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我想了解一個庫實現，但是某些方法是動態鏈接的方式，讓我感到困惑。 我知道使用派生類的對象但沒有對象的調度機制，我不知道它是如何工作的。 我想了解的庫是gcc的libitm。在類之外聲明的方法的動態分派
頭文件libitm.h將所有ABI方法聲明爲沒有圍繞它們的類或結構的頂級方法。而且對於他們中的大多數人來說，我找到了一個獨特的定義，所以我對他們毫無疑問，並且在此省略。但下面的摘錄顯示了70種方法的聲明，這些定義讓我感到困惑。
typedef uint8_t _ITM_TYPE_U1;
typedef uint16_t _ITM_TYPE_U2;
typedef uint32_t _ITM_TYPE_U4;
typedef uint64_t _ITM_TYPE_U8;
typedef float _ITM_TYPE_F;
typedef double _ITM_TYPE_D;
typedef long double _ITM_TYPE_E;
typedef float _Complex _ITM_TYPE_CF;
typedef double _Complex _ITM_TYPE_CD;
typedef long double _Complex _ITM_TYPE_CE;
#define ITM_BARRIERS(T) \
extern _ITM_TYPE_##T _ITM_R##T(const _ITM_TYPE_##T *) ITM_REGPARM; \
extern _ITM_TYPE_##T _ITM_RaR##T(const _ITM_TYPE_##T *) ITM_REGPARM; \
extern _ITM_TYPE_##T _ITM_RaW##T(const _ITM_TYPE_##T *) ITM_REGPARM; \
extern _ITM_TYPE_##T _ITM_RfW##T(const _ITM_TYPE_##T *) ITM_REGPARM; \
extern void _ITM_W##T (_ITM_TYPE_##T *, _ITM_TYPE_##T) ITM_REGPARM; \
extern void _ITM_WaR##T (_ITM_TYPE_##T *, _ITM_TYPE_##T) ITM_REGPARM; \
extern void _ITM_WaW##T (_ITM_TYPE_##T *, _ITM_TYPE_##T) ITM_REGPARM;
ITM_BARRIERS(U1)
ITM_BARRIERS(U2)
ITM_BARRIERS(U4)
ITM_BARRIERS(U8)
ITM_BARRIERS(F)
ITM_BARRIERS(D)
ITM_BARRIERS(E)
ITM_BARRIERS(CF)
ITM_BARRIERS(CD)
ITM_BARRIERS(CE)
在文件dispatch.h一個結構abi_dispatch被聲明，其被用作用於TM-算法的特定調度的位置。在這個結構體中，上面70個方法的聲明是純虛擬方法。以下摘錄顯示了方法和結構的宏定義。
#define ITM_READ_M(T, LSMOD, M, M2) \
M _ITM_TYPE_##T ITM_REGPARM ITM_##LSMOD##T##M2 (const _ITM_TYPE_##T *ptr) \
{ \
return load(ptr, abi_dispatch::LSMOD); \
}
#define ITM_READ_M_PV(T, LSMOD, M, M2) \
M _ITM_TYPE_##T ITM_REGPARM ITM_##LSMOD##T##M2 (const _ITM_TYPE_##T *ptr) \
= 0;
#define ITM_WRITE_M(T, LSMOD, M, M2) \
M void ITM_REGPARM ITM_##LSMOD##T##M2 (_ITM_TYPE_##T *ptr, \
_ITM_TYPE_##T val) \
{ \
store(ptr, val, abi_dispatch::LSMOD); \
}
#define ITM_WRITE_M_PV(T, LSMOD, M, M2) \
M void ITM_REGPARM ITM_##LSMOD##T##M2 (_ITM_TYPE_##T *ptr, \
_ITM_TYPE_##T val) \
= 0;
#define CREATE_DISPATCH_METHODS_T(T, M, M2) \
ITM_READ_M(T, R, M, M2) \
ITM_READ_M(T, RaR, M, M2) \
ITM_READ_M(T, RaW, M, M2) \
ITM_READ_M(T, RfW, M, M2) \
ITM_WRITE_M(T, W, M, M2) \
ITM_WRITE_M(T, WaR, M, M2) \
ITM_WRITE_M(T, WaW, M, M2)
#define CREATE_DISPATCH_METHODS_T_PV(T, M, M2) \
ITM_READ_M_PV(T, R, M, M2) \
ITM_READ_M_PV(T, RaR, M, M2) \
ITM_READ_M_PV(T, RaW, M, M2) \
ITM_READ_M_PV(T, RfW, M, M2) \
ITM_WRITE_M_PV(T, W, M, M2) \
ITM_WRITE_M_PV(T, WaR, M, M2) \
ITM_WRITE_M_PV(T, WaW, M, M2)
#define CREATE_DISPATCH_METHODS(M, M2) \
CREATE_DISPATCH_METHODS_T (U1, M, M2) \
CREATE_DISPATCH_METHODS_T (U2, M, M2) \
CREATE_DISPATCH_METHODS_T (U4, M, M2) \
CREATE_DISPATCH_METHODS_T (U8, M, M2) \
CREATE_DISPATCH_METHODS_T (F, M, M2) \
CREATE_DISPATCH_METHODS_T (D, M, M2) \
CREATE_DISPATCH_METHODS_T (E, M, M2) \
CREATE_DISPATCH_METHODS_T (CF, M, M2) \
CREATE_DISPATCH_METHODS_T (CD, M, M2) \
CREATE_DISPATCH_METHODS_T (CE, M, M2)
#define CREATE_DISPATCH_METHODS_PV(M, M2) \
CREATE_DISPATCH_METHODS_T_PV (U1, M, M2) \
CREATE_DISPATCH_METHODS_T_PV (U2, M, M2) \
CREATE_DISPATCH_METHODS_T_PV (U4, M, M2) \
CREATE_DISPATCH_METHODS_T_PV (U8, M, M2) \
CREATE_DISPATCH_METHODS_T_PV (F, M, M2) \
CREATE_DISPATCH_METHODS_T_PV (D, M, M2) \
CREATE_DISPATCH_METHODS_T_PV (E, M, M2) \
CREATE_DISPATCH_METHODS_T_PV (CF, M, M2) \
CREATE_DISPATCH_METHODS_T_PV (CD, M, M2) \
CREATE_DISPATCH_METHODS_T_PV (CE, M, M2)
struct abi_dispatch
{
public:
enum ls_modifier { NONTXNAL, R, RaR, RaW, RfW, W, WaR, WaW };
public:
CREATE_DISPATCH_METHODS_PV(virtual,)
}
abi_dispatch的衍生結構可以在例如method-ml或method-gl找到。他們使用CREATE_DISPATCH_METHODS（virtual，）和上面的宏來生成70個讀/寫方法，並將它們映射到加載/存儲模板函數。
我的一個大問題是：當調用某個庫函數時，運行系統如何知道應該使用哪個方法定義（method-gl或method-ml中的那個）？在讀/寫方法的定義中，沒有提到abi_dispatch對象。在線程本地存儲中存在一個abi-dispatch對象，但我不知道如何適合這個。
謝謝你的幫助。