rust/clippy_lints/src/mutex_atomic.rs

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//! Checks for uses of mutex where an atomic value could be used
//!
//! This lint is **warn** by default
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use crate::utils::{match_type, paths, span_lint};
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use rustc::lint::{LateContext, LateLintPass};
use rustc::ty::{self, Ty};
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use rustc_hir::Expr;
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use rustc_session::{declare_lint_pass, declare_tool_lint};
use syntax::ast;
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declare_clippy_lint! {
/// **What it does:** Checks for usages of `Mutex<X>` 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
/// # use std::sync::Mutex;
/// # let y = 1;
/// let x = Mutex::new(&y);
/// ```
pub MUTEX_ATOMIC,
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perf,
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"using a mutex where an atomic value could be used instead"
}
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declare_clippy_lint! {
/// **What it does:** Checks for usages of `Mutex<X>` 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);
/// ```
pub MUTEX_INTEGER,
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nursery,
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"using a mutex for an integer type"
}
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declare_lint_pass!(Mutex => [MUTEX_ATOMIC, MUTEX_INTEGER]);
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Mutex {
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fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) {
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let ty = cx.tables.expr_ty(expr);
if let ty::Adt(_, subst) = ty.kind {
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if match_type(cx, ty, &paths::MUTEX) {
let mutex_param = subst.type_at(0);
if let Some(atomic_name) = get_atomic_name(mutex_param) {
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let msg = format!(
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"Consider using an `{}` instead of a `Mutex` here. If you just want the locking \
behavior and not the internal type, consider using `Mutex<()>`.",
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atomic_name
);
match mutex_param.kind {
ty::Uint(t) if t != ast::UintTy::Usize => span_lint(cx, MUTEX_INTEGER, expr.span, &msg),
ty::Int(t) if t != ast::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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};
}
}
}
}
}
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"),
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_ => None,
}
}