godot/core/templates/paged_allocator.h

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/*  paged_allocator.h                                                     */
/**************************************************************************/
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/* Copyright (c) 2007-2014 Juan Linietsky, Ariel Manzur.                  */
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#pragma once

#include "core/core_globals.h"
#include "core/os/memory.h"
#include "core/os/spin_lock.h"
#include "core/string/ustring.h"
#include "core/typedefs.h"

#include <type_traits>
#include <typeinfo> // IWYU pragma: keep // Used in macro.

template <typename T, bool thread_safe = false, uint32_t DEFAULT_PAGE_SIZE = 4096>
class PagedAllocator {
	T **page_pool = nullptr;
	T ***available_pool = nullptr;
	uint32_t pages_allocated = 0;
	uint32_t allocs_available = 0;

	uint32_t page_shift = 0;
	uint32_t page_mask = 0;
	uint32_t page_size = 0;
	SpinLock spin_lock;

public:
	template <typename... Args>
	T *alloc(Args &&...p_args) {
		if constexpr (thread_safe) {
			spin_lock.lock();
		}
		if (unlikely(allocs_available == 0)) {
			uint32_t pages_used = pages_allocated;

			pages_allocated++;
			page_pool = (T **)memrealloc(page_pool, sizeof(T *) * pages_allocated);
			available_pool = (T ***)memrealloc(available_pool, sizeof(T **) * pages_allocated);

			page_pool[pages_used] = (T *)memalloc(sizeof(T) * page_size);
			available_pool[pages_used] = (T **)memalloc(sizeof(T *) * page_size);

			for (uint32_t i = 0; i < page_size; i++) {
				available_pool[0][i] = &page_pool[pages_used][i];
			}
			allocs_available += page_size;
		}

		allocs_available--;
		T *alloc = available_pool[allocs_available >> page_shift][allocs_available & page_mask];
		if constexpr (thread_safe) {
			spin_lock.unlock();
		}
		memnew_placement(alloc, T(p_args...));
		return alloc;
	}

	void free(T *p_mem) {
		if constexpr (thread_safe) {
			spin_lock.lock();
		}
		p_mem->~T();
		available_pool[allocs_available >> page_shift][allocs_available & page_mask] = p_mem;
		allocs_available++;
		if constexpr (thread_safe) {
			spin_lock.unlock();
		}
	}

	template <typename... Args>
	T *new_allocation(Args &&...p_args) { return alloc(p_args...); }
	void delete_allocation(T *p_mem) { free(p_mem); }

private:
	void _reset(bool p_allow_unfreed) {
		if (!p_allow_unfreed || !std::is_trivially_destructible_v<T>) {
			ERR_FAIL_COND(allocs_available < pages_allocated * page_size);
		}
		if (pages_allocated) {
			for (uint32_t i = 0; i < pages_allocated; i++) {
				memfree(page_pool[i]);
				memfree(available_pool[i]);
			}
			memfree(page_pool);
			memfree(available_pool);
			page_pool = nullptr;
			available_pool = nullptr;
			pages_allocated = 0;
			allocs_available = 0;
		}
	}

public:
	void reset(bool p_allow_unfreed = false) {
		if constexpr (thread_safe) {
			spin_lock.lock();
		}
		_reset(p_allow_unfreed);
		if constexpr (thread_safe) {
			spin_lock.unlock();
		}
	}

	bool is_configured() const {
		if constexpr (thread_safe) {
			spin_lock.lock();
		}
		bool result = page_size > 0;
		if constexpr (thread_safe) {
			spin_lock.unlock();
		}
		return result;
	}

	void configure(uint32_t p_page_size) {
		if constexpr (thread_safe) {
			spin_lock.lock();
		}
		ERR_FAIL_COND(page_pool != nullptr); // Safety check.
		ERR_FAIL_COND(p_page_size == 0);
		page_size = nearest_power_of_2_templated(p_page_size);
		page_mask = page_size - 1;
		page_shift = get_shift_from_power_of_2(page_size);
		if constexpr (thread_safe) {
			spin_lock.unlock();
		}
	}

	// Power of 2 recommended because of alignment with OS page sizes.
	// Even if element is bigger, it's still a multiple and gets rounded to amount of pages.
	PagedAllocator(uint32_t p_page_size = DEFAULT_PAGE_SIZE) {
		configure(p_page_size);
	}

	~PagedAllocator() {
		if constexpr (thread_safe) {
			spin_lock.lock();
		}
		bool leaked = allocs_available < pages_allocated * page_size;
		if (leaked) {
			if (CoreGlobals::leak_reporting_enabled) {
				ERR_PRINT(String("Pages in use exist at exit in PagedAllocator: ") + String(typeid(T).name()));
			}
		} else {
			_reset(false);
		}
		if constexpr (thread_safe) {
			spin_lock.unlock();
		}
	}
};