Add Stdexec to the build system

CMakeLists.txt

@@ -567,6 +567,49 @@ 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: OFF)"
+  OFF
+  CATEGORY "Executor"
+  ADVANCED
+)
+
+# if STDEXEC_ROOT was provided, HPX_WITH_STDEXEC is set to ON
+if(STDEXEC_ROOT OR HPX_WITH_FETCH_STDEXEC)
+  set(HPX_WITH_STDEXEC ON)
+
+  hpx_add_config_define(HPX_HAVE_STDEXEC)
+elseif(HPX_WITH_STDEXEC)
+  hpx_error(
+    "HPX_WITH_STDEXEC is set to ON, but STDEXEC_ROOT is not provided. Please provide STDEXEC_ROOT or set HPX_WITH_FETCH_STDEXEC to ON."
+  )
+endif()
+
+if(HPX_WITH_STDEXEC)
+  # need cxx20 and over
+  if(HPX_WITH_CXX_STANDARD LESS 20)
+    hpx_error(
+      "HPX_WITH_STDEXEC is set to ON, but HPX_WITH_CXX_STANDARD is less than 20. Please set HPX_WITH_CXX_STANDARD to 20 or higher."
+    )
+  endif()
+  hpx_info("STDEXEC is enabled.")
+endif()
+
 # ##############################################################################
 # HPX SYCL configuration
 # ##############################################################################
@@ -1308,7 +1351,7 @@ 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
@@ -2228,6 +2271,9 @@ 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 +1,32 @@
+
+if(NOT TARGET STDEXEC::stdexec)
+    find_path(
+      Stdexec_INCLUDE_DIR 
+        stdexec
+      HINTS ${Stdexec_ROOT}
+      PATH_SUFFIXES include
+    )
+
+    message(STATUS "Stdexec_INCLUDE_DIR: ${Stdexec_INCLUDE_DIR}")
+
+    # set(Stdexec_INCLUDE_DIR ${Stdexec_INCLUDE_DIR})
+
+    if (NOT Stdexec_INCLUDE_DIR)
+      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 INTERFACE ${Stdexec_INCLUDE_DIR})
+    target_link_libraries(STDEXEC::stdexec INTERFACE stdexec)
+
+    mark_as_advanced(Stdexec_INCLUDE_DIR Stdexec_ROOT)
+endif()

cmake/HPX_SetupStdexec.cmake

@@ -0,0 +1,34 @@
+if(STDEXEC_ROOT AND NOT Stdexec_ROOT)
+    set(Stdexec_ROOT
+        ${STDEXEC_ROOT}
+        CACHE PATH "STDEXEC base directory"
+    )
+    unset(STDEXEC_ROOT CACHE)
+endif()
+
+if(HPX_WITH_FETCH_STDEXEC AND NOT Stdexec_ROOT)
+    hpx_info(
+        "HPX_WITH_FETCH_STDEXEC=${HPX_WITH_FETCH_STDEXEC}, Stdexec will be fetched using CMake's FetchContent."
+    )
+    if(UNIX)
+        include(FetchContent)
+        FetchContent_Declare(
+            Stdexec
+            GIT_REPOSITORY https://github.com/NVIDIA/stdexec.git
+            GIT_TAG        main
+        )
+        FetchContent_MakeAvailable(Stdexec)
+    endif()
+
+    add_library(STDEXEC::stdexec INTERFACE IMPORTED)
+    target_include_directories(STDEXEC::stdexec INTERFACE ${stdexec_SOURCE_DIR}/include)
+    target_link_libraries(STDEXEC::stdexec INTERFACE ${Stdexec_LIBRARY})
+elseif(HPX_WITH_STDEXEC)
+    find_package(Stdexec REQUIRED)
+
+    if(NOT Stdexec_FOUND)
+        hpx_error(
+            "Stdexec could not be found, please specify Stdexec_ROOT to point to the correct location"
+        )
+    endif()
+endif()

libs/core/execution_base/CMakeLists.txt

@@ -63,5 +63,7 @@ add_hpx_module(
     hpx_lock_registration
     hpx_timing
     hpx_type_support
+  DEPENDENCIES
+    STDEXEC::stdexec
   CMAKE_SUBDIRS examples tests
 )

libs/core/execution_base/include/hpx/execution_base/stdexec_forward.hpp

@@ -0,0 +1,15 @@
+//  Copyright (c) 2023 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)
+
+#pragma once
+
+#if defined(HPX_HAVE_STDEXEC)
+#include <stdexec/execution.hpp>
+
+namespace hpx::execution::experimental {
+    using namespace stdexec;
+}
+#endif

libs/core/execution_base/tests/unit/CMakeLists.txt

@@ -15,6 +15,7 @@ set(tests
     execution_context
     get_env
     execute_may_block_caller
+    stdexec
 )
 
 if(HPX_WITH_CXX20_COROUTINES)

libs/core/execution_base/tests/unit/stdexec.cpp

@@ -0,0 +1,24 @@
+//  Copyright (c) 2023 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)
+
+#include <hpx/init.hpp>
+#include <hpx/execution_base/stdexec_forward.hpp>
+
+#include <hpx/modules/testing.hpp>
+
+#include <utility>
+
+using namespace hpx::execution::experimental;
+
+int main() {
+	auto x = just(42);
+
+	auto [a] = sync_wait(std::move(x)).value();
+
+  HPX_TEST(a == 42);
+
+  return hpx::util::report_errors();
+}