AutoSharedLibrary -- 基於模板元編程技術的跨平臺C++動態連接載入庫

 基於模板元編程技術的跨平臺C++動態連接載入庫。經過模板技術，使用者僅需經過簡單的宏，就能夠使編譯器在編譯期本身主動生成載入動態連接庫導出符號的代碼，無不論什麼額外的執行時開銷。

extern "C"
{
    typedef int(*Proc_fnTestDll)();
    typedef const char* (*Proc_fnTestDll2)(const char*);
}


ASL_LIBRARY_BEGIN(Test)
    // 強制載入名爲fnTestDll的接口，假設沒有該接口。則拋SymbolNotFound異常
    ASL_SYMBOL_EXPLICIT(Proc_fnTestDll, fnTestDll)
 // 載入名爲<span style="font-family: Arial, Helvetica, sans-serif;">fnTestDll2的接口，假設沒有該接口，則爲NULL</span>
ASL_SYMBOL_OPTIONAL(Proc_fnTestDll2, fnTestDll2)
// 載入名爲shouldFail的接口，假設沒有該接口。則爲NULL</span>
ASL_SYMBOL_OPTIONAL(Proc_fnTestDll2, shouldFail) // non-exists
    // 載入名爲testFunc的接口，接口函數的類型由調用時的實參類型決定
    ASL_SYMBOL_EXPLICIT_T(testFunc) // Enabled only when ' #define  ASL_USE_CPP11 1 ' and compliler supports c++ 11
ASL_LIBRARY_END()

int _tmain(int argc, _TCHAR* argv[])
{
    using namespace std;

    Test test;

    try {
        test.Load(_T("testDll.dll"));
    }
    catch (const ASL::LibraryNotFoundException& e)
    {
        cout << "Lib not found " <<  e.what() << endl;
    }
    catch (const ASL::SymbolNotFoundException& e) {
        cout << "Sym not found " <<  e.what() << endl;
    }

    assert(test.shouldFail == NULL);
    cout << test.fnTestDll() << endl;
    cout << test.fnTestDll2("hELLO, WORLD") << endl;
 // testFunc函數的簽名由此處的實參類型推導出來，int爲其返回值類型,
    // 這樣的調用方式並不安全。慎用！
   cout << test.testFunc<int>(ASL_ARGS_T（(int)1, (int)2.f)) << endl;

   test.Unload();

   getchar();

   return 0;

}

ASL_SYMBOL宏的第三個參數表示。假設該符號載入失敗（模塊並無導出該接口），是否拋出SymbolNotFoundException。 爲false時，拋出異常，終止連接庫載入流程，並且e.what()爲載入失敗的符號名稱。爲true時，忽略錯誤，仍然繼續載入其它符號。client可以依據相應的接口是否爲NULL來推斷該符號是否載入成功。

/********************************************************************
	created:	2014/05/31
	file base:	AutoSharedLibrary
	file ext:	h
	author:		qiuhan (hanzz2007@hotmail.com)

	purpose:	Cross platform classes and macros to make dynamic loaded module
	easy to use by using c++ template meta-programming technic.

	No need to make any changes to existing module code.

	Support both windows(*.dll) and linux(*.so) platforms (wchar_t & char).

	SPECIAL THANKS TO TRL (Template Relection Library)

	usage:
	Following codes are all in client side:

	ASL_LIBRARY_BEGIN(ClassName)
		ASL_SYMBOL_OPTIONAL(Func1Type, func1)
		ASL_SYMBOL_EXPLICIT(Func2Type, func2)
		// Enabled only when ' #define  ASL_USE_CPP11 1 ' and compliler supports c++ 11
		ASL_SYMBOL_EXPLICIT_T(func4) // only need to declare the name
	ASL_LIBRARY_END()

	ClassName theLib;
	try {
	theLib.Load("./1.so");
	}
	catch (LibraryNotFoundException& e) {
	}
	catch (SymbolNotFoundException& e) {
	}
	theLib.func1(1);
	theLib.func2("aa");

	// The function type is deduced with the args
	// retType => int, args => const char* AND float
	// So this calling is UNSAFE!
	// You'd better explicitly specifiy the type of args like this
	theLib.func4<int>(ASL_ARGS_T((const char*)"test", (float)2.3));

	theLib.Unload();


*********************************************************************/

#ifndef ASL_INCLUDE_H
#define  ASL_INCLUDE_H

#ifdef WIN32
#include <windows.h>
#else
#include <dlfcn.h>
#endif


#include <cstdlib>
#include <exception>
#include <string>

#if ASL_USE_CPP11
#include <functional>
#include <tuple>
#endif


namespace ASL {

	namespace Private {

		template <class Head_, class Tail_>
		struct TypeList
		{
			typedef Head_ Head;
			typedef Tail_ Tail;
		};

		class NullType {};

		template <int i_>
		struct Int2Type
		{
			enum { value = i_ };
		};

		template <int condition_, class T0_, class T1_>
		struct Select
		{
			typedef T0_ Result;
		};

		template <class T0_, class T1_>
		struct Select<false, T0_, T1_>
		{
			typedef T1_ Result;
		};

		template <int condition_, int v0_, int v1_>
		struct SelectInt
		{
			enum { value = v0_ };
		};

		template <int v0_, int v1_>
		struct SelectInt<false, v0_, v1_>
		{
			enum { value = v1_ };
		};

		template <class Type_, int Ignore_>
		struct MemberInfo
		{
			typedef Type_ Type;
			enum {
				ignore = Ignore_
			};
		};


		template <class TList_, int startLine_, int endLine_, class ConcreteClass_>
		struct CreateMemberIndicesImpl
		{
			typedef typename ConcreteClass_::template IsMemberPresent<endLine_> IsMemberPresent;
			enum { isMemberPresent = IsMemberPresent::value };

			typedef typename Select< isMemberPresent
				, TypeList<MemberInfo<Int2Type<IsMemberPresent::index>, IsMemberPresent::ignoreError >, TList_>
				, TList_ >::Result NewTList;

			typedef CreateMemberIndicesImpl<NewTList, startLine_, endLine_ - 1, ConcreteClass_> MemberIndicesImpl;
			typedef typename MemberIndicesImpl::Indices Indices;
		};


		template <class TList_, int startLine_, class ConcreteClass_>
		struct CreateMemberIndicesImpl<TList_, startLine_, startLine_, ConcreteClass_>
		{
			typedef TList_ Indices;
		};


		template <int startLine_, int endLine_, class ConcreteClass_>
		struct CreateMemberIndices
		{
			typedef CreateMemberIndicesImpl< NullType, startLine_
				, endLine_ - 1, ConcreteClass_ > MemberIndicesImpl;
			typedef typename MemberIndicesImpl::Indices Indices;
		};


		template <class ConcreteClass_, int startLine_, int currentLine_>
		struct GetMemberIndex
		{
			typedef typename ConcreteClass_::template IsMemberPresent<currentLine_> IsMemberPresent;

			enum {
				index = SelectInt< IsMemberPresent::value
				, IsMemberPresent::index
				, GetMemberIndex<ConcreteClass_, startLine_, currentLine_ - 1>::index >::value + 1
			};
		};

		template <class ConcreteClass_, int startLine_>
		struct GetMemberIndex<ConcreteClass_, startLine_, startLine_>
		{
			enum { index = -1 };
		};


#if ASL_USE_CPP11
		typedef	void* FuncType;

		// Pack of numbers.
		// Nice idea, found at http://stackoverflow.com/questions/7858817/unpacking-a-tuple-to-call-a-matching-function-pointer
		template<int ...> struct Seq {};

		// Metaprogramming Expansion
		template<int N, int ...S> struct GenList : GenList < N - 1, N - 1, S... > {};
		template<int ...S> struct GenList < 0, S... >
		{
			typedef Seq<S...> Result;
		};

			// Function that performs the actual call
			template<typename Ret_, int ...S_, typename...Args_>
			Ret_ ActualCall(Seq<S_...>, std::tuple<Args_...> tpl, const std::function<Ret_(Args_...)>& func)
			{
				// It calls the function while expanding the std::tuple to it's arguments via std::get<S>
				return func(std::get<S_>(tpl) ...);
			}
#endif
	}

	class DefaultLibraryLoader
	{
	public:
		typedef void* LibHandle;

		DefaultLibraryLoader()
		{
			lib_handle = NULL;
		}

		template<class Char_>
		bool Load(const Char_* name)
		{
#if defined(WIN32)
			lib_handle = LoadLibrary(name);
#else
			lib_handle = dlopen(name, RTLD_LAZY);
#endif
			return lib_handle != NULL;
		}

		void Unload()
		{
			if (!IsLoaded()) {
				return;
			}

#if defined(WIN32)
			FreeLibrary((HMODULE)lib_handle);
#elif !defined(_ANDROID)
			dlclose(lib_handle);
#endif

			lib_handle = NULL;
		}

		template<class Char_>
		void* LoadSymbol(const Char_* fun_name)
		{
#if defined(WIN32)
			return (void *)GetProcAddress((HMODULE)lib_handle, fun_name);
#elif !defined(_ANDROID)
			return dlsym(lib_handle, fun_name);
#endif
		}

		bool IsLoaded() const
		{
			return lib_handle != NULL;
		}

	private:
		LibHandle lib_handle;
	};

	class LibraryNotFoundException : public std::exception
	{
	public:
		LibraryNotFoundException(const char* err)
		{
			_err = err;
		}

		LibraryNotFoundException(const wchar_t* err)
		{
			static const size_t CONVERT_LEN = 256;
#if _MSC_VER
#pragma warning(push)
#pragma warning(disable: 4996)
#endif
			char mbsBuff[CONVERT_LEN + 1] = { 0 };
			std::wcstombs(mbsBuff, err, CONVERT_LEN);
			_err = mbsBuff;
#if _MSC_VER
#pragma warning(pop)
#endif
		}

		~LibraryNotFoundException() throw() {}

		virtual const char* what() const throw() {
			return _err.c_str();
		}
	private:
		std::string _err;
	};

	class SymbolNotFoundException : public std::exception
	{
	public:
		SymbolNotFoundException(const char* err)
		{
			_err = err;
		}

		SymbolNotFoundException(const wchar_t* err)
		{
			static const size_t CONVERT_LEN = 256;
#if _MSC_VER
#pragma warning(push)
#pragma warning(disable: 4996)
#endif
			char mbsBuff[CONVERT_LEN + 1] = { 0 };
			std::wcstombs(mbsBuff, err, CONVERT_LEN);
			_err = mbsBuff;
#if _MSC_VER
#pragma warning(pop)
#endif
		}

		~SymbolNotFoundException() throw() { }

		virtual const char* what() const throw() {
			return _err.c_str();
		}

	private:
		std::string _err;
	};

	struct DefaultErrorHandler
	{
		template<class Char_>
		static void OnLoadLibrary(const Char_* libName)
		{
			throw LibraryNotFoundException(libName);
		}

		template<class Char_>
		static void OnLoadSymbol(const Char_* symbolName, const bool ignore)
		{
			if (!ignore) {
				throw SymbolNotFoundException(symbolName);
			}
		}
	};

	template < class ConcreteClass_,
				class Loader_ = DefaultLibraryLoader,
				class ErrorHandler_ = DefaultErrorHandler >
	class AutoSharedLibrary
	{
	public:
		AutoSharedLibrary()
		{
		}

		~AutoSharedLibrary()
		{
			Unload();
		}

		template<class Char_>
		void Load(ConcreteClass_& object, const Char_* p)
		{
			if (!_loader.Load(p)) {
				ErrorHandler_::OnLoadLibrary(p);
			}
			typedef typename ConcreteClass_::MemberIndices Indices;
			LoadSymbols(object, Indices());
		}

		void Unload()
		{
			_loader.Unload();
		}

	private:
		template <class Indices_>
		void LoadSymbols(ConcreteClass_& object, Indices_ indices)
		{
			typedef typename Indices_::Head SymInfo;
			typedef typename SymInfo::Type Index;

			bool ret = LoadSymbol(ConcreteClass_::getLoadName(Index()),
				object.*ConcreteClass_::getMemberPtr(Index()));
			if (!ret) {
				ErrorHandler_::OnLoadSymbol(ConcreteClass_::getLoadName(Index()), (bool)SymInfo::ignore);
			}
			LoadSymbols(object, typename Indices_::Tail());
		}

		void LoadSymbols(ConcreteClass_& object, Private::NullType indices)
		{
		}

		template <class FuncType_, class Char_>
		bool LoadSymbol(const Char_* funcName, FuncType_& func)
		{
			func = (FuncType_)_loader.LoadSymbol(funcName);
			return func != NULL;
		}

		Loader_ _loader;
	};

}

#define ASL_LIBRARY_BEGIN(ConcreteClass_) \
    ASL_LIBRARY_BEGIN_2(ConcreteClass_, ASL::DefaultLibraryLoader, ASL::DefaultErrorHandler)

#define ASL_LIBRARY_BEGIN_2(ConcreteClass_, LibraryLoader_, ErrorHandler_) \
class ConcreteClass_ {                                  \
private:                                                \
    typedef ConcreteClass_ ConcreteClass;               \
enum { startLine = __LINE__ };                          \
    ASL::AutoSharedLibrary<ConcreteClass_, LibraryLoader_, ErrorHandler_> _libLoader;  \
public:                                                 \
    ConcreteClass_() { }                                \
    \
    ~ConcreteClass_() { Unload(); }                     \
    \
    template<class Char_> void Load(const Char_* p)     \
{                                                       \
    _libLoader.Load(*this, p);                          \
}                                                       \
    void Unload()                                       \
{                                                       \
    _libLoader.Unload();                                \
}                                                       \
    template <int lineNb_, class Dummy_ = ASL::Private::NullType> \
struct IsMemberPresent                                  \
{                                                    \
enum { value = false };                                 \
enum { index = 0 };                                     \
enum { ignoreError = false };                           \
};

#define ASL_SYMBOL(DataType, name, loadName, ignoreNotFound)          \
public:                                                 \
    DataType name;                                      \
private:                                                \
    typedef DataType ConcreteClass::* MemberPtr##name;  \
public:                                                 \
    template <class Dummy_>                             \
struct IsMemberPresent<__LINE__, Dummy_>                \
{                                                    \
enum { value = true };                                  \
enum { index = ASL::Private::GetMemberIndex<            \
    ConcreteClass, startLine, __LINE__ - 1>::index }; \
enum { ignoreError = ignoreNotFound};           \
};                                                  \
    static const char* getLoadName(                     \
    ASL::Private::Int2Type<IsMemberPresent<__LINE__>::index >) \
{ return #loadName; }                           \
    static MemberPtr##name getMemberPtr(            \
    ASL::Private::Int2Type< IsMemberPresent<__LINE__>::index >) \
{ return &ConcreteClass::name; }

#if ASL_USE_CPP11

#define ASL_SYMBOL_T(name, loadName, ignoreNotFound)					\
		ASL_SYMBOL(ASL::Private::FuncType, name##_private_, loadName, ignoreNotFound)   \
		template<class Ret_, class... Args_> Ret_ name (std::tuple<Args_...> args)		\
		{ \
			typedef Ret_(*FuncPointer)(Args_...); \
			std::function<Ret_(Args_...)> func = reinterpret_cast<FuncPointer>(name##_private_);  \
			return ASL::Private::ActualCall(typename ASL::Private::GenList<sizeof...(Args_)>::Result(), args, func); \
		}

#define ASL_SYMBOL_EXPLICIT_T(name) \
		ASL_SYMBOL_T(name, name, false)

#define ASL_ARGS_T(...) (std::make_tuple<>(__VA_ARGS__))

#endif

#define ASL_SYMBOL_DEFAULT(DataType, name, ignoreNotFound) \
		ASL_SYMBOL(DataType, name, name, ignoreNotFound)

#define ASL_SYMBOL_OPTIONAL(DataType, name) \
	    ASL_SYMBOL_DEFAULT(DataType, name, true)

#define ASL_SYMBOL_EXPLICIT(DataType, name) \
	    ASL_SYMBOL_DEFAULT(DataType, name, false)


#define ASL_LIBRARY_END()                               \
private:                                                \
enum { endLine = __LINE__ };                            \
public:                                                 \
    typedef ASL::Private::CreateMemberIndices<startLine, endLine, ConcreteClass> \
    ::Indices MemberIndices;                            \
};

#endif