1 //! Checks for uses of mutex where an atomic value could be used
3 //! This lint is **allow** by default
5 use clippy_utils::diagnostics::span_lint;
6 use clippy_utils::ty::is_type_diagnostic_item;
8 use rustc_lint::{LateContext, LateLintPass};
9 use rustc_middle::ty::{self, Ty};
10 use rustc_session::{declare_lint_pass, declare_tool_lint};
13 declare_clippy_lint! {
15 /// Checks for usages of `Mutex<X>` where an atomic will do.
17 /// ### Why is this bad?
18 /// Using a mutex just to make access to a plain bool or
19 /// reference sequential is shooting flies with cannons.
20 /// `std::sync::atomic::AtomicBool` and `std::sync::atomic::AtomicPtr` are leaner and
23 /// On the other hand, `Mutex`es are, in general, easier to
24 /// verify correctness. An atomic does not behave the same as
25 /// an equivalent mutex. See [this issue](https://github.com/rust-lang/rust-clippy/issues/4295)'s commentary for more details.
27 /// ### Known problems
28 /// This lint cannot detect if the mutex is actually used
29 /// for waiting before a critical section.
34 /// # use std::sync::Mutex;
35 /// let x = Mutex::new(&y);
41 /// # use std::sync::atomic::AtomicBool;
42 /// let x = AtomicBool::new(y);
44 #[clippy::version = "pre 1.29.0"]
47 "using a mutex where an atomic value could be used instead."
50 declare_clippy_lint! {
52 /// Checks for usages of `Mutex<X>` where `X` is an integral
55 /// ### Why is this bad?
56 /// Using a mutex just to make access to a plain integer
58 /// shooting flies with cannons. `std::sync::atomic::AtomicUsize` is leaner and faster.
60 /// ### Known problems
61 /// This lint cannot detect if the mutex is actually used
62 /// for waiting before a critical section.
66 /// # use std::sync::Mutex;
67 /// let x = Mutex::new(0usize);
72 /// # use std::sync::atomic::AtomicUsize;
73 /// let x = AtomicUsize::new(0usize);
75 #[clippy::version = "pre 1.29.0"]
78 "using a mutex for an integer type"
81 declare_lint_pass!(Mutex => [MUTEX_ATOMIC, MUTEX_INTEGER]);
83 impl<'tcx> LateLintPass<'tcx> for Mutex {
84 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
85 let ty = cx.typeck_results().expr_ty(expr);
86 if let ty::Adt(_, subst) = ty.kind() {
87 if is_type_diagnostic_item(cx, ty, sym::Mutex) {
88 let mutex_param = subst.type_at(0);
89 if let Some(atomic_name) = get_atomic_name(mutex_param) {
91 "consider using an `{atomic_name}` instead of a `Mutex` here; if you just want the locking \
92 behavior and not the internal type, consider using `Mutex<()>`"
94 match *mutex_param.kind() {
95 ty::Uint(t) if t != ty::UintTy::Usize => span_lint(cx, MUTEX_INTEGER, expr.span, &msg),
96 ty::Int(t) if t != ty::IntTy::Isize => span_lint(cx, MUTEX_INTEGER, expr.span, &msg),
97 _ => span_lint(cx, MUTEX_ATOMIC, expr.span, &msg),
105 fn get_atomic_name(ty: Ty<'_>) -> Option<&'static str> {
107 ty::Bool => Some("AtomicBool"),
108 ty::Uint(_) => Some("AtomicUsize"),
109 ty::Int(_) => Some("AtomicIsize"),
110 ty::RawPtr(_) => Some("AtomicPtr"),