/src/poco/Foundation/include/Poco/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:
  using Type = C;

  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) noexcept
  {
    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

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Created: 2025-08-28 07:02