X-Git-Url: http://info.iut-bm.univ-fcomte.fr/pub/gitweb/simgrid.git/blobdiff_plain/1cce0801abcad7c884f9e72ceda87e36d6635104..c1103c3a2b794d6f7e4599cf0182d72937b9a021:/include/xbt/functional.hpp

diff --git a/include/xbt/functional.hpp b/include/xbt/functional.hpp
index f37b9dd0d7..7596ef6f1e 100644
--- a/include/xbt/functional.hpp
+++ b/include/xbt/functional.hpp
@@ -9,12 +9,15 @@
 
 #include <cstddef>
 #include <cstdlib>
+#include <cstring>
 
+#include <array>
 #include <exception>
 #include <functional>
 #include <memory>
 #include <string>
 #include <tuple>
+#include <type_traits>
 #include <utility>
 #include <vector>
 
@@ -34,7 +37,7 @@ public:
     code_(std::move(code)),
     args_(std::make_shared<const std::vector<std::string>>(std::move(args)))
   {}
-  int operator()() const
+  void operator()() const
   {
     const int argc = args_->size();
     std::vector<std::string> args = *args_;
@@ -42,7 +45,7 @@ public:
     for (int i = 0; i != argc; ++i)
       argv[i] = args[i].empty() ? const_cast<char*>(""): &args[i].front();
     argv[argc] = nullptr;
-    return code_(argc, argv.get());
+    code_(argc, argv.get());
   }
 };
 
@@ -75,7 +78,7 @@ 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)
@@ -106,42 +109,169 @@ template<class T> class Task;
 template<class R, class... Args>
 class Task<R(Args...)> {
 private:
-  // Type-erasure for the code:
-  class Base {
-  public:
-    virtual ~Base() {}
-    virtual R operator()(Args...) = 0;
+
+  // Placeholder for some class type:
+  struct whatever {};
+
+  // Union used for storage:
+#if 0
+  typedef typename std::aligned_union<0,
+    void*,
+    std::pair<void(*)(),void*>,
+    std::pair<void(whatever::*)(), whatever*>
+  >::type TaskUnion;
+#else
+  union TaskUnion {
+    void* ptr;
+    std::pair<void(*)(),void*> funcptr;
+    std::pair<void(whatever::*)(), whatever*> memberptr;
+    char any1[sizeof(std::pair<void(*)(),void*>)];
+    char any2[sizeof(std::pair<void(whatever::*)(), whatever*>)];
+    TaskUnion() {}
+    ~TaskUnion() {}
   };
+#endif
+
+  // Is F suitable for small buffer optimization?
   template<class F>
-  class Impl : public Base {
-  public:
-    Impl(F&& code) : code_(std::move(code)) {}
-    Impl(F const& code) : code_(code) {}
-    ~Impl() override {}
-    R operator()(Args... args) override
-    {
-      return code_(std::forward<Args>(args)...);
-    }
-  private:
-    F code_;
+  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:
+  typedef R (*call_function)(TaskUnion&, Args...);
+  // Destroy the function (of needed):
+  typedef void (*destroy_function)(TaskUnion&);
+  // Move the function (otherwise memcpy):
+  typedef void (*move_function)(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;
   };
-  std::unique_ptr<Base> code_;
+
+  TaskUnion buffer_;
+  const TaskVtable* vtable_ = nullptr;
+
+  void clear()
+  {
+    if (vtable_ && vtable_->destroy)
+      vtable_->destroy(buffer_);
+  }
+
 public:
+
   Task() {}
   Task(std::nullptr_t) {}
+  ~Task()
+  {
+    this->clear();
+  }
+
+  Task(Task const&) = delete;
+
+  Task(Task&& that)
+  {
+    if (that.vtable_ && that.vtable_->move)
+      that.vtable_->move(buffer_, that.buffer_);
+    else
+      std::memcpy(&buffer_, &that.buffer_, sizeof(buffer_));
+    vtable_ = that.vtable_;
+    that.vtable_ = nullptr;
+  }
+  Task& operator=(Task that)
+  {
+    this->clear();
+    if (that.vtable_ && that.vtable_->move)
+      that.vtable_->move(buffer_, that.buffer_);
+    else
+      std::memcpy(&buffer_, &that.buffer_, sizeof(buffer_));
+    vtable_ = that.vtable_;
+    that.vtable_ = nullptr;
+    return *this;
+  }
+
+private:
+
+  template<class F>
+  typename std::enable_if<canSBO<F>()>::type
+  init(F code)
+  {
+    const static TaskVtable vtable {
+      // Call:
+      [](TaskUnion& buffer, Args... args) -> R {
+        F* src = reinterpret_cast<F*>(&buffer);
+        F code = std::move(*src);
+        src->~F();
+        code(std::forward<Args>(args)...);
+      },
+      // Destroy:
+      std::is_trivially_destructible<F>::value ?
+      static_cast<destroy_function>(nullptr) :
+      [](TaskUnion& buffer) {
+        F* code = reinterpret_cast<F*>(&buffer);
+        code->~F();
+      },
+      // Move:
+      [](TaskUnion& dst, TaskUnion& src) {
+        F* src_code = reinterpret_cast<F*>(&src);
+        F* dst_code = reinterpret_cast<F*>(&dst);
+        new(dst_code) F(std::move(*src_code));
+        src_code->~F();
+      }
+    };
+    new(&buffer_) F(std::move(code));
+    vtable_ = &vtable;
+  }
 
   template<class F>
-  Task(F&& code) :
-    code_(new Impl<F>(std::forward<F>(code))) {}
+  typename std::enable_if<!canSBO<F>()>::type
+  init(F code)
+  {
+    const static TaskVtable vtable {
+      // Call:
+      [](TaskUnion& buffer, Args... args) -> R {
+        // Delete F when we go out of scope:
+        std::unique_ptr<F> code(*reinterpret_cast<F**>(&buffer));
+        return (*code)(std::forward<Args>(args)...);
+      },
+      // Destroy:
+      [](TaskUnion& buffer) {
+        F* code = *reinterpret_cast<F**>(&buffer);
+        delete code;
+      },
+      // Move:
+      nullptr
+    };
+    *reinterpret_cast<F**>(&buffer_) = new F(std::move(code));
+    vtable_ = &vtable;
+  }
+
+public:
+
+  template<class F>
+  Task(F code)
+  {
+    this->init(std::move(code));
+  }
 
-  operator bool() const { return code_ != nullptr; }
-  bool operator!() const { return code_ == nullptr; }
+  operator bool() const { return vtable_ != nullptr; }
+  bool operator!() const { return vtable_ == nullptr; }
 
-  template<class... OtherArgs>
-  R operator()(OtherArgs&&... args)
+  R operator()(Args... args)
   {
-    std::unique_ptr<Base> code = std::move(code_);
-    return (*code)(std::forward<OtherArgs>(args)...);
+    if (vtable_ == nullptr)
+      throw std::bad_function_call();
+    const TaskVtable* vtable = vtable_;
+    vtable_ = nullptr;
+    return vtable->call(buffer_, std::forward<Args>(args)...);
   }
 };