virtualx-engine/core/pooled_list.h

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/*  pooled_list.h                                                        */
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#pragma once

// Simple template to provide a pool with O(1) allocate and free.
// The freelist could alternatively be a linked list placed within the unused elements
// to use less memory, however a separate freelist is probably more cache friendly.

// NOTE : Take great care when using this with non POD types. The construction and destruction
// is done in the LocalVector, NOT as part of the pool. So requesting a new item does not guarantee
// a constructor is run, and free does not guarantee a destructor.
// You should generally handle clearing
// an item explicitly after a request, as it may contain 'leftovers'.
// This is by design for fastest use in the BVH. If you want a more general pool
// that does call constructors / destructors on request / free, this should probably be
// a separate template.

#include "core/local_vector.h"

template <class T, bool force_trivial = false>
class PooledList {
	LocalVector<T, uint32_t, force_trivial> list;
	LocalVector<uint32_t, uint32_t, true> freelist;

	// not all list members are necessarily used
	int _used_size;

public:
	PooledList() {
		_used_size = 0;
	}

	int estimate_memory_use() const {
		return (list.size() * sizeof(T)) + (freelist.size() * sizeof(uint32_t));
	}

	const T &operator[](uint32_t p_index) const {
		return list[p_index];
	}
	T &operator[](uint32_t p_index) {
		return list[p_index];
	}

	int size() const { return _used_size; }

	T *request(uint32_t &r_id) {
		_used_size++;

		if (freelist.size()) {
			// pop from freelist
			int new_size = freelist.size() - 1;
			r_id = freelist[new_size];
			freelist.resize(new_size);
			return &list[r_id];
		}

		r_id = list.size();
		list.resize(r_id + 1);
		return &list[r_id];
	}
	void free(const uint32_t &p_id) {
		// should not be on free list already
		CRASH_COND(p_id >= list.size());
		freelist.push_back(p_id);
		_used_size--;
	}
};

// a pooled list which automatically keeps a list of the active members
template <class T, bool force_trivial = false>
class TrackedPooledList {
public:
	int pool_size() const { return _pool.size(); }
	int active_size() const { return _active_list.size(); }

	uint32_t get_active_id(uint32_t p_index) const {
		return _active_list[p_index];
	}

	const T &get_active(uint32_t p_index) const {
		return _pool[get_active_id(p_index)];
	}

	T &get_active(uint32_t p_index) {
		return _pool[get_active_id(p_index)];
	}

	const T &operator[](uint32_t p_index) const {
		return _pool[p_index];
	}
	T &operator[](uint32_t p_index) {
		return _pool[p_index];
	}

	T *request(uint32_t &r_id) {
		T *item = _pool.request(r_id);

		// add to the active list
		uint32_t active_list_id = _active_list.size();
		_active_list.push_back(r_id);

		// expand the active map (this should be in sync with the pool list
		if (_pool.size() > (int)_active_map.size()) {
			_active_map.resize(_pool.size());
		}

		// store in the active map
		_active_map[r_id] = active_list_id;

		return item;
	}

	void free(const uint32_t &p_id) {
		_pool.free(p_id);

		// remove from the active list.
		uint32_t list_id = _active_map[p_id];

		// zero the _active map to detect bugs (only in debug?)
		_active_map[p_id] = -1;

		_active_list.remove_unordered(list_id);

		// keep the replacement in sync with the correct list Id
		if (list_id < (uint32_t)_active_list.size()) {
			// which pool id has been replaced in the active list
			uint32_t replacement_id = _active_list[list_id];

			// keep that replacements map up to date with the new position
			_active_map[replacement_id] = list_id;
		}
	}

private:
	PooledList<T, force_trivial> _pool;
	LocalVector<uint32_t, uint32_t> _active_map;
	LocalVector<uint32_t, uint32_t> _active_list;
};