//! Checks for uses of mutex where an atomic value could be used //! //! This lint is **warn** by default use clippy_utils::diagnostics::span_lint; use clippy_utils::ty::is_type_diagnostic_item; use rustc_hir::Expr; use rustc_lint::{LateContext, LateLintPass}; use rustc_middle::ty::{self, Ty}; use rustc_session::{declare_lint_pass, declare_tool_lint}; declare_clippy_lint! { /// ### What it does /// Checks for usages of `Mutex` where an atomic will do. /// /// ### Why is this bad? /// Using a mutex just to make access to a plain bool or /// reference sequential is shooting flies with cannons. /// `std::sync::atomic::AtomicBool` and `std::sync::atomic::AtomicPtr` are leaner and /// faster. /// /// ### Known problems /// This lint cannot detect if the mutex is actually used /// for waiting before a critical section. /// /// ### Example /// ```rust /// # let y = true; /// /// // Bad /// # use std::sync::Mutex; /// let x = Mutex::new(&y); /// /// // Good /// # use std::sync::atomic::AtomicBool; /// let x = AtomicBool::new(y); /// ``` pub MUTEX_ATOMIC, perf, "using a mutex where an atomic value could be used instead" } declare_clippy_lint! { /// ### What it does /// Checks for usages of `Mutex` where `X` is an integral /// type. /// /// ### Why is this bad? /// Using a mutex just to make access to a plain integer /// sequential is /// shooting flies with cannons. `std::sync::atomic::AtomicUsize` is leaner and faster. /// /// ### Known problems /// This lint cannot detect if the mutex is actually used /// for waiting before a critical section. /// /// ### Example /// ```rust /// # use std::sync::Mutex; /// let x = Mutex::new(0usize); /// /// // Good /// # use std::sync::atomic::AtomicUsize; /// let x = AtomicUsize::new(0usize); /// ``` pub MUTEX_INTEGER, nursery, "using a mutex for an integer type" } declare_lint_pass!(Mutex => [MUTEX_ATOMIC, MUTEX_INTEGER]); impl<'tcx> LateLintPass<'tcx> for Mutex { fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) { let ty = cx.typeck_results().expr_ty(expr); if let ty::Adt(_, subst) = ty.kind() { if is_type_diagnostic_item(cx, ty, sym!(mutex_type)) { let mutex_param = subst.type_at(0); if let Some(atomic_name) = get_atomic_name(mutex_param) { let msg = format!( "consider using an `{}` instead of a `Mutex` here; if you just want the locking \ behavior and not the internal type, consider using `Mutex<()>`", atomic_name ); match *mutex_param.kind() { ty::Uint(t) if t != ty::UintTy::Usize => span_lint(cx, MUTEX_INTEGER, expr.span, &msg), ty::Int(t) if t != ty::IntTy::Isize => span_lint(cx, MUTEX_INTEGER, expr.span, &msg), _ => span_lint(cx, MUTEX_ATOMIC, expr.span, &msg), }; } } } } } fn get_atomic_name(ty: Ty<'_>) -> Option<&'static str> { match ty.kind() { ty::Bool => Some("AtomicBool"), ty::Uint(_) => Some("AtomicUsize"), ty::Int(_) => Some("AtomicIsize"), ty::RawPtr(_) => Some("AtomicPtr"), _ => None, } }