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Auto merge of #11210 - y21:readonly_write_lock, r=giraffate
new lint: [`readonly_write_lock`] Closes #8555 A new lint that catches `RwLock::write` calls to acquire a write lock only to read from it and not actually do any writes (mutations). changelog: new lint: [`readonly_write_lock`]
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d3c5b488db
6 changed files with 148 additions and 0 deletions
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@ -5181,6 +5181,7 @@ Released 2018-09-13
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[`rc_mutex`]: https://rust-lang.github.io/rust-clippy/master/index.html#rc_mutex
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[`read_line_without_trim`]: https://rust-lang.github.io/rust-clippy/master/index.html#read_line_without_trim
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[`read_zero_byte_vec`]: https://rust-lang.github.io/rust-clippy/master/index.html#read_zero_byte_vec
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[`readonly_write_lock`]: https://rust-lang.github.io/rust-clippy/master/index.html#readonly_write_lock
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[`recursive_format_impl`]: https://rust-lang.github.io/rust-clippy/master/index.html#recursive_format_impl
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[`redundant_allocation`]: https://rust-lang.github.io/rust-clippy/master/index.html#redundant_allocation
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[`redundant_async_block`]: https://rust-lang.github.io/rust-clippy/master/index.html#redundant_async_block
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@ -398,6 +398,7 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
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crate::methods::OR_THEN_UNWRAP_INFO,
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crate::methods::PATH_BUF_PUSH_OVERWRITE_INFO,
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crate::methods::RANGE_ZIP_WITH_LEN_INFO,
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crate::methods::READONLY_WRITE_LOCK_INFO,
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crate::methods::READ_LINE_WITHOUT_TRIM_INFO,
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crate::methods::REPEAT_ONCE_INFO,
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crate::methods::RESULT_MAP_OR_INTO_OPTION_INFO,
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@ -76,6 +76,7 @@ mod or_then_unwrap;
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mod path_buf_push_overwrite;
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mod range_zip_with_len;
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mod read_line_without_trim;
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mod readonly_write_lock;
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mod repeat_once;
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mod search_is_some;
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mod seek_from_current;
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@ -3507,6 +3508,37 @@ declare_clippy_lint! {
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"checks for usage of `bool::then` in `Iterator::filter_map`"
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}
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declare_clippy_lint! {
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/// ### What it does
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/// Looks for calls to `RwLock::write` where the lock is only used for reading.
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///
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/// ### Why is this bad?
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/// The write portion of `RwLock` is exclusive, meaning that no other thread
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/// can access the lock while this writer is active.
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///
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/// ### Example
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/// ```rust
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/// use std::sync::RwLock;
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/// fn assert_is_zero(lock: &RwLock<i32>) {
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/// let num = lock.write().unwrap();
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/// assert_eq!(*num, 0);
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/// }
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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::RwLock;
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/// fn assert_is_zero(lock: &RwLock<i32>) {
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/// let num = lock.read().unwrap();
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/// assert_eq!(*num, 0);
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/// }
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/// ```
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#[clippy::version = "1.73.0"]
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pub READONLY_WRITE_LOCK,
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nursery,
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"acquiring a write lock when a read lock would work"
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}
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pub struct Methods {
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avoid_breaking_exported_api: bool,
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msrv: Msrv,
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@ -3645,6 +3677,7 @@ impl_lint_pass!(Methods => [
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STRING_LIT_CHARS_ANY,
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ITER_SKIP_ZERO,
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FILTER_MAP_BOOL_THEN,
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READONLY_WRITE_LOCK
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]);
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/// Extracts a method call name, args, and `Span` of the method name.
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@ -4188,6 +4221,9 @@ impl Methods {
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range_zip_with_len::check(cx, expr, iter_recv, arg);
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}
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},
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("write", []) => {
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readonly_write_lock::check(cx, expr, recv);
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}
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_ => {},
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}
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}
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52
clippy_lints/src/methods/readonly_write_lock.rs
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52
clippy_lints/src/methods/readonly_write_lock.rs
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@ -0,0 +1,52 @@
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use super::READONLY_WRITE_LOCK;
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use clippy_utils::diagnostics::span_lint_and_sugg;
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use clippy_utils::mir::{enclosing_mir, visit_local_usage};
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use clippy_utils::source::snippet;
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use clippy_utils::ty::is_type_diagnostic_item;
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use rustc_errors::Applicability;
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use rustc_hir::{Expr, ExprKind, Node};
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use rustc_lint::LateContext;
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use rustc_middle::mir::{Location, START_BLOCK};
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use rustc_span::sym;
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fn is_unwrap_call(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
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if let ExprKind::MethodCall(path, receiver, ..) = expr.kind
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&& path.ident.name == sym::unwrap
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{
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is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(receiver).peel_refs(), sym::Result)
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} else {
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false
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}
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}
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pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, receiver: &Expr<'_>) {
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if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(receiver).peel_refs(), sym::RwLock)
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&& let Node::Expr(unwrap_call_expr) = cx.tcx.hir().get_parent(expr.hir_id)
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&& is_unwrap_call(cx, unwrap_call_expr)
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&& let parent = cx.tcx.hir().get_parent(unwrap_call_expr.hir_id)
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&& let Node::Local(local) = parent
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&& let Some(mir) = enclosing_mir(cx.tcx, expr.hir_id)
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&& let Some((local, _)) = mir.local_decls.iter_enumerated().find(|(_, decl)| {
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local.span.contains(decl.source_info.span)
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})
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&& let Some(usages) = visit_local_usage(&[local], mir, Location {
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block: START_BLOCK,
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statement_index: 0,
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})
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&& let [usage] = usages.as_slice()
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{
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let writer_never_mutated = usage.local_consume_or_mutate_locs.is_empty();
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if writer_never_mutated {
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span_lint_and_sugg(
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cx,
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READONLY_WRITE_LOCK,
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expr.span,
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"this write lock is used only for reading",
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"consider using a read lock instead",
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format!("{}.read()", snippet(cx, receiver.span, "<receiver>")),
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Applicability::MaybeIncorrect // write lock might be intentional for enforcing exclusiveness
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);
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}
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}
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}
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42
tests/ui/readonly_write_lock.rs
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42
tests/ui/readonly_write_lock.rs
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@ -0,0 +1,42 @@
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#![warn(clippy::readonly_write_lock)]
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use std::sync::RwLock;
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fn mutate_i32(x: &mut i32) {
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*x += 1;
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}
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fn accept_i32(_: i32) {}
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fn main() {
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let lock = RwLock::new(42);
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let lock2 = RwLock::new(1234);
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{
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let writer = lock.write().unwrap();
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dbg!(&writer);
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}
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{
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let writer = lock.write().unwrap();
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accept_i32(*writer);
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}
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{
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let mut writer = lock.write().unwrap();
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mutate_i32(&mut writer);
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dbg!(&writer);
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}
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{
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let mut writer = lock.write().unwrap();
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*writer += 1;
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}
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{
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let mut writer1 = lock.write().unwrap();
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let mut writer2 = lock2.write().unwrap();
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*writer2 += 1;
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*writer1 = *writer2;
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}
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}
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16
tests/ui/readonly_write_lock.stderr
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16
tests/ui/readonly_write_lock.stderr
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@ -0,0 +1,16 @@
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error: this write lock is used only for reading
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--> $DIR/readonly_write_lock.rs:16:22
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LL | let writer = lock.write().unwrap();
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| ^^^^^^^^^^^^ help: consider using a read lock instead: `lock.read()`
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= note: `-D clippy::readonly-write-lock` implied by `-D warnings`
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error: this write lock is used only for reading
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--> $DIR/readonly_write_lock.rs:21:22
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LL | let writer = lock.write().unwrap();
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| ^^^^^^^^^^^^ help: consider using a read lock instead: `lock.read()`
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error: aborting due to 2 previous errors
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