127 lines
4.7 KiB
C++
127 lines
4.7 KiB
C++
/* file ArenaAlloc.hpp
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*
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* author: Roland Conybeare, Jul 2025
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*/
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#pragma once
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#include "IAlloc.hpp"
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#include "ObjectStatistics.hpp"
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namespace xo {
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namespace gc {
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/** @class ArenaAlloc
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* @brief Bump allocator with fixed capacity
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*
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* @text
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*
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* <-----allocated----> <--------free------->
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* XXXXXXXXXXXXXXXXXXXX______________________
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* ^ ^ ^
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* lo free hi
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* limit
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* @endtext
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**/
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class ArenaAlloc : public IAlloc {
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public:
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ArenaAlloc(const ArenaAlloc &) = delete;
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ArenaAlloc(ArenaAlloc &&) = delete;
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~ArenaAlloc();
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/** Create allocator with capacity @p z,
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* Reserve memory addresses for @p z bytes,
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* but don't commit them until needed
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**/
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static up<ArenaAlloc> make(const std::string & name,
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std::size_t z,
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bool debug_flag);
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/** size of virtual address range reserved for this allocator **/
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std::size_t reserved() const { return this->size(); }
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std::size_t page_size() const { return page_z_; }
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std::byte * free_ptr() const { return free_ptr_; }
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void set_free_ptr(std::byte * x);
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/** if address @p x is allocated from this arena,
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* return true along with offset relative to base address @ref lo_
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* otherwise return false with 0
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**/
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std::pair<bool, std::size_t> location_of(const void * x) const;
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/** allocated span **/
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std::pair<const std::byte *, const std::byte *> allocated_span() const {
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return std::make_pair(lo_, free_ptr_);
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}
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/** Reset to empty state **/
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void reset(std::size_t /*z_ignored*/) { this->clear(); }
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void capture_object_statistics(capture_phase phase,
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ObjectStatistics * p_dest) const;
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/** expand available (i.e. committed) space to size @p z **/
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bool expand(std::size_t z);
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// inherited from IAlloc...
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virtual const std::string & name() const final override;
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virtual std::size_t size() const final override;
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virtual std::size_t committed() const final override;
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virtual std::size_t available() const final override;
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virtual std::size_t allocated() const final override;
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virtual bool contains(const void * x) const final override;
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virtual bool is_before_checkpoint(const void * x) const final override;
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virtual std::size_t before_checkpoint() const final override;
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virtual std::size_t after_checkpoint() const final override;
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virtual bool debug_flag() const final override;
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virtual void clear() final override;
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virtual void checkpoint() final override;
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virtual std::byte * alloc(std::size_t z) final override;
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ArenaAlloc & operator=(const ArenaAlloc &) = delete;
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ArenaAlloc & operator=(ArenaAlloc &&) = delete;
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private:
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ArenaAlloc(const std::string & name,
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std::size_t z, bool debug_flag);
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private:
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/**
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* Invariants:
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* - @ref free_ always a multiple of word size (assumed to be sizeof(void*))
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**/
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/** optional instance name, for diagnostics **/
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std::string name_;
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/** size of a VM page **/
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std::size_t page_z_;
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/** allocator owns memory in range [@ref lo_, @ref hi_) **/
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std::byte * lo_ = nullptr;
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/** prefix of this size is actually committed.
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* Remainder uses uncommitted virtual address space
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**/
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std::size_t committed_z_ = 0;
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/** checkpoint (for GC support); divides objects into
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* older (addresses below checkpoint)
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* and younger (addresses above checkpoint)
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**/
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std::byte * checkpoint_;
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/** free pointer. memory in range [@ref free_, @ref limit_) available **/
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std::byte * free_ptr_ = nullptr;
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/** soft limit: end of committed virtual memory **/
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std::byte * limit_ = nullptr;
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/** hard limit: end of reserved virtual memory **/
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std::byte * hi_ = nullptr;
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/** true to enable detailed debug logging **/
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bool debug_flag_ = false;
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};
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} /*namespace gc*/
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} /*namespace xo*/
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/* end ArenaAlloc.hpp */
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