ATL 核心COM继承类之CComObjectRootEx及CComObjectLock

参考:

1. ATL 临界区

2. ATL 引用计数线程模型

• CComObjectRootEx Manages reference counting for both aggregated and nonaggregated objects. Allows you to specify a threading model.

• CComObjectRoot Manages reference counting for both aggregated and nonaggregated objects. Uses the default threading model of the server.

记住这句话就可以了:Manages reference counting.

template <class ThreadModel>
class CComObjectRootEx : 
    public CComObjectRootBase
{
public:
    typedef ThreadModel _ThreadModel;
    typedef typename _ThreadModel::AutoCriticalSection _CritSec;
    typedef typename _ThreadModel::AutoDeleteCriticalSection _AutoDelCritSec;
    typedef CComObjectLockT<_ThreadModel> ObjectLock;

    ~CComObjectRootEx() 
    {
    }

    ULONG InternalAddRef()
    {
        ATLASSUME(m_dwRef != -1L);
        return _ThreadModel::Increment(&m_dwRef);
    }
    ULONG InternalRelease()
    {
#ifdef _DEBUG
        LONG nRef = _ThreadModel::Decrement(&m_dwRef);
        if (nRef < -(LONG_MAX / 2))
        {
            ATLASSERT(0 && _T("Release called on a pointer that has already been released"));
        }
        return nRef;
#else
        return _ThreadModel::Decrement(&m_dwRef);
#endif
    }

    HRESULT _AtlInitialConstruct()
    {
        return m_critsec.Init();
    }
    void Lock() 
    {
        m_critsec.Lock();
    }
    void Unlock() 
    {
        m_critsec.Unlock();
    }
private:
    _AutoDelCritSec m_critsec;
};

template <>
class CComObjectRootEx<CComSingleThreadModel> : 
    public CComObjectRootBase
{
public:
    typedef CComSingleThreadModel _ThreadModel;
    typedef _ThreadModel::AutoCriticalSection _CritSec;
    typedef _ThreadModel::AutoDeleteCriticalSection _AutoDelCritSec;
    typedef CComObjectLockT<_ThreadModel> ObjectLock;

    ~CComObjectRootEx() {}

    ULONG InternalAddRef()
    {
        ATLASSUME(m_dwRef != -1L);
        return _ThreadModel::Increment(&m_dwRef);
    }
    ULONG InternalRelease()
    {
#ifdef _DEBUG
        long nRef = _ThreadModel::Decrement(&m_dwRef);
        if (nRef < -(LONG_MAX / 2))
        {
            ATLASSERT(0 && _T("Release called on a pointer that has already been released"));
        }
        return nRef;
#else
        return _ThreadModel::Decrement(&m_dwRef);
#endif    
    }

    HRESULT _AtlInitialConstruct()
    {
        return S_OK;
    }

    void Lock() 
    {
    }
    void Unlock() 
    {
    }
};

typedef CComObjectRootEx<CComObjectThreadModel> CComObjectRoot;

CComObjectLockT

为ComObject锁方法提供便利

template <class ThreadModel>
class CComObjectRootEx;

template <class ThreadModel>
class CComObjectLockT
{
public:
    CComObjectLockT(_Inout_opt_ CComObjectRootEx<ThreadModel>* p)
    {
        if (p)
            p->Lock();
        m_p = p;
    }

    ~CComObjectLockT()
    {
        if (m_p)
            m_p->Unlock();
    }
    CComObjectRootEx<ThreadModel>* m_p;
};

前后对比

class CPenguin
    : public CComObjectRootEx<CComMultiThreadModel>, ... {
        STDMETHODIMP get_Wingspan(long* pnWingspan) {
            Lock();
            if( !pnWingspan ) return E_POINTER; // Forgot to Unlock
            *pnWingSpan = m_nWingspan;
            Unlock();
            return S_OK;
        }
        ...
};

class CPenguin
    : public CComObjectRootEx<CComMultiThreadModel>, ... {
        STDMETHODIMP get_Wingspan(long* pnWingspan) {
            ObjectLock lock(this);
            if( !pnWingspan ) return E_POINTER; // Unlock happens as
            // stack unwinds
            *pnWingSpan = m_nWingspan;
            return S_OK;
        }
        ...
};