small fixes, std implies alloc, dropguarded wrapper with dropguard

Cargo.toml

@@ -6,7 +6,7 @@ edition = "2024"
 [features]
 default = ["alloc"]
 alloc = []
-std = []
+std = ["alloc"]
 nightly = []
 
 [dependencies]

src/drop_guard.rs

@@ -1,4 +1,8 @@
-use core::{cell::UnsafeCell, mem::ManuallyDrop};
+use core::{
+    cell::UnsafeCell,
+    mem::ManuallyDrop,
+    ops::{Deref, DerefMut},
+};
 
 /// A guard that runs a closure when it is dropped.
 pub struct DropGuard<F: FnOnce()>(UnsafeCell<ManuallyDrop<F>>);
@@ -10,6 +14,10 @@ where
     pub fn new(f: F) -> DropGuard<F> {
         Self(UnsafeCell::new(ManuallyDrop::new(f)))
     }
+
+    pub fn guard<T>(self, t: T) -> DropGuarded<T, F> {
+        DropGuarded(t, self)
+    }
 }
 
 impl<F> Drop for DropGuard<F>
@@ -32,3 +40,45 @@ where
         DropGuard::new(f)
     }
 }
+
+pub struct DropGuarded<T, F: FnOnce()>(T, DropGuard<F>);
+
+impl<T, F> DropGuarded<T, F>
+where
+    F: FnOnce(),
+{
+    pub fn new(value: T, f: F) -> Self {
+        Self(value, DropGuard::new(f))
+    }
+
+    pub fn into_inner(self) -> T {
+        self.0
+    }
+
+    pub fn map<U, G>(self, f: G) -> DropGuarded<U, F>
+    where
+        G: FnOnce(T) -> U,
+    {
+        DropGuarded(f(self.0), self.1)
+    }
+}
+
+impl<T, F> Deref for DropGuarded<T, F>
+where
+    F: FnOnce(),
+{
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+impl<T, F> DerefMut for DropGuarded<T, F>
+where
+    F: FnOnce(),
+{
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.0
+    }
+}

src/sync.rs

@@ -46,6 +46,8 @@ impl Lock {
     }
 
     pub fn unlock(&self) {
+        // use release semantics to ensure that all previous writes are
+        // available to other threads.
         self.inner.fetch_and(!LOCKED_BIT, Ordering::Release);
     }
 
@@ -115,6 +117,16 @@ impl Lock {
             state = self.inner.load(Ordering::Relaxed);
         }
     }
+
+    pub fn wait(&self) {
+        let state = self.inner.load(Ordering::Acquire);
+        atomic_wait::wait(&self.inner, state);
+    }
+
+    pub fn wake_one(&self) {
+        // Notify one thread waiting on this lock.
+        atomic_wait::wake_one(&self.inner);
+    }
 }
 
 pub struct SpinWait {

src/util.rs

@@ -1,7 +1,8 @@
 use core::ops::{Deref, DerefMut};
 
 #[repr(transparent)]
-pub struct Send<T>(pub(self) T);
+#[derive(Debug, PartialEq, Eq, Hash, PartialOrd, Ord, Clone, Copy)]
+pub struct Send<T>(pub T);
 
 unsafe impl<T> core::marker::Send for Send<T> {}
 
@@ -22,6 +23,9 @@ impl<T> Send<T> {
     pub unsafe fn new(value: T) -> Self {
         Self(value)
     }
+    pub fn into_inner(self) -> T {
+        self.0
+    }
 }
 
 /// returns the number of available hardware threads, or 1 if it cannot be determined.