Add Box type

src/boxed.rs

@@ -0,0 +1,213 @@
+//! A pointer type for heap allocation.
+
+use crate::alloc;
+use std::{borrow, fmt, hash, mem, ptr};
+
+/// A loom version of `std::boxed::Box` based on the leak tracking in `loom::alloc`.
+///
+/// # Known problems
+///
+/// This `Box` version can't be dereferenced in order to take the value
+/// from the heap and bring it back to the stack. This is because `std::boxed::Box`
+/// is tightly integrated with the compiler and uses magic that normal crates can't.
+/// This version instead provides [`Box::into_value`] which does the same thing.
+pub struct Box<T: ?Sized> {
+    ptr: ptr::NonNull<T>,
+}
+
+impl<T> Box<T> {
+    /// Allocates memory on the heap and then places `x` into it.
+    pub fn new(x: T) -> Self {
+        let layout = alloc::Layout::new::<T>();
+        let ptr = unsafe { alloc::alloc(layout) } as *mut T;
+        unsafe { ptr::write(ptr, x) };
+        // SAFETY: `alloc::alloc` should never return a null pointer.
+        Self {
+            ptr: unsafe { ptr::NonNull::new_unchecked(ptr) },
+        }
+    }
+
+    /// Consumes the box and returns the value in it.
+    /// This is a a workaround. The standard library `Box` does not have this. Instead a
+    /// a standard box can be dereferenced like `*std_box` to get the `T`. This can't be
+    /// implemented outside of the standard library due to magic. so we need this workaround.
+    ///
+    /// In order to transparently switch between using loom and the standard library, consider
+    /// introducing a function like this in your code and use it instead of directly
+    /// dereferencing `Box`es:
+    /// ```rust
+    /// fn take<T>(b: Box<T>) -> T {
+    ///     #[cfg(not(loom))]
+    ///     {
+    ///         *b
+    ///     }
+    ///     #[cfg(loom)]
+    ///     {
+    ///         b.into_value()
+    ///     }
+    /// }
+    /// ```
+    pub fn into_value(self) -> T {
+        let value = unsafe { ptr::read(self.ptr.as_ptr()) };
+        let layout = alloc::Layout::new::<T>();
+        unsafe { alloc::dealloc(self.ptr.as_ptr() as *mut u8, layout) };
+        mem::forget(self);
+        value
+    }
+}
+
+impl<T: ?Sized> Box<T> {
+    /// Constructs a box from a raw pointer.
+    ///
+    /// After calling this function, the raw pointer is owned by the resulting Box. Specifically,
+    /// the Box destructor will call the destructor of T and free the allocated memory.
+    /// For this to be safe, the memory must have been allocated in accordance with the memory
+    /// layout used by Box.
+    ///
+    /// # Safety
+    ///
+    /// This function is unsafe because improper use may lead to memory problems. For example,
+    /// a double-free may occur if the function is called twice on the same raw pointer.
+    #[inline]
+    pub const unsafe fn from_raw(ptr: *mut T) -> Box<T> {
+        Self {
+            ptr: ptr::NonNull::new_unchecked(ptr),
+        }
+    }
+
+    /// Consumes the Box, returning a wrapped raw pointer.
+    ///
+    /// The pointer will be properly aligned and non-null.
+    ///
+    /// After calling this function, the caller is responsible for the memory previously
+    /// managed by the Box.
+    #[inline]
+    pub fn into_raw(b: Box<T>) -> *mut T {
+        let ptr = b.ptr;
+        mem::forget(b);
+        ptr.as_ptr()
+    }
+}
+
+impl<T: ?Sized> Drop for Box<T> {
+    fn drop(&mut self) {
+        unsafe {
+            let size = mem::size_of_val(self.ptr.as_ref());
+            let align = mem::align_of_val(self.ptr.as_ref());
+            let layout = alloc::Layout::from_size_align(size, align).unwrap();
+            ptr::drop_in_place(self.ptr.as_ptr());
+            alloc::dealloc(self.ptr.as_ptr() as *mut u8, layout);
+        }
+    }
+}
+
+unsafe impl<T: Send> Send for Box<T> {}
+unsafe impl<T: Sync> Sync for Box<T> {}
+
+impl<T: ?Sized> std::ops::Deref for Box<T> {
+    type Target = T;
+
+    fn deref(&self) -> &T {
+        unsafe { self.ptr.as_ref() }
+    }
+}
+
+impl<T: ?Sized> std::ops::DerefMut for Box<T> {
+    fn deref_mut(&mut self) -> &mut T {
+        unsafe { self.ptr.as_mut() }
+    }
+}
+
+impl<T: ?Sized> borrow::Borrow<T> for Box<T> {
+    fn borrow(&self) -> &T {
+        &**self
+    }
+}
+
+impl<T: ?Sized> borrow::BorrowMut<T> for Box<T> {
+    fn borrow_mut(&mut self) -> &mut T {
+        &mut **self
+    }
+}
+
+impl<T: ?Sized> AsRef<T> for Box<T> {
+    fn as_ref(&self) -> &T {
+        &**self
+    }
+}
+
+impl<T: ?Sized> AsMut<T> for Box<T> {
+    fn as_mut(&mut self) -> &mut T {
+        &mut **self
+    }
+}
+
+impl<T: fmt::Display + ?Sized> fmt::Display for Box<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(&**self, f)
+    }
+}
+
+impl<T: fmt::Debug + ?Sized> fmt::Debug for Box<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+impl<T: Clone> Clone for Box<T> {
+    #[inline]
+    fn clone(&self) -> Box<T> {
+        Self::new(self.as_ref().clone())
+    }
+}
+
+impl<T: ?Sized + PartialEq> PartialEq for Box<T> {
+    #[inline]
+    fn eq(&self, other: &Box<T>) -> bool {
+        PartialEq::eq(&**self, &**other)
+    }
+
+    #[allow(clippy::partialeq_ne_impl)]
+    #[inline]
+    fn ne(&self, other: &Box<T>) -> bool {
+        PartialEq::ne(&**self, &**other)
+    }
+}
+
+impl<T: ?Sized + Eq> Eq for Box<T> {}
+
+impl<T: ?Sized + PartialOrd> PartialOrd for Box<T> {
+    #[inline]
+    fn partial_cmp(&self, other: &Box<T>) -> Option<core::cmp::Ordering> {
+        PartialOrd::partial_cmp(&**self, &**other)
+    }
+    #[inline]
+    fn lt(&self, other: &Box<T>) -> bool {
+        PartialOrd::lt(&**self, &**other)
+    }
+    #[inline]
+    fn le(&self, other: &Box<T>) -> bool {
+        PartialOrd::le(&**self, &**other)
+    }
+    #[inline]
+    fn ge(&self, other: &Box<T>) -> bool {
+        PartialOrd::ge(&**self, &**other)
+    }
+    #[inline]
+    fn gt(&self, other: &Box<T>) -> bool {
+        PartialOrd::gt(&**self, &**other)
+    }
+}
+
+impl<T: ?Sized + Ord> Ord for Box<T> {
+    #[inline]
+    fn cmp(&self, other: &Box<T>) -> core::cmp::Ordering {
+        Ord::cmp(&**self, &**other)
+    }
+}
+
+impl<T: ?Sized + hash::Hash> hash::Hash for Box<T> {
+    fn hash<H: hash::Hasher>(&self, state: &mut H) {
+        (**self).hash(state);
+    }
+}

src/lib.rs

@@ -149,6 +149,7 @@ macro_rules! dbg {
 mod rt;
 
 pub mod alloc;
+pub mod boxed;
 pub mod cell;
 pub mod lazy_static;
 pub mod model;

tests/boxed.rs

@@ -0,0 +1,124 @@
+#![deny(warnings, rust_2018_idioms)]
+
+use loom::boxed::Box;
+use loom::sync::atomic::{AtomicU8, Ordering};
+use loom::sync::Arc;
+use std::mem;
+
+#[derive(Clone)]
+struct DetectDrop(Arc<AtomicU8>);
+
+impl DetectDrop {
+    pub fn new() -> (Self, Arc<AtomicU8>) {
+        let drop_count = Arc::new(AtomicU8::new(0));
+        (Self(drop_count.clone()), drop_count)
+    }
+}
+
+impl Drop for DetectDrop {
+    fn drop(&mut self) {
+        self.0.fetch_add(1, Ordering::SeqCst);
+    }
+}
+
+#[test]
+fn allocate_and_drop() {
+    loom::model(|| {
+        let (detect_drop, drop_count) = DetectDrop::new();
+        let detect_drop = Box::new(detect_drop);
+        assert_eq!(drop_count.load(Ordering::SeqCst), 0);
+        mem::drop(detect_drop);
+        assert_eq!(drop_count.load(Ordering::SeqCst), 1);
+    });
+}
+
+#[test]
+fn allocate_via_raw_and_drop() {
+    loom::model(|| {
+        let (detect_drop, drop_count) = DetectDrop::new();
+        let detect_drop = Box::new(detect_drop);
+        assert_eq!(drop_count.load(Ordering::SeqCst), 0);
+        let detect_drop_ptr: *mut DetectDrop = Box::into_raw(detect_drop);
+        assert_eq!(drop_count.load(Ordering::SeqCst), 0);
+        let detect_drop = unsafe { Box::from_raw(detect_drop_ptr) };
+        assert_eq!(drop_count.load(Ordering::SeqCst), 0);
+        mem::drop(detect_drop);
+        assert_eq!(drop_count.load(Ordering::SeqCst), 1);
+    });
+}
+
+#[test]
+fn into_value() {
+    loom::model(|| {
+        let (detect_drop, drop_count) = DetectDrop::new();
+        let detect_drop = Box::new(detect_drop);
+        let value: DetectDrop = detect_drop.into_value();
+        assert_eq!(drop_count.load(Ordering::SeqCst), 0);
+        mem::drop(value);
+        assert_eq!(drop_count.load(Ordering::SeqCst), 1);
+    });
+}
+
+#[test]
+fn clone() {
+    loom::model(|| {
+        let (detect_drop, drop_count) = DetectDrop::new();
+        let detect_drop = Box::new(detect_drop);
+        let detect_drop2: Box<DetectDrop> = detect_drop.clone();
+        assert_eq!(drop_count.load(Ordering::SeqCst), 0);
+        mem::drop(detect_drop);
+        assert_eq!(drop_count.load(Ordering::SeqCst), 1);
+        mem::drop(detect_drop2);
+        assert_eq!(drop_count.load(Ordering::SeqCst), 2);
+    });
+}
+
+#[test]
+#[should_panic]
+#[ignore]
+fn allocate_and_leak() {
+    loom::model(|| {
+        let (detect_drop, _detect_drop) = DetectDrop::new();
+        let detect_drop = Box::new(detect_drop);
+        Box::into_raw(detect_drop);
+    });
+}
+
+#[test]
+fn same_size_as_std_box() {
+    use std::boxed::Box as StdBox;
+
+    macro_rules! same_size_and_alignment {
+        ($t:ty) => {
+            assert_eq!(
+                mem::size_of::<Box<$t>>(),
+                mem::size_of::<StdBox<$t>>(),
+                "size of Box<{}>",
+                stringify!($t),
+            );
+            assert_eq!(
+                mem::align_of::<Box<$t>>(),
+                mem::align_of::<StdBox<$t>>(),
+                "align of Box<{}>",
+                stringify!($t),
+            );
+            assert_eq!(
+                mem::size_of::<Option<Box<$t>>>(),
+                mem::size_of::<Option<StdBox<$t>>>(),
+                "size of Option<Box<{}>>",
+                stringify!($t),
+            );
+            assert_eq!(
+                mem::align_of::<Option<Box<$t>>>(),
+                mem::align_of::<Option<StdBox<$t>>>(),
+                "align of Option<Box<{}>>",
+                stringify!($t),
+            );
+        };
+    }
+
+    same_size_and_alignment!(std::convert::Infallible);
+    same_size_and_alignment!(());
+    same_size_and_alignment!(u8);
+    same_size_and_alignment!([u32; 1024]);
+}