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67a260d63f
This PR implements a worked thread pool. It uses a fixed amount of threads in a pool and allows scheduling tasks that can be run on threads (and then waited for). It satisfies the following use cases: * HTML5 thread count is fixed (and similar restrictions are known in consoles) so we need to reuse threads. * Thread spawning is slow in general, so reusing threads is faster anyway. * This implementation supports recursive waiting for tasks, making it less prone to deadlocks if threads from the pool also run tasks. After this is approved and merged, subsequent PRs will be needed to replace the ThreadWorkPool usage by this class.
332 lines
8.4 KiB
C++
332 lines
8.4 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) 2007-2022 Juan Linietsky, Ariel Manzur. */
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/* Copyright (c) 2014-2022 Godot Engine contributors (cf. AUTHORS.md). */
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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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#if !defined(NO_THREADS)
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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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// This is 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<std::atomic<m_type>>::value);
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template <class 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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// 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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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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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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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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#else
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template <class T>
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class SafeNumeric {
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protected:
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T value;
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public:
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_ALWAYS_INLINE_ void set(T p_value) {
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value = p_value;
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}
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_ALWAYS_INLINE_ T get() const {
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return value;
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}
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_ALWAYS_INLINE_ T increment() {
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return ++value;
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}
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_ALWAYS_INLINE_ T postincrement() {
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return value++;
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}
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_ALWAYS_INLINE_ T decrement() {
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return --value;
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}
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_ALWAYS_INLINE_ T postdecrement() {
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return value--;
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}
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_ALWAYS_INLINE_ T add(T p_value) {
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return value += p_value;
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}
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_ALWAYS_INLINE_ T postadd(T p_value) {
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T old = value;
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value += p_value;
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return old;
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}
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_ALWAYS_INLINE_ T sub(T p_value) {
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return value -= p_value;
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}
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_ALWAYS_INLINE_ T postsub(T p_value) {
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T old = value;
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value -= p_value;
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return old;
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}
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_ALWAYS_INLINE_ T exchange_if_greater(T p_value) {
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if (value < p_value) {
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value = p_value;
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}
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return value;
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}
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_ALWAYS_INLINE_ T conditional_increment() {
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if (value == 0) {
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return 0;
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} else {
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return ++value;
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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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value(p_value) {
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}
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};
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class SafeFlag {
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protected:
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bool flag;
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public:
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_ALWAYS_INLINE_ bool is_set() const {
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return flag;
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}
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_ALWAYS_INLINE_ void set() {
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flag = true;
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}
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_ALWAYS_INLINE_ void clear() {
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flag = false;
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}
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_ALWAYS_INLINE_ void set_to(bool p_value) {
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flag = p_value;
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}
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_ALWAYS_INLINE_ explicit SafeFlag(bool p_value = false) :
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flag(p_value) {}
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};
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class SafeRefCount {
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uint32_t count = 0;
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public:
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_ALWAYS_INLINE_ bool ref() { // true on success
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if (count != 0) {
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++count;
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return true;
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} else {
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return false;
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}
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}
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_ALWAYS_INLINE_ uint32_t refval() { // none-zero on success
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if (count != 0) {
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return ++count;
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} else {
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return 0;
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}
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}
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_ALWAYS_INLINE_ bool unref() { // true if must be disposed of
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return --count == 0;
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}
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_ALWAYS_INLINE_ uint32_t unrefval() { // 0 if must be disposed of
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return --count;
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}
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_ALWAYS_INLINE_ uint32_t get() const {
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return count;
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}
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_ALWAYS_INLINE_ void init(uint32_t p_value = 1) {
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count = p_value;
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}
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};
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#endif
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#endif // SAFE_REFCOUNT_H
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