cowdata.h

/*************************************************************************/
/*  cowdata.h                                                            */
/*************************************************************************/
/*                       This file is part of:                           */
/*                           GODOT ENGINE                                */
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/* Copyright (c) 2007-2020 Juan Linietsky, Ariel Manzur.                 */
/* Copyright (c) 2014-2020 Godot Engine contributors (cf. AUTHORS.md).   */
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#ifndef COWDATA_H
#define COWDATA_H

#include "core/error_macros.h"
#include "core/os/memory.h"
#include "core/safe_refcount.h"

#include <string.h>

template <class T>
class Vector;
class String;
class Char16String;
class CharString;
template <class T, class V>
class VMap;

template <class T>
class CowData {
	template <class TV>
	friend class Vector;
	friend class String;
	friend class Char16String;
	friend class CharString;
	template <class TV, class VV>
	friend class VMap;

private:
	mutable T *_ptr = nullptr;

	// internal helpers

	_FORCE_INLINE_ uint32_t *_get_refcount() const {
		if (!_ptr) {
			return nullptr;
		}

		return reinterpret_cast<uint32_t *>(_ptr) - 2;
	}

	_FORCE_INLINE_ uint32_t *_get_size() const {
		if (!_ptr) {
			return nullptr;
		}

		return reinterpret_cast<uint32_t *>(_ptr) - 1;
	}

	_FORCE_INLINE_ T *_get_data() const {
		if (!_ptr) {
			return nullptr;
		}
		return reinterpret_cast<T *>(_ptr);
	}

	_FORCE_INLINE_ size_t _get_alloc_size(size_t p_elements) const {
		return next_power_of_2(p_elements * sizeof(T));
	}

	_FORCE_INLINE_ bool _get_alloc_size_checked(size_t p_elements, size_t *out) const {
#if defined(__GNUC__)
		size_t o;
		size_t p;
		if (__builtin_mul_overflow(p_elements, sizeof(T), &o)) {
			*out = 0;
			return false;
		}
		*out = next_power_of_2(o);
		if (__builtin_add_overflow(o, static_cast<size_t>(32), &p)) {
			return false; // No longer allocated here.
		}
		return true;
#else
		// Speed is more important than correctness here, do the operations unchecked
		// and hope for the best.
		*out = _get_alloc_size(p_elements);
		return true;
#endif
	}

	void _unref(void *p_data);
	void _ref(const CowData *p_from);
	void _ref(const CowData &p_from);
	void _copy_on_write();

public:
	void operator=(const CowData<T> &p_from) { _ref(p_from); }

	_FORCE_INLINE_ T *ptrw() {
		_copy_on_write();
		return (T *)_get_data();
	}

	_FORCE_INLINE_ const T *ptr() const {
		return _get_data();
	}

	_FORCE_INLINE_ int size() const {
		uint32_t *size = (uint32_t *)_get_size();
		if (size) {
			return *size;
		} else {
			return 0;
		}
	}

	_FORCE_INLINE_ void clear() { resize(0); }
	_FORCE_INLINE_ bool empty() const { return _ptr == nullptr; }

	_FORCE_INLINE_ void set(int p_index, const T &p_elem) {
		CRASH_BAD_INDEX(p_index, size());
		_copy_on_write();
		_get_data()[p_index] = p_elem;
	}

	_FORCE_INLINE_ T &get_m(int p_index) {
		CRASH_BAD_INDEX(p_index, size());
		_copy_on_write();
		return _get_data()[p_index];
	}

	_FORCE_INLINE_ const T &get(int p_index) const {
		CRASH_BAD_INDEX(p_index, size());

		return _get_data()[p_index];
	}

	Error resize(int p_size);

	_FORCE_INLINE_ void remove(int p_index) {
		ERR_FAIL_INDEX(p_index, size());
		T *p = ptrw();
		int len = size();
		for (int i = p_index; i < len - 1; i++) {
			p[i] = p[i + 1];
		}

		resize(len - 1);
	}

	Error insert(int p_pos, const T &p_val) {
		ERR_FAIL_INDEX_V(p_pos, size() + 1, ERR_INVALID_PARAMETER);
		resize(size() + 1);
		for (int i = (size() - 1); i > p_pos; i--) {
			set(i, get(i - 1));
		}
		set(p_pos, p_val);

		return OK;
	}

	int find(const T &p_val, int p_from = 0) const;

	_FORCE_INLINE_ CowData() {}
	_FORCE_INLINE_ ~CowData();
	_FORCE_INLINE_ CowData(CowData<T> &p_from) { _ref(p_from); };
};

template <class T>
void CowData<T>::_unref(void *p_data) {
	if (!p_data) {
		return;
	}

	uint32_t *refc = _get_refcount();

	if (atomic_decrement(refc) > 0) {
		return; // still in use
	}
	// clean up

	if (!__has_trivial_destructor(T)) {
		uint32_t *count = _get_size();
		T *data = (T *)(count + 1);

		for (uint32_t i = 0; i < *count; ++i) {
			// call destructors
			data[i].~T();
		}
	}

	// free mem
	Memory::free_static((uint8_t *)p_data, true);
}

template <class T>
void CowData<T>::_copy_on_write() {
	if (!_ptr) {
		return;
	}

	uint32_t *refc = _get_refcount();

	if (unlikely(*refc > 1)) {
		/* in use by more than me */
		uint32_t current_size = *_get_size();

		uint32_t *mem_new = (uint32_t *)Memory::alloc_static(_get_alloc_size(current_size), true);

		*(mem_new - 2) = 1; //refcount
		*(mem_new - 1) = current_size; //size

		T *_data = (T *)(mem_new);

		// initialize new elements
		if (__has_trivial_copy(T)) {
			memcpy(mem_new, _ptr, current_size * sizeof(T));

		} else {
			for (uint32_t i = 0; i < current_size; i++) {
				memnew_placement(&_data[i], T(_get_data()[i]));
			}
		}

		_unref(_ptr);
		_ptr = _data;
	}
}

template <class T>
Error CowData<T>::resize(int p_size) {
	ERR_FAIL_COND_V(p_size < 0, ERR_INVALID_PARAMETER);

	int current_size = size();

	if (p_size == current_size) {
		return OK;
	}

	if (p_size == 0) {
		// wants to clean up
		_unref(_ptr);
		_ptr = nullptr;
		return OK;
	}

	// possibly changing size, copy on write
	_copy_on_write();

	size_t current_alloc_size = _get_alloc_size(current_size);
	size_t alloc_size;
	ERR_FAIL_COND_V(!_get_alloc_size_checked(p_size, &alloc_size), ERR_OUT_OF_MEMORY);

	if (p_size > current_size) {
		if (alloc_size != current_alloc_size) {
			if (current_size == 0) {
				// alloc from scratch
				uint32_t *ptr = (uint32_t *)Memory::alloc_static(alloc_size, true);
				ERR_FAIL_COND_V(!ptr, ERR_OUT_OF_MEMORY);
				*(ptr - 1) = 0; //size, currently none
				*(ptr - 2) = 1; //refcount

				_ptr = (T *)ptr;

			} else {
				void *_ptrnew = (T *)Memory::realloc_static(_ptr, alloc_size, true);
				ERR_FAIL_COND_V(!_ptrnew, ERR_OUT_OF_MEMORY);
				_ptr = (T *)(_ptrnew);
			}
		}

		// construct the newly created elements

		if (!__has_trivial_constructor(T)) {
			T *elems = _get_data();

			for (int i = *_get_size(); i < p_size; i++) {
				memnew_placement(&elems[i], T);
			}
		}

		*_get_size() = p_size;

	} else if (p_size < current_size) {
		if (!__has_trivial_destructor(T)) {
			// deinitialize no longer needed elements
			for (uint32_t i = p_size; i < *_get_size(); i++) {
				T *t = &_get_data()[i];
				t->~T();
			}
		}

		if (alloc_size != current_alloc_size) {
			void *_ptrnew = (T *)Memory::realloc_static(_ptr, alloc_size, true);
			ERR_FAIL_COND_V(!_ptrnew, ERR_OUT_OF_MEMORY);

			_ptr = (T *)(_ptrnew);
		}

		*_get_size() = p_size;
	}

	return OK;
}

template <class T>
int CowData<T>::find(const T &p_val, int p_from) const {
	int ret = -1;

	if (p_from < 0 || size() == 0) {
		return ret;
	}

	for (int i = p_from; i < size(); i++) {
		if (get(i) == p_val) {
			ret = i;
			break;
		}
	}

	return ret;
}

template <class T>
void CowData<T>::_ref(const CowData *p_from) {
	_ref(*p_from);
}

template <class T>
void CowData<T>::_ref(const CowData &p_from) {
	if (_ptr == p_from._ptr) {
		return; // self assign, do nothing.
	}

	_unref(_ptr);
	_ptr = nullptr;

	if (!p_from._ptr) {
		return; //nothing to do
	}

	if (atomic_conditional_increment(p_from._get_refcount()) > 0) { // could reference
		_ptr = p_from._ptr;
	}
}

template <class T>
CowData<T>::~CowData() {
	_unref(_ptr);
}

#endif // COWDATA_H