nordic-dev.net/rust
nordic-dev.net/rust
2
0
Fork 0
mirror of https://github.com/rust-lang/rust.git synced 2025-05-14 02:49:40 +00:00
Code Issues Packages Projects Releases Wiki Activity

document when atomic loads are guaranteed read-only

Browse Source
This commit is contained in:
Ralf Jung 2023-09-05 19:50:48 +02:00
parent 481d45abec
commit b5e67a00d9
1 changed files with 20 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

20
library/core/src/sync/atomic.rs
View File

@ -79,6 +79,26 @@
//!
//! [lock-free]: https://en.wikipedia.org/wiki/Non-blocking_algorithm
//!
//! # Atomic accesses to read-only memory
//!
//! In general, atomic accesses on read-only memory are Undefined Behavior. For instance, attempting
//! to do a `compare_exchange` that will definitely fail (making it conceptually a read-only
//! operation) can still cause a page fault if the underlying memory page is mapped read-only. Since
//! atomic `load`s might be implemented using compare-exchange operations, even a `load` can fault
//! on read-only memory.
//!
//! However, as an exception from this general rule, Rust guarantees that "sufficiently small"
//! atomic loads are implemented in a way that works on read-only memory. This threshold of
//! "sufficiently small" depends on the architecture:
//!
//! | Target architecture | Maximal atomic `load` size that is guaranteed read-only |
//! |----------|---------|
//! | `x86` | 4 bytes |
//! | `x86_64` | 8 bytes |
//!
//! Any atomic `load` on read-only memory larger than the given size are Undefined Behavior. For
//! architectures not listed above, all atomic `load` on read-only memory are Undefined Behavior.
//!
//! # Examples
//!
//! A simple spinlock: