627 lines
16 KiB
C++
627 lines
16 KiB
C++
/*
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----
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This file is part of SECONDO.
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Copyright (C) 2004, University in Hagen, Department of Computer Science,
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Database Systems for New Applications.
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SECONDO is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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SECONDO is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with SECONDO; if not, write to the Free Software
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Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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----
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//[_] [\_]
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//characters [1] verbatim: [$] [$]
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//characters [2] formula: [$] [$]
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//characters [3] capital: [\textsc{] [}]
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//characters [4] teletype: [\texttt{] [}]
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//paragraph [11] Title: [{\Large \bf \begin{center}] [\end{center}}]
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//[TOC] [\tableofcontents]
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[11] Headerfile "SmartPtr.h"[4]
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January-February 2008, Mirko Dibbert
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[TOC]
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\newpage
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1 Overview
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This headerfile contains two classes, which implement a smart pointer for any object type. Smart pointers could be used similar to regular pointers, but additionally, they use a reference count mechanism, which increments a reference counter when calling the copy constructor, clone method or assignement operator instead of copying the refered object. When a smart pointer is deleted, the reference counter will be decreased. The refered object will be deleted as soon as the reference counter reaches zero.
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This file contains two implementations of smart pointers: "SmartPtr"[4] and "SaveSmartPtr"[4]. Both classes are nearly equal, but the "SaveSmartPtr"[4] class also handles overflow of the reference counter. For this, the refered object must provide a "clone"[4] method, that returns a copy of the object. A "clone"[4] method is also needed for both smart pointer types, if the "clone"[4] method of the smart pointer should be used.
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To assign an object to a smart pointer, use the respctive constructur or the assingment operator.
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Warning: Never assign the same object to more than one smart pointer, since each assignment creates a new reference counter and if one of these counters reaches 0, the object would be deleted, even if it is stored in another smart pointer (if needed, assign a copy of the object to the second smart pointer instead).
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The following example show, how an object reference could be assigned to a smart pointer:
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---- SmartPtr<myClass> ptr1(new myClass());
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SmartPtr<myClass> ptr2 = new myClass();
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----
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To get a new reference of an object and increment the reference couter, use the copy constructor or the assignment operator for smart pointers:
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---- SaveSmartPtr<myClass> ptr1(new myClass());
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SaveSmartPtr<myClass> ptr2 = ptr1;
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SaveSmartPtr<myClass> ptr3(ptr1);
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----
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All these pointers refer to the same instance of "myClass"[4] and the common reference counter has a value of 3. If the pointers will be deleted, the reference counter will be automatically decreased and - if the counter reaches a value of 0 - the refered object will be deleted.
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It is also possible to assign a "SmartPointer"[4] to a "SaveSmartPointer"[4] and vice versa.
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The refered object could be accessed by the "{->}"[4] operator, similar to regular pointers.
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\\[3ex]
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The smart pointer classes are designed as template classes, which template parameters have the following meaning:
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* "BaseT"[4] : (object type, which should be stored in the pointer)
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* "CntrT"[4] : (type of the reference counter (optional), which is "unsigned long" by default)
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\newpage
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Both smart pointers classes provide the following methods:
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---- const CntrT refs()
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const CntrT maxRefs()
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bool defined() const
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void reset()
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(Save)SmartPtr& clone()
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----
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The "refs"[4] and "maxRefs"[4] methods could be used to return the current count of references and the maximum count of references, that the reference counter could store, unless it overflows. The "defined"[4] method returns "true"[4] if the smart pointer curently refers to an object. The "reset"[4] method removes the reference to the object (if no reference exists, nothing happens). The "clone"[4] method returns a new smart pointer, which refers to a copy of the refered object, that means, the refered object will also be copied. If only the reference counter should be increased, use the copy constructor instead.
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Beyond the mentioned methods, the following operators are avaliable:
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---- operator =
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operator ->
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operator ==
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operator !=
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----
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The "="[4] operator could be used to assign a regular pointer, a "SmartPointer"[4] or a "SaveSmart-"[4] "Pointer"[4] to the smart pointer on left hand side. The "->"[4] operator is used to access the refered object, equal to regular pointers. The "=="[4] operator returns true, if both smart pointers refer to the same object.
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2 Includes and defines
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*/
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#ifndef __SMART_PTR_H____
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#define __SMART_PTR_H____
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#include <limits>
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template <typename BaseT, typename CntrT = unsigned long>
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class SaveSmartPtr; // forward declaration
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template <typename BaseT, typename CntrT = unsigned long>
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class SmartPtr; // forward declaration
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/********************************************************************
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3 Class declarations
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3.1 Class "RCHandle"[4]
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This class is used in the "SmartPtr"[4] and the "SaveSmartPtr"[4] class to provide a reference counter for a "BaseT"[4] instance. The type of the counter could be selected by the "CntrT"[4] template paremeter.
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********************************************************************/
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template <typename BaseT, typename CntrT>
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class RCHandle
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{
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public:
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/*
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Constructor (creates a new RCHandle with one reference).
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*/
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inline RCHandle(BaseT* _ptr)
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: cntr(1), ptr(_ptr)
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{}
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/*
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Destructor (removes the reference counter and pointer).
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*/
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inline ~RCHandle()
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{ delete ptr;}
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CntrT cntr; // the reference counter
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BaseT* const ptr; // pointer to refered object
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};
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/********************************************************************
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3.2 Class "SmartPtr"[4]
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********************************************************************/
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template <typename BaseT, typename CntrT>
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class SmartPtr
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{
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public:
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friend class SaveSmartPtr<BaseT, CntrT>;
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typedef CntrT counterType;
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/*
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Constructor (creates a undefined smart pointer).
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*/
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inline SmartPtr()
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: rcHandle(0)
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{}
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/*
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Constructor (assigns "ptr"[4] to the new "SmartPtr"[4] instance).
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*/
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inline SmartPtr(BaseT* ptr)
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: rcHandle(ptr ? new RCHandle<BaseT, CntrT>(ptr) : 0)
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{}
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/*
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Copy constructor (increases reference counter).
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*/
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inline SmartPtr(const SmartPtr<BaseT, CntrT>& ptr)
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{
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rcHandle = ptr.rcHandle;
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if (defined())
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++rcHandle->cntr;
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}
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/*
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Copy constructor for "SaveSmartPtr"[4] (increases reference counter).
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*/
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inline SmartPtr(const SaveSmartPtr<BaseT, CntrT>& ptr)
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{
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rcHandle = ptr.rcHandle;
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if (defined())
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++rcHandle->cntr;
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}
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/*
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Destructor (decreases reference counter and deletes the assigned object, if no further references exist).
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*/
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inline ~SmartPtr()
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{
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if (defined() && (--rcHandle->cntr == 0))
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delete rcHandle;
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}
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/*
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Returns a new "SmartPointer"[4], which points to a deep copy of the refered object. The new pointer will have a reference count of 1.
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*/
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inline SmartPtr& clone() const
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{
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if (!defined())
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return new SmartPtr;
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else
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return new SmartPtr(rcHandle->ptr->clone());
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}
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/*
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Reference operator.
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*/
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inline BaseT* operator->()
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{
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if (!defined())
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return 0;
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else
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return rcHandle->ptr;
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}
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/*
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Constant reference operator.
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*/
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inline const BaseT* operator->() const
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{
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if (!defined())
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return 0;
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else
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return rcHandle->ptr;
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}
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/*
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Assignment operator (assigns another "SmartPtr"[4] instance to the current smart pointer).
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*/
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inline SmartPtr<BaseT, CntrT>& operator=(
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const SmartPtr<BaseT, CntrT>& rhs)
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{
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if (rhs.defined())
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++rhs.rcHandle->cntr;
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reset();
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rcHandle = rhs.rcHandle;
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return *this;
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}
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/*
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Assignment operator (assigns a "SaveSmartPtr"[4] instance to the current pointer instance).
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*/
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inline SmartPtr<BaseT, CntrT>& operator=(
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const SaveSmartPtr<BaseT, CntrT>& rhs)
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{
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if (rhs.defined())
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++rhs.rcHandle->cntr;
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reset();
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rcHandle = rhs.rcHandle;
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return *this;
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}
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/*
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Assignment operator (assigns a new "BaseT"[4] object to the current smart pointer).
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*/
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inline SmartPtr<BaseT, CntrT>& operator=(BaseT* rhs)
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{
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reset();
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if (rhs)
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rcHandle = new RCHandle<BaseT, CntrT>(rhs);
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return *this;
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}
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/*
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Returns a reference to the reference counter.
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*/
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inline CntrT* getRefCntr() const
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{
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if (rcHandle)
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return rcHandle->cntr;
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else
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return 0;
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}
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/*
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Returns current count of references to the object.
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*/
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inline CntrT refs() const
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{
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if (rcHandle)
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return *rcHandle->cntr;
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else
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return CntrT();
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}
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/*
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Returns the maximum number of referencses, which the counter can hold.
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*/
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inline CntrT maxRefs() const
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{
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return std::numeric_limits<CntrT>::max();
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}
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/*
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Equal operator for assigned object references.
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*/
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friend inline bool operator==(
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const SmartPtr<BaseT, CntrT>& lhs,
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const SmartPtr<BaseT, CntrT>& rhs)
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{
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if (!lhs.defined())
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return (!rhs.defined());
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else if (!rhs.defined())
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return false;
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else
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return lhs.rcHandle->ptr == rhs.rcHandle->ptr;
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}
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/*
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Unequal operator for assigned object references.
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*/
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friend inline bool operator!=(
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const SmartPtr<BaseT, CntrT>& lhs,
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const SmartPtr<BaseT, CntrT>& rhs)
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{ return !(lhs == rhs); }
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/*
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Returns "true"[4], if an object has been assigned to the pointer.
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*/
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inline bool defined() const
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{ return (rcHandle != 0); }
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/*
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Removes object assignment and deletes the assigned object,
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if no further references exist.
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*/
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inline void reset()
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{
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if (defined() && --rcHandle->cntr == 0)
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delete rcHandle;
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rcHandle = 0;
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}
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protected:
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RCHandle<BaseT, CntrT>* rcHandle;
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// reference counter and ref. to object
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};
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/********************************************************************
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3.3 Class "SaveSmartPtr"[4]
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This class is equal to "SmartPtr"[4], but could handle counter overflows, which leads to a slightly reduced performace of the copy-constructor and assignment method. Furthermore the refered object needs to provide a clone() method, which calls the copy constructor of the respective class.
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********************************************************************/
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template <typename BaseT, typename CntrT>
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class SaveSmartPtr
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{
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public:
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friend class SmartPtr<BaseT, CntrT>;
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typedef CntrT counterType;
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/*
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Constructor (creates a undefined "SaveSmartPtr"[4] instance):
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*/
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inline SaveSmartPtr()
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: rcHandle(0)
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{}
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/*
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Constructor (assigns "ptr"[4] to the new "SaveSmartPtr"[4] instance).
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*/
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inline SaveSmartPtr(BaseT* ptr)
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: rcHandle(ptr ? new RCHandle<BaseT, CntrT>(ptr) : 0)
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{}
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/*
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Copy constructor (increases the reference counter. If neccesary, a copy of the refered object would be created instead).
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*/
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SaveSmartPtr(const SaveSmartPtr<BaseT, CntrT>& ptr)
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{
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/* increment reference counter of ptr - in case of counter
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overflow a new reference counter object will be created */
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if (ptr.defined())
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{
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if(ptr.refs() < maxRefs())
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{
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rcHandle = ptr.rcHandle;
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++rcHandle->cntr;
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}
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else
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{
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rcHandle = new RCHandle<BaseT, CntrT>(
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ptr.rcHandle->ptr->clone());
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}
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}
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else
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rcHandle = 0;
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}
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/*
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Destructor (decreases reference counter and deletes the assigned object, if no further references exist).
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*/
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inline ~SaveSmartPtr()
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{
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if (defined() && (--rcHandle->cntr == 0))
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delete rcHandle;
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}
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/*
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Returns a new smart pointer, which points to a deep copy of the refered object. The new pointer will have a reference count of 1.
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*/
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inline SaveSmartPtr& clone() const
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{
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if (!defined())
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return new SaveSmartPtr;
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else
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return new SaveSmartPtr(rcHandle->ptr->clone());
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}
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/*
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Reference operator.
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*/
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inline BaseT* operator->()
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{
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if (!defined())
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return 0;
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else
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return rcHandle->ptr;
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}
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/*
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Constant reference oparator.
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*/
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inline const BaseT* operator->() const
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{
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if (!defined())
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return 0;
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else
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return rcHandle->ptr;
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}
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/*
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Assignment operator (assigns another "SaveSmartPtr"[4] instance to the current pointer instance).
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*/
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SaveSmartPtr<BaseT, CntrT>& operator=(
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const SaveSmartPtr<BaseT, CntrT>& rhs)
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{
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/* increment reference counter of rhs - in case of counter
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overflow a new reference counter object will be created */
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RCHandle<BaseT, CntrT>* newRCHandle;
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if (rhs.defined())
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{
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if(rhs.refs() < maxRefs())
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{
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++rhs.rcHandle->cntr;
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newRCHandle = rhs.rcHandle;
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}
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else
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{
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newRCHandle = new RCHandle<BaseT, CntrT>(
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rhs.rcHandle->ptr->clone());
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}
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}
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else
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newRCHandle = 0;
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// remove currently stored reference
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if (defined() && (--rcHandle->cntr == 0))
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delete rcHandle;
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// assign new reference counter
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rcHandle = newRCHandle;
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return *this;
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}
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/*
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Assignment operator (assigns a "SmartPtr"[4] instance to the current pointer instance).
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*/
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SaveSmartPtr<BaseT, CntrT>& operator=(
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const SmartPtr<BaseT, CntrT>& rhs)
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{
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/* increment reference counter of rhs - in case of counter
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overflow a new reference counter object will be created */
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RCHandle<BaseT, CntrT>* newRCHandle;
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if (rhs.defined())
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{
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if(rhs.refs() < maxRefs())
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{
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++rhs.rcHandle->cntr;
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newRCHandle = rhs.rcHandle;
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}
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else
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{
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newRCHandle = new RCHandle<BaseT, CntrT>(
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rhs.rcHandle->ptr->clone());
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}
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}
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else
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newRCHandle = 0;
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// remove currently stored reference
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if (defined() && (--rcHandle->cntr == 0))
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delete rcHandle;
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// assign new reference counter
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rcHandle = newRCHandle;
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return *this;
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}
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/*
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Assignment operator (assigns a new object reference to the current pointer instance).
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*/
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inline SaveSmartPtr<BaseT, CntrT>& operator=(BaseT* rhs)
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{
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if (defined() && (--rcHandle->cntr == 0))
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delete rcHandle;
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if (rhs)
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rcHandle = new RCHandle<BaseT, CntrT>(rhs);
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return *this;
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}
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/*
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Returns a reference to the reference counter.
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*/
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inline CntrT* getRefCntr() const
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{
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if (rcHandle)
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return rcHandle->cntr;
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else
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return 0;
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}
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/*
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Returns current count of references to the object.
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*/
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inline CntrT refs() const
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{
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if (rcHandle)
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return *rcHandle->cntr;
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else
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return CntrT();
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}
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/*
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Returns the maximum number of referencses, which the counter can hold.
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*/
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inline CntrT maxRefs() const
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{
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return std::numeric_limits<CntrT>::max();
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}
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/*
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Equal operator for assigned object references.
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*/
|
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friend inline bool operator==(
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const SaveSmartPtr<BaseT, CntrT>& lhs,
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const SaveSmartPtr<BaseT, CntrT>& rhs)
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{
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if (!lhs.defined())
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return (!rhs.defined());
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|
else if (!rhs.defined())
|
|
return false;
|
|
else
|
|
return lhs.rcHandle->ptr == rhs.rcHandle->ptr;
|
|
}
|
|
|
|
/*
|
|
Unequal operator for assigned object references.
|
|
|
|
*/
|
|
friend inline bool operator!=(
|
|
const SaveSmartPtr<BaseT, CntrT>& lhs,
|
|
const SaveSmartPtr<BaseT, CntrT>& rhs)
|
|
{ return !(lhs == rhs); }
|
|
|
|
/*
|
|
Returns "true"[4], if an object has been assigned to the pointer.
|
|
|
|
*/
|
|
inline bool defined() const
|
|
{ return rcHandle != 0; }
|
|
|
|
/*
|
|
Removes object assignment and deletes the assigned object, if no further references exist.
|
|
|
|
*/
|
|
inline void reset()
|
|
{
|
|
if (defined() && --rcHandle->cntr == 0)
|
|
delete rcHandle;
|
|
rcHandle = 0;
|
|
}
|
|
|
|
protected:
|
|
RCHandle<BaseT, CntrT>* rcHandle;
|
|
// reference counter and ref. to object
|
|
};
|
|
|
|
#endif // #ifndef __SMART_PTR_H__
|