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Commit | Line | Data |
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ea8adc8c XL |
1 | //! Checks for uses of mutex where an atomic value could be used |
2 | //! | |
3 | //! This lint is **warn** by default | |
4 | ||
abe05a73 | 5 | use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass}; |
ea8adc8c XL |
6 | use rustc::ty::{self, Ty}; |
7 | use rustc::hir::Expr; | |
8 | use syntax::ast; | |
9 | use utils::{match_type, paths, span_lint}; | |
10 | ||
11 | /// **What it does:** Checks for usages of `Mutex<X>` where an atomic will do. | |
12 | /// | |
13 | /// **Why is this bad?** Using a mutex just to make access to a plain bool or | |
14 | /// reference sequential is shooting flies with cannons. | |
15 | /// `std::atomic::AtomicBool` and `std::atomic::AtomicPtr` are leaner and | |
16 | /// faster. | |
17 | /// | |
18 | /// **Known problems:** This lint cannot detect if the mutex is actually used | |
19 | /// for waiting before a critical section. | |
20 | /// | |
21 | /// **Example:** | |
22 | /// ```rust | |
23 | /// let x = Mutex::new(&y); | |
24 | /// ``` | |
25 | declare_lint! { | |
26 | pub MUTEX_ATOMIC, | |
27 | Warn, | |
28 | "using a mutex where an atomic value could be used instead" | |
29 | } | |
30 | ||
31 | /// **What it does:** Checks for usages of `Mutex<X>` where `X` is an integral | |
32 | /// type. | |
33 | /// | |
34 | /// **Why is this bad?** Using a mutex just to make access to a plain integer | |
35 | /// sequential is | |
36 | /// shooting flies with cannons. `std::atomic::usize` is leaner and faster. | |
37 | /// | |
38 | /// **Known problems:** This lint cannot detect if the mutex is actually used | |
39 | /// for waiting before a critical section. | |
40 | /// | |
41 | /// **Example:** | |
42 | /// ```rust | |
43 | /// let x = Mutex::new(0usize); | |
44 | /// ``` | |
45 | declare_lint! { | |
46 | pub MUTEX_INTEGER, | |
47 | Allow, | |
48 | "using a mutex for an integer type" | |
49 | } | |
50 | ||
51 | impl LintPass for MutexAtomic { | |
52 | fn get_lints(&self) -> LintArray { | |
53 | lint_array!(MUTEX_ATOMIC, MUTEX_INTEGER) | |
54 | } | |
55 | } | |
56 | ||
57 | pub struct MutexAtomic; | |
58 | ||
59 | impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MutexAtomic { | |
60 | fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) { | |
61 | let ty = cx.tables.expr_ty(expr); | |
62 | if let ty::TyAdt(_, subst) = ty.sty { | |
63 | if match_type(cx, ty, &paths::MUTEX) { | |
64 | let mutex_param = subst.type_at(0); | |
65 | if let Some(atomic_name) = get_atomic_name(mutex_param) { | |
66 | let msg = format!( | |
67 | "Consider using an {} instead of a Mutex here. If you just want the locking \ | |
abe05a73 | 68 | behaviour and not the internal type, consider using Mutex<()>.", |
ea8adc8c XL |
69 | atomic_name |
70 | ); | |
71 | match mutex_param.sty { | |
72 | ty::TyUint(t) if t != ast::UintTy::Us => span_lint(cx, MUTEX_INTEGER, expr.span, &msg), | |
73 | ty::TyInt(t) if t != ast::IntTy::Is => span_lint(cx, MUTEX_INTEGER, expr.span, &msg), | |
74 | _ => span_lint(cx, MUTEX_ATOMIC, expr.span, &msg), | |
75 | }; | |
76 | } | |
77 | } | |
78 | } | |
79 | } | |
80 | } | |
81 | ||
82 | fn get_atomic_name(ty: Ty) -> Option<(&'static str)> { | |
83 | match ty.sty { | |
84 | ty::TyBool => Some("AtomicBool"), | |
85 | ty::TyUint(_) => Some("AtomicUsize"), | |
86 | ty::TyInt(_) => Some("AtomicIsize"), | |
87 | ty::TyRawPtr(_) => Some("AtomicPtr"), | |
88 | _ => None, | |
89 | } | |
90 | } |