1 /* Copyright (c) 2015-2022. The SimGrid Team. All rights reserved. */
3 /* This program is free software; you can redistribute it and/or modify it
4 * under the terms of the license (GNU LGPL) which comes with this package. */
6 #ifndef XBT_FUNCTIONAL_HPP
7 #define XBT_FUNCTIONAL_HPP
9 #include <xbt/sysdep.h>
22 #include <type_traits>
29 template <class F> class MainFunction {
31 std::shared_ptr<const std::vector<std::string>> args_;
34 MainFunction(F code, std::vector<std::string>&& args)
35 : code_(std::move(code)), args_(std::make_shared<const std::vector<std::string>>(std::move(args)))
38 void operator()() const
40 const int argc = args_->size();
41 std::vector<std::string> args = *args_;
42 std::vector<char*> argv(args.size() + 1); // argv[argc] is nullptr
43 std::transform(begin(args), end(args), begin(argv), [](std::string& s) { return &s.front(); });
44 code_(argc, argv.data());
48 template <class F> inline std::function<void()> wrap_main(F code, std::vector<std::string>&& args)
50 return MainFunction<F>(std::move(code), std::move(args));
53 template <class F> inline std::function<void()> wrap_main(F code, int argc, const char* const argv[])
55 std::vector<std::string> args(argv, argv + argc);
56 return MainFunction<F>(std::move(code), std::move(args));
60 template <class F, class Tuple, std::size_t... I>
61 constexpr auto apply(F&& f, Tuple&& t, std::index_sequence<I...>)
62 -> decltype(std::forward<F>(f)(std::get<I>(std::forward<Tuple>(t))...))
64 return std::forward<F>(f)(std::get<I>(std::forward<Tuple>(t))...);
68 /** Call a functional object with the values in the given tuple (from C++17)
71 * int foo(int a, bool b);
73 * auto args = std::make_tuple(1, false);
74 * int res = apply(foo, args);
77 template <class F, class Tuple>
78 constexpr auto apply(F&& f, Tuple&& t) -> decltype(
79 simgrid::xbt::bits::apply(std::forward<F>(f), std::forward<Tuple>(t),
80 std::make_index_sequence<std::tuple_size<typename std::decay_t<Tuple>>::value>()))
82 return simgrid::xbt::bits::apply(std::forward<F>(f), std::forward<Tuple>(t),
83 std::make_index_sequence<std::tuple_size<typename std::decay_t<Tuple>>::value>());
86 template<class T> class Task;
88 /** Type-erased run-once task
90 * * Like std::function but callable only once.
91 * However, it works with move-only types.
93 * * Like std::packaged_task<> but without the shared state.
95 template<class R, class... Args>
96 class Task<R(Args...)> {
97 // Placeholder for some class type:
100 // Union used for storage:
102 typename std::aligned_union_t<0, void*, std::pair<void (*)(), void*>, std::pair<void (whatever::*)(), whatever*>>;
104 // Is F suitable for small buffer optimization?
106 static constexpr bool canSBO()
108 return sizeof(F) <= sizeof(TaskUnion) &&
109 alignof(F) <= alignof(TaskUnion);
112 static_assert(canSBO<std::reference_wrapper<whatever>>(),
113 "SBO not working for reference_wrapper");
115 // Call (and possibly destroy) the function:
116 using call_function = R (*)(TaskUnion&, Args...);
117 // Destroy the function (of needed):
118 using destroy_function = void (*)(TaskUnion&);
119 // Move the function (otherwise memcpy):
120 using move_function = void (*)(TaskUnion& dest, TaskUnion& src);
122 // Vtable of functions for manipulating whatever is in the TaskUnion:
125 destroy_function destroy;
129 TaskUnion buffer_ = {};
130 const TaskVtable* vtable_ = nullptr;
134 if (vtable_ && vtable_->destroy)
135 vtable_->destroy(buffer_);
140 explicit Task(std::nullptr_t) { /* Nothing to do */}
146 Task(Task const&) = delete;
148 Task(Task&& that) noexcept
150 if (that.vtable_ && that.vtable_->move)
151 that.vtable_->move(buffer_, that.buffer_);
153 std::memcpy(&buffer_, &that.buffer_, sizeof(buffer_));
154 vtable_ = std::move(that.vtable_);
155 that.vtable_ = nullptr;
157 Task& operator=(Task const& that) = delete;
158 Task& operator=(Task&& that) noexcept
161 if (that.vtable_ && that.vtable_->move)
162 that.vtable_->move(buffer_, that.buffer_);
164 std::memcpy(&buffer_, &that.buffer_, sizeof(buffer_));
165 vtable_ = std::move(that.vtable_);
166 that.vtable_ = nullptr;
171 template <class F> typename std::enable_if_t<canSBO<F>()> init(F code)
173 const static TaskVtable vtable {
175 [](TaskUnion& buffer, Args... args) {
176 auto* src = reinterpret_cast<F*>(&buffer);
177 F code = std::move(*src);
179 // NOTE: std::forward<Args>(args)... is correct.
180 return code(std::forward<Args>(args)...);
183 std::is_trivially_destructible<F>::value ?
184 static_cast<destroy_function>(nullptr) :
185 [](TaskUnion& buffer) {
186 auto* code = reinterpret_cast<F*>(&buffer);
190 [](TaskUnion& dst, TaskUnion& src) {
191 auto* src_code = reinterpret_cast<F*>(&src);
192 auto* dst_code = reinterpret_cast<F*>(&dst);
193 new(dst_code) F(std::move(*src_code));
197 new(&buffer_) F(std::move(code));
201 template <class F> typename std::enable_if_t<not canSBO<F>()> init(F code)
203 const static TaskVtable vtable {
205 [](TaskUnion& buffer, Args... args) {
206 // Delete F when we go out of scope:
207 std::unique_ptr<F> code(*reinterpret_cast<F**>(&buffer));
208 // NOTE: std::forward<Args>(args)... is correct.
209 return (*code)(std::forward<Args>(args)...);
212 [](TaskUnion& buffer) {
213 F* code = *reinterpret_cast<F**>(&buffer);
219 *reinterpret_cast<F**>(&buffer_) = new F(std::move(code));
224 template <class F> explicit Task(F code) { this->init(std::move(code)); }
226 operator bool() const { return vtable_ != nullptr; }
227 bool operator!() const { return vtable_ == nullptr; }
229 R operator()(Args... args)
231 if (vtable_ == nullptr)
232 throw std::bad_function_call();
233 const TaskVtable* vtable = vtable_;
235 // NOTE: std::forward<Args>(args)... is correct.
236 // see C++ [func.wrap.func.inv] for an example
237 return vtable->call(buffer_, std::forward<Args>(args)...);
241 template<class F, class... Args>
244 std::tuple<Args...> args_;
245 using result_type = decltype(simgrid::xbt::apply(std::move(code_), std::move(args_)));
248 TaskImpl(F code, std::tuple<Args...> args) :
249 code_(std::move(code)),
250 args_(std::move(args))
252 result_type operator()()
254 return simgrid::xbt::apply(std::move(code_), std::move(args_));
258 template <class F, class... Args> auto make_task(F code, Args... args) -> Task<decltype(code(std::move(args)...))()>
260 TaskImpl<F, Args...> task(std::move(code), std::make_tuple(std::move(args)...));
261 return Task<decltype(code(std::move(args)...))()>(std::move(task));
265 } // namespace simgrid