X-Git-Url: http://info.iut-bm.univ-fcomte.fr/pub/gitweb/simgrid.git/blobdiff_plain/d18e17592e7aabd2cb96fd154858e0a3987d2800..e71a2a302d28430dc1bfee906f842f5f3d0fa3ce:/include/xbt/functional.hpp

diff --git a/include/xbt/functional.hpp b/include/xbt/functional.hpp
index 0a07a96c37..4f5ca2ce32 100644
--- a/include/xbt/functional.hpp
+++ b/include/xbt/functional.hpp
@@ -1,5 +1,4 @@
-/* Copyright (c) 2015-2016. The SimGrid Team.
- * All rights reserved.                                                     */
+/* Copyright (c) 2015-2021. The SimGrid Team. All rights reserved.          */
 
 /* This program is free software; you can redistribute it and/or modify it
  * under the terms of the license (GNU LGPL) which comes with this package. */
@@ -7,10 +6,13 @@
 #ifndef XBT_FUNCTIONAL_HPP
 #define XBT_FUNCTIONAL_HPP
 
+#include <xbt/sysdep.h>
+
 #include <cstddef>
 #include <cstdlib>
 #include <cstring>
 
+#include <algorithm>
 #include <array>
 #include <exception>
 #include <functional>
@@ -21,42 +23,34 @@
 #include <utility>
 #include <vector>
 
-#include <xbt/sysdep.h>
-#include <xbt/utility.hpp>
-
 namespace simgrid {
 namespace xbt {
 
-template<class F>
-class MainFunction {
-private:
+template <class F> class MainFunction {
   F code_;
   std::shared_ptr<const std::vector<std::string>> args_;
+
 public:
-  MainFunction(F code, std::vector<std::string> args) :
-    code_(std::move(code)),
-    args_(std::make_shared<const std::vector<std::string>>(std::move(args)))
-  {}
+  MainFunction(F code, std::vector<std::string>&& args)
+      : code_(std::move(code)), args_(std::make_shared<const std::vector<std::string>>(std::move(args)))
+  {
+  }
   void operator()() const
   {
-    const int argc = args_->size();
+    const int argc                = args_->size();
     std::vector<std::string> args = *args_;
-    std::unique_ptr<char*[]> argv(new char*[argc + 1]);
-    for (int i = 0; i != argc; ++i)
-      argv[i] = args[i].empty() ? const_cast<char*>(""): &args[i].front();
-    argv[argc] = nullptr;
-    code_(argc, argv.get());
+    std::vector<char*> argv(args.size() + 1); // argv[argc] is nullptr
+    std::transform(begin(args), end(args), begin(argv), [](std::string& s) { return &s.front(); });
+    code_(argc, argv.data());
   }
 };
 
-template<class F> inline
-std::function<void()> wrapMain(F code, std::vector<std::string> args)
+template <class F> inline std::function<void()> wrap_main(F code, std::vector<std::string>&& args)
 {
   return MainFunction<F>(std::move(code), std::move(args));
 }
 
-template<class F> inline
-std::function<void()> wrapMain(F code, int argc, const char*const argv[])
+template <class F> inline std::function<void()> wrap_main(F code, int argc, const char* const argv[])
 {
   std::vector<std::string> args(argv, argv + argc);
   return MainFunction<F>(std::move(code), std::move(args));
@@ -64,8 +58,8 @@ std::function<void()> wrapMain(F code, int argc, const char*const argv[])
 
 namespace bits {
 template <class F, class Tuple, std::size_t... I>
-constexpr auto apply(F&& f, Tuple&& t, simgrid::xbt::index_sequence<I...>)
-  -> decltype(std::forward<F>(f)(std::get<I>(std::forward<Tuple>(t))...))
+constexpr auto apply(F&& f, Tuple&& t, std::index_sequence<I...>)
+    -> decltype(std::forward<F>(f)(std::get<I>(std::forward<Tuple>(t))...))
 {
   return std::forward<F>(f)(std::get<I>(std::forward<Tuple>(t))...);
 }
@@ -78,87 +72,19 @@ constexpr auto apply(F&& f, Tuple&& t, simgrid::xbt::index_sequence<I...>)
  *
  *  auto args = std::make_tuple(1, false);
  *  int res = apply(foo, args);
- *  @encode
+ *  @endcode
  **/
 template <class F, class Tuple>
-constexpr auto apply(F&& f, Tuple&& t)
-  -> decltype(simgrid::xbt::bits::apply(
-    std::forward<F>(f),
-    std::forward<Tuple>(t),
-    simgrid::xbt::make_index_sequence<
-      std::tuple_size<typename std::decay<Tuple>::type>::value
-    >()))
+constexpr auto apply(F&& f, Tuple&& t) -> decltype(
+    simgrid::xbt::bits::apply(std::forward<F>(f), std::forward<Tuple>(t),
+                              std::make_index_sequence<std::tuple_size<typename std::decay_t<Tuple>>::value>()))
 {
-  return simgrid::xbt::bits::apply(
-    std::forward<F>(f),
-    std::forward<Tuple>(t),
-    simgrid::xbt::make_index_sequence<
-      std::tuple_size<typename std::decay<Tuple>::type>::value
-    >());
+  return simgrid::xbt::bits::apply(std::forward<F>(f), std::forward<Tuple>(t),
+                                   std::make_index_sequence<std::tuple_size<typename std::decay_t<Tuple>>::value>());
 }
 
 template<class T> class Task;
 
-namespace bits {
-
-  // Compute the maximum size taken by any of the given types:
-  template <class... T> struct max_size;
-  template <>
-  struct max_size<> : public std::integral_constant<std::size_t, 0> {};
-  template <class T>
-  struct max_size<T> : public std::integral_constant<std::size_t, sizeof(T)> {};
-  template <class T, class... U>
-  struct max_size<T, U...> : public std::integral_constant<std::size_t,
-    (sizeof(T) > max_size<U...>::value) ? sizeof(T) : max_size<U...>::value
-  > {};
-
-  struct whatever {};
-
-  // What we can store in a Task:
-  typedef void* ptr_callback;
-  struct funcptr_callback {
-    // Placeholder for any function pointer:
-    void(*callback)();
-    void* data;
-  };
-  struct member_funcptr_callback {
-    // Placeholder for any pointer to member function:
-    void (whatever::* callback)();
-    whatever* data;
-  };
-  constexpr std::size_t any_size = max_size<
-    ptr_callback,
-    funcptr_callback,
-    member_funcptr_callback
-  >::value;
-  typedef std::array<char, any_size> any_callback;
-
-  // Union of what we can store in a Task:
-  union TaskErasure {
-    ptr_callback ptr;
-    funcptr_callback funcptr;
-    member_funcptr_callback member_funcptr;
-    any_callback any;
-  };
-
-  // Can we copy F in Task (or do we have to use the heap)?
-  template<class F>
-  constexpr bool isUsableDirectlyInTask()
-  {
-    // TODO, detect availability std::is_trivially_copyable / workaround
-#if 1
-    // std::is_trivially_copyable is not available before GCC 5.
-    return false;
-#else
-    // The only types we can portably store directly in the Task are the
-    // trivially copyable ones (we can memcpy) which are small enough to fit:
-    return std::is_trivially_copyable<F>::value &&
-      sizeof(F) <= sizeof(bits::any_callback);
-#endif
-  }
-
-}
-
 /** Type-erased run-once task
  *
  *  * Like std::function but callable only once.
@@ -168,135 +94,156 @@ namespace bits {
  */
 template<class R, class... Args>
 class Task<R(Args...)> {
-private:
+  // Placeholder for some class type:
+  struct whatever {};
+
+  // Union used for storage:
+  using TaskUnion =
+      typename std::aligned_union_t<0, void*, std::pair<void (*)(), void*>, std::pair<void (whatever::*)(), whatever*>>;
 
-  typedef bits::TaskErasure TaskErasure;
-  struct TaskErasureVtable {
-    // Call (and possibly destroy) the function:
-    R (*call)(TaskErasure&, Args...);
-    // Destroy the function:
-    void (*destroy)(TaskErasure&);
+  // Is F suitable for small buffer optimization?
+  template<class F>
+  static constexpr bool canSBO()
+  {
+    return sizeof(F) <= sizeof(TaskUnion) &&
+      alignof(F) <= alignof(TaskUnion);
+  }
+
+  static_assert(canSBO<std::reference_wrapper<whatever>>(),
+    "SBO not working for reference_wrapper");
+
+  // Call (and possibly destroy) the function:
+  using call_function = R (*)(TaskUnion&, Args...);
+  // Destroy the function (of needed):
+  using destroy_function = void (*)(TaskUnion&);
+  // Move the function (otherwise memcpy):
+  using move_function = void (*)(TaskUnion& dest, TaskUnion& src);
+
+  // Vtable of functions for manipulating whatever is in the TaskUnion:
+  struct TaskVtable {
+    call_function call;
+    destroy_function destroy;
+    move_function move;
   };
 
-  TaskErasure code_;
-  const TaskErasureVtable* vtable_ = nullptr;
+  TaskUnion buffer_;
+  const TaskVtable* vtable_ = nullptr;
+
+  void clear()
+  {
+    if (vtable_ && vtable_->destroy)
+      vtable_->destroy(buffer_);
+  }
 
 public:
-  Task() {}
-  Task(std::nullptr_t) {}
+  Task() = default;
+  explicit Task(std::nullptr_t) { /* Nothing to do */}
   ~Task()
   {
-    if (vtable_ && vtable_->destroy)
-      vtable_->destroy(code_);
+    this->clear();
   }
 
   Task(Task const&) = delete;
-  Task& operator=(Task const&) = delete;
 
-  Task(Task&& that)
+  Task(Task&& that) noexcept
   {
-    std::memcpy(&code_, &that.code_, sizeof(code_));
-    vtable_ = that.vtable_;
+    if (that.vtable_ && that.vtable_->move)
+      that.vtable_->move(buffer_, that.buffer_);
+    else
+      std::memcpy(&buffer_, &that.buffer_, sizeof(buffer_));
+    vtable_      = std::move(that.vtable_);
     that.vtable_ = nullptr;
   }
-  Task& operator=(Task&& that)
+  Task& operator=(Task const& that) = delete;
+  Task& operator=(Task&& that) noexcept
   {
-    if (vtable_ && vtable_->destroy)
-      vtable_->destroy(code_);
-    std::memcpy(&code_, &that.code_, sizeof(code_));
-    vtable_ = that.vtable_;
+    this->clear();
+    if (that.vtable_ && that.vtable_->move)
+      that.vtable_->move(buffer_, that.buffer_);
+    else
+      std::memcpy(&buffer_, &that.buffer_, sizeof(buffer_));
+    vtable_      = std::move(that.vtable_);
     that.vtable_ = nullptr;
     return *this;
   }
 
-  template<class F,
-    typename = typename std::enable_if<bits::isUsableDirectlyInTask<F>()>::type>
-  Task(F const& code)
+private:
+  template <class F> typename std::enable_if_t<canSBO<F>()> init(F code)
   {
-    const static TaskErasureVtable vtable {
+    const static TaskVtable vtable {
       // Call:
-      [](TaskErasure& erasure, Args... args) -> R {
-        // We need to wrap F un a union because F might not have a default
-        // constructor: this is especially the case for lambdas.
-        union no_ctor {
-          no_ctor() {}
-          ~no_ctor() {}
-          F code ;
-        } code;
-        if (!std::is_empty<F>::value)
-          // AFAIU, this is safe as per [basic.types]:
-          std::memcpy(&code.code, erasure.any.data(), sizeof(code.code));
-        code.code(std::forward<Args>(args)...);
+      [](TaskUnion& buffer, Args... args) {
+        auto* src = reinterpret_cast<F*>(&buffer);
+        F code = std::move(*src);
+        src->~F();
+        // NOTE: std::forward<Args>(args)... is correct.
+        return code(std::forward<Args>(args)...);
       },
       // Destroy:
-      nullptr
+      std::is_trivially_destructible<F>::value ?
+      static_cast<destroy_function>(nullptr) :
+      [](TaskUnion& buffer) {
+        auto* code = reinterpret_cast<F*>(&buffer);
+        code->~F();
+      },
+      // Move:
+      [](TaskUnion& dst, TaskUnion& src) {
+        auto* src_code = reinterpret_cast<F*>(&src);
+        auto* dst_code = reinterpret_cast<F*>(&dst);
+        new(dst_code) F(std::move(*src_code));
+        src_code->~F();
+      }
     };
-    if (!std::is_empty<F>::value)
-      std::memcpy(code_.any.data(), &code, sizeof(code));
+    new(&buffer_) F(std::move(code));
     vtable_ = &vtable;
   }
 
-  template<class F,
-    typename = typename std::enable_if<!bits::isUsableDirectlyInTask<F>()>::type>
-  Task(F code)
+  template <class F> typename std::enable_if_t<not canSBO<F>()> init(F code)
   {
-    const static TaskErasureVtable vtable {
+    const static TaskVtable vtable {
       // Call:
-      [](TaskErasure& erasure, Args... args) -> R {
+      [](TaskUnion& buffer, Args... args) {
         // Delete F when we go out of scope:
-        std::unique_ptr<F> code(static_cast<F*>(erasure.ptr));
-        (*code)(std::forward<Args>(args)...);
+        std::unique_ptr<F> code(*reinterpret_cast<F**>(&buffer));
+        // NOTE: std::forward<Args>(args)... is correct.
+        return (*code)(std::forward<Args>(args)...);
       },
       // Destroy:
-      [](TaskErasure& erasure) {
-        F* code = static_cast<F*>(erasure.ptr);
+      [](TaskUnion& buffer) {
+        F* code = *reinterpret_cast<F**>(&buffer);
         delete code;
-      }
-    };
-    code_.ptr = new F(std::move(code));
-    vtable_ = &vtable;
-  }
-
-  template<class F>
-  Task(std::reference_wrapper<F> code)
-  {
-    const static TaskErasureVtable vtable {
-      // Call:
-      [](TaskErasure& erasure, Args... args) -> R {
-        F* code = static_cast<F*>(erasure.ptr);
-        (*code)(std::forward<Args>(args)...);
       },
-      // Destroy:
+      // Move:
       nullptr
     };
-    code.code_.ptr = code.get();
+    *reinterpret_cast<F**>(&buffer_) = new F(std::move(code));
     vtable_ = &vtable;
   }
 
-  // TODO, Task(funcptr)
-  // TODO, Task(funcptr, data)
-  // TODO, Task(method, object)
-  // TODO, Task(stateless lambda)
+public:
+  template <class F> explicit Task(F code) { this->init(std::move(code)); }
 
   operator bool() const { return vtable_ != nullptr; }
   bool operator!() const { return vtable_ == nullptr; }
 
   R operator()(Args... args)
   {
-    if (!vtable_)
+    if (vtable_ == nullptr)
       throw std::bad_function_call();
-    const TaskErasureVtable* vtable = vtable_;
+    const TaskVtable* vtable = vtable_;
     vtable_ = nullptr;
-    return vtable->call(code_, std::forward<Args>(args)...);
+    // NOTE: std::forward<Args>(args)... is correct.
+    // see C++ [func.wrap.func.inv] for an example
+    return vtable->call(buffer_, std::forward<Args>(args)...);
   }
 };
 
 template<class F, class... Args>
 class TaskImpl {
-private:
   F code_;
   std::tuple<Args...> args_;
-  typedef decltype(simgrid::xbt::apply(std::move(code_), std::move(args_))) result_type;
+  using result_type = decltype(simgrid::xbt::apply(std::move(code_), std::move(args_)));
+
 public:
   TaskImpl(F code, std::tuple<Args...> args) :
     code_(std::move(code)),
@@ -308,15 +255,12 @@ public:
   }
 };
 
-template<class F, class... Args>
-auto makeTask(F code, Args... args)
--> Task< decltype(code(std::move(args)...))() >
+template <class F, class... Args> auto make_task(F code, Args... args) -> Task<decltype(code(std::move(args)...))()>
 {
   TaskImpl<F, Args...> task(std::move(code), std::make_tuple(std::move(args)...));
-  return std::move(task);
-}
-
-}
+  return Task<decltype(code(std::move(args)...))()>(std::move(task));
 }
 
+} // namespace xbt
+} // namespace simgrid
 #endif