Android 源码中使用的很多的一个东西，做个简单记录

强指针 `sp`

~\frameworks\rs\cpp\util\StrongPointer.h
~\system\core\libutils\include\utils\StrongPointer.h

template<typename T>
class sp 
{
public:
    inline sp() : m_ptr(nullptr) { }
    ···
     sp(T* other); // 构造函数
    ···
}

弱指针 `wp`

~\system\core\libutils\include\utils\RefBase.h

template <typename T>
class wp
{
public:
    typedef typename RefBase::weakref_type weakref_type;

    inline wp() : m_ptr(nullptr), m_refs(nullptr) { }
    ···
    void set_object_and_refs(T* other, weakref_type* refs);

    wp(T* other);  // NOLINT(implicit)
    wp& operator=(T* other);

    // promotion to sp
    sp<T> promote() const;/*升级为强指针*/
    ···
}

class RefBase
{
public:
            void            incStrong(const void* id) const;
            void            incStrongRequireStrong(const void* id) const;
            void            decStrong(const void* id) const;
    
            void            forceIncStrong(const void* id) const;

            //! DEBUGGING ONLY: Get current strong ref count.
            int32_t         getStrongCount() const;

    class weakref_type
    {
    public:
        RefBase*            refBase() const;

        void                incWeak(const void* id);
        void                incWeakRequireWeak(const void* id);
        void                decWeak(const void* id);

        // acquires a strong reference if there is already one.
        bool                attemptIncStrong(const void* id);

        // acquires a weak reference if there is already one.
        // This is not always safe. see ProcessState.cpp and BpBinder.cpp
        // for proper use.
        bool                attemptIncWeak(const void* id);

        //! DEBUGGING ONLY: Get current weak ref count.
        int32_t             getWeakCount() const;

        //! DEBUGGING ONLY: Print references held on object.
        void                printRefs() const;

        //! DEBUGGING ONLY: Enable tracking for this object.
        // enable -- enable/disable tracking
        // retain -- when tracking is enable, if true, then we save a stack trace
        //           for each reference and dereference; when retain == false, we
        //           match up references and dereferences and keep only the
        //           outstanding ones.

        void                trackMe(bool enable, bool retain);
    };

            weakref_type*   createWeak(const void* id) const;
            
            weakref_type*   getWeakRefs() const;

            //! DEBUGGING ONLY: Print references held on object.
    inline  void            printRefs() const { getWeakRefs()->printRefs(); }

            //! DEBUGGING ONLY: Enable tracking of object.
    inline  void            trackMe(bool enable, bool retain)
    { 
        getWeakRefs()->trackMe(enable, retain); 
    }

protected:
    // When constructing these objects, prefer using sp::make<>. Using a RefBase
    // object on the stack or with other refcount mechanisms (e.g.
    // std::shared_ptr) is inherently wrong. RefBase types have an implicit
    // ownership model and cannot be safely used with other ownership models.

                            RefBase();
    virtual                 ~RefBase();
    
    //! Flags for extendObjectLifetime()
    enum {
        OBJECT_LIFETIME_STRONG  = 0x0000,
        OBJECT_LIFETIME_WEAK    = 0x0001,
        OBJECT_LIFETIME_MASK    = 0x0001
    };
    
            void            extendObjectLifetime(int32_t mode);
            
    //! Flags for onIncStrongAttempted()
    enum {
        FIRST_INC_STRONG = 0x0001
    };
    
    // Invoked after creation of initial strong pointer/reference.
    virtual void            onFirstRef();
    // Invoked when either the last strong reference goes away, or we need to undo
    // the effect of an unnecessary onIncStrongAttempted.
    virtual void            onLastStrongRef(const void* id);
    // Only called in OBJECT_LIFETIME_WEAK case.  Returns true if OK to promote to
    // strong reference. May have side effects if it returns true.
    // The first flags argument is always FIRST_INC_STRONG.
    // TODO: Remove initial flag argument.
    virtual bool            onIncStrongAttempted(uint32_t flags, const void* id);
    // Invoked in the OBJECT_LIFETIME_WEAK case when the last reference of either
    // kind goes away.  Unused.
    // TODO: Remove.
    virtual void            onLastWeakRef(const void* id);

private:
    friend class weakref_type;
    class weakref_impl;
    
                            RefBase(const RefBase& o);
            RefBase&        operator=(const RefBase& o);

private:
    friend class ReferenceMover;

    static void renameRefs(size_t n, const ReferenceRenamer& renamer);

    static void renameRefId(weakref_type* ref,
            const void* old_id, const void* new_id);

    static void renameRefId(RefBase* ref,
            const void* old_id, const void* new_id);

        weakref_impl* const mRefs;
};