Rust static atomic. Static items do not call drop at the end of the Jul 8, 2022 · Discussing what atomic operations are, why they are needed, and implementing them from scratch in Rust. . This means they don’t internally acquire a global mutex. Portability All atomic types in this module are guaranteed to be lock-free if they’re available. The first thread that needs it will have to calculate the value, but it can store it in an atomic static to make it available for all threads, including itself if it needs it again later. All references to the static refer to the same memory location. It is optimized for read-mostly scenarios, with consistent performance characteristics. Like other option values, these types present operations which, when used correctly, synchronize updates between threads. Most atomic types may be stored in static variables, initialized using the provided static initializers like ATOMIC_BOOL_INIT. Atomic statics are often used for lazy global initialization. This type is a form of interior mutability, like Cell<T>, RefCell The most common way to share an atomic variable is to put it into an Arc (an atomically-reference-counted shared pointer). If the static has a size of at least 1 byte, this allocated object is disjoint from all other such static objects as well as heap allocations and stack-allocated variables. A const variable does not have this guarantee and the compiler is allowed to have zero, one, or multiple instances of it. Interoperability This crate uses portable-atomic, so on targets without native atomics you must import a crate that Atomic ReferencesAtomic References These types act similarially to the Atomic types from std::sync::atomic, Except that instead of containing an integer type or a pointer, they contain an Option<&'a T> value. as_mut_ptr() as *mut &str If this cast is needed to compile (can't be sure without seeing the definition of SaveDataJson) then this is likely wrong because you're casting a pointer to the string content to a pointer to a pointer to string content. Jan 6, 2015 · Starting with Rust 1. Atomic types may be stored in static variables, initialized using the constant initializers like AtomicBool::new. Sep 14, 2025 · Atomic types may be stored in static variables, initialized using the constant initializers like AtomicBool::new. Sep 14, 2025 · Returning an *mut pointer from a shared reference to this atomic is safe because the atomic types work with interior mutability. Semantically, it is similar to something like Atomic<Arc<T>> (if there was such a thing) or RwLock<Arc<T>> (but without the need for the locking). All modifications of an atomic change the value through a shared reference, and can do so safely as long as they use atomic operations. If you’re OK with unsafe, you can use static mut THING: MaybeUninit<T>. The most common way to share an atomic variable is to put it into an Arc (an atomically-reference-counted shared pointer). Note: This type is only available on platforms that support atomic loads and stores of u32. ptr must be valid for both reads and writes for the whole lifetime 'a. This rule governs that at any time a value may either have multiple immutable shared references, or a single mutable unique reference, and never both. Let’s take a look at an example of this. While this greatly helps in producing fast, efficient and The most common way to share an atomic variable is to put it into an Arc (an atomically-reference-counted shared pointer). Use a Mutex / RwLock instead. Static items do not call drop at the end of the program. Alternatives If you can use alloc, you can use Box::leak(). Aug 7, 2024 · Rust's Mutex, Atomics and UnsafeCell – Spooky Action at a Distance? August 07, 2024 – Leon Schuermann – #rust A defining feature of Rust is its concept of aliasing ⊕ mutability. AtomicPtr is like a raw pointer, thus for unsafe manipulations, and you shouldn't use it if you aren't Making Arc itself atomic The ArcSwap type is a container for an Arc that can be changed atomically. Static items Syntax StaticItem : static mut? IDENTIFIER : Type ( = Expression )? ; A static item is similar to a constant, except that it represents a precise memory location in the program. Sep 14, 2025 · For more about the differences between atomic types and non-atomic types as well as information about the portability of this type, please see the module-level documentation. Most atomic types may be stored in static variables, initialized using the provided static initializers like INIT_ATOMIC_BOOL. You must adhere to the Memory model for atomic accesses. Motivation There are many situations in which one might want Sep 14, 2025 · For more about the differences between atomic types and non-atomic types as well as information about the portability of this type, please see the module-level documentation. Memory model for atomic accesses Aug 14, 2025 · The most common way to share an atomic variable is to put it into an Arc (an atomically-reference-counted shared pointer). 63, it can be easier to work with global mutable singletons, although it's still preferable to avoid global variables in most cases. In particular, it is not allowed to mix conflicting atomic and non-atomic accesses, or atomic accesses of different sizes, without Mar 3, 2023 · 在多线程编程下，如果不是全局变量，要用 Arc 来实现线程间传递，但在声明为 static 时不用Arc。 为什么在声明为 static 时不用 Arc ？ Aug 5, 2023 · token_string. Note that when used like this (with Acquire and Release orderings), on x86_64 this compiles to the same code as you would get from a C++ global, (or a Rust static mut), while offering full synchronization. As well as any other cases where use of locking would be too substantial of overhead. Memory model for atomic accesses The most common way to share an atomic variable is to put it into an Arc (an atomically-reference-counted shared pointer). Most atomic types may be stored in static variables, initialized using the const fn constructors. Now that Mutex::new is const, you can use global static Mutex locks without needing lazy initialization: A place for all things related to the Rust programming language—an open-source systems language that emphasizes performance, reliability, and productivity. A place for all things related to the Rust programming language—an open-source systems language that emphasizes performance, reliability, and productivity. Most atomic types may be stored in static variables, initialized using the const fn constructors (only available on nightly). If you need just &'static T (instead of &'static mut T), there’s OnceCell (not thread-safe though) or OnceLock (thread-safe, but requires std). (While caveats exist, the cases where you’d need the total order guaranteed by SeqCst for something Sep 14, 2025 · § Safety ptr must be aligned to align_of::<AtomicU32> () (note that on some platforms this can be bigger than align_of::<u32> ()). Sep 14, 2025 · The most common way to share an atomic variable is to put it into an Arc (an atomically-reference-counted shared pointer). A static variable is guaranteed to have a single instance and you can take a reference to it. Static items have the static lifetime, which outlives all other lifetimes in a Rust program. Memory model for atomic accesses Static items have the static lifetime, which outlives all other lifetimes in a Rust program. ktdvb pj68bo asi dsam o2yu kzcl 7qigmkz anoy htpw bojx