rust-clippy/clippy_lints/src/mutex_atomic.rs
Konrad Borowski 3f62fc3a7e Remove crate:: prefixes from crate paths
This is somewhat misleading, as those are actually external crates,
and don't need a crate:: prefix.
2018-12-29 16:05:49 +01:00

100 lines
3.4 KiB
Rust

// Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
//! Checks for uses of mutex where an atomic value could be used
//!
//! This lint is **warn** by default
use crate::utils::{match_type, paths, span_lint};
use rustc::hir::Expr;
use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
use rustc::ty::{self, Ty};
use rustc::{declare_tool_lint, lint_array};
use syntax::ast;
/// **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
/// let x = Mutex::new(&y);
/// ```
declare_clippy_lint! {
pub MUTEX_ATOMIC,
perf,
"using a mutex where an atomic value could be used instead"
}
/// **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
/// let x = Mutex::new(0usize);
/// ```
declare_clippy_lint! {
pub MUTEX_INTEGER,
nursery,
"using a mutex for an integer type"
}
impl LintPass for MutexAtomic {
fn get_lints(&self) -> LintArray {
lint_array!(MUTEX_ATOMIC, MUTEX_INTEGER)
}
}
pub struct MutexAtomic;
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MutexAtomic {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
let ty = cx.tables.expr_ty(expr);
if let ty::Adt(_, subst) = ty.sty {
if match_type(cx, ty, &paths::MUTEX) {
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 \
behaviour and not the internal type, consider using Mutex<()>.",
atomic_name
);
match mutex_param.sty {
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),
_ => span_lint(cx, MUTEX_ATOMIC, expr.span, &msg),
};
}
}
}
}
}
fn get_atomic_name(ty: Ty<'_>) -> Option<(&'static str)> {
match ty.sty {
ty::Bool => Some("AtomicBool"),
ty::Uint(_) => Some("AtomicUsize"),
ty::Int(_) => Some("AtomicIsize"),
ty::RawPtr(_) => Some("AtomicPtr"),
_ => None,
}
}