114 lines
3.8 KiB
Rust
114 lines
3.8 KiB
Rust
//! Checks for usage of mutex where an atomic value could be used
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//!
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//! This lint is **allow** by default
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use clippy_utils::diagnostics::span_lint;
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use clippy_utils::ty::is_type_diagnostic_item;
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use rustc_hir::Expr;
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_middle::ty::{self, Ty};
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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use rustc_span::sym;
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declare_clippy_lint! {
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/// ### What it does
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/// Checks for usage of `Mutex<X>` where an atomic will do.
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///
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/// ### Why is this bad?
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/// Using a mutex just to make access to a plain bool or
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/// reference sequential is shooting flies with cannons.
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/// `std::sync::atomic::AtomicBool` and `std::sync::atomic::AtomicPtr` are leaner and
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/// faster.
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///
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/// On the other hand, `Mutex`es are, in general, easier to
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/// verify correctness. An atomic does not behave the same as
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/// an equivalent mutex. See [this issue](https://github.com/rust-lang/rust-clippy/issues/4295)'s commentary for more details.
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///
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/// ### Known problems
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/// This lint cannot detect if the mutex is actually used
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/// for waiting before a critical section.
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///
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/// ### Example
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/// ```rust
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/// # let y = true;
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/// # use std::sync::Mutex;
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/// let x = Mutex::new(&y);
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/// ```
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///
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/// Use instead:
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/// ```rust
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/// # let y = true;
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/// # use std::sync::atomic::AtomicBool;
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/// let x = AtomicBool::new(y);
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/// ```
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#[clippy::version = "pre 1.29.0"]
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pub MUTEX_ATOMIC,
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restriction,
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"using a mutex where an atomic value could be used instead."
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}
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declare_clippy_lint! {
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/// ### What it does
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/// Checks for usage of `Mutex<X>` where `X` is an integral
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/// type.
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///
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/// ### Why is this bad?
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/// Using a mutex just to make access to a plain integer
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/// sequential is
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/// shooting flies with cannons. `std::sync::atomic::AtomicUsize` is leaner and faster.
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///
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/// ### Known problems
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/// This lint cannot detect if the mutex is actually used
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/// for waiting before a critical section.
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///
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/// ### Example
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/// ```rust
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/// # use std::sync::Mutex;
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/// let x = Mutex::new(0usize);
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/// ```
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///
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/// Use instead:
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/// ```rust
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/// # use std::sync::atomic::AtomicUsize;
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/// let x = AtomicUsize::new(0usize);
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/// ```
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#[clippy::version = "pre 1.29.0"]
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pub MUTEX_INTEGER,
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nursery,
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"using a mutex for an integer type"
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}
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declare_lint_pass!(Mutex => [MUTEX_ATOMIC, MUTEX_INTEGER]);
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impl<'tcx> LateLintPass<'tcx> for Mutex {
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fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
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let ty = cx.typeck_results().expr_ty(expr);
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if let ty::Adt(_, subst) = ty.kind() {
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if is_type_diagnostic_item(cx, ty, sym::Mutex) {
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let mutex_param = subst.type_at(0);
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if let Some(atomic_name) = get_atomic_name(mutex_param) {
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let msg = format!(
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"consider using an `{atomic_name}` instead of a `Mutex` here; if you just want the locking \
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behavior and not the internal type, consider using `Mutex<()>`"
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);
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match *mutex_param.kind() {
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ty::Uint(t) if t != ty::UintTy::Usize => span_lint(cx, MUTEX_INTEGER, expr.span, &msg),
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ty::Int(t) if t != ty::IntTy::Isize => span_lint(cx, MUTEX_INTEGER, expr.span, &msg),
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_ => span_lint(cx, MUTEX_ATOMIC, expr.span, &msg),
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};
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}
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}
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}
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}
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}
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fn get_atomic_name(ty: Ty<'_>) -> Option<&'static str> {
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match ty.kind() {
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ty::Bool => Some("AtomicBool"),
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ty::Uint(_) => Some("AtomicUsize"),
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ty::Int(_) => Some("AtomicIsize"),
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ty::RawPtr(_) => Some("AtomicPtr"),
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_ => None,
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}
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}
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