Cleanup.

Closes #975

Author: Lee-Janggun

homework/src/boc.rs

@@ -241,7 +241,8 @@ pub unsafe trait CownPtrs {
 }
 
 unsafe impl CownPtrs for () {
-    type CownRefs<'l> = ()
+    type CownRefs<'l>
+        = ()
     where
         Self: 'l;
 
@@ -253,7 +254,8 @@ unsafe impl CownPtrs for () {
 }
 
 unsafe impl<T: Send + 'static, Ts: CownPtrs> CownPtrs for (CownPtr<T>, Ts) {
-    type CownRefs<'l> = (&'l mut T, Ts::CownRefs<'l>)
+    type CownRefs<'l>
+        = (&'l mut T, Ts::CownRefs<'l>)
     where
         Self: 'l;
 
@@ -270,7 +272,8 @@ unsafe impl<T: Send + 'static, Ts: CownPtrs> CownPtrs for (CownPtr<T>, Ts) {
 }
 
 unsafe impl<T: Send + 'static> CownPtrs for Vec<CownPtr<T>> {
-    type CownRefs<'l> = Vec<&'l mut T>
+    type CownRefs<'l>
+        = Vec<&'l mut T>
     where
         Self: 'l;
 

homework/src/elim_stack/base.rs

@@ -68,15 +68,13 @@ pub struct ElimStack<T, S: Stack<T>> {
     // - 2: pop request
     // - 3: request acknowledged
     pub(crate) slots: [Atomic<S::PushReq>; ELIM_SIZE],
-    _marker: PhantomData<T>,
 }
 
 impl<T, S: Stack<T>> Default for ElimStack<T, S> {
     fn default() -> Self {
         Self {
             inner: Default::default(),
             slots: Default::default(),
-            _marker: PhantomData,
         }
     }
 }

homework/src/hazard_pointer/hazard.rs

@@ -45,10 +45,7 @@ impl Shield {
     /// means that this shield is validated.
     pub fn try_protect<T>(&self, pointer: *mut T, src: &AtomicPtr<T>) -> Result<(), *mut T> {
         self.set(pointer);
-        Self::validate(pointer, src).map_err(|new| {
-            self.clear();
-            new
-        })
+        Self::validate(pointer, src).inspect_err(|_| self.clear())
     }
 
     /// Get a protected pointer from `src`.

homework/src/list_set/optimistic_fine_grained.rs

@@ -2,10 +2,11 @@ use std::cmp::Ordering::*;
 use std::mem::{self, ManuallyDrop};
 use std::sync::atomic::Ordering;
 
-use crate::ConcurrentSet;
 use crossbeam_epoch::{pin, Atomic, Guard, Owned, Shared};
 use cs431::lock::seqlock::{ReadGuard, SeqLock};
 
+use crate::ConcurrentSet;
+
 #[derive(Debug)]
 struct Node<T> {
     data: T,
@@ -92,7 +93,7 @@ pub struct Iter<'g, T> {
 impl<T> OptimisticFineGrainedListSet<T> {
     /// An iterator visiting all elements. `next()` returns `Some(Err(()))` when validation fails.
     /// In that case, the user must restart the iteration.
-    pub fn iter<'g>(&'g self, guard: &'g Guard) -> Iter<'_, T> {
+    pub fn iter<'g>(&'g self, guard: &'g Guard) -> Iter<'g, T> {
         Iter {
             cursor: ManuallyDrop::new(self.head(guard)),
             guard,

homework/tests/growable_array.rs

@@ -63,7 +63,7 @@ impl<V> ConcurrentMap<u32, V> for ArrayMap<V> {
             return Err(());
         }
         match slot.compare_exchange(curr, Shared::null(), AcqRel, Acquire, guard) {
-            Ok(_) => Ok(unsafe { curr.deref() }.deref()),
+            Ok(_) => Ok(unsafe { curr.deref() }),
             Err(_) => Err(()), // already removed
         }
     }
@@ -132,8 +132,11 @@ mod stack {
         pub(super) unsafe fn push_node<'g>(&self, n: Shared<'g, Node<T>>, guard: &'g Guard) {
             let mut head = self.head.load(Relaxed, guard);
             loop {
+                // SAEFTY: as n is pused only once, and after the push, n is not used again, we are
+                // the unique accessor of `n.next`. Hence non-atomic write is safe.
                 unsafe { *n.deref().next.get() = head.as_raw() };
 
+                // TODO: Relaxed fine here? Might need release so that it syncs with `drop`?
                 match self.head.compare_exchange(head, n, Relaxed, Relaxed, guard) {
                     Ok(_) => break,
                     Err(e) => head = e.current,

src/lock/api.rs

@@ -12,8 +12,9 @@ use core::ops::{Deref, DerefMut};
 pub unsafe trait RawLock: Default + Send + Sync {
     /// Raw lock's token type.
     ///
-    /// Send + Sync is needed to make LockGuard Send + Sync.
-    type Token: Send + Sync;
+    /// We don't enforce Send + Sync, as some locks may not satisfy it. Nessecary bounds will be
+    /// auto-derived.
+    type Token;
 
     /// Acquires the raw lock.
     fn lock(&self) -> Self::Token;
@@ -49,6 +50,8 @@ pub struct Lock<L: RawLock, T> {
 }
 
 // Send is automatically implemented for Lock.
+
+// SATEFY: threads can only access `&mut T` via the lock, and `L` is `Sync`.
 unsafe impl<L: RawLock, T: Send> Sync for Lock<L, T> {}
 
 impl<L: RawLock, T: Default> Default for Lock<L, T>
@@ -99,7 +102,7 @@ impl<L: RawTryLock, T> Lock<L, T> {
 }
 
 /// A guard that holds the lock and dereferences the inner value.
-// Send/Sync are automatically implemented.
+// `Send` and `Sync` are automatically derived.
 #[derive(Debug)]
 pub struct LockGuard<'s, L: RawLock, T> {
     lock: &'s Lock<L, T>,