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/*************************************************************************/
/* safe_refcount.h */
/*************************************************************************/
/* This file is part of: */
/* GODOT ENGINE */
/* https://godotengine.org */
/*************************************************************************/
/* Copyright (c) 2007-2022 Juan Linietsky, Ariel Manzur. */
/* Copyright (c) 2014-2022 Godot Engine contributors (cf. AUTHORS.md). */
/* */
/* Permission is hereby granted, free of charge, to any person obtaining */
/* a copy of this software and associated documentation files (the */
/* "Software"), to deal in the Software without restriction, including */
/* without limitation the rights to use, copy, modify, merge, publish, */
/* distribute, sublicense, and/or sell copies of the Software, and to */
/* permit persons to whom the Software is furnished to do so, subject to */
/* the following conditions: */
/* */
/* The above copyright notice and this permission notice shall be */
/* included in all copies or substantial portions of the Software. */
/* */
/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, */
/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF */
/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY */
/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, */
/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE */
/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. */
/*************************************************************************/
#ifndef SAFE_REFCOUNT_H
#define SAFE_REFCOUNT_H
#include "core/typedefs.h"
#include <atomic>
#include <type_traits>
// Design goals for these classes:
// - No automatic conversions or arithmetic operators,
// to keep explicit the use of atomics everywhere.
// - Using acquire-release semantics, even to set the first value.
// The first value may be set relaxedly in many cases, but adding the distinction
// between relaxed and unrelaxed operation to the interface would make it needlessly
// flexible. There's negligible waste in having release semantics for the initial
// value and, as an important benefit, you can be sure the value is properly synchronized
// even with threads that are already running.
// This is used in very specific areas of the engine where it's critical that these guarantees are held
#define SAFE_NUMERIC_TYPE_PUN_GUARANTEES(m_type) \
static_assert(sizeof(SafeNumeric<m_type>) == sizeof(m_type)); \
static_assert(alignof(SafeNumeric<m_type>) == alignof(m_type)); \
static_assert(std::is_trivially_destructible<std::atomic<m_type>>::value);
template <class T>
class SafeNumeric {
std::atomic<T> value;
static_assert(std::atomic<T>::is_always_lock_free);
public:
_ALWAYS_INLINE_ void set(T p_value) {
value.store(p_value, std::memory_order_release);
}
_ALWAYS_INLINE_ T get() const {
return value.load(std::memory_order_acquire);
}
_ALWAYS_INLINE_ T increment() {
return value.fetch_add(1, std::memory_order_acq_rel) + 1;
}
// Returns the original value instead of the new one
_ALWAYS_INLINE_ T postincrement() {
return value.fetch_add(1, std::memory_order_acq_rel);
}
_ALWAYS_INLINE_ T decrement() {
return value.fetch_sub(1, std::memory_order_acq_rel) - 1;
}
// Returns the original value instead of the new one
_ALWAYS_INLINE_ T postdecrement() {
return value.fetch_sub(1, std::memory_order_acq_rel);
}
_ALWAYS_INLINE_ T add(T p_value) {
return value.fetch_add(p_value, std::memory_order_acq_rel) + p_value;
}
// Returns the original value instead of the new one
_ALWAYS_INLINE_ T postadd(T p_value) {
return value.fetch_add(p_value, std::memory_order_acq_rel);
}
_ALWAYS_INLINE_ T sub(T p_value) {
return value.fetch_sub(p_value, std::memory_order_acq_rel) - p_value;
}
// Returns the original value instead of the new one
_ALWAYS_INLINE_ T postsub(T p_value) {
return value.fetch_sub(p_value, std::memory_order_acq_rel);
}
_ALWAYS_INLINE_ T exchange_if_greater(T p_value) {
while (true) {
T tmp = value.load(std::memory_order_acquire);
if (tmp >= p_value) {
return tmp; // already greater, or equal
}
if (value.compare_exchange_weak(tmp, p_value, std::memory_order_acq_rel)) {
return p_value;
}
}
}
_ALWAYS_INLINE_ T conditional_increment() {
while (true) {
T c = value.load(std::memory_order_acquire);
if (c == 0) {
return 0;
}
if (value.compare_exchange_weak(c, c + 1, std::memory_order_acq_rel)) {
return c + 1;
}
}
}
_ALWAYS_INLINE_ explicit SafeNumeric<T>(T p_value = static_cast<T>(0)) {
set(p_value);
}
};
class SafeFlag {
std::atomic_bool flag;
static_assert(std::atomic_bool::is_always_lock_free);
public:
_ALWAYS_INLINE_ bool is_set() const {
return flag.load(std::memory_order_acquire);
}
_ALWAYS_INLINE_ void set() {
flag.store(true, std::memory_order_release);
}
_ALWAYS_INLINE_ void clear() {
flag.store(false, std::memory_order_release);
}
_ALWAYS_INLINE_ void set_to(bool p_value) {
flag.store(p_value, std::memory_order_release);
}
_ALWAYS_INLINE_ explicit SafeFlag(bool p_value = false) {
set_to(p_value);
}
};
class SafeRefCount {
SafeNumeric<uint32_t> count;
public:
_ALWAYS_INLINE_ bool ref() { // true on success
return count.conditional_increment() != 0;
}
_ALWAYS_INLINE_ uint32_t refval() { // none-zero on success
return count.conditional_increment();
}
_ALWAYS_INLINE_ bool unref() { // true if must be disposed of
return count.decrement() == 0;
}
_ALWAYS_INLINE_ uint32_t unrefval() { // 0 if must be disposed of
return count.decrement();
}
_ALWAYS_INLINE_ uint32_t get() const {
return count.get();
}
_ALWAYS_INLINE_ void init(uint32_t p_value = 1) {
count.set(p_value);
}
};
#endif // SAFE_REFCOUNT_H
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