Fix Stacked Borrows UB (and format the code) (zesterer#136)

* Fixed stacked borrows UB

* fmt

Author: zesterer

src/barrier.rs

@@ -115,8 +115,7 @@ impl<R: RelaxStrategy> Barrier<R> {
             // not the leader
             let local_gen = lock.generation_id;
 
-            while local_gen == lock.generation_id &&
-                lock.count < self.num_threads {
+            while local_gen == lock.generation_id && lock.count < self.num_threads {
                 drop(lock);
                 R::relax();
                 lock = self.lock.lock();
@@ -176,7 +175,9 @@ impl BarrierWaitResult {
     /// let barrier_wait_result = barrier.wait();
     /// println!("{:?}", barrier_wait_result.is_leader());
     /// ```
-    pub fn is_leader(&self) -> bool { self.0 }
+    pub fn is_leader(&self) -> bool {
+        self.0
+    }
 }
 
 #[cfg(test)]
@@ -192,12 +193,13 @@ mod tests {
     fn use_barrier(n: usize, barrier: Arc<Barrier>) {
         let (tx, rx) = channel();
 
+        let mut ts = Vec::new();
         for _ in 0..n - 1 {
             let c = barrier.clone();
             let tx = tx.clone();
-            thread::spawn(move|| {
+            ts.push(thread::spawn(move || {
                 tx.send(c.wait().is_leader()).unwrap();
-            });
+            }));
         }
 
         // At this point, all spawned threads should be blocked,
@@ -217,6 +219,10 @@ mod tests {
             }
         }
         assert!(leader_found);
+
+        for t in ts {
+            t.join().unwrap();
+        }
     }
 
     #[test]

src/lazy.rs

@@ -3,8 +3,8 @@
 //! Implementation adapted from the `SyncLazy` type of the standard library. See:
 //! <https://doc.rust-lang.org/std/lazy/struct.SyncLazy.html>
 
-use core::{cell::Cell, fmt, ops::Deref};
 use crate::{once::Once, RelaxStrategy, Spin};
+use core::{cell::Cell, fmt, ops::Deref};
 
 /// A value which is initialized on the first access.
 ///
@@ -45,7 +45,10 @@ pub struct Lazy<T, F = fn() -> T, R = Spin> {
 
 impl<T: fmt::Debug, F, R> fmt::Debug for Lazy<T, F, R> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_struct("Lazy").field("cell", &self.cell).field("init", &"..").finish()
+        f.debug_struct("Lazy")
+            .field("cell", &self.cell)
+            .field("init", &"..")
+            .finish()
     }
 }
 
@@ -61,7 +64,10 @@ impl<T, F, R> Lazy<T, F, R> {
     /// Creates a new lazy value with the given initializing
     /// function.
     pub const fn new(f: F) -> Self {
-        Self { cell: Once::new(), init: Cell::new(Some(f)) }
+        Self {
+            cell: Once::new(),
+            init: Cell::new(Some(f)),
+        }
     }
     /// Retrieves a mutable pointer to the inner data.
     ///

src/lib.rs

@@ -54,7 +54,7 @@
 //! - `lock_api` enables support for [`lock_api`](https://crates.io/crates/lock_api)
 //!
 //! - `ticket_mutex` uses a ticket lock for the implementation of `Mutex`
-//! 
+//!
 //! - `fair_mutex` enables a fairer implementation of `Mutex` that uses eventual fairness to avoid
 //!   starvation
 //!
@@ -66,10 +66,10 @@ extern crate core;
 #[cfg(feature = "portable_atomic")]
 extern crate portable_atomic;
 
-#[cfg(feature = "portable_atomic")]
-use portable_atomic as atomic;
 #[cfg(not(feature = "portable_atomic"))]
 use core::sync::atomic;
+#[cfg(feature = "portable_atomic")]
+use portable_atomic as atomic;
 
 #[cfg(feature = "barrier")]
 #[cfg_attr(docsrs, doc(cfg(feature = "barrier")))]
@@ -83,21 +83,21 @@ pub mod mutex;
 #[cfg(feature = "once")]
 #[cfg_attr(docsrs, doc(cfg(feature = "once")))]
 pub mod once;
+pub mod relax;
 #[cfg(feature = "rwlock")]
 #[cfg_attr(docsrs, doc(cfg(feature = "rwlock")))]
 pub mod rwlock;
-pub mod relax;
 
 #[cfg(feature = "mutex")]
 #[cfg_attr(docsrs, doc(cfg(feature = "mutex")))]
 pub use mutex::MutexGuard;
-#[cfg(feature = "rwlock")]
-#[cfg_attr(docsrs, doc(cfg(feature = "rwlock")))]
-pub use rwlock::RwLockReadGuard;
-pub use relax::{Spin, RelaxStrategy};
 #[cfg(feature = "std")]
 #[cfg_attr(docsrs, doc(cfg(feature = "std")))]
 pub use relax::Yield;
+pub use relax::{RelaxStrategy, Spin};
+#[cfg(feature = "rwlock")]
+#[cfg_attr(docsrs, doc(cfg(feature = "rwlock")))]
+pub use rwlock::RwLockReadGuard;
 
 // Avoid confusing inference errors by aliasing away the relax strategy parameter. Users that need to use a different
 // relax strategy can do so by accessing the types through their fully-qualified path. This is a little bit horrible
@@ -198,7 +198,7 @@ pub mod lock_api {
 
 /// In the event of an invalid operation, it's best to abort the current process.
 #[cfg(feature = "fair_mutex")]
-fn abort() -> !{
+fn abort() -> ! {
     #[cfg(not(feature = "std"))]
     {
         // Panicking while panicking is defined by Rust to result in an abort.
@@ -218,4 +218,4 @@ fn abort() -> !{
     {
         std::process::abort();
     }
-}
+}

src/mutex.rs

@@ -34,11 +34,11 @@ pub mod fair;
 #[cfg_attr(docsrs, doc(cfg(feature = "fair_mutex")))]
 pub use self::fair::{FairMutex, FairMutexGuard, Starvation};
 
+use crate::{RelaxStrategy, Spin};
 use core::{
     fmt,
     ops::{Deref, DerefMut},
 };
-use crate::{RelaxStrategy, Spin};
 
 #[cfg(all(not(feature = "spin_mutex"), not(feature = "use_ticket_mutex")))]
 compile_error!("The `mutex` feature flag was used (perhaps through another feature?) without either `spin_mutex` or `use_ticket_mutex`. One of these is required.");
@@ -85,9 +85,11 @@ type InnerMutexGuard<'a, T> = self::ticket::TicketMutexGuard<'a, T>;
 /// // We use a barrier to ensure the readout happens after all writing
 /// let barrier = Arc::new(Barrier::new(thread_count + 1));
 ///
+/// # let mut ts = Vec::new();
 /// for _ in (0..thread_count) {
 ///     let my_barrier = barrier.clone();
 ///     let my_lock = spin_mutex.clone();
+/// # let t =
 ///     std::thread::spawn(move || {
 ///         let mut guard = my_lock.lock();
 ///         *guard += 1;
@@ -96,12 +98,17 @@ type InnerMutexGuard<'a, T> = self::ticket::TicketMutexGuard<'a, T>;
 ///         drop(guard);
 ///         my_barrier.wait();
 ///     });
+/// # ts.push(t);
 /// }
 ///
 /// barrier.wait();
 ///
 /// let answer = { *spin_mutex.lock() };
 /// assert_eq!(answer, thread_count);
+///
+/// # for t in ts {
+/// #     t.join().unwrap();
+/// # }
 /// ```
 pub struct Mutex<T: ?Sized, R = Spin> {
     inner: InnerMutex<T, R>,
@@ -139,7 +146,9 @@ impl<T, R> Mutex<T, R> {
     /// ```
     #[inline(always)]
     pub const fn new(value: T) -> Self {
-        Self { inner: InnerMutex::new(value) }
+        Self {
+            inner: InnerMutex::new(value),
+        }
     }
 
     /// Consumes this [`Mutex`] and unwraps the underlying data.