Implement task and task_scheduler

include/beman/execution/detail/find_allocator.hpp

@@ -4,39 +4,39 @@
 #ifndef INCLUDED_BEMAN_EXECUTION_DETAIL_FIND_ALLOCATOR
 #define INCLUDED_BEMAN_EXECUTION_DETAIL_FIND_ALLOCATOR
 
+#include <beman/execution/detail/common.hpp>
+#ifdef BEMAN_HAS_IMPORT_STD
+import std;
+#else
 #include <concepts>
 #include <memory>
+#endif
 
 // ----------------------------------------------------------------------------
 
 namespace beman::execution::detail {
-/*!
- * \brief Utility locating an allocator_arg/allocator pair
- * \headerfile beman/execution/task.hpp <beman/execution/task.hpp>
- * \internal
- */
 template <typename Allocator>
-Allocator find_allocator() {
+Allocator find_allocator() noexcept {
     return Allocator();
 }
 template <typename Allocator>
-Allocator find_allocator(const std::allocator_arg_t&) {
+Allocator find_allocator(const ::std::allocator_arg_t&) noexcept {
     static_assert(
         requires {
-            { Allocator() } -> std::same_as<void>;
+            { Allocator() } -> ::std::same_as<void>;
         }, "There needs to be an allocator argument following std::allocator_arg");
     return Allocator();
 }
 
 template <typename Allocator, typename Alloc, typename... A>
-Allocator find_allocator(const std::allocator_arg_t&, const Alloc& alloc, const A&...) {
+Allocator find_allocator(const ::std::allocator_arg_t&, const Alloc& alloc, const A&...) noexcept {
     static_assert(
         requires(const Alloc& a) { Allocator(a); },
         "The allocator needs to be constructible from the argument following std::allocator");
     return Allocator(alloc);
 }
 template <typename Allocator, typename A0, typename... A>
-Allocator find_allocator(A0 const&, const A&... a) {
+Allocator find_allocator(A0 const&, const A&... a) noexcept {
     return ::beman::execution::detail::find_allocator<Allocator>(a...);
 }
 

include/beman/execution/detail/meta_index.hpp

@@ -0,0 +1,33 @@
+// include/beman/execution/detail/meta_index.hpp                     -*-C++-*-
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#ifndef INCLUDED_BEMAN_EXECUTION_DETAIL_META_INDEX
+#define INCLUDED_BEMAN_EXECUTION_DETAIL_META_INDEX
+
+#include <beman/execution/detail/common.hpp>
+#ifdef BEMAN_HAS_IMPORT_STD
+import std;
+#else
+#include <cstddef>
+#endif
+
+// ----------------------------------------------------------------------------
+
+namespace beman::execution::detail::meta {
+template <::std::size_t, typename, typename>
+struct index {
+    static constexpr ::std::size_t value = static_cast<::std::size_t>(-1);
+};
+template <::std::size_t I, template <typename...> class L, typename First, typename... Rest, typename T>
+struct index<I, L<First, Rest...>, T> : index<I + 1uz, L<Rest...>, T> {};
+template <::std::size_t I, template <typename...> class L, typename... Rest, typename T>
+struct index<I, L<T, Rest...>, T> {
+    static constexpr ::std::size_t value = I;
+};
+template <typename List, typename T>
+inline constexpr ::std::size_t index_v{::beman::execution::detail::meta::index<0uz, List, T>::value};
+} // namespace beman::execution::detail::meta
+
+// ----------------------------------------------------------------------------
+
+#endif // INCLUDED_BEMAN_EXECUTION_DETAIL_META_INDEX

include/beman/execution/detail/new_object.hpp

@@ -0,0 +1,45 @@
+// include/beman/execution/detail/new_object.hpp                      -*-C++-*-
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#ifndef INCLUDED_INCLUDE_BEMAN_EXECUTION_DETAIL_NEW_OBJECT
+#define INCLUDED_INCLUDE_BEMAN_EXECUTION_DETAIL_NEW_OBJECT
+
+#include <beman/execution/detail/common.hpp>
+#ifdef BEMAN_HAS_IMPORT_STD
+import std;
+#else
+#include <memory>
+#include <utility>
+#endif
+
+// ----------------------------------------------------------------------------
+
+namespace beman::execution::detail {
+template <typename T, typename Allocator, typename... Args>
+[[nodiscard]] auto new_object(const Allocator& allocator, Args&&... args) -> T* {
+    using alloc_t      = typename ::std::allocator_traits<Allocator>::template rebind_alloc<T>;
+    using alloc_traits = ::std::allocator_traits<alloc_t>;
+    alloc_t alloc(allocator);
+    auto    ptr = alloc_traits::allocate(alloc, 1);
+    try {
+        alloc_traits::construct(alloc, ptr, ::std::forward<Args>(args)...);
+        return ptr;
+    } catch (...) {
+        alloc_traits::deallocate(alloc, ptr, 1);
+        throw;
+    }
+}
+
+template <typename Allocator, typename T>
+auto delete_object(const Allocator& allocator, T* ptr) noexcept -> void {
+    using alloc_t      = typename ::std::allocator_traits<Allocator>::template rebind_alloc<T>;
+    using alloc_traits = ::std::allocator_traits<alloc_t>;
+    alloc_t alloc(allocator);
+    alloc_traits::destroy(alloc, ptr);
+    alloc_traits::deallocate(alloc, ptr, 1);
+}
+} // namespace beman::execution::detail
+
+// ----------------------------------------------------------------------------
+
+#endif // INCLUDED_INCLUDE_BEMAN_EXECUTION_DETAIL_NEW_OBJECT