FastDelegate 和 lambda - 无法让它们工作(Don Clugston 最快的可能代表)
FastDelegate and lambdas - can't get them to work (Don Clugston's fastest possible delegates)
我正在尝试创建Don Clugston的成员函数指针和最快的C++委托的C++11实现，并使其作为直接std::function替代品。
这就是我到目前为止得到的。
我像这样构造 lambda FastDelegate：
// FastFunc is my name for FastDelegate
template<typename LambdaType> FastFunc(LambdaType lambdaExpression)
{
this->m_Closure.bindmemfunc(&lambdaExpression, &LambdaType::operator());
}
现在，一些测试：
FastFunc<void()> test = []{ std::cout << "hello" << std::endl; };
test();
// Correctly prints "hello"
bool b{false};
FastFunc<void()> test2 = [&b]{ std::cout << b << std::endl; };
test2();
// Crash!
如您所见，当 lambda 是"微不足道的"（没有捕获）时，按值复制它并获取其地址是有效的。但是当lambda存储某种状态（捕获）时，我不能只是按值将其复制到FastFunc中。
尝试通过引用获取 lambda，但是当它是临时的时，我无法做到这一点，就像示例中一样。
我必须以某种方式将lambda存储在FastFunc中，但我不想使用std::shared_ptr因为它很慢（我尝试了使用它的不同fastdelegate实现，其性能与std::function相当）。
如何使 Don Clugston 的最快可能C++委托的实现与捕获状态的 lambda 一起工作，从而保留快速委托的惊人性能？
您已经很好地诊断了情况：您需要存储状态。
由于 lambda 是一个临时对象，因此您实际上可以（通常）从它移动，如果可能的话，它应该优先于副本（因为移动比复制更通用）。
现在，您需要做的就是为其保留一些存储，如果这需要动态分配，则确实可能会降低性能。另一方面，一个物体需要有一个固定的脚印，那么？
一种可能的解决方案是提供可配置（但有限）的存储容量：
static size_t const Size = 32;
static size_t const Alignment = alignof(std::max_align_t);
typedef std::aligned_storage<Size, Alignment>::type Storage;
Storage storage;
现在，您可以（根据需要使用reinterpret_cast）将您的 lambda 存储在storage只要其大小合适（可以使用 static_assert 检测到）。
最后设法得到了一个工作示例（必须从头开始，因为上帝是那么快速的委托代码冗长！！
我只是触及了表面，特别是因为它缺少复制和移动运算符。若要正确执行此操作，需要按照与其他两个操作相同的模式将这些操作添加到处理程序中。
法典：
#include <cstddef>
#include <iostream>
#include <memory>
#include <type_traits>
template <typename, size_t> class FastFunc;
template <typename R, typename... Args, size_t Size>
class FastFunc<R(Args...), Size> {
public:
template <typename F>
FastFunc(F f): handler(&Get<F>()) {
new (&storage) F(std::move(f));
}
~FastFunc() {
handler->destroy(&storage);
}
R operator()(Args&&... args) {
return handler->apply(&storage, std::forward<Args>(args)...);
}
private:
using Storage = typename std::aligned_storage<Size, alignof(max_align_t)>::type;
struct Handler {
R (*apply)(void*, Args&&...);
void (*destroy)(void*);
}; // struct Handler
template <typename F>
static R Apply(void* f, Args&&... args) {
(*reinterpret_cast<F*>(f))(std::forward<Args>(args)...);
}
template <typename F>
static void Destroy(void* f) {
reinterpret_cast<F*>(f)->~F();
}
template <typename F>
Handler const& Get() {
static Handler const H = { &Apply<F>, &Destroy<F> };
return H;
} // Get
Handler const* handler;
Storage storage;
}; // class FastFunc
int main() {
FastFunc<void(), 32> stateless = []() { std::cout << "statelessn"; };
stateless();
bool b = true;
FastFunc<void(), 32> stateful = [&b]() { std::cout << "stateful: " << b << "n"; };
stateful();
b = false;
stateful();
return 0;
}
你不能。
事情是这样的。快速委托仅适用于极少数非常特殊的情况。这就是使它更快的原因。您不会在实现std::function方面击败您的标准库实施者。
我提出了一个解决方案，使用艰苦的劳动和其他几个线程将 lambda 函数作为指针仅放入 FastDelegate（它不存储任何其他内容），例如： 获取 lambda 参数类型
在这里：
namespace details{
template<class FPtr> struct function_traits;
template<class RT, class CT >struct function_traits<RT (CT::*)( ) >{ typedef RT Result; typedef RT (CT::*Signature)( );};
template<class RT, class CT >struct function_traits<RT (CT::*)( )const>{ typedef RT Result; typedef RT (CT::*Signature)( );};
template<class RT >struct function_traits<RT ( ) >{ typedef RT Result; typedef RT Signature ( );};
template<class RT, class CT, class P1T >struct function_traits<RT (CT::*)(P1T ) >{ typedef RT Result; typedef P1T Param1; typedef RT (CT::*Signature)(P1T );};
template<class RT, class CT, class P1T >struct function_traits<RT (CT::*)(P1T )const>{ typedef RT Result; typedef P1T Param1; typedef RT (CT::*Signature)(P1T );};
template<class RT , class P1T >struct function_traits<RT (P1T ) >{ typedef RT Result; typedef P1T Param1; typedef RT Signature (P1T );};
template<class RT, class CT, class P1T, class P2T >struct function_traits<RT (CT::*)(P1T, P2T ) >{ typedef RT Result; typedef P1T Param1; typedef P2T Param2; typedef RT (CT::*Signature)(P1T, P2T );};
template<class RT, class CT, class P1T, class P2T >struct function_traits<RT (CT::*)(P1T, P2T )const>{ typedef RT Result; typedef P1T Param1; typedef P2T Param2; typedef RT (CT::*Signature)(P1T, P2T );};
template<class RT , class P1T, class P2T >struct function_traits<RT (P1T, P2T ) >{ typedef RT Result; typedef P1T Param1; typedef P2T Param2; typedef RT Signature (P1T, P2T );};
template<class RT, class CT, class P1T, class P2T, class P3T >struct function_traits<RT (CT::*)(P1T, P2T, P3T ) >{ typedef RT Result; typedef P1T Param1; typedef P2T Param2; typedef P3T Param3; typedef RT (CT::*Signature)(P1T, P2T, P3T );};
template<class RT, class CT, class P1T, class P2T, class P3T >struct function_traits<RT (CT::*)(P1T, P2T, P3T )const>{ typedef RT Result; typedef P1T Param1; typedef P2T Param2; typedef P3T Param3; typedef RT (CT::*Signature)(P1T, P2T, P3T );};
template<class RT , class P1T, class P2T, class P3T >struct function_traits<RT (P1T, P2T, P3T ) >{ typedef RT Result; typedef P1T Param1; typedef P2T Param2; typedef P3T Param3; typedef RT Signature (P1T, P2T, P3T );};
template<class RT, class CT, class P1T, class P2T, class P3T, class P4T >struct function_traits<RT (CT::*)(P1T, P2T, P3T, P4T ) >{ typedef RT Result; typedef P1T Param1; typedef P2T Param2; typedef P3T Param3; typedef P4T Param4; typedef RT (CT::*Signature)(P1T, P2T, P3T, P4T );};
template<class RT, class CT, class P1T, class P2T, class P3T, class P4T >struct function_traits<RT (CT::*)(P1T, P2T, P3T, P4T )const>{ typedef RT Result; typedef P1T Param1; typedef P2T Param2; typedef P3T Param3; typedef P4T Param4; typedef RT (CT::*Signature)(P1T, P2T, P3T, P4T );};
template<class RT , class P1T, class P2T, class P3T, class P4T >struct function_traits<RT (P1T, P2T, P3T, P4T ) >{ typedef RT Result; typedef P1T Param1; typedef P2T Param2; typedef P3T Param3; typedef P4T Param4; typedef RT Signature (P1T, P2T, P3T, P4T );};
template<class RT, class CT, class P1T, class P2T, class P3T, class P4T, class P5T >struct function_traits<RT (CT::*)(P1T, P2T, P3T, P4T, P5T ) >{ typedef RT Result; typedef P1T Param1; typedef P2T Param2; typedef P3T Param3; typedef P4T Param4; typedef P5T Param5; typedef RT (CT::*Signature)(P1T, P2T, P3T, P4T, P5T );};
template<class RT, class CT, class P1T, class P2T, class P3T, class P4T, class P5T >struct function_traits<RT (CT::*)(P1T, P2T, P3T, P4T, P5T )const>{ typedef RT Result; typedef P1T Param1; typedef P2T Param2; typedef P3T Param3; typedef P4T Param4; typedef P5T Param5; typedef RT (CT::*Signature)(P1T, P2T, P3T, P4T, P5T );};
template<class RT , class P1T, class P2T, class P3T, class P4T, class P5T >struct function_traits<RT (P1T, P2T, P3T, P4T, P5T ) >{ typedef RT Result; typedef P1T Param1; typedef P2T Param2; typedef P3T Param3; typedef P4T Param4; typedef P5T Param5; typedef RT Signature (P1T, P2T, P3T, P4T, P5T );};
template<class RT, class CT, class P1T, class P2T, class P3T, class P4T, class P5T, class P6T >struct function_traits<RT (CT::*)(P1T, P2T, P3T, P4T, P5T, P6T ) >{ typedef RT Result; typedef P1T Param1; typedef P2T Param2; typedef P3T Param3; typedef P4T Param4; typedef P5T Param5; typedef P6T Param6; typedef RT (CT::*Signature)(P1T, P2T, P3T, P4T, P5T, P6T );};
template<class RT, class CT, class P1T, class P2T, class P3T, class P4T, class P5T, class P6T >struct function_traits<RT (CT::*)(P1T, P2T, P3T, P4T, P5T, P6T )const>{ typedef RT Result; typedef P1T Param1; typedef P2T Param2; typedef P3T Param3; typedef P4T Param4; typedef P5T Param5; typedef P6T Param6; typedef RT (CT::*Signature)(P1T, P2T, P3T, P4T, P5T, P6T );};
template<class RT , class P1T, class P2T, class P3T, class P4T, class P5T, class P6T >struct function_traits<RT (P1T, P2T, P3T, P4T, P5T, P6T ) >{ typedef RT Result; typedef P1T Param1; typedef P2T Param2; typedef P3T Param3; typedef P4T Param4; typedef P5T Param5; typedef P6T Param6; typedef RT Signature (P1T, P2T, P3T, P4T, P5T, P6T );};
template<class RT, class CT, class P1T, class P2T, class P3T, class P4T, class P5T, class P6T, class P7T >struct function_traits<RT (CT::*)(P1T, P2T, P3T, P4T, P5T, P6T, P7T ) >{ typedef RT Result; typedef P1T Param1; typedef P2T Param2; typedef P3T Param3; typedef P4T Param4; typedef P5T Param5; typedef P6T Param6; typedef P7T Param7; typedef RT (CT::*Signature)(P1T, P2T, P3T, P4T, P5T, P6T, P7T );};
template<class RT, class CT, class P1T, class P2T, class P3T, class P4T, class P5T, class P6T, class P7T >struct function_traits<RT (CT::*)(P1T, P2T, P3T, P4T, P5T, P6T, P7T )const>{ typedef RT Result; typedef P1T Param1; typedef P2T Param2; typedef P3T Param3; typedef P4T Param4; typedef P5T Param5; typedef P6T Param6; typedef P7T Param7; typedef RT (CT::*Signature)(P1T, P2T, P3T, P4T, P5T, P6T, P7T );};
template<class RT , class P1T, class P2T, class P3T, class P4T, class P5T, class P6T, class P7T >struct function_traits<RT (P1T, P2T, P3T, P4T, P5T, P6T, P7T ) >{ typedef RT Result; typedef P1T Param1; typedef P2T Param2; typedef P3T Param3; typedef P4T Param4; typedef P5T Param5; typedef P6T Param6; typedef P7T Param7; typedef RT Signature (P1T, P2T, P3T, P4T, P5T, P6T, P7T );};
template<class RT, class CT, class P1T, class P2T, class P3T, class P4T, class P5T, class P6T, class P7T, class P8T>struct function_traits<RT (CT::*)(P1T, P2T, P3T, P4T, P5T, P6T, P7T, P8T) >{ typedef RT Result; typedef P1T Param1; typedef P2T Param2; typedef P3T Param3; typedef P4T Param4; typedef P5T Param5; typedef P6T Param6; typedef P7T Param7; typedef P8T Param8; typedef RT (CT::*Signature)(P1T, P2T, P3T, P4T, P5T, P6T, P7T, P8T);};
template<class RT, class CT, class P1T, class P2T, class P3T, class P4T, class P5T, class P6T, class P7T, class P8T>struct function_traits<RT (CT::*)(P1T, P2T, P3T, P4T, P5T, P6T, P7T, P8T)const>{ typedef RT Result; typedef P1T Param1; typedef P2T Param2; typedef P3T Param3; typedef P4T Param4; typedef P5T Param5; typedef P6T Param6; typedef P7T Param7; typedef P8T Param8; typedef RT (CT::*Signature)(P1T, P2T, P3T, P4T, P5T, P6T, P7T, P8T);};
template<class RT , class P1T, class P2T, class P3T, class P4T, class P5T, class P6T, class P7T, class P8T>struct function_traits<RT (P1T, P2T, P3T, P4T, P5T, P6T, P7T, P8T) >{ typedef RT Result; typedef P1T Param1; typedef P2T Param2; typedef P3T Param3; typedef P4T Param4; typedef P5T Param5; typedef P6T Param6; typedef P7T Param7; typedef P8T Param8; typedef RT Signature (P1T, P2T, P3T, P4T, P5T, P6T, P7T, P8T);};
template<class T>
typename function_traits<T>::Signature* bar_helper(T);
template<class F>
class FuncTraitsOf{
public:
typedef decltype(bar_helper(&F::operator())) fptr;
typedef typename std::remove_pointer<fptr>::type Signature; //Signature = bool __cdecl(int,float)
typedef typename function_traits< Signature > R; //R = struct function_traits<bool __cdecl(int,float)>
};
template< class FuncTraits>class FDSel;
template<class RT, class CT > struct FDSel< function_traits< RT (CT::*)( ) > >{ typedef fastdelegate::FastDelegate0< RT> R; };
template<class RT, class CT > struct FDSel< function_traits< RT (CT::*)( )const > >{ typedef fastdelegate::FastDelegate0< RT> R; };
template<class RT > struct FDSel< function_traits< RT ( ) > >{ typedef fastdelegate::FastDelegate0< RT> R; };
template<class RT, class CT, class P1T > struct FDSel< function_traits< RT (CT::*)(P1T ) > >{ typedef fastdelegate::FastDelegate1<P1T ,RT> R; };
template<class RT, class CT, class P1T > struct FDSel< function_traits< RT (CT::*)(P1T )const > >{ typedef fastdelegate::FastDelegate1<P1T ,RT> R; };
template<class RT , class P1T > struct FDSel< function_traits< RT (P1T ) > >{ typedef fastdelegate::FastDelegate1<P1T ,RT> R; };
template<class RT, class CT, class P1T, class P2T > struct FDSel< function_traits< RT (CT::*)(P1T, P2T ) > >{ typedef fastdelegate::FastDelegate2<P1T, P2T ,RT> R; };
template<class RT, class CT, class P1T, class P2T > struct FDSel< function_traits< RT (CT::*)(P1T, P2T )const > >{ typedef fastdelegate::FastDelegate2<P1T, P2T ,RT> R; };
template<class RT , class P1T, class P2T > struct FDSel< function_traits< RT (P1T, P2T ) > >{ typedef fastdelegate::FastDelegate2<P1T, P2T ,RT> R; };
template<class RT, class CT, class P1T, class P2T, class P3T > struct FDSel< function_traits< RT (CT::*)(P1T, P2T, P3T ) > >{ typedef fastdelegate::FastDelegate3<P1T, P2T, P3T ,RT> R; };
template<class RT, class CT, class P1T, class P2T, class P3T > struct FDSel< function_traits< RT (CT::*)(P1T, P2T, P3T )const > >{ typedef fastdelegate::FastDelegate3<P1T, P2T, P3T ,RT> R; };
template<class RT , class P1T, class P2T, class P3T > struct FDSel< function_traits< RT (P1T, P2T, P3T ) > >{ typedef fastdelegate::FastDelegate3<P1T, P2T, P3T ,RT> R; };
template<class RT, class CT, class P1T, class P2T, class P3T, class P4T > struct FDSel< function_traits< RT (CT::*)(P1T, P2T, P3T, P4T ) > >{ typedef fastdelegate::FastDelegate4<P1T, P2T, P3T, P4T ,RT> R; };
template<class RT, class CT, class P1T, class P2T, class P3T, class P4T > struct FDSel< function_traits< RT (CT::*)(P1T, P2T, P3T, P4T )const > >{ typedef fastdelegate::FastDelegate4<P1T, P2T, P3T, P4T ,RT> R; };
template<class RT , class P1T, class P2T, class P3T, class P4T > struct FDSel< function_traits< RT (P1T, P2T, P3T, P4T ) > >{ typedef fastdelegate::FastDelegate4<P1T, P2T, P3T, P4T ,RT> R; };
template<class RT, class CT, class P1T, class P2T, class P3T, class P4T, class P5T > struct FDSel< function_traits< RT (CT::*)(P1T, P2T, P3T, P4T, P5T ) > >{ typedef fastdelegate::FastDelegate5<P1T, P2T, P3T, P4T, P5T ,RT> R; };
template<class RT, class CT, class P1T, class P2T, class P3T, class P4T, class P5T > struct FDSel< function_traits< RT (CT::*)(P1T, P2T, P3T, P4T, P5T )const > >{ typedef fastdelegate::FastDelegate5<P1T, P2T, P3T, P4T, P5T ,RT> R; };
template<class RT , class P1T, class P2T, class P3T, class P4T, class P5T > struct FDSel< function_traits< RT (P1T, P2T, P3T, P4T, P5T ) > >{ typedef fastdelegate::FastDelegate5<P1T, P2T, P3T, P4T, P5T ,RT> R; };
template<class RT, class CT, class P1T, class P2T, class P3T, class P4T, class P5T, class P6T > struct FDSel< function_traits< RT (CT::*)(P1T, P2T, P3T, P4T, P5T, P6T ) > >{ typedef fastdelegate::FastDelegate6<P1T, P2T, P3T, P4T, P5T, P6T ,RT> R; };
template<class RT, class CT, class P1T, class P2T, class P3T, class P4T, class P5T, class P6T > struct FDSel< function_traits< RT (CT::*)(P1T, P2T, P3T, P4T, P5T, P6T )const > >{ typedef fastdelegate::FastDelegate6<P1T, P2T, P3T, P4T, P5T, P6T ,RT> R; };
template<class RT , class P1T, class P2T, class P3T, class P4T, class P5T, class P6T > struct FDSel< function_traits< RT (P1T, P2T, P3T, P4T, P5T, P6T ) > >{ typedef fastdelegate::FastDelegate6<P1T, P2T, P3T, P4T, P5T, P6T ,RT> R; };
template<class RT, class CT, class P1T, class P2T, class P3T, class P4T, class P5T, class P6T, class P7T > struct FDSel< function_traits< RT (CT::*)(P1T, P2T, P3T, P4T, P5T, P6T, P7T ) > >{ typedef fastdelegate::FastDelegate7<P1T, P2T, P3T, P4T, P5T, P6T, P7T ,RT> R; };
template<class RT, class CT, class P1T, class P2T, class P3T, class P4T, class P5T, class P6T, class P7T > struct FDSel< function_traits< RT (CT::*)(P1T, P2T, P3T, P4T, P5T, P6T, P7T )const > >{ typedef fastdelegate::FastDelegate7<P1T, P2T, P3T, P4T, P5T, P6T, P7T ,RT> R; };
template<class RT , class P1T, class P2T, class P3T, class P4T, class P5T, class P6T, class P7T > struct FDSel< function_traits< RT (P1T, P2T, P3T, P4T, P5T, P6T, P7T ) > >{ typedef fastdelegate::FastDelegate7<P1T, P2T, P3T, P4T, P5T, P6T, P7T ,RT> R; };
template<class RT, class CT, class P1T, class P2T, class P3T, class P4T, class P5T, class P6T, class P7T, class P8T> struct FDSel< function_traits< RT (CT::*)(P1T, P2T, P3T, P4T, P5T, P6T, P7T, P8T) > >{ typedef fastdelegate::FastDelegate8<P1T, P2T, P3T, P4T, P5T, P6T, P7T, P8T,RT> R; };
template<class RT, class CT, class P1T, class P2T, class P3T, class P4T, class P5T, class P6T, class P7T, class P8T> struct FDSel< function_traits< RT (CT::*)(P1T, P2T, P3T, P4T, P5T, P6T, P7T, P8T)const > >{ typedef fastdelegate::FastDelegate8<P1T, P2T, P3T, P4T, P5T, P6T, P7T, P8T,RT> R; };
template<class RT , class P1T, class P2T, class P3T, class P4T, class P5T, class P6T, class P7T, class P8T> struct FDSel< function_traits< RT (P1T, P2T, P3T, P4T, P5T, P6T, P7T, P8T) > >{ typedef fastdelegate::FastDelegate8<P1T, P2T, P3T, P4T, P5T, P6T, P7T, P8T,RT> R; };
}
template<class F>
typename details::FDSel< typename details::FuncTraitsOf<F>::R >::R MakeDelegate(F& f){
return fastdelegate::MakeDelegate(&f, &F::operator());
}
将其复制/粘贴到您的 FastDelegate.h 文件中。
不要像这样使用它：
home.visit(fastdelegate::MakeDelegate([&](const Room& a){ /* ... */ }));
而是这样做：
auto d = [&](const Room& a){ /* ... */ };
home.visit(fastdelegate::MakeDelegate(d));
如果我错过了什么，请告诉我。
"平凡"函数和一般 lambda 函数之间的区别在于，如果它不属于第一个类（没有捕获），它就是一个函数对象。
如果您复制对象 （lambda） 并且它包含对临时对象的引用，或对堆栈分配对象的引用，这些对象将在 FastDelegate 被销毁之前释放，则您有一个悬而未决的引用，因此崩溃。
尝试通过复制而不是引用捕获
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