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/** @file
* IPRT - C++ Resource Management.
*/
/*
* Copyright (C) 2008-2022 Oracle and/or its affiliates.
*
* This file is part of VirtualBox base platform packages, as
* available from https://www.virtualbox.org.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation, in version 3 of the
* License.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, see <https://www.gnu.org/licenses>.
*
* The contents of this file may alternatively be used under the terms
* of the Common Development and Distribution License Version 1.0
* (CDDL), a copy of it is provided in the "COPYING.CDDL" file included
* in the VirtualBox distribution, in which case the provisions of the
* CDDL are applicable instead of those of the GPL.
*
* You may elect to license modified versions of this file under the
* terms and conditions of either the GPL or the CDDL or both.
*
* SPDX-License-Identifier: GPL-3.0-only OR CDDL-1.0
*/
#ifndef IPRT_INCLUDED_cpp_autores_h
#define IPRT_INCLUDED_cpp_autores_h
#ifndef RT_WITHOUT_PRAGMA_ONCE
# pragma once
#endif
#include <iprt/types.h>
#include <iprt/assert.h>
#include <iprt/cpp/utils.h>
/** @defgroup grp_rt_cpp_autores C++ Resource Management
* @ingroup grp_rt_cpp
* @{
*/
/**
* A callable class template which returns the correct value against which an
* IPRT type must be compared to see if it is invalid.
*
* @warning This template *must* be specialised for the types it is to work with.
*/
template <class T>
inline T RTAutoResNil(void)
{
AssertFatalMsgFailed(("Unspecialized template!\n"));
return (T)0;
}
/** Specialisation of RTAutoResNil for RTFILE */
template <>
inline RTFILE RTAutoResNil(void)
{
return NIL_RTFILE;
}
/**
* A function template which calls the correct destructor for an IPRT type.
*
* @warning This template *must* be specialised for the types it is to work with.
*/
template <class T>
inline void RTAutoResDestruct(T a_h)
{
AssertFatalMsgFailed(("Unspecialized template!\n"));
NOREF(a_h);
}
/**
* An auto pointer-type class for resources which take a C-style destructor
* (RTMemFree() or equivalent).
*
* The idea of this class is to manage resources which the current code is
* responsible for freeing. By wrapping the resource in an RTCAutoRes, you
* ensure that the resource will be freed when you leave the scope in which
* the RTCAutoRes is defined, unless you explicitly release the resource.
*
* A typical use case is when a function is allocating a number of resources.
* If any single allocation fails then all other resources must be freed. If
* all allocations succeed, then the resources should be returned to the
* caller. By placing all allocated resources in RTCAutoRes containers, you
* ensure that they will be freed on failure, and only have to take care of
* releasing them when you return them.
*
* @param T The type of the resource.
* @param Destruct The function to be used to free the resource.
* This parameter must be supplied if there is no
* specialisation of RTAutoDestruct available for @a T.
* @param NilRes The function returning the NIL value for T. Required.
* This parameter must be supplied if there is no
* specialisation of RTAutoResNil available for @a T.
*
* @note The class can not be initialised directly using assignment, due
* to the lack of a copy constructor. This is intentional.
*/
template <class T, void Destruct(T) = RTAutoResDestruct<T>, T NilRes(void) = RTAutoResNil<T> >
class RTCAutoRes
: public RTCNonCopyable
{
protected:
/** The resource handle. */
T m_hRes;
public:
/**
* Constructor
*
* @param a_hRes The handle to resource to manage. Defaults to NIL.
*/
RTCAutoRes(T a_hRes = NilRes())
: m_hRes(a_hRes)
{
}
/**
* Destructor.
*
* This destroys any resource currently managed by the object.
*/
~RTCAutoRes()
{
if (m_hRes != NilRes())
Destruct(m_hRes);
}
/**
* Assignment from a value.
*
* This destroys any resource currently managed by the object
* before taking on the new one.
*
* @param a_hRes The handle to the new resource.
*/
RTCAutoRes &operator=(T a_hRes)
{
if (m_hRes != NilRes())
Destruct(m_hRes);
m_hRes = a_hRes;
return *this;
}
/**
* Checks if the resource handle is NIL or not.
*/
bool operator!()
{
return m_hRes == NilRes();
}
/**
* Give up ownership the current resource, handing it to the caller.
*
* @returns The current resource handle.
*
* @note Nothing happens to the resource when the object goes out of scope.
*/
T release(void)
{
T Tmp = m_hRes;
m_hRes = NilRes();
return Tmp;
}
/**
* Deletes the current resources.
*
* @param a_hRes Handle to a new resource to manage. Defaults to NIL.
*/
void reset(T a_hRes = NilRes())
{
if (a_hRes != m_hRes)
{
if (m_hRes != NilRes())
Destruct(m_hRes);
m_hRes = a_hRes;
}
}
/**
* Get the raw resource handle.
*
* Typically used passing the handle to some IPRT function while
* the object remains in scope.
*
* @returns The raw resource handle.
*/
T get(void)
{
return m_hRes;
}
};
/** @} */
/* include after template definition */
#include <iprt/mem.h>
#endif /* !IPRT_INCLUDED_cpp_autores_h */
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