Oracle Coherence for C++ API
Release 3.6.1.0
E18813-01

coherence/lang/MemberHandle.hpp

/*
* MemberHandle.hpp
*
* Copyright (c) 2000, 2010, Oracle and/or its affiliates. All rights reserved.
*
* Oracle is a registered trademarks of Oracle Corporation and/or its
* affiliates.
*
* This software is the confidential and proprietary information of Oracle
* Corporation. You shall not disclose such confidential and proprietary
* information and shall use it only in accordance with the terms of the
* license agreement you entered into with Oracle.
*
* This notice may not be removed or altered.
*/
#ifndef COH_MEMBER_HANDLE_HPP
#define COH_MEMBER_HANDLE_HPP

#include "coherence/lang/compatibility.hpp"

#include "coherence/lang/Object.hpp"
#include "coherence/lang/SmartMember.hpp"
#include "coherence/lang/SynchronizedMemberReadBlock.hpp"
#include "coherence/lang/SynchronizedMemberWriteBlock.hpp"
#include "coherence/lang/TypedHandle.hpp"

#include <ostream>
#include <sstream>

COH_OPEN_NAMESPACE2(coherence,lang)

template<class> class MemberView;


/**
* MemberHandle is a thread-safe handle used by an Object to reference its
* non-const child Objects.
*
* MemberHandles transfer the constness of their guardian Object. When a
* MemberHandle is accessed from within a const method of the enclosing
* "parent" class, it will only provide const access to the Object which it
* references. If the enclosing Object becomes only accessed via views the
* MemberHandle will also automatically, and permanently switch its reference
* type from a handle to a view.
*
* Note: In the rare case that a MemberHandle is declared via the mutable
*       keyword, the MemberHandle must be informed of this fact by setting
*       fMutable to true during construction.
*
* @author mf  2007.07.05
*
* @see MemberView
* @see MemberHolder
*/
template<class T>
class MemberHandle
    : public SmartMember
    {
    // ----- typedefs -------------------------------------------------------

    public:
        /**
        * The type of the values the handle can reference.
        */
        typedef T ValueType;

        /**
        * The Handle type for the referenced Object.
        */
        typedef typename T::Handle ValueHandle;

        /**
        * The View type for the referenced Object.
        */
        typedef typename T::View ValueView;

        /**
        * Result type for a non-const get operation.
        */
        typedef ValueHandle GetType;

        /**
        * Result type for a non-const get operation.
        */
        typedef ValueView ConstGetType;


    // -------- constructors ------------------------------------------------

    public:
        /**
        * Construct a new MemberHandle referencing NULL via a handle.
        *
        * @param oGuardian  the object that protects this member
        */
        MemberHandle(const Object& oGuardian)
            : SmartMember(oGuardian), m_po(NULL)
            {
            }

        /**
        * Construct a new MemberHandle referencing the specified Object via
        * a handle.
        *
        * @param oGuardian   the object that protects this member
        * @param that        the Object to reference
        */
        MemberHandle(const Object& oGuardian, const ValueHandle& that)
            : SmartMember(oGuardian),
              m_po(NULL)
            {
            T* po = get_pointer(that);
            if (po != NULL)
                {
                po->_attach(oGuardian._isEscaped());
                m_po = po;
                }
            }

        /**
        * Construct a new MemberHandle referencing the specified Object via
        * a handle.
        *
        * @param oGuardian  the object that protects this member
        * @param that       the Object to reference
        * @param fMutable   true if the member is declared as mutable, false
        *                   if declared as const
        */
        MemberHandle(const Object& oGuardian, const ValueHandle& that,
                bool fMutable)
            : SmartMember(oGuardian, fMutable ? MUTABLE : SAFE_CONST),
              m_po(NULL)
            {
            T* po = get_pointer(that);
            if (po != NULL)
                {
                if (fMutable)
                    {
                    po->_attach(oGuardian._isEscaped());
                    }
                else
                    {
                    ((const T*) po)->_attach(oGuardian._isEscaped());
                    }
                m_po = po;
                }
            }

        /**
        * Destroy the MemberHandle.
        */
        ~MemberHandle()
            {
            T*         po          = m_po;
            Mutability nMutability = m_nMutability;

            if (NULL != po)
                {
                m_po = NULL;
                try
                    {
                    bool fEscaped = getGuardian()._isEscaped();
                    if (nMutability >= CONST)
                        {
                        ((const T*) po)->_detach(fEscaped);
                        }
                    else
                        {
                        po->_detach(fEscaped);
                        }
                    }
                catch (const std::exception& e)
                    {
                    // Exception::View is not a known type within this file
                    std::cerr << "Error during ~MemberHandle: " << e.what() << std::endl;
                    return; // can't re-throw from within destructor
                    }
                }
            }

    private:
        /**
        * Blocked copy constructor.
        */
        MemberHandle(const MemberHandle&);


    // ----- operators ------------------------------------------------------

    public:
        /**
        * Assign the MemberHandle to reference another object.
        *
        * @param that  the object to reference
        *
        * @return a reference to this MemberHandle
        */
        MemberHandle& operator=(const ValueHandle& that)
            {
            set(that);
            return *this;
            }

        /**
        * Assign this MemberHandle to reference the same Object as the
        * specified MemberHandle.
        *
        * @param that  the object to reference
        *
        * @return a reference to this MemberHandle
        */
        MemberHandle& operator=(MemberHandle& that)
            {
            operator=((ValueHandle) that); // assign from snapshot
            return *this;
            }

        /**
        * Return a View to the referenced Object.
        *
        * @return a View to the referenced Object
        */
        operator ValueView() const
            {
            return get();
            }

        /**
        * Return a Handle to the referenced Object.
        *
        * @return a Handle to the referenced Object
        */
        operator ValueHandle()
            {
            return get();
            }

        /**
        * Return a View to the referenced Object.
        *
        * @return a View to the referenced Object
        */
        template<class PT>
        operator TypedHandle<const PT>() const
            {
            return get();
            }

        /**
        * Return a Handle to the referenced Object.
        *
        * @return a Handle to the referenced Object
        */
        template<class PT>
        operator TypedHandle<PT>()
            {
            return get();
            }

        /**
        * Return a TypedHolder to the referenced Object.
        *
        * @return a TypedHolder to the referenced Object
        *
        */
        template<class PT>
        operator TypedHolder<PT>() const
            {
            return get();
            }

        /**
        * Return a TypedHolder to the referenced Object.
        *
        * @return a TypedHolder to the referenced Object
        */
        template<class PT>
        operator TypedHolder<PT>()
            {
            return get();
            }

        /**
        * Dereference the MemberHandle.
        *
        * @return a const pointer to the referenced Object
        */
        ValueView operator->() const
            {
            return get();
            }

        /**
        * Dereference the MemberHandle.
        *
        * @return a const pointer to the referenced Object
        */
        ValueHandle operator->()
            {
            return get();
            }

        /**
        * Dereference this handle, returning <tt>T&</tt>.
        *
        * @return a raw <tt>T&</tt> reference to the referenced Object
        *
        * @throws NullPointerException if the this handle is @c NULL
        */
        const T& operator*() const
            {
            return *get();
            }

        /**
        * Dereference this handle, returning <tt>T&</tt>.
        *
        * @return a raw <tt>T&</tt> reference to the referenced Object
        *
        * @throws NullPointerException if the this handle is @c NULL
        */
        T& operator*()
            {
            return *get();
            }

    private:
        /**
        * Blocked assignment operator.
        */
        MemberHandle<T>& operator=(const MemberHandle<T>&);


    // ----- helper methods -------------------------------------------------

    protected:
        /**
        * Set the MemberHandle to reference the same Object as the supplied
        * Handle.
        *
        * @param that   the handle to copy
        * @param pSync  optional external SyncornizedMemberBlock to use
        *               to avoid internal synchronization.
        */
        void set(const TypedHandle<T>& that,
                SynchronizedMemberWriteBlock* pSync = NULL)
            {
            const Object& oGuardian = getGuardian();
            T*            po        = get_pointer(that);
            T*            pDetach   = NULL;
            bool          fEscaped  = oGuardian._isEscaped();
            Object*       pAttach   = po == NULL ? NULL : po->_attach(fEscaped);

            if (pSync != NULL)
                {
                // sync block
                SynchronizedMemberWriteBlock syncWrite(oGuardian, pSync);
                if (m_nMutability >= CONST)
                    {
                    coh_throw_illegal_state("attempt to set const MemberHandle");
                    }
                pDetach = m_po;
                m_po    = NULL == pAttach ? NULL : po;
                }
            else if (fEscaped)
                {
                // sync block
                SynchronizedMemberWriteBlock::Guard guard(oGuardian);
                if (m_nMutability >= CONST)
                    {
                    coh_throw_illegal_state("attempt to set const MemberHandle");
                    }
                pDetach = m_po;
                m_po    = NULL == pAttach ? NULL : po;
                }
            else
                {
                if (m_nMutability >= CONST)
                    {
                    coh_throw_illegal_state("attempt to set const MemberHandle");
                    }
                pDetach = m_po;
                m_po    = NULL == pAttach ? NULL : po;
                }

            if (pDetach)
                {
                pDetach->_detach(fEscaped);
                }
            }

        /**
        * Return a View to the referenced Object.
        *
        * @param pSync  optional external SyncornizedMemberReadBlock to use
        *               to avoid internal synchronization.
        *
        * @return a View to the referenced Object
        */
        ValueView get(SynchronizedMemberReadBlock* pSync = NULL) const
            {
            const Object& oGuardian = getGuardian();
            if (pSync != NULL)
                {
                SynchronizedMemberReadBlock syncRead(oGuardian, pSync);
                // return of escaped must occur within scope of syncRead
                return ValueView((const T*) m_po);
                }
            else if (m_nMutability == SAFE_CONST || !oGuardian._isEscaped())
                {
                // non-escaped, or SAFE_CONST, synchronization not required
                return ValueView((const T*) m_po);
                }
            else
                {
                SynchronizedMemberReadBlock::Guard guard(oGuardian);
                // return of escaped must occur within scope of guard
                return ValueView((const T*) m_po);
                }
            }

        /**
        * Return a Handle to the referenced Object.
        *
        * @param pSync  optional external SyncornizedMemberReadBlock to use
        *               to avoid internal synchronization.
        *
        * @return a Handle to the referenced Object
        */
        ValueHandle get(SynchronizedMemberReadBlock* pSync = NULL)
            {
            const Object& oGuardian = getGuardian();
            if (pSync != NULL)
                {
                SynchronizedMemberReadBlock syncRead(oGuardian, pSync);
                if (m_nMutability >= CONST)
                    {
                    coh_throw_illegal_state(
                        "attempt to access handle from const MemberHandle");
                    }
                return m_po; // must occur within scope of syncRead
                }
            else if (oGuardian._isEscaped())
                {
                SynchronizedMemberReadBlock::Guard guard(oGuardian);
                if (m_nMutability >= CONST)
                    {
                    coh_throw_illegal_state(
                        "attempt to access handle from const MemberHandle");
                    }
                return m_po; // must occur within scope of syncRead
                }

            if (m_nMutability >= CONST)
                {
                coh_throw_illegal_state(
                    "attempt to access handle from const MemberHandle");
                }
            return m_po;
            }


    // ----- SmartMember interface ------------------------------------------

    protected:
        /**
        * {@inheritDoc}
        *
        * The MemberHandle is automatically flipped when the guardian Object
        * becomes only referenced via consts.
        */
        virtual void onConst()
            {
            const Object& oGuardian = getGuardian();
            bool          fEscaped  = oGuardian._isEscaped();
            T*            po        = NULL;

            if (fEscaped)
                {
                SynchronizedMemberWriteBlock::Guard guard(oGuardian);
                po = m_po;
                }
            else
                {
                po = m_po;
                }

            if (NULL != po)
                {
                // re-attach as const, then detach the old reference
                ((const T*) po)->_attach(fEscaped);
                po->_detach(fEscaped);
                }

            SmartMember::onConst();
            }

        /**
        * {@inheritDoc}
        */
        virtual void onEscape(bool fEscaped) const
            {
            T* po = m_po;
            if (po != NULL)
                {
                if (m_nMutability >= CONST)
                    {
                    const T* cpo = po;
                    cpo->_attach(fEscaped);  // new attach
                    cpo->_detach(!fEscaped); // old detach
                    }
                else
                    {
                    po->_attach(fEscaped);  // new attach
                    po->_detach(!fEscaped); // old detach
                    }
                }

            SmartMember::onEscape(fEscaped);
            }


    // ----- data members ---------------------------------------------------

    protected:
       /**
        * The referenced Object.
        */
        T* m_po;


    // ----- friends --------------------------------------------------------

    /**
    * @internal
    */
    template<class D, class H> friend D cast(MemberHandle<T>& mh, bool fThrow);

    /**
    * @internal
    */
    friend class SynchronizedMemberReadBlock;

    /**
    * @internal
    */
    friend class SynchronizedMemberWriteBlock;
    };


// ----- non-member operators and functions ---------------------------------

/**
* Output a human-readable description of the given MemberHandle to the
* specified stream.
*
* @param out  the stream used to output the description
* @param mh   the MemberHandle to describe
*
* @return the supplied stream
*/
template<class T> std::ostream& operator<<(std::ostream& out, const MemberHandle<T>& mh)
    {
    out << (typename T::View) mh;
    return out;
    }

/**
* Assign the specified handle to NULL.
*
* @param mh the handle to clear
*/
template<class T> void clear_handle(MemberHandle<T>& mh)
    {
    mh = NULL;
    }

/**
* Return true if the supplied handle equals NULL.
*
* @param mh  the member handle to test
*
* @return true iff the supplied handle equals NULL
*/
template<class T>
bool is_null(const MemberHandle<T>& mh)
    {
    return mh == NULL;
    }

/**
* Perform a dynamic cast the pointer associated with the MemberHandle
* to a the specified handle/view type.
*
* @param mh      the MemberHandle from which to perform the cast
* @param fThrow  true if an exception is to be thrown on a failed cast
*
* @return the casted pointer, or NULL if the cast fails and fThrow is false
*
* @throws ClassCastException if the cast fails and fThrow is true
*/
template<class D, class T>
D cast(MemberHandle<T>& mh, bool fThrow = true)
    {
    return cast<D>((typename MemberHandle<T>::ValueHandle) mh, fThrow);
    }

/**
* Perform a dynamic cast the pointer associated with the MemberHandle
* to a the specified handle/view type.
*
* @param mh      the MemberHandle from which to perform the cast
* @param fThrow  true if an exception is to be thrown on a failed cast
*
* @return the casted pointer, or NULL if the cast fails and fThrow is false
*
* @throws ClassCastException if the cast fails and fThrow is true
*/
template<class D, class T>
D cast(const MemberHandle<T>& mh, bool fThrow = true)
    {
    return cast<D>((typename MemberHandle<T>::ValueView) mh, fThrow);
    }

/**
* Perform an instanceof check on a MemberHandle.
*
* @param mh  the MemberHandle from which to perform the test
*
* @return true if the supplied handle is an instance of the specified type
*/
template<class D, class T>
bool instanceof(MemberHandle<T>& mh)
    {
    return NULL != cast<D>(mh, false);
    }

/**
* Perform an instanceof check on a MemberHandle.
*
* @param mh  the MemberHandle from which to perform the test
*
* @return true if the supplied handle is an instance of the specified type
*/
template<class D, class T>
bool instanceof(const MemberHandle<T>& mh)
    {
    return NULL != cast<D>(mh, false);
    }

COH_CLOSE_NAMESPACE2

#endif // COH_MEMBER_HANDLE_HPP

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