Brew中的Module的实现方法
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Chunlin Zhang
May 20, 2009, 2:18:47 AM5/20/09
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http://haorui215.javaeye.com/blog/385580
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Brew中的Module的实现方法：
【原创作者：shosh，http://www.yuleyx.com/shosh】
我们从AEEModGen.c中提供的用于创建Module对象的对外接口入手，函数如下：
01int AEEStaticMod_New(int16 nSize, IShell *pIShell, void *ph, IModule **ppMod,
02 PFNMODCreateINST pfnMC,PFNFREEMODDATA pfnMF)
03{
04 AEEMod *pMe = NULL;
05 VTBL(IModule) *modFuncs;
……………省略第6到73行的代码…………………
74}
01int AEEStaticMod_New(int16 nSize, IShell *pIShell, void *ph, IModule **ppMod,
02 PFNMODCreateINST pfnMC,PFNFREEMODDATA pfnMF)
03{
04 AEEMod *pMe = NULL;
05 VTBL(IModule) *modFuncs;
……………省略第6到73行的代码…………………
74}
第4行申请AEEMod结构体类型的pMe指针，该结构体的定义如下：
01//Structure that implements the IModule interface
02typedef struct _AEEMod
03{
04 DECLARE_VTBL(IModule) // Virtual Table with pointers to IModule functions
05
06 uint32 m_nRefs; // Reference count for this module
07 IShell * m_pIShell; // Pointer to IShell
08
09 //Address of CreateInstance function of the module. This is needed for
10 // static modules
11 PFNMODCreateINST pfnModCrInst;
12
13 //Address of the function to free the module data. This is needed for static
14 // modules that define their own data.
15 PFNFREEMODDATA pfnModFreeData;
16
17} AEEMod;
01//Structure that implements the IModule interface
02typedef struct _AEEMod
03{
04 DECLARE_VTBL(IModule) // Virtual Table with pointers to IModule functions
05
06 uint32 m_nRefs; // Reference count for this module
07 IShell * m_pIShell; // Pointer to IShell
08
09 //Address of CreateInstance function of the module. This is needed for
10 // static modules
11 PFNMODCreateINST pfnModCrInst;
12
13 //Address of the function to free the module data. This is needed for static
14 // modules that define their own data.
15 PFNFREEMODDATA pfnModFreeData;
16
17} AEEMod;
在该结构体的第4行，声明了一个Virtual Table(虚拟表：专门用来来存放函数指针的结构体，不过此处是指向该结构体的指针），这个是重点，待会将展开来讲。第6行的m_nRefs是模仿COM中的计数器，第11行和第15行的两个函数指针成员，其中pfnModCrInst是用来存放创建Module本身的函数（地址），而pfnModFreeData是Module自身提供释放自身数据的函数指针。
下面我们将结构体中的第四行DECLARE_VTBL(IModule)展开：
先来看看DECLARE_VTBL的定义：
1// Use as first member of classes that override QINTERFACE()
2#define DECLARE_VTBL(iname) iname vt##iname;
1// Use as first member of classes that override QINTERFACE()
2#define DECLARE_VTBL(iname) iname vt##iname;
所以DECLARE_VTBL(IModule)就是： IModule vtIModule;
IModule是一个结构体类型，定义如下：
1typedef struct _IModule IModule;
1typedef struct _IModule IModule;
所以，我们需要了解_IModule的结构体是什么样子的。我们需要从下面的四行代码入手，不过下面主要是两个宏定义，需要展开才能够明白它们到底是什么东西。
1QINTERFACE(IModule)
2{
3 INHERIT_IModule(IModule);
4};
1QINTERFACE(IModule)
2{
3 INHERIT_IModule(IModule);
4};
下面是所有相关的宏定义，先贴出来，然后再用这些定义将上面的4行慢慢展开：
01typedef struct _IModule IModule;
02#define INHERIT_IModule(iname) \
03 INHERIT_IBase(iname); \
04 int (*CreateInstance)(iname * po,IShell * pIShell,AEECLSID ClsId,void ** ppObj); \
05 void (*FreeResources)(iname * po, IHeap * ph, IFileMgr * pfm)
06
07QINTERFACE(IModule)
08{
09 INHERIT_IModule(IModule);
10};
11#define IMODULE_AddRef(p) GET_PVTBL(p,IModule)->AddRef(p)
12#define IMODULE_Release(p) GET_PVTBL(p,IModule)->Release(p)
13#define IMODULE_CreateInstance(p,ps,id,ppo) GET_PVTBL(p,IModule)->CreateInstance(p,ps,id,ppo)
14#define IMODULE_FreeResources(p,ph,pfm) GET_PVTBL(p,IModule)->FreeResources(p,ph,pfm)
15
16#define QINTERFACE(iname) struct _##iname {\
17 struct VTBL(iname) *pvt;\
18 };\
19 typedef struct VTBL(iname) VTBL(iname);\
20 struct VTBL(iname)
21
22#define VTBL(iname) iname##Vtbl
23
24#define INHERIT_IBase(iname) \
25 uint32 (*AddRef) (iname*);\
26 uint32 (*Release) (iname*)
01typedef struct _IModule IModule;
02#define INHERIT_IModule(iname) \
03 INHERIT_IBase(iname); \
04 int (*CreateInstance)(iname * po,IShell * pIShell,AEECLSID ClsId,void ** ppObj); \
05 void (*FreeResources)(iname * po, IHeap * ph, IFileMgr * pfm)
06
07QINTERFACE(IModule)
08{
09 INHERIT_IModule(IModule);
10};
11#define IMODULE_AddRef(p) GET_PVTBL(p,IModule)->AddRef(p)
12#define IMODULE_Release(p) GET_PVTBL(p,IModule)->Release(p)
13#define IMODULE_CreateInstance(p,ps,id,ppo) GET_PVTBL(p,IModule)->CreateInstance(p,ps,id,ppo)
14#define IMODULE_FreeResources(p,ph,pfm) GET_PVTBL(p,IModule)->FreeResources(p,ph,pfm)
15
16#define QINTERFACE(iname) struct _##iname {\
17 struct VTBL(iname) *pvt;\
18 };\
19 typedef struct VTBL(iname) VTBL(iname);\
20 struct VTBL(iname)
21
22#define VTBL(iname) iname##Vtbl
23
24#define INHERIT_IBase(iname) \
25 uint32 (*AddRef) (iname*);\
26 uint32 (*Release) (iname*)
先将QINTERFACE(IModule)展开，根据上面第16到20行的定义以及第22行VTBL的定义，得到：
1struct _IModule {
2 struct IModuleVtbl *pvt;
3 };
4 typedef struct IModuleVtbl IModuleVtbl;
5 struct IModuleVtbl
1struct _IModule {
2 struct IModuleVtbl *pvt;
3 };
4 typedef struct IModuleVtbl IModuleVtbl;
5 struct IModuleVtbl
再将INHERIT_IModule(IModule);展开，根据上面第2到5行的定义以及第24到26行INHERIT_IBase的定义，得到：
1 uint32 (*AddRef) (IModule*);
2 uint32 (*Release) (IModule*);
3 int (*CreateInstance)(IModule * po,IShell * pIShell,AEECLSID ClsId,void ** ppObj);
4 void (*FreeResources)(IModule * po, IHeap * ph, IFileMgr * pfm);
1 uint32 (*AddRef) (IModule*);
2 uint32 (*Release) (IModule*);
3 int (*CreateInstance)(IModule * po,IShell * pIShell,AEECLSID ClsId,void ** ppObj);
4 void (*FreeResources)(IModule * po, IHeap * ph, IFileMgr * pfm);
将以上结果合并起来，就可以得到如下代码：
01struct _IModule
02{
03 struct IModuleVtbl *pvt;
04};
05typedef struct IModuleVtbl IModuleVtbl;
06struct IModuleVtbl
07{
08 uint32 (*AddRef) (IModule*);
09 uint32 (*Release) (IModule*);
10 int (*CreateInstance)(IModule * po,IShell * pIShell,AEECLSID ClsId,void ** ppObj);
11 void (*FreeResources)(IModule * po, IHeap * ph, IFileMgr * pfm);
12};
01struct _IModule
02{
03 struct IModuleVtbl *pvt;
04};
05typedef struct IModuleVtbl IModuleVtbl;
06struct IModuleVtbl
07{
08 uint32 (*AddRef) (IModule*);
09 uint32 (*Release) (IModule*);
10 int (*CreateInstance)(IModule * po,IShell * pIShell,AEECLSID ClsId,void ** ppObj);
11 void (*FreeResources)(IModule * po, IHeap * ph, IFileMgr * pfm);
12};
好，现在来总结一下：
前面已经说到DECLARE_VTBL(IModule)就是： IModule vtIModule;，它作为AEEMod结构体的第一个成员。IModule是_IModule的结构体类型，_IModule结构体只有一个成员，就是结构体IModuleVtbl的指针。而IModuleVtbl指向的是虚拟函数表的首地址，所以如果有一个IModule* p的指针，p->pvt就是IModuleVtbl*的类型，再用p->pvt->functionName找到对应的函数。为了方便，虚拟函数表中函数的调用是使用宏来定义的，从结构体IModuleVtbl中我们可以看到Module提供了四种方法，宏定义如下，其中还用到GET_PVTBL宏定义：
1#define IMODULE_AddRef(p) GET_PVTBL(p,IModule)->AddRef(p)
2#define IMODULE_Release(p) GET_PVTBL(p,IModule)->Release(p)
3#define IMODULE_CreateInstance(p,ps,id,ppo) GET_PVTBL(p,IModule)->CreateInstance(p,ps,id,ppo)
4#define IMODULE_FreeResources(p,ph,pfm) GET_PVTBL(p,IModule)->FreeResources(p,ph,pfm)
5#define GET_PVTBL(p,iname) ((iname*)p)->pvt
1#define IMODULE_AddRef(p) GET_PVTBL(p,IModule)->AddRef(p)
2#define IMODULE_Release(p) GET_PVTBL(p,IModule)->Release(p)
3#define IMODULE_CreateInstance(p,ps,id,ppo) GET_PVTBL(p,IModule)->CreateInstance(p,ps,id,ppo)
4#define IMODULE_FreeResources(p,ph,pfm) GET_PVTBL(p,IModule)->FreeResources(p,ph,pfm)
5#define GET_PVTBL(p,iname) ((iname*)p)->pvt
我们以AddRef函数为例，我们调用的时候会使用"IMODULE_AddRef(p);"语句，将其展开，其实就是：
((IModule*)p)->pvt->AddRef(p);
这样就实现了虚拟函数表中函数的调用了。
下面再回到用于创建Module对象的对外接口AEEStaticMod_New，具体代码如下：
01int AEEStaticMod_New(int16 nSize, IShell *pIShell, void *ph, IModule **ppMod,
02 PFNMODCreateINST pfnMC,PFNFREEMODDATA pfnMF)
03{
04 AEEMod *pMe = NULL;
05 VTBL(IModule) *modFuncs; //将其展开就是 IModuleVtbl *modFuncs;
06
07 if (!ppMod || !pIShell) {
08 return EFAILED;
09 }
10
11 if (nSize < 0) {
12 return EBADPARM;
13 }
14 *ppMod = NULL;
15
16#ifdef AEE_SIMULATOR
17 // IMPORTANT NOTE: g_pvtAEEStdLibEntry global variable is defined for
18 // SDK ONLY! This variable should NOT BE:
19 //
20 // (1) overwritten
21 // (2) USED DIRECTLY by BREW SDK users.
22 //
23 // g_pvtAEEStdLibEntry is used as an entry point to AEEStdLib,
24 // DO NOT REMOVE the next five lines.
25 if (!ph) {
26 return EFAILED;
27 } else {
28 g_pvtAEEStdLibEntry = (AEEHelperFuncs *)ph;
29 }
30#endif
31
32 //Allocate memory for the AEEMod object
33
34 if (nSize < sizeof(AEEMod)) {
35 nSize += sizeof(AEEMod);
36 }
37
38 if (NULL == (pMe = (AEEMod *)MALLOC(nSize + sizeof(IModuleVtbl)))) {
39 return ENOMEMORY;
40 }
41
42 // Allocate the vtbl and initialize it. Note that the modules and apps
43 // must not have any static data. Hence, we need to allocate the vtbl as
44 // well.
45
46 modFuncs = (IModuleVtbl *)((byte *)pMe + nSize);
47
48 // Initialize individual entries in the VTBL
49 modFuncs->AddRef = AEEMod_AddRef;
50 modFuncs->Release = AEEMod_Release;
51 modFuncs->CreateInstance = AEEMod_CreateInstance;
52 modFuncs->FreeResources = AEEMod_FreeResources;
53
54
55 // initialize the vtable
56 INIT_VTBL(pMe, IModule, *modFunc
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02 PFNMODCreateINST pfnMC,PFNFREEMODDATA pfnMF)
03{
04 AEEMod *pMe = NULL;
05 VTBL(IModule) *modFuncs; //将其展开就是 IModuleVtbl *modFuncs;
06
07 if (!ppMod || !pIShell) {
08 return EFAILED;
09 }
10
11 if (nSize < 0) {
12 return EBADPARM;
13 }
14 *ppMod = NULL;
15
16#ifdef AEE_SIMULATOR
17 // IMPORTANT NOTE: g_pvtAEEStdLibEntry global variable is defined for
18 // SDK ONLY! This variable should NOT BE:
19 //
20 // (1) overwritten
21 // (2) USED DIRECTLY by BREW SDK users.
22 //
23 // g_pvtAEEStdLibEntry is used as an entry point to AEEStdLib,
24 // DO NOT REMOVE the next five lines.
25 if (!ph) {
26 return EFAILED;
27 } else {
28 g_pvtAEEStdLibEntry = (AEEHelperFuncs *)ph;
29 }
30#endif
31
32 //Allocate memory for the AEEMod object
33
34 if (nSize < sizeof(AEEMod)) {
35 nSize += sizeof(AEEMod);
36 }
37
38 if (NULL == (pMe = (AEEMod *)MALLOC(nSize + sizeof(IModuleVtbl)))) {
39 return ENOMEMORY;
40 }
41
42 // Allocate the vtbl and initialize it. Note that the modules and apps
43 // must not have any static data. Hence, we need to allocate the vtbl as
44 // well.
45
46 modFuncs = (IModuleVtbl *)((byte *)pMe + nSize);
47
48 // Initialize individual entries in the VTBL
49 modFuncs->AddRef = AEEMod_AddRef;
50 modFuncs->Release = AEEMod_Release;
51 modFuncs->CreateInstance = AEEMod_CreateInstance;
52 modFuncs->FreeResources = AEEMod_FreeResources;
53
54
55 // initialize the vtable
56 INIT_VTBL(pMe, IModule, *modFunc
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