godot/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--;
	}
};