Integrate NVIDIA's S/R implementation into HPX

CMakeLists.txt

@@ -1,6 +1,7 @@
 # Copyright (c)      2020 Mikael Simberg
 # Copyright (c) 2007-2024 Hartmut Kaiser
 # Copyright (c) 2011-2014 Thomas Heller
+# Copyright (c)      2024 Isidoros Tsaousis-Seiras
 # Copyright (c) 2007-2008 Chirag Dekate
 # Copyright (c)      2011 Bryce Lelbach
 # Copyright (c)      2011 Vinay C Amatya
@@ -578,6 +579,27 @@ if(HPX_WITH_CUDA AND HPX_WITH_HIP)
   )
 endif()
 
+# ## HPX STDEXEC configuration ##
+
+hpx_option(
+  HPX_WITH_STDEXEC BOOL
+  "Use STDEXEC executors instead of native HPX.(default: OFF)" OFF
+  CATEGORY "Executor"
+  ADVANCED
+)
+
+hpx_option(
+  HPX_WITH_FETCH_STDEXEC BOOL "Use FetchContent to fetch STDEXEC.(default: ON)"
+  ON
+  CATEGORY "Executor"
+  ADVANCED
+)
+
+hpx_option(
+  HPX_WITH_STDEXEC_TAG STRING "STDEXEC repository tag or branch" "main"
+  CATEGORY "Executor"
+)
+
 # ##############################################################################
 # HPX SYCL configuration
 # ##############################################################################
@@ -1346,7 +1368,7 @@ if(HPX_WITH_NETWORKING AND HPX_WITH_PARCELPORT_LCI)
   endif()
 endif()
 
-# External libraries/frameworks used by sme of the examples and benchmarks
+# External libraries/frameworks used by some of the examples and benchmarks
 hpx_option(
   HPX_WITH_EXAMPLES_OPENMP BOOL
   "Enable examples requiring OpenMP support (default: OFF)." OFF
@@ -2265,6 +2287,9 @@ if(HPX_WITH_CUDA OR HPX_WITH_HIP)
   hpx_add_config_define(HPX_HAVE_GPU_SUPPORT)
 endif()
 
+# Setup NVIDIA's stdexec if requested
+include(HPX_SetupStdexec)
+
 if(HPX_WITH_SANITIZERS)
   hpx_add_config_define(HPX_HAVE_SANITIZERS)
 endif()

cmake/FindStdexec.cmake

@@ -0,0 +1,39 @@
+#  Copyright (c) 2024 Isidoros Tsaousis-Seiras
+#
+#  SPDX-License-Identifier: BSL-1.0
+#  Distributed under the Boost Software License, Version 1.0. (See accompanying
+#  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+if(NOT TARGET STDEXEC::stdexec)
+  if(STDEXEC_ROOT AND NOT Stdexec_ROOT)
+    set(Stdexec_ROOT
+        ${STDEXEC_ROOT}
+        CACHE PATH "stdexec base directory"
+    )
+    unset(STDEXEC_ROOT CACHE)
+  endif()
+
+  find_path(Stdexec_INCLUDE_DIR stdexec HINTS ${Stdexec_ROOT})
+  message(STATUS "stdexec include dir: ${Stdexec_INCLUDE_DIR}")
+  if(Stdexec_INCLUDE_DIR)
+    file(TO_CMAKE_PATH ${Stdexec_INCLUDE_DIR} Stdexec_INCLUDE_DIR)
+  else()
+    message(FATAL_ERROR "stdexec not found")
+  endif()
+
+  include(FindPackageHandleStandardArgs)
+  find_package_handle_standard_args(
+    Stdexec
+    REQUIRED_VARS Stdexec_INCLUDE_DIR
+    FOUND_VAR Stdexec_FOUND
+    VERSION_VAR Stdexec_VERSION
+    FAIL_MESSAGE "stdexec not found"
+  )
+
+  add_library(STDEXEC::stdexec INTERFACE IMPORTED)
+  target_include_directories(
+    STDEXEC::stdexec SYSTEM INTERFACE ${Stdexec_INCLUDE_DIR}
+  )
+
+  mark_as_advanced(Stdexec_INCLUDE_DIR Stdexec_ROOT)
+endif()

cmake/HPX_AddConfigTest.cmake

@@ -633,6 +633,15 @@ function(hpx_check_for_cxx20_std_bit_cast)
   )
 endfunction()
 
+# ##############################################################################
+function(hpx_check_for_cxx20_std_identity)
+  add_hpx_config_test(
+    HPX_WITH_CXX20_STD_IDENTITY
+    SOURCE cmake/tests/cxx20_std_identity.cpp
+    FILE ${ARGN}
+  )
+endfunction()
+
 # ##############################################################################
 function(hpx_check_for_cxx20_constexpr_destructor)
   add_hpx_config_test(

cmake/HPX_PerformCxxFeatureTests.cmake

@@ -152,6 +152,8 @@ function(hpx_perform_cxx_feature_tests)
 
     hpx_check_for_cxx20_std_bit_cast(DEFINITIONS HPX_HAVE_CXX20_STD_BIT_CAST)
 
+    hpx_check_for_cxx20_std_identity(DEFINITIONS HPX_HAVE_CXX20_STD_IDENTITY)
+
     hpx_check_for_cxx20_constexpr_destructor(
       DEFINITIONS HPX_HAVE_CXX20_CONSTEXPR_DESTRUCTOR
     )

cmake/HPX_SetupStdexec.cmake

@@ -0,0 +1,104 @@
+#  Copyright (c) 2024 Isidoros Tsaousis-Seiras
+#
+#  SPDX-License-Identifier: BSL-1.0
+#  Distributed under the Boost Software License, Version 1.0. (See accompanying
+#  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+if(HPX_WITH_STDEXEC)
+  if(HPX_WITH_CXX_STANDARD LESS 20)
+    hpx_error("HPX_WITH_STDEXEC Requires C++20 or later.")
+  endif()
+  if(NOT HPX_WITH_CXX20_STD_IDENTITY)
+    hpx_error("HPX_WITH_STDEXEC Requires std::identity.")
+  endif()
+  if(MSVC)
+    hpx_error("HPX_WITH_STDEXEC is not available on MSVC.")
+  endif()
+endif()
+
+if(STDEXEC_ROOT AND NOT Stdexec_ROOT)
+  set(Stdexec_ROOT ${STDEXEC_ROOT})
+  # remove STDEXEC_ROOT from the cache
+  unset(STDEXEC_ROOT CACHE)
+endif()
+
+if(HPX_WITH_STDEXEC)
+  # prefer HPX_WITH_FETCH_STDEXEC by default
+  if(Stdexec_ROOT AND HPX_WITH_FETCH_STDEXEC)
+    hpx_warn(
+      "Both Stdexec_ROOT and HPX_WITH_FETCH_STDEXEC are provided. HPX_WITH_FETCH_STDEXEC will take precedence."
+    )
+  endif()
+
+  hpx_add_config_define(HPX_HAVE_STDEXEC)
+
+  if(HPX_WITH_FETCH_STDEXEC)
+    hpx_info(
+      "HPX_WITH_FETCH_STDEXEC=${HPX_WITH_FETCH_STDEXEC}, Stdexec will be fetched using CMake's FetchContent and installed alongside HPX (HPX_WITH_STDEXEC_TAG=${HPX_WITH_STDEXEC_TAG})"
+    )
+    if(UNIX)
+      include(FetchContent)
+      fetchcontent_declare(
+        Stdexec
+        GIT_REPOSITORY https://github.com/NVIDIA/stdexec.git
+        GIT_TAG ${HPX_WITH_STDEXEC_TAG}
+      )
+
+      fetchcontent_getproperties(Stdexec)
+      if(NOT Stdexec_POPULATED)
+        fetchcontent_populate(Stdexec)
+      endif()
+      set(Stdexec_ROOT ${stdexec_SOURCE_DIR})
+
+      add_library(Stdexec INTERFACE)
+      target_include_directories(
+        Stdexec INTERFACE $<BUILD_INTERFACE:${stdexec_SOURCE_DIR}/include>
+                          $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>
+      )
+
+      install(
+        TARGETS Stdexec
+        EXPORT HPXStdexecTarget
+        COMPONENT core
+      )
+
+      install(
+        DIRECTORY ${Stdexec_ROOT}/include/
+        DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}
+        COMPONENT core
+        FILES_MATCHING
+        PATTERN "*.hpp"
+      )
+
+      export(
+        TARGETS Stdexec
+        NAMESPACE Stdexec::
+        FILE "${CMAKE_CURRENT_BINARY_DIR}/lib/cmake/${HPX_PACKAGE_NAME}/HPXStdexecTarget.cmake"
+      )
+
+      install(
+        EXPORT HPXStdexecTarget
+        NAMESPACE Stdexec::
+        FILE HPXStdexecTarget.cmake
+        DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/${HPX_PACKAGE_NAME}
+        COMPONENT cmake
+      )
+
+      # TODO: Enforce a single spelling
+      add_library(Stdexec::Stdexec ALIAS Stdexec)
+      add_library(STDEXEC::stdexec ALIAS Stdexec)
+
+    endif()
+
+  else()
+    find_package(Stdexec REQUIRED)
+
+    if(Stdexec_FOUND)
+      hpx_add_config_define(HPX_HAVE_STDEXEC)
+    else()
+      hpx_error(
+        "Stdexec could not be found, please specify Stdexec_ROOT to point to the correct location or enable HPX_WITH_FETCH_STDEXEC"
+      )
+    endif()
+  endif()
+endif()

cmake/templates/HPXConfig.cmake.in

@@ -27,6 +27,20 @@ else()
   include(HPX_SetupAsio)
 endif()
 
+
+# Stdexec can be installed by HPX or externally installed. In the first case we use
+# exported targets, in the second we find Stdexec again using find_package.
+if(HPX_WITH_STDEXEC)
+  if(HPX_WITH_FETCH_STDEXEC)
+    include("${CMAKE_CURRENT_LIST_DIR}/HPXStdexecTarget.cmake")
+  else()
+    set(Stdexec_ROOT "@Stdexec_ROOT@")
+    include(HPX_SetupStdexec)
+  endif()
+endif()
+
+
+
 # NLohnmann JSON can be installed by HPX or externally installed. In the first
 # case we use exported targets, in the second we find JSON again using
 # find_package.

cmake/tests/cxx20_std_identity.cpp

@@ -0,0 +1,14 @@
+//  Copyright (c) 2024 Isidoros Tsaousis-Seiras
+//
+//  SPDX-License-Identifier: BSL-1.0
+//  Distributed under the Boost Software License, Version 1.0. (See accompanying
+//  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+// test for availability of std::identity
+
+#include <functional>
+
+int main()
+{
+    auto f = std::identity{}(3);
+}

libs/CMakeLists.txt

@@ -376,6 +376,10 @@ if(HPX_WITH_ITTNOTIFY)
   target_link_libraries(hpx_core PUBLIC Amplifier::amplifier)
 endif()
 
+if(TARGET STDEXEC::stdexec)
+  target_link_libraries(hpx_core INTERFACE STDEXEC::stdexec)
+endif()
+
 if(HPX_WITH_PARCELPORT_GASNET AND GASNET_LIBRARY_DIRS)
   target_link_directories(hpx_core PUBLIC ${GASNET_LIBRARY_DIRS})
 endif()

libs/core/algorithms/include/hpx/parallel/algorithms/rotate.hpp

@@ -4,10 +4,9 @@
 //  SPDX-License-Identifier: BSL-1.0
 //  Distributed under the Boost Software License, Version 1.0. (See accompanying
 //  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
-
-/// \file hpx/parallel/algorithms/rotate.hpp
 /// \page hpx::rotate, hpx::rotate_copy
 /// \headerfile hpx/algorithm.hpp
+/// \file hpx/parallel/algorithms/rotate.hpp
 
 #pragma once
 
@@ -266,27 +265,58 @@ namespace hpx::parallel {
 
             detail::reverse<FwdIter> r;
 
-            return hpx::dataflow(
-                hpx::launch::sync,
-                [=](auto&& f1, auto&& f2) mutable {
-                    // propagate exceptions, if appropriate
-                    constexpr bool handle_futures =
-                        hpx::traits::is_future_v<decltype((f1))> &&
-                        hpx::traits::is_future_v<decltype((f2))>;
-
-                    if constexpr (handle_futures)
-                    {
-                        f1.get();
-                        f2.get();
-                    }
-
-                    r.call(p(hpx::execution::non_task), first, last);
-
-                    std::advance(first, size_right);
-                    return util::in_out_result<FwdIter, Sent>{first, last};
-                },
-                r.call(left_policy, first, new_first),
-                r.call(right_policy, new_first, last));
+            auto&& process = [=](auto&& f1, auto&& f2) mutable {
+                // propagate exceptions, if appropriate
+                constexpr bool handle_futures =
+                    hpx::traits::is_future_v<decltype((f1))> &&
+                    hpx::traits::is_future_v<decltype((f2))>;
+
+                if constexpr (handle_futures)
+                {
+                    f1.get();
+                    f2.get();
+                }
+
+                r.call(p(hpx::execution::non_task), first, last);
+
+                std::advance(first, size_right);
+                return util::in_out_result<FwdIter, Sent>{first, last};
+            };
+
+            using rcall_left_t =
+                decltype(r.call(left_policy, first, new_first));
+            using rcall_right_t =
+                decltype(r.call(right_policy, new_first, last));
+
+            // Sanity check
+            static_assert(std::is_same_v<rcall_left_t, rcall_right_t>);
+
+            constexpr bool handle_senders =
+                hpx::execution::experimental::is_sender_v<rcall_left_t>;
+            constexpr bool handle_futures =
+                hpx::traits::is_future_v<rcall_left_t>;
+            constexpr bool handle_both = handle_senders && handle_futures;
+
+            static_assert(handle_senders || handle_futures,
+                "the reverse operation must return either a sender or a "
+                "future");
+
+            // Futures pass the concept check for senders, so if something is
+            // both a future and a sender we treat it as a future.
+            if constexpr (handle_futures || handle_both)
+            {
+                return hpx::dataflow(hpx::launch::sync, std::move(process),
+                    r.call(left_policy, first, new_first),
+                    r.call(right_policy, new_first, last));
+            }
+            else if constexpr (handle_senders && !handle_both)
+            {
+                return hpx::execution::experimental::then(
+                    hpx::execution::experimental::when_all(
+                        r.call(left_policy, first, new_first),
+                        r.call(right_policy, new_first, last)),
+                    std::move(process));
+            }
         }
 
         template <typename IterPair>

libs/core/algorithms/include/hpx/parallel/util/detail/algorithm_result.hpp

@@ -18,6 +18,11 @@
 #include <hpx/futures/future.hpp>
 #include <hpx/type_support/unused.hpp>
 
+#if defined(HPX_HAVE_STDEXEC)
+// For is_sender
+#include <hpx/execution_base/completion_signatures.hpp>
+#endif
+
 #include <type_traits>
 #include <utility>