我有以下类似于我的代码库的程序。一个FunctionState类,它执行某种算法(可能在多个线程中),一个Function类控制FunctionState类的使用方式,并可能进行一些算法设置/拆卸操作。
#include <iostream>
#include <vector>
class FunctionState;
class Function {
public:
virtual FunctionState* NewFunctionState() = 0;
protected:
std::vector<FunctionState*> states;
};
class FunctionState {
public:
FunctionState(Function* func) : mFunc(func) {}
virtual void RunState() = 0;
void ExecuteFunctionLotsAndLotsOfTimes();
private:
Function* mFunc;
};
#define VERY_BIG_NUMBER 10
void FunctionState::ExecuteFunctionLotsAndLotsOfTimes() {
for(int i = 0; i < VERY_BIG_NUMBER; ++i) {
RunState();
}
};
class PrintFunction : public Function {
FunctionState* NewFunctionState();
};
class PrintFunctionState : public FunctionState {
public:
PrintFunctionState(PrintFunction* func) : FunctionState(func) {}
void RunState() override {
std::cout << "in print function state" << '\n';
}
};
FunctionState* PrintFunction::NewFunctionState() {
FunctionState* state = new PrintFunctionState(this);
states.push_back(state);
return state;
}
class AddFunction : public Function {
FunctionState* NewFunctionState();
};
class AddFunctionState : public FunctionState {
public:
AddFunctionState(AddFunction* func) : FunctionState(func), x(0) {}
void RunState() override {
++x;
}
private:
int x;
};
FunctionState* AddFunction::NewFunctionState() {
FunctionState* state = new AddFunctionState(this);
states.push_back(state);
return state;
}
int main() {
Function* func = new PrintFunction();
Function* func2 = new AddFunction();
std::vector<Function*> vec = {func, func2};
for(auto& func : vec) {
func->NewFunctionState()->ExecuteFunctionLotsAndLotsOfTimes();
}
return 0;
}
现在我已经分析了我的代码,并且已经看到FunctionState :: ExecuteFunctionLotsAndLotsOfTimes()有一个热点。问题是这个函数循环很多次并调用RunState(),它是FunctionState类的虚函数。在那里,我执行了许多操作,这些操作可能会从L1缓存中清除vtable指针,导致循环的每次迭代都会丢失L1缓存。
所以我想删除虚拟呼叫的需要。我决定用CRTP做一个好方法。 FunctionState类将获取实现它的类的类型的模板参数,并调用它的适当方法,不需要对RunState()进行虚拟调用。
现在,当我尝试将其移至CRTP时,我遇到了一些与Function类有关的问题:
我是否还需要将模板参数添加到Function类中?
第3。如果我模板化,那么Function对象的构造会是什么样子?如何删除使用Function对象指定类型参数的类的需要?
请注意,这只是我真实代码库的一个简单版本。真正的代码库是10K +代码行(不是无法管理的,但完全重写是不可能的)。
此外,如果有另一种方法可以删除不涉及CRTP的RunState()虚拟调用,那么这也是值得赞赏的。
我尝试使用CRTP:
#include <iostream>
#include <vector>
class Function;
template<class T>
class FunctionState {
public:
FunctionState(Function* func) : mFunc(func) {}
void RunState() {
static_cast<T*>(this)->RunState();
};
void ExecuteFunctionLotsAndLotsOfTimes();
private:
Function* mFunc;
};
class Function {
public:
virtual FunctionState* NewFunctionState() = 0;
protected:
std::vector<FunctionState*> states;
};
#define VERY_BIG_NUMBER 10
template <typename T>
void FunctionState<T>::ExecuteFunctionLotsAndLotsOfTimes() {
for(int i = 0; i < VERY_BIG_NUMBER; ++i) {
RunState();
}
};
class PrintFunctionState;
class PrintFunction : public Function {
PrintFunctionState* NewFunctionState();
};
class PrintFunctionState : public FunctionState<PrintFunctionState> {
public:
PrintFunctionState(PrintFunction* func) : FunctionState<PrintFunctionState>(func) {}
void RunState() {
std::cout << "in print function state" << '\n';
}
};
PrintFunctionState* PrintFunction::NewFunctionState() {
PrintFunctionState* state = new PrintFunctionState(this);
states.push_back(state);
return state;
}
class AddFunctionState;
class AddFunction : public Function {
AddFunctionState* NewFunctionState();
};
class AddFunctionState : public FunctionState<AddFunctionState> {
public:
AddFunctionState(AddFunction* func) : FunctionState<AddFunctionState>(func), x(0) {}
void RunState() {
++x;
}
private:
int x;
};
AddFunctionState* AddFunction::NewFunctionState() {
AddFunctionState* state = new AddFunctionState(this);
states.push_back(state);
return state;
}
int main() {
Function* func = new PrintFunction();
Function* func2 = new AddFunction();
std::vector<Function*> vec = {func, func2};
for(auto& func : vec) {
func->NewFunctionState()->ExecuteFunctionLotsAndLotsOfTimes();
}
return 0;
}
答案 0 :(得分:2)
基于类型擦除和CRTP的混合解决方案怎么样? 它遵循一个基于问题片段的最小的工作示例:
#include <iostream>
#include <vector>
class PrintFunctionState;
class AddFunctionState;
class FunctionState;
class Function {
template<typename T>
static FunctionState * InternalNewFunctionState(Function *self, std::vector<FunctionState*> &states) {
FunctionState* state = new T(self);
states.push_back(state);
return state;
}
public:
template<typename T>
static Function * create() {
Function *func = new Function;
func->internalNewFunctionState = &InternalNewFunctionState<T>;
return func;
}
FunctionState* NewFunctionState() {
return internalNewFunctionState(this, states);
}
private:
FunctionState * (*internalNewFunctionState)(Function *, std::vector<FunctionState*> &);
std::vector<FunctionState*> states;
};
class FunctionState {
public:
FunctionState() = default;
virtual ~FunctionState() = default;
virtual void ExecuteFunctionLotsAndLotsOfTimes() = 0;
};
template<typename Derived>
class IntermediateFunctionState: public FunctionState {
public:
IntermediateFunctionState(Function* func) : mFunc(func) {}
void ExecuteFunctionLotsAndLotsOfTimes() override {
Derived *self = static_cast<Derived *>(this);
for(int i = 0; i < 10; ++i) {
self->RunState();
}
}
private:
Function* mFunc;
};
class PrintFunctionState : public IntermediateFunctionState<PrintFunctionState> {
public:
PrintFunctionState(Function* func) : IntermediateFunctionState(func) {}
void RunState() {
std::cout << "in print function state" << '\n';
}
};
class AddFunctionState : public IntermediateFunctionState<AddFunctionState> {
public:
AddFunctionState(Function* func) : IntermediateFunctionState(func), x(0) {}
void RunState() {
std::cout << "in add function state" << '\n';
++x;
}
private:
int x;
};
int main() {
Function* func = Function::create<PrintFunctionState>();
Function* func2 = Function::create<AddFunctionState>();
std::vector<Function*> vec = { func, func2 };
for(auto& func : vec) {
func->NewFunctionState()->ExecuteFunctionLotsAndLotsOfTimes();
}
return 0;
}
我删除了几个不再需要的课程 希望代码说明一切,请在评论中告诉我是否可以添加更多详细信息。
答案 1 :(得分:0)
Function
必须使用非模板类型作为NewFunctionState
的返回值,因此您需要一个额外的基类
class FunctionStateBase {
virtual void ExecuteFunctionLotsAndLotsOfTimes() = 0;
// No void RunState()!
}
template<typename T>
class FunctionState {
void ExecuteFunctionLotsAndLotsOfTimes();
// Still no void RunState()!
}
class PrintFunctionState : public FunctionState<PrintFunctionState> {
void RunState();
}
template <typename T>
void FunctionState<T>::ExecuteFunctionLotsAndLotsOfTimes() {
for(int i = 0; i < VERY_BIG_NUMBER; ++i) {
static_cast<T*>(this)->RunState(); // Statically bound!
}
};
答案 2 :(得分:0)
如果我正确理解您的问题,可以使用模板链接解决这个问题。这是一个很好的例子:
#include <iostream>
/*
Just make print invocations a little less cluttered for our purposes here.
*/
template <typename Type>
void Show(Type value)
{
std::cout << value << std::endl;
}
/*
Base class for function types
*/
template <typename Self>
class Function
{
public:
/*
For the best performance possible, we'll always inline this function.
*/
inline void RunState()
{
static_cast<Self*>(this)->RunState();
}
void ExecuteFunctionLotsAndLotsOfTimes(int iterations = 1)
{
for(int i = 0; i < iterations; ++i)
{
Show("...Loop...");
RunState();
}
}
};
/*
Everything here is placed in an internal namespace, as none of it will be used by the caller.
*/
namespace Internal_
{
/*
ChainFunctionLink works like an array of functions. Each of it's members
is either some kind of function object or another ChainFunctionLink.
*/
template <typename First, typename Second>
struct ChainFunctionLink : Function<ChainFunctionLink<First, Second>>
{
ChainFunctionLink(First first, Second second)
: first(first), second(second)
{ }
inline void RunState()
{
first.RunState();
second.RunState();
}
First
first;
Second
second;
};
/*
We won't be able to explicitly specify the template parameters of ChainFunctionLink
later, so a generating function will be needed to deduce them for us.
*/
template <typename First, typename Second>
ChainFunctionLink<First, Second> MakeChainFunctionLink(First first, Second second)
{
return ChainFunctionLink<First, Second>(first, second);
}
} // namespace Internal_
/*
ChainFunction generates ChainFunctionLink's for the caller.
*/
template <typename First, typename Second, typename ...Next>
auto ChainFunction(First first, Second second, Next ...next)
{
return Internal_::MakeChainFunctionLink(first, ChainFunction(second, next...));
}
/*
The last link in the chain.
*/
template <typename Last>
Last ChainFunction(Last last)
{
return last;
}
// Example usage:
class PrintFunction : public Function<PrintFunction>
{
public:
inline void RunState()
{
Show("PrintFunction::RunState()");
}
};
class AddFunction : public Function<AddFunction>
{
public:
inline void RunState()
{
Show("AddFunction::RunState()");
}
};
int main()
{
auto
chain = ChainFunction(AddFunction(), AddFunction(), AddFunction(), PrintFunction());
chain.ExecuteFunctionLotsAndLotsOfTimes(4);
}
当然,以这种方式将成千上万个功能对象链接在一起可能是不切实际的,但它确实允许你内联(和解耦)几乎所有东西。
修改强>
该特定类型的实现还有一个警告:链式函数按值 存储 。如果您想避免这种情况,只需重新定义ChainFunctionLink
的成员first
和second
作为参考。暂时不允许您将临时值作为参数传递给ChainFunction
,当然......