Use Layout::extend and clean up code around alloc

crossbeam-epoch/src/atomic.rs

@@ -1,3 +1,5 @@
+use alloc::boxed::Box;
+use core::alloc::Layout;
 use core::borrow::{Borrow, BorrowMut};
 use core::cmp;
 use core::fmt;
@@ -7,8 +9,6 @@ use core::ops::{Deref, DerefMut};
 use core::ptr;
 use core::slice;
 
-use crate::alloc::alloc;
-use crate::alloc::boxed::Box;
 use crate::guard::Guard;
 #[cfg(not(miri))]
 use crate::primitive::sync::atomic::AtomicUsize;
@@ -191,31 +191,36 @@ impl<T> Pointable for T {
 ///
 /// Elements are not present in the type, but they will be in the allocation.
 /// ```
-///
-// TODO(@jeehoonkang): once we bump the minimum required Rust version to 1.44 or newer, use
-// [`alloc::alloc::Layout::extend`] instead.
 #[repr(C)]
 struct Array<T> {
     /// The number of elements (not the number of bytes).
     len: usize,
     elements: [MaybeUninit<T>; 0],
 }
 
+impl<T> Array<T> {
+    fn layout(len: usize) -> Layout {
+        Layout::new::<Self>()
+            .extend(Layout::array::<MaybeUninit<T>>(len).unwrap())
+            .unwrap()
+            .0
+            .pad_to_align()
+    }
+}
+
 impl<T> Pointable for [MaybeUninit<T>] {
     const ALIGN: usize = mem::align_of::<Array<T>>();
 
     type Init = usize;
 
     unsafe fn init(len: Self::Init) -> *mut () {
-        let size = mem::size_of::<Array<T>>() + mem::size_of::<MaybeUninit<T>>() * len;
-        let align = mem::align_of::<Array<T>>();
-        let layout = alloc::Layout::from_size_align(size, align).unwrap();
+        let layout = Array::<T>::layout(len);
         unsafe {
-            let ptr = alloc::alloc(layout).cast::<Array<T>>();
+            let ptr = alloc::alloc::alloc(layout).cast::<Array<T>>();
             if ptr.is_null() {
-                alloc::handle_alloc_error(layout);
+                alloc::alloc::handle_alloc_error(layout);
             }
-            (*ptr).len = len;
+            ptr::addr_of_mut!((*ptr).len).write(len);
             ptr.cast::<()>()
         }
     }
@@ -236,11 +241,9 @@ impl<T> Pointable for [MaybeUninit<T>] {
 
     unsafe fn drop(ptr: *mut ()) {
         unsafe {
-            let array = &*ptr.cast::<Array<T>>();
-            let size = mem::size_of::<Array<T>>() + mem::size_of::<MaybeUninit<T>>() * array.len;
-            let align = mem::align_of::<Array<T>>();
-            let layout = alloc::Layout::from_size_align(size, align).unwrap();
-            alloc::dealloc(ptr.cast::<u8>(), layout);
+            let len = (*ptr.cast::<Array<T>>()).len;
+            let layout = Array::<T>::layout(len);
+            alloc::alloc::dealloc(ptr.cast::<u8>(), layout);
         }
     }
 }

crossbeam-skiplist/src/base.rs

@@ -98,18 +98,18 @@ impl<K, V> Node<K, V> {
     /// with null pointers. However, the key and the value will be left uninitialized, and that is
     /// why this function is unsafe.
     unsafe fn alloc(height: usize, ref_count: usize) -> *mut Self {
+        let layout = Self::get_layout(height);
         unsafe {
-            let layout = Self::get_layout(height);
             let ptr = alloc(layout).cast::<Self>();
             if ptr.is_null() {
                 handle_alloc_error(layout);
             }
 
-            ptr::write(
-                &mut (*ptr).refs_and_height,
-                AtomicUsize::new((height - 1) | ref_count << HEIGHT_BITS),
-            );
-            ptr::write_bytes((*ptr).tower.pointers.as_mut_ptr(), 0, height);
+            ptr::addr_of_mut!((*ptr).refs_and_height)
+                .write(AtomicUsize::new((height - 1) | ref_count << HEIGHT_BITS));
+            ptr::addr_of_mut!((*ptr).tower.pointers)
+                .cast::<Atomic<Self>>()
+                .write_bytes(0, height);
             ptr
         }
     }
@@ -126,14 +126,14 @@ impl<K, V> Node<K, V> {
     }
 
     /// Returns the layout of a node with the given `height`.
-    unsafe fn get_layout(height: usize) -> Layout {
+    fn get_layout(height: usize) -> Layout {
         assert!((1..=MAX_HEIGHT).contains(&height));
 
-        let size_self = mem::size_of::<Self>();
-        let align_self = mem::align_of::<Self>();
-        let size_pointer = mem::size_of::<Atomic<Self>>();
-
-        unsafe { Layout::from_size_align_unchecked(size_self + size_pointer * height, align_self) }
+        Layout::new::<Self>()
+            .extend(Layout::array::<Atomic<Self>>(height).unwrap())
+            .unwrap()
+            .0
+            .pad_to_align()
     }
 
     /// Returns the height of this node's tower.
@@ -912,8 +912,8 @@ where
                 let n = Node::<K, V>::alloc(height, 2);
 
                 // Write the key and the value into the node.
-                ptr::write(&mut (*n).key, key);
-                ptr::write(&mut (*n).value, value);
+                ptr::addr_of_mut!((*n).key).write(key);
+                ptr::addr_of_mut!((*n).value).write(value);
 
                 (Shared::<Node<K, V>>::from(n as *const _), &*n)
             };