CUnknown和INonDelegatingUnknown

CUnknown继承于INonDelegatingUnknown,并且CUnknown是所有COM的基类。

class CUnknown : public INonDelegatingUnknown

而INonDelegatingUnknown是一个虚基结构体。

INonDelegatingUnknown

basetype.h

DECLARE_INTERFACE(INonDelegatingUnknown)
{
    STDMETHOD_(NTSTATUS,NonDelegatingQueryInterface)
    (   THIS_
        _In_             REFIID,
        _COM_Outptr_     PVOID *
    )   PURE;

    STDMETHOD_(ULONG,NonDelegatingAddRef)
    (   THIS
    )   PURE;

    STDMETHOD_(ULONG,NonDelegatingRelease)
    (   THIS
    )   PURE;
};

typedef INonDelegatingUnknown *PNONDELEGATINGUNKNOWN;

以上的宏：

#define __STRUCT__ struct
#define interface __STRUCT__

#define DECLSPEC_NOVTABLE   __declspec(novtable)

#define DECLARE_INTERFACE(iface)    interface DECLSPEC_NOVTABLE iface

故DECLARE_INTERFACE(INonDelegatingUnknown)宏展开为：

struct __declspec(novtable) INonDelegatingUnknown

而STDMETHOD_宏定义如下：

#define DECLSPEC_NOTHROW   __declspec(nothrow)
#define COM_DECLSPEC_NOTHROW DECLSPEC_NOTHROW

#define STDMETHODCALLTYPE       __stdcall
#define PURE                    = 0

#define STDMETHOD_(type,method)  virtual COM_DECLSPEC_NOTHROW type STDMETHODCALLTYPE method

故 STDMETHOD_(NTSTATUS,NonDelegatingQueryInterface)展开如下：

virtual 
_declspec(nothrow) 
NTSTATUS 
__stdcall 
NonDelegatingQueryInterface
(   THIS_
    _In_             REFIID,
    _COM_Outptr_     PVOID *
)   = 0;

可以看到，其实现的是一个纯虚函数

CUnknown

class CUnknown : public INonDelegatingUnknown
{
private:

    LONG            m_lRefCount;        // Reference count.
    PUNKNOWN        m_pUnknownOuter;    // Outer IUnknown.

public:

    /*************************************************************************
        * CUnknown methods.
     */
    CUnknown(PUNKNOWN pUnknownOuter);
        virtual ~CUnknown(void);
    PUNKNOWN GetOuterUnknown(void)
    {
        return m_pUnknownOuter;
    }

    /*************************************************************************
         * INonDelegatingUnknown methods.
     */
     STDMETHODIMP_(ULONG) NonDelegatingAddRef
    (   void
    );
    STDMETHODIMP_(ULONG) NonDelegatingRelease
    (   void
    );
    STDMETHODIMP_(NTSTATUS) NonDelegatingQueryInterface
        (
                __in REFIID          rIID,
                __out PVOID *     ppVoid
        );
};

可以看到，CUnknown重写了INonDelegatingUnknown的三个方法，当然CUnknown也实现了自己的构造函数（带一个参数）和对构造函数指针的引用函数GetOuterUnknown。

CUnkonw的具体实现可参考WDK的stdunk.cpp文件

CUnknown构造和成员函数

/*****************************************************************************
 * CUnknown::CUnknown()
 *****************************************************************************
 * Constructor.
 */
CUnknown::CUnknown(PUNKNOWN pUnknownOuter)
:   m_lRefCount(0)
{
    if (pUnknownOuter)
    {
        m_pUnknownOuter = pUnknownOuter;
    }
    else
    {
        m_pUnknownOuter = PUNKNOWN(dynamic_cast<PNONDELEGATINGUNKNOWN>(this));
    }
}

/*****************************************************************************
 * CUnknown::~CUnknown()
 *****************************************************************************
 * Destructor.
 */
CUnknown::~CUnknown(void)
{
}

CUnknown继承的三个虚函数实现

• NonDelegatingAddRef：增加引用计数
• NonDelegatingQueryInterface：减少引用计数
• NonDelegatingQueryInterface：通过接口GUID返回接口

/*****************************************************************************
 * CUnknown::NonDelegatingAddRef()
 *****************************************************************************
 * Register a new reference to the object without delegating to the outer
 * unknown.
 */
STDMETHODIMP_(ULONG) CUnknown::NonDelegatingAddRef(void)
{
    ASSERT(m_lRefCount >= 0);

    InterlockedIncrement(&m_lRefCount);

    return ULONG(m_lRefCount);
}

/*****************************************************************************
 * CUnknown::NonDelegatingRelease()
 *****************************************************************************
 * Release a reference to the object without delegating to the outer unknown.
 */
STDMETHODIMP_(ULONG) CUnknown::NonDelegatingRelease(void)
{
    ASSERT(m_lRefCount > 0);

    if (InterlockedDecrement(&m_lRefCount) == 0)
    {
        m_lRefCount++;
        delete this;
        return 0;
    }

    return ULONG(m_lRefCount); 
}

/*****************************************************************************
 * CUnknown::NonDelegatingQueryInterface()
 *****************************************************************************
 * Obtains an interface.
 */
STDMETHODIMP_(NTSTATUS) CUnknown::NonDelegatingQueryInterface
(
    REFIID  rIID,
    PVOID * ppVoid
)
{
    ASSERT(ppVoid);

    if (IsEqualGUIDAligned(rIID,IID_IUnknown))
    {
        *ppVoid = PVOID(PUNKNOWN(this));
    }
    else
    {
        *ppVoid = NULL;
    }

    if (*ppVoid)
    {
        PUNKNOWN(*ppVoid)->AddRef();
        return STATUS_SUCCESS;
    }

    return STATUS_INVALID_PARAMETER;
}