godot/core/allocators.h

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/*  allocators.h                                                         */
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#ifndef ALLOCATORS_H
#define ALLOCATORS_H

#include "core/os/memory.h"

template <int PREALLOC_COUNT = 64, int MAX_HANDS = 8>
class BalloonAllocator {

	enum {

		USED_FLAG = (1 << 30),
		USED_MASK = USED_FLAG - 1
	};

	struct Balloon {

		Balloon *next;
		Balloon *prev;
		uint32_t hand;
	};

	struct Hand {

		int used;
		int allocated;
		Balloon *first;
		Balloon *last;
	};

	Hand hands[MAX_HANDS];

public:
	void *alloc(size_t p_size) {

		size_t max = (1 << MAX_HANDS);
		ERR_FAIL_COND_V(p_size > max, NULL);

		unsigned int hand = 0;

		while (p_size > (size_t)(1 << hand))
			++hand;

		Hand &h = hands[hand];

		if (h.used == h.allocated) {

			for (int i = 0; i < PREALLOC_COUNT; i++) {

				Balloon *b = (Balloon *)memalloc(sizeof(Balloon) + (1 << hand));
				b->hand = hand;
				if (h.last) {

					b->prev = h.last;
					h.last->next = b;
					h.last = b;
				} else {

					b->prev = NULL;
					h.last = b;
					h.first = b;
				}
			}

			h.last->next = NULL;
			h.allocated += PREALLOC_COUNT;
		}

		Balloon *pick = h.last;

		ERR_FAIL_COND_V((pick->hand & USED_FLAG), NULL);

		// remove last
		h.last = h.last->prev;
		h.last->next = NULL;

		pick->next = h.first;
		h.first->prev = pick;
		pick->prev = NULL;
		h.first = pick;
		h.used++;
		pick->hand |= USED_FLAG;

		return (void *)(pick + 1);
	}

	void free(void *p_ptr) {

		Balloon *b = (Balloon *)p_ptr;
		b -= 1;

		ERR_FAIL_COND(!(b->hand & USED_FLAG));

		b->hand = b->hand & USED_MASK; // not used
		int hand = b->hand;

		Hand &h = hands[hand];

		if (b == h.first)
			h.first = b->next;

		if (b->prev)
			b->prev->next = b->next;
		if (b->next)
			b->next->prev = b->prev;

		if (h.last != b) {
			h.last->next = b;
			b->prev = h.last;
			b->next = NULL;
			h.last = b;
		}

		h.used--;

		if (h.used <= (h.allocated - (PREALLOC_COUNT * 2))) { // this is done to ensure no alloc/free is done constantly

			for (int i = 0; i < PREALLOC_COUNT; i++) {
				ERR_CONTINUE(h.last->hand & USED_FLAG);

				Balloon *new_last = h.last->prev;
				if (new_last)
					new_last->next = NULL;
				memfree(h.last);
				h.last = new_last;
			}
			h.allocated -= PREALLOC_COUNT;
		}
	}

	BalloonAllocator() {

		for (int i = 0; i < MAX_HANDS; i++) {

			hands[i].allocated = 0;
			hands[i].used = 0;
			hands[i].first = NULL;
			hands[i].last = NULL;
		}
	}

	void clear() {

		for (int i = 0; i < MAX_HANDS; i++) {

			while (hands[i].first) {

				Balloon *b = hands[i].first;
				hands[i].first = b->next;
				memfree(b);
			}

			hands[i].allocated = 0;
			hands[i].used = 0;
			hands[i].first = NULL;
			hands[i].last = NULL;
		}
	}

	~BalloonAllocator() {

		clear();
	}
};

#endif // ALLOCATORS_H