SharedPtr.h

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//
// SharedPtr.h
//
// Library: Foundation
// Package: Core
// Module:  SharedPtr
//
// Definition of the SharedPtr template class.
//
// Copyright (c) 2005-2008, Applied Informatics Software Engineering GmbH.
// and Contributors.
//
// SPDX-License-Identifier: BSL-1.0
//
 
 
#ifndef Foundation_SharedPtr_INCLUDED
#define Foundation_SharedPtr_INCLUDED
 
 
#include "Poco/Foundation.h"
#include "Poco/Exception.h"
#include "Poco/AtomicCounter.h"
#include <algorithm>
#include <cstddef>
 
 
namespace Poco {
 
 
class ReferenceCounter
    /// Simple ReferenceCounter object, does not delete itself when count reaches 0.
{
public:
    ReferenceCounter(): _cnt(1)
    {
    }
 
    void duplicate()
    {
        ++_cnt;
    }
 
    int release()
    {
        return --_cnt;
    }
 
    int referenceCount() const
    {
        return _cnt.value();
    }
 
private:
    AtomicCounter _cnt;
};
 
 
template <class C>
class ReleasePolicy
    /// The default release policy for SharedPtr, which
    /// simply uses the delete operator to delete an object.
{
public:
    static void release(C* pObj) noexcept
        /// Delete the object.
        /// Note that pObj can be nullptr.
    {
        delete pObj;
    }
};
 
 
template <class C>
class ReleaseArrayPolicy
    /// The release policy for SharedPtr holding arrays.
{
public:
    static void release(C* pObj) noexcept
        /// Delete the object.
        /// Note that pObj can be nullptr.
    {
        delete [] pObj;
    }
};
 
 
template <class C, class RC = ReferenceCounter, class RP = ReleasePolicy<C>>
class SharedPtr
    /// SharedPtr is a "smart" pointer for classes implementing
    /// reference counting based garbage collection.
    /// SharedPtr is thus similar to AutoPtr. Unlike the
    /// AutoPtr template, which can only be used with
    /// classes that support reference counting, SharedPtr
    /// can be used with any class. For this to work, a
    /// SharedPtr manages a reference count for the object
    /// it manages.
    ///
    /// SharedPtr works in the following way:
    /// If an SharedPtr is assigned an ordinary pointer to
    /// an object (via the constructor or the assignment operator),
    /// it takes ownership of the object and the object's reference
    /// count is initialized to one.
    /// If the SharedPtr is assigned another SharedPtr, the
    /// object's reference count is incremented by one.
    /// The destructor of SharedPtr decrements the object's
    /// reference count by one and deletes the object if the
    /// reference count reaches zero.
    /// SharedPtr supports dereferencing with both the ->
    /// and the * operator. An attempt to dereference a null
    /// SharedPtr results in a NullPointerException being thrown.
    /// SharedPtr also implements all relational operators and
    /// a cast operator in case dynamic casting of the encapsulated data types
    /// is required.
{
public:
    typedef C Type;
 
    SharedPtr():
        _pCounter(nullptr),
        _ptr(nullptr)
    {
    }
 
    SharedPtr(C* ptr)
    try:
        _pCounter(ptr ? new RC : nullptr),
        _ptr(ptr)
    {
    }
    catch (...)
    {
        RP::release(ptr);
    }
 
    template <class Other, class OtherRP>
    SharedPtr(const SharedPtr<Other, RC, OtherRP>& ptr):
        _pCounter(ptr._pCounter),
        _ptr(const_cast<Other*>(ptr.get()))
    {
        if (_pCounter) _pCounter->duplicate();
    }
 
    SharedPtr(const SharedPtr& ptr):
        _pCounter(ptr._pCounter),
        _ptr(ptr._ptr)
    {
        if (_pCounter) _pCounter->duplicate();
    }
 
    SharedPtr(SharedPtr&& ptr) noexcept:
        _pCounter(ptr._pCounter),
        _ptr(ptr._ptr)
    {
        ptr._pCounter = nullptr;
        ptr._ptr = nullptr;
    }
 
    ~SharedPtr()
    {
        release();
    }
 
    SharedPtr& assign(C* ptr)
    {
        if (get() != ptr)
        {
            SharedPtr tmp(ptr);
            swap(tmp);
        }
        return *this;
    }
 
    SharedPtr& assign(const SharedPtr& ptr)
    {
        if (&ptr != this)
        {
            SharedPtr tmp(ptr);
            swap(tmp);
        }
        return *this;
    }
 
    template <class Other, class OtherRP>
    SharedPtr& assign(const SharedPtr<Other, RC, OtherRP>& ptr)
    {
        if (ptr.get() != _ptr)
        {
            SharedPtr tmp(ptr);
            swap(tmp);
        }
        return *this;
    }
 
    void reset()
    {
        assign(nullptr);
    }
 
    void reset(C* ptr)
    {
        assign(ptr);
    }
 
    void reset(const SharedPtr& ptr)
    {
        assign(ptr);
    }
 
    template <class Other, class OtherRP>
    void reset(const SharedPtr<Other, RC, OtherRP>& ptr)
    {
        assign<Other, OtherRP>(ptr);
    }
 
    SharedPtr& operator = (C* ptr)
    {
        return assign(ptr);
    }
 
    SharedPtr& operator = (const SharedPtr& ptr)
    {
        return assign(ptr);
    }
 
    SharedPtr& operator = (SharedPtr&& ptr) noexcept
    {
        release();
        _ptr = ptr._ptr;
        ptr._ptr = nullptr;
        _pCounter = ptr._pCounter;
        ptr._pCounter = nullptr;
        return *this;
    }
 
    template <class Other, class OtherRP>
    SharedPtr& operator = (const SharedPtr<Other, RC, OtherRP>& ptr)
    {
        return assign<Other>(ptr);
    }
 
    void swap(SharedPtr& ptr)
    {
        std::swap(_ptr, ptr._ptr);
        std::swap(_pCounter, ptr._pCounter);
    }
 
    template <class Other>
    SharedPtr<Other, RC, RP> cast() const
        /// Casts the SharedPtr via a dynamic cast to the given type.
        /// Returns an SharedPtr containing NULL if the cast fails.
        /// Example: (assume class Sub: public Super)
        ///    SharedPtr<Super> super(new Sub());
        ///    SharedPtr<Sub> sub = super.cast<Sub>();
        ///    poco_assert (sub.get());
    {
        Other* pOther = dynamic_cast<Other*>(_ptr);
        if (pOther)
            return SharedPtr<Other, RC, RP>(_pCounter, pOther);
        return SharedPtr<Other, RC, RP>();
    }
 
    template <class Other>
    SharedPtr<Other, RC, RP> unsafeCast() const
        /// Casts the SharedPtr via a static cast to the given type.
        /// Example: (assume class Sub: public Super)
        ///    SharedPtr<Super> super(new Sub());
        ///    SharedPtr<Sub> sub = super.unsafeCast<Sub>();
        ///    poco_assert (sub.get());
    {
        Other* pOther = static_cast<Other*>(_ptr);
        return SharedPtr<Other, RC, RP>(_pCounter, pOther);
    }
 
    C* operator -> ()
    {
        return deref();
    }
 
    const C* operator -> () const
    {
        return deref();
    }
 
    C& operator * ()
    {
        return *deref();
    }
 
    const C& operator * () const
    {
        return *deref();
    }
 
    C* get()
    {
        return _ptr;
    }
 
    const C* get() const
    {
        return _ptr;
    }
 
    operator C* ()
    {
        return _ptr;
    }
 
    operator const C* () const
    {
        return _ptr;
    }
 
    bool operator ! () const
    {
        return _ptr == nullptr;
    }
 
    bool isNull() const
    {
        return _ptr == nullptr;
    }
 
    bool operator == (const SharedPtr& ptr) const
    {
        return get() == ptr.get();
    }
 
    bool operator == (const C* ptr) const
    {
        return get() == ptr;
    }
 
    bool operator == (C* ptr) const
    {
        return get() == ptr;
    }
 
    bool operator == (std::nullptr_t ptr) const
    {
        return get() == ptr;
    }
 
    bool operator != (const SharedPtr& ptr) const
    {
        return get() != ptr.get();
    }
 
    bool operator != (const C* ptr) const
    {
        return get() != ptr;
    }
 
    bool operator != (C* ptr) const
    {
        return get() != ptr;
    }
 
    bool operator != (std::nullptr_t ptr) const
    {
        return get() != ptr;
    }
 
    bool operator < (const SharedPtr& ptr) const
    {
        return get() < ptr.get();
    }
 
    bool operator < (const C* ptr) const
    {
        return get() < ptr;
    }
 
    bool operator < (C* ptr) const
    {
        return get() < ptr;
    }
 
    bool operator <= (const SharedPtr& ptr) const
    {
        return get() <= ptr.get();
    }
 
    bool operator <= (const C* ptr) const
    {
        return get() <= ptr;
    }
 
    bool operator <= (C* ptr) const
    {
        return get() <= ptr;
    }
 
    bool operator > (const SharedPtr& ptr) const
    {
        return get() > ptr.get();
    }
 
    bool operator > (const C* ptr) const
    {
        return get() > ptr;
    }
 
    bool operator > (C* ptr) const
    {
        return get() > ptr;
    }
 
    bool operator >= (const SharedPtr& ptr) const
    {
        return get() >= ptr.get();
    }
 
    bool operator >= (const C* ptr) const
    {
        return get() >= ptr;
    }
 
    bool operator >= (C* ptr) const
    {
        return get() >= ptr;
    }
 
    int referenceCount() const
    {
        return _pCounter ? _pCounter->referenceCount() : 0;
    }
 
private:
    C* deref() const
    {
        if (!_ptr)
            throw NullPointerException();
 
        return _ptr;
    }
 
    void release() noexcept
    {
        if (_pCounter && _pCounter->release() == 0)
        {
            RP::release(_ptr);
            _ptr = nullptr;
 
            delete _pCounter;
            _pCounter = nullptr;
        }
    }
 
    SharedPtr(RC* pCounter, C* ptr): _pCounter(pCounter), _ptr(ptr)
        /// for cast operation
    {
        poco_assert_dbg (_pCounter);
        _pCounter->duplicate();
    }
 
private:
    RC* _pCounter;
    C*  _ptr;
 
    template <class OtherC, class OtherRC, class OtherRP> friend class SharedPtr;
};
 
 
template <class C, class RC, class RP>
inline void swap(SharedPtr<C, RC, RP>& p1, SharedPtr<C, RC, RP>& p2)
{
    p1.swap(p2);
}
 
 
template <typename T, typename... Args>
SharedPtr<T> makeShared(Args&&... args)
{
    return SharedPtr<T>(new T(std::forward<Args>(args)...));
}
 
 
template <typename T>
SharedPtr<T, ReferenceCounter, ReleaseArrayPolicy<T>> makeSharedArray(std::size_t size)
{
    return SharedPtr<T, ReferenceCounter, ReleaseArrayPolicy<T>>(new T[size]);
}
 
 
} // namespace Poco
 
 
#endif // Foundation_SharedPtr_INCLUDED