56 lines
2.3 KiB
C++
56 lines
2.3 KiB
C++
/* file Forwarding1.hpp
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*
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* author: Roland Conybeare, Aug 2025
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*/
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#include "Object.hpp"
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namespace xo {
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namespace obj {
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/** @class Forwarding1
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* @brief forwarding pointer for garbage collector.
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*
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* Used internally by garbage collector (see @ref GC).
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* During evacuate phase overwrite from-space objects in-place
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* with an instance of this class.
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*
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* This class suitable only for singly-inheriting objects,
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* i.e. those that have exactly one vtable.
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**/
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class Forwarding1 : public Object {
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public:
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explicit Forwarding1(gp<Object> dest);
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// inherited from Object..
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virtual TaggedPtr self_tp() const final override;
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virtual void display(std::ostream & os) const final override;
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virtual bool _is_forwarded() const final override { return true; }
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virtual Object * _offset_destination(Object * src) const final override;
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virtual Object * _destination() final override;
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/** required by Object i/face, but never called on Forwarding1 **/
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virtual std::size_t _shallow_size() const final override;
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/** required by Object i/face, but never called on Forwarding1 **/
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virtual Object * _shallow_copy() const final override;
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/** required by Object i/face, but never called on Forwarding1 **/
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virtual std::size_t _forward_children() final override;
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private:
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/** the object that used to be located at this address (i.e. @c this)
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* has been moved to @ref destination_ ,
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* with original location overwritten by a forwarding pointer
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*
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* Require:
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* - can only use Forwarding with types that have a single vtable.
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* To forward a multiply-inheriting class with two vtables, use Forwarding2.
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* - if you try to use Forwarding for an object with multiple vtables,
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* one of the vtable pointers will be replaced by @ref destination_.
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* UB revealed when GC traverses a pointer that relies on the 2nd
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* vtable to index virtual methods.
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**/
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gp<Object> dest_;
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};
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} /*namespace obj*/
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} /*namespace xo*/
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/* end Forwarding1.hpp */
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