1 //! Checks for uses of mutex where an atomic value could be used
3 //! This lint is **warn** 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};
12 declare_clippy_lint! {
14 /// Checks for usages of `Mutex<X>` where an atomic will do.
16 /// ### Why is this bad?
17 /// Using a mutex just to make access to a plain bool or
18 /// reference sequential is shooting flies with cannons.
19 /// `std::sync::atomic::AtomicBool` and `std::sync::atomic::AtomicPtr` are leaner and
22 /// ### Known problems
23 /// This lint cannot detect if the mutex is actually used
24 /// for waiting before a critical section.
31 /// # use std::sync::Mutex;
32 /// let x = Mutex::new(&y);
35 /// # use std::sync::atomic::AtomicBool;
36 /// let x = AtomicBool::new(y);
40 "using a mutex where an atomic value could be used instead"
43 declare_clippy_lint! {
45 /// Checks for usages of `Mutex<X>` where `X` is an integral
48 /// ### Why is this bad?
49 /// Using a mutex just to make access to a plain integer
51 /// shooting flies with cannons. `std::sync::atomic::AtomicUsize` is leaner and faster.
53 /// ### Known problems
54 /// This lint cannot detect if the mutex is actually used
55 /// for waiting before a critical section.
59 /// # use std::sync::Mutex;
60 /// let x = Mutex::new(0usize);
63 /// # use std::sync::atomic::AtomicUsize;
64 /// let x = AtomicUsize::new(0usize);
68 "using a mutex for an integer type"
71 declare_lint_pass!(Mutex => [MUTEX_ATOMIC, MUTEX_INTEGER]);
73 impl<'tcx> LateLintPass<'tcx> for Mutex {
74 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
75 let ty = cx.typeck_results().expr_ty(expr);
76 if let ty::Adt(_, subst) = ty.kind() {
77 if is_type_diagnostic_item(cx, ty, sym!(mutex_type)) {
78 let mutex_param = subst.type_at(0);
79 if let Some(atomic_name) = get_atomic_name(mutex_param) {
81 "consider using an `{}` instead of a `Mutex` here; if you just want the locking \
82 behavior and not the internal type, consider using `Mutex<()>`",
85 match *mutex_param.kind() {
86 ty::Uint(t) if t != ty::UintTy::Usize => span_lint(cx, MUTEX_INTEGER, expr.span, &msg),
87 ty::Int(t) if t != ty::IntTy::Isize => span_lint(cx, MUTEX_INTEGER, expr.span, &msg),
88 _ => span_lint(cx, MUTEX_ATOMIC, expr.span, &msg),
96 fn get_atomic_name(ty: Ty<'_>) -> Option<&'static str> {
98 ty::Bool => Some("AtomicBool"),
99 ty::Uint(_) => Some("AtomicUsize"),
100 ty::Int(_) => Some("AtomicIsize"),
101 ty::RawPtr(_) => Some("AtomicPtr"),