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65e73074d9
This patch makes the handling of constructor arguments consistent among the Volatile_object and Lazy_volatile_object classes. Arguments are always forwarded. Otherwise, passing a reference as argument would result in an unwanted copy of the passed object.
156 lines
3.4 KiB
C++
156 lines
3.4 KiB
C++
/*
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* \brief Utility for manual in-place construction of objects
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* \author Norman Feske
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* \date 2014-01-10
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*/
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/*
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* Copyright (C) 2014 Genode Labs GmbH
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*
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* This file is part of the Genode OS framework, which is distributed
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* under the terms of the GNU General Public License version 2.
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*/
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#ifndef _INCLUDE__UTIL__VOLATILE_OBJECT_H_
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#define _INCLUDE__UTIL__VOLATILE_OBJECT_H_
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#include <util/construct_at.h>
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#include <base/printf.h>
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#include <base/stdint.h>
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namespace Genode {
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template<typename> class Volatile_object;
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template<typename> class Lazy_volatile_object;
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}
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/**
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* Place holder for an object to be repeatedly constructed and destructed
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*
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* This class template acts as a smart pointer that refers to an object
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* contained within the smart pointer itself. The contained object may be
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* repeatedly constructed and destructed while staying in the same place. This
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* is useful for replacing aggregated members during the lifetime of a compound
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* object.
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*
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* \param MT type
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*/
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template <typename MT>
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class Genode::Volatile_object
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{
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private:
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/**
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* Static reservation of memory for the embedded object
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*/
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char _space[sizeof(MT)] __attribute__((aligned(sizeof(addr_t))));
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/**
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* True if the volatile object contains a constructed object
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*/
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bool _constructed = false;
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template <typename... ARGS> void _do_construct(ARGS &&... args)
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{
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construct_at<MT>(_space, args...);
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_constructed = true;
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}
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MT *_ptr() { return reinterpret_cast<MT *>(_space); }
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MT const *_const_ptr() const { return reinterpret_cast<MT const *>(_space); }
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void _check_constructed() const
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{
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if (!_constructed)
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throw Deref_unconstructed_object();
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}
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protected:
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/**
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* Dummy type used as a hook for 'Lazy_volatile_object' to bypass the
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* default constructor by invoking the 'Volatile_object(Lazy *)'
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* constructor.
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*/
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struct Lazy { };
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/**
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* Constructor that omits the initial construction of the object
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*/
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Volatile_object(Lazy *) { }
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public:
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class Deref_unconstructed_object { };
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/**
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* Constructor
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*
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* The arguments are forwarded to the constructor of the embedded
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* object.
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*/
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template <typename... ARGS>
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Volatile_object(ARGS &&... args)
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{
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_do_construct(args...);
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}
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~Volatile_object() { destruct(); }
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/**
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* Construct new object in place
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*
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* If the 'Volatile_object' already hosts a constructed object, the old
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* object will be destructed first.
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*/
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template <typename... ARGS>
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void construct(ARGS &&... args)
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{
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destruct();
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_do_construct(args...);
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}
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/**
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* Destruct object
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*/
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void destruct()
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{
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if (!_constructed)
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return;
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/* invoke destructor */
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_ptr()->~MT();
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_constructed = false;
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}
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/**
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* Return true of volatile object contains a constructed object
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*/
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bool is_constructed() const { return _constructed; }
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/**
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* Access contained object
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*/
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MT *operator -> () { _check_constructed(); return _ptr(); }
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MT const *operator -> () const { _check_constructed(); return _const_ptr(); }
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MT &operator * () { _check_constructed(); return *_ptr(); }
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};
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/**
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* Volatile object that holds no initially constructed object
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*/
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template <typename MT>
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struct Genode::Lazy_volatile_object : Volatile_object<MT>
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{
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template <typename... ARGS>
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Lazy_volatile_object(ARGS &&... args)
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:
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Volatile_object<MT>((typename Volatile_object<MT>::Lazy *)0)
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{ }
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};
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#endif /* _INCLUDE__UTIL__VOLATILE_OBJECT_H_ */
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