227 lines
7.5 KiB
C++
227 lines
7.5 KiB
C++
/**************************************************************************/
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/* safe_refcount.h */
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/**************************************************************************/
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/* This file is part of: */
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/* GODOT ENGINE */
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/* https://godotengine.org */
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/**************************************************************************/
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/* Copyright (c) 2014-present Godot Engine contributors (see AUTHORS.md). */
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/* Copyright (c) 2007-2014 Juan Linietsky, Ariel Manzur. */
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/* */
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/* Permission is hereby granted, free of charge, to any person obtaining */
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/* a copy of this software and associated documentation files (the */
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/* "Software"), to deal in the Software without restriction, including */
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/* without limitation the rights to use, copy, modify, merge, publish, */
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/* distribute, sublicense, and/or sell copies of the Software, and to */
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/* permit persons to whom the Software is furnished to do so, subject to */
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/* the following conditions: */
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/* */
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/* The above copyright notice and this permission notice shall be */
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/* included in all copies or substantial portions of the Software. */
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/* */
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/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, */
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/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF */
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/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. */
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/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY */
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/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, */
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/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE */
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/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. */
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/**************************************************************************/
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#ifndef SAFE_REFCOUNT_H
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#define SAFE_REFCOUNT_H
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#include "core/typedefs.h"
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#ifdef DEV_ENABLED
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#include "core/error/error_macros.h"
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#endif
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#include <atomic>
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#include <type_traits>
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// Design goals for these classes:
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// - No automatic conversions or arithmetic operators,
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// to keep explicit the use of atomics everywhere.
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// - Using acquire-release semantics, even to set the first value.
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// The first value may be set relaxedly in many cases, but adding the distinction
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// between relaxed and unrelaxed operation to the interface would make it needlessly
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// flexible. There's negligible waste in having release semantics for the initial
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// value and, as an important benefit, you can be sure the value is properly synchronized
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// even with threads that are already running.
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// These are used in very specific areas of the engine where it's critical that these guarantees are held
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#define SAFE_NUMERIC_TYPE_PUN_GUARANTEES(m_type) \
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static_assert(sizeof(SafeNumeric<m_type>) == sizeof(m_type)); \
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static_assert(alignof(SafeNumeric<m_type>) == alignof(m_type)); \
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static_assert(std::is_trivially_destructible_v<std::atomic<m_type>>);
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#define SAFE_FLAG_TYPE_PUN_GUARANTEES \
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static_assert(sizeof(SafeFlag) == sizeof(bool)); \
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static_assert(alignof(SafeFlag) == alignof(bool));
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template <typename T>
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class SafeNumeric {
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std::atomic<T> value;
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static_assert(std::atomic<T>::is_always_lock_free);
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public:
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_ALWAYS_INLINE_ void set(T p_value) {
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value.store(p_value, std::memory_order_release);
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}
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_ALWAYS_INLINE_ T get() const {
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return value.load(std::memory_order_acquire);
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}
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_ALWAYS_INLINE_ T increment() {
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return value.fetch_add(1, std::memory_order_acq_rel) + 1;
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}
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// Returns the original value instead of the new one
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_ALWAYS_INLINE_ T postincrement() {
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return value.fetch_add(1, std::memory_order_acq_rel);
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}
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_ALWAYS_INLINE_ T decrement() {
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return value.fetch_sub(1, std::memory_order_acq_rel) - 1;
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}
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// Returns the original value instead of the new one
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_ALWAYS_INLINE_ T postdecrement() {
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return value.fetch_sub(1, std::memory_order_acq_rel);
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}
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_ALWAYS_INLINE_ T add(T p_value) {
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return value.fetch_add(p_value, std::memory_order_acq_rel) + p_value;
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}
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// Returns the original value instead of the new one
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_ALWAYS_INLINE_ T postadd(T p_value) {
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return value.fetch_add(p_value, std::memory_order_acq_rel);
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}
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_ALWAYS_INLINE_ T sub(T p_value) {
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return value.fetch_sub(p_value, std::memory_order_acq_rel) - p_value;
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}
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_ALWAYS_INLINE_ T bit_or(T p_value) {
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return value.fetch_or(p_value, std::memory_order_acq_rel);
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}
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_ALWAYS_INLINE_ T bit_and(T p_value) {
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return value.fetch_and(p_value, std::memory_order_acq_rel);
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}
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_ALWAYS_INLINE_ T bit_xor(T p_value) {
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return value.fetch_xor(p_value, std::memory_order_acq_rel);
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}
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// Returns the original value instead of the new one
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_ALWAYS_INLINE_ T postsub(T p_value) {
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return value.fetch_sub(p_value, std::memory_order_acq_rel);
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}
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_ALWAYS_INLINE_ T exchange_if_greater(T p_value) {
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while (true) {
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T tmp = value.load(std::memory_order_acquire);
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if (tmp >= p_value) {
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return tmp; // already greater, or equal
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}
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if (value.compare_exchange_weak(tmp, p_value, std::memory_order_acq_rel)) {
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return p_value;
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}
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}
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}
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_ALWAYS_INLINE_ T conditional_increment() {
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while (true) {
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T c = value.load(std::memory_order_acquire);
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if (c == 0) {
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return 0;
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}
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if (value.compare_exchange_weak(c, c + 1, std::memory_order_acq_rel)) {
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return c + 1;
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}
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}
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}
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_ALWAYS_INLINE_ explicit SafeNumeric<T>(T p_value = static_cast<T>(0)) {
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set(p_value);
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}
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};
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class SafeFlag {
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std::atomic_bool flag;
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static_assert(std::atomic_bool::is_always_lock_free);
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public:
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_ALWAYS_INLINE_ bool is_set() const {
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return flag.load(std::memory_order_acquire);
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}
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_ALWAYS_INLINE_ void set() {
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flag.store(true, std::memory_order_release);
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}
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_ALWAYS_INLINE_ void clear() {
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flag.store(false, std::memory_order_release);
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}
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_ALWAYS_INLINE_ void set_to(bool p_value) {
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flag.store(p_value, std::memory_order_release);
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}
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_ALWAYS_INLINE_ explicit SafeFlag(bool p_value = false) {
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set_to(p_value);
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}
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};
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class SafeRefCount {
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SafeNumeric<uint32_t> count;
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#ifdef DEV_ENABLED
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_ALWAYS_INLINE_ void _check_unref_safety() {
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// This won't catch every misuse, but it's better than nothing.
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CRASH_COND_MSG(count.get() == 0,
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"Trying to unreference a SafeRefCount which is already zero is wrong and a symptom of it being misused.\n"
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"Upon a SafeRefCount reaching zero any object whose lifetime is tied to it, as well as the ref count itself, must be destroyed.\n"
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"Moreover, to guarantee that, no multiple threads should be racing to do the final unreferencing to zero.");
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}
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#endif
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public:
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_ALWAYS_INLINE_ bool ref() { // true on success
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return count.conditional_increment() != 0;
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}
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_ALWAYS_INLINE_ uint32_t refval() { // none-zero on success
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return count.conditional_increment();
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}
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_ALWAYS_INLINE_ bool unref() { // true if must be disposed of
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#ifdef DEV_ENABLED
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_check_unref_safety();
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#endif
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return count.decrement() == 0;
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}
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_ALWAYS_INLINE_ uint32_t unrefval() { // 0 if must be disposed of
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#ifdef DEV_ENABLED
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_check_unref_safety();
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#endif
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return count.decrement();
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}
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_ALWAYS_INLINE_ uint32_t get() const {
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return count.get();
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}
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_ALWAYS_INLINE_ void init(uint32_t p_value = 1) {
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count.set(p_value);
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}
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};
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#endif // SAFE_REFCOUNT_H
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