70 lines
2.7 KiB
C++
70 lines
2.7 KiB
C++
/** @file MutationLogEntry.hpp
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*
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* @author Roland Conybeare, Mar 2026
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**/
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#pragma once
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#include <xo/alloc2/GCObject.hpp>
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namespace xo {
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namespace mm {
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class GCObjectStore; // see xo-gc/ GCObjectStore.hpp
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/** @brief Track a cross-generational pointer
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*
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* GC must update pointer when collecting space that target occupies
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*
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* Design notes:
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* - parent must be located at the beginning of an allocation,
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* (so that it's immediately preceded by allocation header)
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* - destination can be something like
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* obj<AGCObject>
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* but also something else such as
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* {obj<AType>, obj<ASyntaxStateMachine>, ..}
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* - for collector need to traverse data pointer *data
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**/
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class MutationLogEntry {
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public:
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using AGCObject = xo::mm::AGCObject;
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public:
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MutationLogEntry() = default;
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MutationLogEntry(void * parent, void ** p_data, obj<AGCObject> snap);
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void * parent() const { return parent_; }
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void ** p_data() const { return p_data_; }
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obj<AGCObject> snap() const { return snap_; }
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/** true iff child pointer matches value when this mlog entry created **/
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bool is_active() const noexcept { return *p_data_ == snap_.data(); }
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/** true iff child pointer has been altered since this mlog entry created **/
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bool is_superseded() const noexcept { return *p_data_ != snap_.data(); }
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/** Refresh snapshot when *p_data_ does not match snap_.data_
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* Get updated facet information from destination alloc header.
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* It's possible that *p_data_ no longer points to gc-owned space
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*
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* @return true if snapshot updated. false if this entry should be discarded
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**/
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bool refresh_snapshot(Generation parent_gen,
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GCObjectStore * gcos) noexcept;
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private:
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/** address of object containing logged mutation **/
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void * parent_ = nullptr;
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/** address of target member of object at address @ref parent_,
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* driving this log entry.
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**/
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void ** p_data_ = nullptr;
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/** AGCObject child pointer, asof assignment responsible for this log entry.
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* If *p_data_ matches snap_.data(), then AGCObject interface is snap_.iface().
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* Otherwise log entry has been superseded by another assignment.
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**/
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obj<AGCObject> snap_;
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};
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} /*namespace mm*/
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} /*namespace xo*/
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/* end MutationLogEntry.hpp */
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