godot/core/os/pool_allocator.h

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/*  pool_allocator.h                                                      */
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#ifndef POOL_ALLOCATOR_H
#define POOL_ALLOCATOR_H

#include "core/typedefs.h"

/**
 * Generic Pool Allocator.
 * This is a generic memory pool allocator, with locking, compacting and alignment. (@TODO alignment)
 * It used as a standard way to manage allocation in a specific region of memory, such as texture memory,
 * audio sample memory, or just any kind of memory overall.
 * (@TODO) abstraction should be greater, because in many platforms, you need to manage a nonreachable memory.
 */

enum {
	POOL_ALLOCATOR_INVALID_ID = -1 ///< default invalid value. use INVALID_ID( id ) to test
};

class PoolAllocator {
public:
	typedef int ID;

private:
	enum {
		CHECK_BITS = 8,
		CHECK_LEN = (1 << CHECK_BITS),
		CHECK_MASK = CHECK_LEN - 1

	};

	struct Entry {
		unsigned int pos = 0;
		unsigned int len = 0;
		unsigned int lock = 0;
		unsigned int check = 0;

		inline void clear() {
			pos = 0;
			len = 0;
			lock = 0;
			check = 0;
		}
		Entry() {}
	};

	typedef int EntryArrayPos;
	typedef int EntryIndicesPos;

	Entry *entry_array = nullptr;
	int *entry_indices = nullptr;
	int entry_max = 0;
	int entry_count = 0;

	uint8_t *pool = nullptr;
	void *mem_ptr = nullptr;
	int pool_size = 0;

	int free_mem = 0;
	int free_mem_peak = 0;

	unsigned int check_count = 0;
	int align = 1;

	bool needs_locking = false;

	inline int entry_end(const Entry &p_entry) const {
		return p_entry.pos + aligned(p_entry.len);
	}
	inline int aligned(int p_size) const {
		int rem = p_size % align;
		if (rem) {
			p_size += align - rem;
		}

		return p_size;
	}

	void compact(int p_up_to = -1);
	void compact_up(int p_from = 0);
	bool get_free_entry(EntryArrayPos *p_pos);
	bool find_hole(EntryArrayPos *p_pos, int p_for_size);
	bool find_entry_index(EntryIndicesPos *p_map_pos, const Entry *p_entry);
	Entry *get_entry(ID p_mem);
	const Entry *get_entry(ID p_mem) const;

	void create_pool(void *p_mem, int p_size, int p_max_entries);

protected:
	virtual void mt_lock() const; ///< Reimplement for custom mt locking
	virtual void mt_unlock() const; ///< Reimplement for custom mt locking

public:
	enum {
		DEFAULT_MAX_ALLOCS = 4096,
	};

	ID alloc(int p_size); ///< Alloc memory, get an ID on success, POOL_ALOCATOR_INVALID_ID on failure
	void free(ID p_mem); ///< Free allocated memory
	Error resize(ID p_mem, int p_new_size); ///< resize a memory chunk
	int get_size(ID p_mem) const;

	int get_free_mem(); ///< get free memory
	int get_used_mem() const;
	int get_free_peak(); ///< get free memory

	Error lock(ID p_mem); //@todo move this out
	void *get(ID p_mem);
	const void *get(ID p_mem) const;
	void unlock(ID p_mem);
	bool is_locked(ID p_mem) const;

	PoolAllocator(int p_size, bool p_needs_locking = false, int p_max_entries = DEFAULT_MAX_ALLOCS);
	PoolAllocator(void *p_mem, int p_size, int p_align = 1, bool p_needs_locking = false, int p_max_entries = DEFAULT_MAX_ALLOCS);
	PoolAllocator(int p_align, int p_size, bool p_needs_locking = false, int p_max_entries = DEFAULT_MAX_ALLOCS);

	virtual ~PoolAllocator();
};

#endif // POOL_ALLOCATOR_H