: ISC
 
-cmake_minimum_required(VERSION 3.22)
+cmake_minimum_required(VERSION 3.25)
 set_property(GLOBAL PROPERTY USE_FOLDERS ON)
 
 project(alpaka-ls LANGUAGES CXX)

diff --git a/example/matrixMulWithMdspan/CMakeLists.txt b/example/matrixMulWithMdspan/CMakeLists.txt
@@ -6,7 +6,7 @@
 ################################################################################
 # Required CMake version.
 
-cmake_minimum_required(VERSION 3.22)
+cmake_minimum_required(VERSION 3.25)
 
 set_property(GLOBAL PROPERTY USE_FOLDERS ON)
 

diff --git a/example/monteCarloIntegration/CMakeLists.txt b/example/monteCarloIntegration/CMakeLists.txt
@@ -6,7 +6,7 @@
 ################################################################################
 # Required CMake version.
 
-cmake_minimum_required(VERSION 3.22)
+cmake_minimum_required(VERSION 3.25)
 
 set_property(GLOBAL PROPERTY USE_FOLDERS ON)
 

diff --git a/example/openMPSchedule/CMakeLists.txt b/example/openMPSchedule/CMakeLists.txt
@@ -6,7 +6,7 @@
 ################################################################################
 # Required CMake version.
 
-cmake_minimum_required(VERSION 3.22)
+cmake_minimum_required(VERSION 3.25)
 
 set_property(GLOBAL PROPERTY USE_FOLDERS ON)
 

diff --git a/example/parallelLoopPatterns/CMakeLists.txt b/example/parallelLoopPatterns/CMakeLists.txt
@@ -6,7 +6,7 @@
 ################################################################################
 # Required CMake version.
 
-cmake_minimum_required(VERSION 3.22)
+cmake_minimum_required(VERSION 3.25)
 
 set_property(GLOBAL PROPERTY USE_FOLDERS ON)
 

diff --git a/example/randomCells2D/CMakeLists.txt b/example/randomCells2D/CMakeLists.txt
@@ -6,7 +6,7 @@
 ################################################################################
 # Required CMake version.
 
-cmake_minimum_required(VERSION 3.22)
+cmake_minimum_required(VERSION 3.25)
 
 set_property(GLOBAL PROPERTY USE_FOLDERS ON)