mirror of
https://github.com/mozilla/gecko-dev.git
synced 2025-11-04 10:18:41 +02:00
0d680476b7
Otherwise it doesn't show what the slice contains, which makes restyle logs a bit useless. Differential Revision: https://phabricator.services.mozilla.com/D210929
1202 lines
38 KiB
Rust
1202 lines
38 KiB
Rust
// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
|
|
// file at the top-level directory of this distribution and at
|
|
// http://rust-lang.org/COPYRIGHT.
|
|
//
|
|
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
|
|
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
|
|
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
|
|
// option. This file may not be copied, modified, or distributed
|
|
// except according to those terms.
|
|
|
|
//! Fork of Arc for Servo. This has the following advantages over std::sync::Arc:
|
|
//!
|
|
//! * We don't waste storage on the weak reference count.
|
|
//! * We don't do extra RMU operations to handle the possibility of weak references.
|
|
//! * We can experiment with arena allocation (todo).
|
|
//! * We can add methods to support our custom use cases [1].
|
|
//! * We have support for dynamically-sized types (see from_header_and_iter).
|
|
//! * We have support for thin arcs to unsized types (see ThinArc).
|
|
//! * We have support for references to static data, which don't do any
|
|
//! refcounting.
|
|
//!
|
|
//! [1]: https://bugzilla.mozilla.org/show_bug.cgi?id=1360883
|
|
|
|
// The semantics of `Arc` are already documented in the Rust docs, so we don't
|
|
// duplicate those here.
|
|
#![allow(missing_docs)]
|
|
|
|
#[cfg(feature = "servo")]
|
|
extern crate serde;
|
|
extern crate stable_deref_trait;
|
|
|
|
#[cfg(feature = "servo")]
|
|
use serde::{Deserialize, Serialize};
|
|
use stable_deref_trait::{CloneStableDeref, StableDeref};
|
|
use std::alloc::{self, Layout};
|
|
use std::borrow;
|
|
use std::cmp::Ordering;
|
|
use std::fmt;
|
|
use std::hash::{Hash, Hasher};
|
|
use std::marker::PhantomData;
|
|
use std::mem::{self, align_of, size_of};
|
|
use std::ops::{Deref, DerefMut};
|
|
use std::os::raw::c_void;
|
|
use std::process;
|
|
use std::ptr;
|
|
use std::sync::atomic;
|
|
use std::sync::atomic::Ordering::{Acquire, Relaxed, Release};
|
|
use std::{isize, usize};
|
|
|
|
/// A soft limit on the amount of references that may be made to an `Arc`.
|
|
///
|
|
/// Going above this limit will abort your program (although not
|
|
/// necessarily) at _exactly_ `MAX_REFCOUNT + 1` references.
|
|
const MAX_REFCOUNT: usize = (isize::MAX) as usize;
|
|
|
|
/// Special refcount value that means the data is not reference counted,
|
|
/// and that the `Arc` is really acting as a read-only static reference.
|
|
const STATIC_REFCOUNT: usize = usize::MAX;
|
|
|
|
/// An atomically reference counted shared pointer
|
|
///
|
|
/// See the documentation for [`Arc`] in the standard library. Unlike the
|
|
/// standard library `Arc`, this `Arc` does not support weak reference counting.
|
|
///
|
|
/// See the discussion in https://github.com/rust-lang/rust/pull/60594 for the
|
|
/// usage of PhantomData.
|
|
///
|
|
/// [`Arc`]: https://doc.rust-lang.org/stable/std/sync/struct.Arc.html
|
|
///
|
|
/// cbindgen:derive-eq=false
|
|
/// cbindgen:derive-neq=false
|
|
#[repr(C)]
|
|
pub struct Arc<T: ?Sized> {
|
|
p: ptr::NonNull<ArcInner<T>>,
|
|
phantom: PhantomData<T>,
|
|
}
|
|
|
|
/// An `Arc` that is known to be uniquely owned
|
|
///
|
|
/// When `Arc`s are constructed, they are known to be
|
|
/// uniquely owned. In such a case it is safe to mutate
|
|
/// the contents of the `Arc`. Normally, one would just handle
|
|
/// this by mutating the data on the stack before allocating the
|
|
/// `Arc`, however it's possible the data is large or unsized
|
|
/// and you need to heap-allocate it earlier in such a way
|
|
/// that it can be freely converted into a regular `Arc` once you're
|
|
/// done.
|
|
///
|
|
/// `UniqueArc` exists for this purpose, when constructed it performs
|
|
/// the same allocations necessary for an `Arc`, however it allows mutable access.
|
|
/// Once the mutation is finished, you can call `.shareable()` and get a regular `Arc`
|
|
/// out of it.
|
|
///
|
|
/// Ignore the doctest below there's no way to skip building with refcount
|
|
/// logging during doc tests (see rust-lang/rust#45599).
|
|
///
|
|
/// ```rust,ignore
|
|
/// # use servo_arc::UniqueArc;
|
|
/// let data = [1, 2, 3, 4, 5];
|
|
/// let mut x = UniqueArc::new(data);
|
|
/// x[4] = 7; // mutate!
|
|
/// let y = x.shareable(); // y is an Arc<T>
|
|
/// ```
|
|
pub struct UniqueArc<T: ?Sized>(Arc<T>);
|
|
|
|
impl<T> UniqueArc<T> {
|
|
#[inline]
|
|
/// Construct a new UniqueArc
|
|
pub fn new(data: T) -> Self {
|
|
UniqueArc(Arc::new(data))
|
|
}
|
|
|
|
/// Construct an uninitialized arc
|
|
#[inline]
|
|
pub fn new_uninit() -> UniqueArc<mem::MaybeUninit<T>> {
|
|
unsafe {
|
|
let layout = Layout::new::<ArcInner<mem::MaybeUninit<T>>>();
|
|
let ptr = alloc::alloc(layout);
|
|
let mut p = ptr::NonNull::new(ptr)
|
|
.unwrap_or_else(|| alloc::handle_alloc_error(layout))
|
|
.cast::<ArcInner<mem::MaybeUninit<T>>>();
|
|
ptr::write(&mut p.as_mut().count, atomic::AtomicUsize::new(1));
|
|
#[cfg(feature = "track_alloc_size")]
|
|
ptr::write(&mut p.as_mut().alloc_size, layout.size());
|
|
|
|
#[cfg(feature = "gecko_refcount_logging")]
|
|
{
|
|
NS_LogCtor(p.as_ptr() as *mut _, b"ServoArc\0".as_ptr() as *const _, 8)
|
|
}
|
|
|
|
UniqueArc(Arc {
|
|
p,
|
|
phantom: PhantomData,
|
|
})
|
|
}
|
|
}
|
|
|
|
#[inline]
|
|
/// Convert to a shareable Arc<T> once we're done mutating it
|
|
pub fn shareable(self) -> Arc<T> {
|
|
self.0
|
|
}
|
|
}
|
|
|
|
impl<T> UniqueArc<mem::MaybeUninit<T>> {
|
|
/// Convert to an initialized Arc.
|
|
#[inline]
|
|
pub unsafe fn assume_init(this: Self) -> UniqueArc<T> {
|
|
UniqueArc(Arc {
|
|
p: mem::ManuallyDrop::new(this).0.p.cast(),
|
|
phantom: PhantomData,
|
|
})
|
|
}
|
|
}
|
|
|
|
impl<T> Deref for UniqueArc<T> {
|
|
type Target = T;
|
|
fn deref(&self) -> &T {
|
|
&*self.0
|
|
}
|
|
}
|
|
|
|
impl<T> DerefMut for UniqueArc<T> {
|
|
fn deref_mut(&mut self) -> &mut T {
|
|
// We know this to be uniquely owned
|
|
unsafe { &mut (*self.0.ptr()).data }
|
|
}
|
|
}
|
|
|
|
unsafe impl<T: ?Sized + Sync + Send> Send for Arc<T> {}
|
|
unsafe impl<T: ?Sized + Sync + Send> Sync for Arc<T> {}
|
|
|
|
/// The object allocated by an Arc<T>
|
|
///
|
|
/// See https://github.com/mozilla/cbindgen/issues/937 for the derive-{eq,neq}=false. But we don't
|
|
/// use those anyways so we can just disable them.
|
|
/// cbindgen:derive-eq=false
|
|
/// cbindgen:derive-neq=false
|
|
#[repr(C)]
|
|
struct ArcInner<T: ?Sized> {
|
|
count: atomic::AtomicUsize,
|
|
// NOTE(emilio): This needs to be here so that HeaderSlice<> is deallocated properly if the
|
|
// allocator relies on getting the right Layout. We don't need to track the right alignment,
|
|
// since we know that statically.
|
|
//
|
|
// This member could be completely avoided once min_specialization feature is stable (by
|
|
// implementing a trait for HeaderSlice that gives you the right layout). For now, servo-only
|
|
// since Gecko doesn't need it (its allocator doesn't need the size for the alignments we care
|
|
// about). See https://github.com/rust-lang/rust/issues/31844.
|
|
#[cfg(feature = "track_alloc_size")]
|
|
alloc_size: usize,
|
|
data: T,
|
|
}
|
|
|
|
unsafe impl<T: ?Sized + Sync + Send> Send for ArcInner<T> {}
|
|
unsafe impl<T: ?Sized + Sync + Send> Sync for ArcInner<T> {}
|
|
|
|
/// Computes the offset of the data field within ArcInner.
|
|
fn data_offset<T>() -> usize {
|
|
let size = size_of::<ArcInner<()>>();
|
|
let align = align_of::<T>();
|
|
// https://github.com/rust-lang/rust/blob/1.36.0/src/libcore/alloc.rs#L187-L207
|
|
size.wrapping_add(align).wrapping_sub(1) & !align.wrapping_sub(1)
|
|
}
|
|
|
|
impl<T> Arc<T> {
|
|
/// Construct an `Arc<T>`
|
|
#[inline]
|
|
pub fn new(data: T) -> Self {
|
|
let layout = Layout::new::<ArcInner<T>>();
|
|
let p = unsafe {
|
|
let ptr = ptr::NonNull::new(alloc::alloc(layout))
|
|
.unwrap_or_else(|| alloc::handle_alloc_error(layout))
|
|
.cast::<ArcInner<T>>();
|
|
ptr::write(ptr.as_ptr(), ArcInner {
|
|
count: atomic::AtomicUsize::new(1),
|
|
#[cfg(feature = "track_alloc_size")]
|
|
alloc_size: layout.size(),
|
|
data,
|
|
});
|
|
ptr
|
|
};
|
|
|
|
#[cfg(feature = "gecko_refcount_logging")]
|
|
unsafe {
|
|
// FIXME(emilio): Would be so amazing to have
|
|
// std::intrinsics::type_name() around, so that we could also report
|
|
// a real size.
|
|
NS_LogCtor(p.as_ptr() as *mut _, b"ServoArc\0".as_ptr() as *const _, 8);
|
|
}
|
|
|
|
Arc {
|
|
p,
|
|
phantom: PhantomData,
|
|
}
|
|
}
|
|
|
|
/// Construct an intentionally-leaked arc.
|
|
#[inline]
|
|
pub fn new_leaked(data: T) -> Self {
|
|
let arc = Self::new(data);
|
|
arc.mark_as_intentionally_leaked();
|
|
arc
|
|
}
|
|
|
|
/// Convert the Arc<T> to a raw pointer, suitable for use across FFI
|
|
///
|
|
/// Note: This returns a pointer to the data T, which is offset in the allocation.
|
|
#[inline]
|
|
pub fn into_raw(this: Self) -> *const T {
|
|
let ptr = unsafe { &((*this.ptr()).data) as *const _ };
|
|
mem::forget(this);
|
|
ptr
|
|
}
|
|
|
|
/// Reconstruct the Arc<T> from a raw pointer obtained from into_raw()
|
|
///
|
|
/// Note: This raw pointer will be offset in the allocation and must be preceded
|
|
/// by the atomic count.
|
|
#[inline]
|
|
pub unsafe fn from_raw(ptr: *const T) -> Self {
|
|
// To find the corresponding pointer to the `ArcInner` we need
|
|
// to subtract the offset of the `data` field from the pointer.
|
|
let ptr = (ptr as *const u8).sub(data_offset::<T>());
|
|
Arc {
|
|
p: ptr::NonNull::new_unchecked(ptr as *mut ArcInner<T>),
|
|
phantom: PhantomData,
|
|
}
|
|
}
|
|
|
|
/// Like from_raw, but returns an addrefed arc instead.
|
|
#[inline]
|
|
pub unsafe fn from_raw_addrefed(ptr: *const T) -> Self {
|
|
let arc = Self::from_raw(ptr);
|
|
mem::forget(arc.clone());
|
|
arc
|
|
}
|
|
|
|
/// Create a new static Arc<T> (one that won't reference count the object)
|
|
/// and place it in the allocation provided by the specified `alloc`
|
|
/// function.
|
|
///
|
|
/// `alloc` must return a pointer into a static allocation suitable for
|
|
/// storing data with the `Layout` passed into it. The pointer returned by
|
|
/// `alloc` will not be freed.
|
|
#[inline]
|
|
pub unsafe fn new_static<F>(alloc: F, data: T) -> Arc<T>
|
|
where
|
|
F: FnOnce(Layout) -> *mut u8,
|
|
{
|
|
let layout = Layout::new::<ArcInner<T>>();
|
|
let ptr = alloc(layout) as *mut ArcInner<T>;
|
|
|
|
let x = ArcInner {
|
|
count: atomic::AtomicUsize::new(STATIC_REFCOUNT),
|
|
#[cfg(feature = "track_alloc_size")]
|
|
alloc_size: layout.size(),
|
|
data,
|
|
};
|
|
|
|
ptr::write(ptr, x);
|
|
|
|
Arc {
|
|
p: ptr::NonNull::new_unchecked(ptr),
|
|
phantom: PhantomData,
|
|
}
|
|
}
|
|
|
|
/// Produce a pointer to the data that can be converted back
|
|
/// to an Arc. This is basically an `&Arc<T>`, without the extra indirection.
|
|
/// It has the benefits of an `&T` but also knows about the underlying refcount
|
|
/// and can be converted into more `Arc<T>`s if necessary.
|
|
#[inline]
|
|
pub fn borrow_arc<'a>(&'a self) -> ArcBorrow<'a, T> {
|
|
ArcBorrow(&**self)
|
|
}
|
|
|
|
/// Returns the address on the heap of the Arc itself -- not the T within it -- for memory
|
|
/// reporting.
|
|
///
|
|
/// If this is a static reference, this returns null.
|
|
pub fn heap_ptr(&self) -> *const c_void {
|
|
if self.inner().count.load(Relaxed) == STATIC_REFCOUNT {
|
|
ptr::null()
|
|
} else {
|
|
self.p.as_ptr() as *const ArcInner<T> as *const c_void
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<T: ?Sized> Arc<T> {
|
|
#[inline]
|
|
fn inner(&self) -> &ArcInner<T> {
|
|
// This unsafety is ok because while this arc is alive we're guaranteed
|
|
// that the inner pointer is valid. Furthermore, we know that the
|
|
// `ArcInner` structure itself is `Sync` because the inner data is
|
|
// `Sync` as well, so we're ok loaning out an immutable pointer to these
|
|
// contents.
|
|
unsafe { &*self.ptr() }
|
|
}
|
|
|
|
#[inline(always)]
|
|
fn record_drop(&self) {
|
|
#[cfg(feature = "gecko_refcount_logging")]
|
|
unsafe {
|
|
NS_LogDtor(self.ptr() as *mut _, b"ServoArc\0".as_ptr() as *const _, 8);
|
|
}
|
|
}
|
|
|
|
/// Marks this `Arc` as intentionally leaked for the purposes of refcount
|
|
/// logging.
|
|
///
|
|
/// It's a logic error to call this more than once, but it's not unsafe, as
|
|
/// it'd just report negative leaks.
|
|
#[inline(always)]
|
|
pub fn mark_as_intentionally_leaked(&self) {
|
|
self.record_drop();
|
|
}
|
|
|
|
// Non-inlined part of `drop`. Just invokes the destructor and calls the
|
|
// refcount logging machinery if enabled.
|
|
#[inline(never)]
|
|
unsafe fn drop_slow(&mut self) {
|
|
self.record_drop();
|
|
let inner = self.ptr();
|
|
|
|
let layout = Layout::for_value(&*inner);
|
|
#[cfg(feature = "track_alloc_size")]
|
|
let layout = Layout::from_size_align_unchecked((*inner).alloc_size, layout.align());
|
|
|
|
std::ptr::drop_in_place(inner);
|
|
alloc::dealloc(inner as *mut _, layout);
|
|
}
|
|
|
|
/// Test pointer equality between the two Arcs, i.e. they must be the _same_
|
|
/// allocation
|
|
#[inline]
|
|
pub fn ptr_eq(this: &Self, other: &Self) -> bool {
|
|
this.ptr() as *const () == other.ptr() as *const ()
|
|
}
|
|
|
|
fn ptr(&self) -> *mut ArcInner<T> {
|
|
self.p.as_ptr()
|
|
}
|
|
|
|
/// Returns a raw ptr to the underlying allocation.
|
|
pub fn raw_ptr(&self) -> *const c_void {
|
|
self.p.as_ptr() as *const _
|
|
}
|
|
}
|
|
|
|
#[cfg(feature = "gecko_refcount_logging")]
|
|
extern "C" {
|
|
fn NS_LogCtor(
|
|
aPtr: *mut std::os::raw::c_void,
|
|
aTypeName: *const std::os::raw::c_char,
|
|
aSize: u32,
|
|
);
|
|
fn NS_LogDtor(
|
|
aPtr: *mut std::os::raw::c_void,
|
|
aTypeName: *const std::os::raw::c_char,
|
|
aSize: u32,
|
|
);
|
|
}
|
|
|
|
impl<T: ?Sized> Clone for Arc<T> {
|
|
#[inline]
|
|
fn clone(&self) -> Self {
|
|
// NOTE(emilio): If you change anything here, make sure that the
|
|
// implementation in layout/style/ServoStyleConstsInlines.h matches!
|
|
//
|
|
// Using a relaxed ordering to check for STATIC_REFCOUNT is safe, since
|
|
// `count` never changes between STATIC_REFCOUNT and other values.
|
|
if self.inner().count.load(Relaxed) != STATIC_REFCOUNT {
|
|
// Using a relaxed ordering is alright here, as knowledge of the
|
|
// original reference prevents other threads from erroneously deleting
|
|
// the object.
|
|
//
|
|
// As explained in the [Boost documentation][1], Increasing the
|
|
// reference counter can always be done with memory_order_relaxed: New
|
|
// references to an object can only be formed from an existing
|
|
// reference, and passing an existing reference from one thread to
|
|
// another must already provide any required synchronization.
|
|
//
|
|
// [1]: (www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html)
|
|
let old_size = self.inner().count.fetch_add(1, Relaxed);
|
|
|
|
// However we need to guard against massive refcounts in case someone
|
|
// is `mem::forget`ing Arcs. If we don't do this the count can overflow
|
|
// and users will use-after free. We racily saturate to `isize::MAX` on
|
|
// the assumption that there aren't ~2 billion threads incrementing
|
|
// the reference count at once. This branch will never be taken in
|
|
// any realistic program.
|
|
//
|
|
// We abort because such a program is incredibly degenerate, and we
|
|
// don't care to support it.
|
|
if old_size > MAX_REFCOUNT {
|
|
process::abort();
|
|
}
|
|
}
|
|
|
|
unsafe {
|
|
Arc {
|
|
p: ptr::NonNull::new_unchecked(self.ptr()),
|
|
phantom: PhantomData,
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<T: ?Sized> Deref for Arc<T> {
|
|
type Target = T;
|
|
|
|
#[inline]
|
|
fn deref(&self) -> &T {
|
|
&self.inner().data
|
|
}
|
|
}
|
|
|
|
impl<T: Clone> Arc<T> {
|
|
/// Makes a mutable reference to the `Arc`, cloning if necessary
|
|
///
|
|
/// This is functionally equivalent to [`Arc::make_mut`][mm] from the standard library.
|
|
///
|
|
/// If this `Arc` is uniquely owned, `make_mut()` will provide a mutable
|
|
/// reference to the contents. If not, `make_mut()` will create a _new_ `Arc`
|
|
/// with a copy of the contents, update `this` to point to it, and provide
|
|
/// a mutable reference to its contents.
|
|
///
|
|
/// This is useful for implementing copy-on-write schemes where you wish to
|
|
/// avoid copying things if your `Arc` is not shared.
|
|
///
|
|
/// [mm]: https://doc.rust-lang.org/stable/std/sync/struct.Arc.html#method.make_mut
|
|
#[inline]
|
|
pub fn make_mut(this: &mut Self) -> &mut T {
|
|
if !this.is_unique() {
|
|
// Another pointer exists; clone
|
|
*this = Arc::new((**this).clone());
|
|
}
|
|
|
|
unsafe {
|
|
// This unsafety is ok because we're guaranteed that the pointer
|
|
// returned is the *only* pointer that will ever be returned to T. Our
|
|
// reference count is guaranteed to be 1 at this point, and we required
|
|
// the Arc itself to be `mut`, so we're returning the only possible
|
|
// reference to the inner data.
|
|
&mut (*this.ptr()).data
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<T: ?Sized> Arc<T> {
|
|
/// Provides mutable access to the contents _if_ the `Arc` is uniquely owned.
|
|
#[inline]
|
|
pub fn get_mut(this: &mut Self) -> Option<&mut T> {
|
|
if this.is_unique() {
|
|
unsafe {
|
|
// See make_mut() for documentation of the threadsafety here.
|
|
Some(&mut (*this.ptr()).data)
|
|
}
|
|
} else {
|
|
None
|
|
}
|
|
}
|
|
|
|
/// Whether or not the `Arc` is a static reference.
|
|
#[inline]
|
|
pub fn is_static(&self) -> bool {
|
|
// Using a relaxed ordering to check for STATIC_REFCOUNT is safe, since
|
|
// `count` never changes between STATIC_REFCOUNT and other values.
|
|
self.inner().count.load(Relaxed) == STATIC_REFCOUNT
|
|
}
|
|
|
|
/// Whether or not the `Arc` is uniquely owned (is the refcount 1?) and not
|
|
/// a static reference.
|
|
#[inline]
|
|
pub fn is_unique(&self) -> bool {
|
|
// See the extensive discussion in [1] for why this needs to be Acquire.
|
|
//
|
|
// [1] https://github.com/servo/servo/issues/21186
|
|
self.inner().count.load(Acquire) == 1
|
|
}
|
|
}
|
|
|
|
impl<T: ?Sized> Drop for Arc<T> {
|
|
#[inline]
|
|
fn drop(&mut self) {
|
|
// NOTE(emilio): If you change anything here, make sure that the
|
|
// implementation in layout/style/ServoStyleConstsInlines.h matches!
|
|
if self.is_static() {
|
|
return;
|
|
}
|
|
|
|
// Because `fetch_sub` is already atomic, we do not need to synchronize
|
|
// with other threads unless we are going to delete the object.
|
|
if self.inner().count.fetch_sub(1, Release) != 1 {
|
|
return;
|
|
}
|
|
|
|
// FIXME(bholley): Use the updated comment when [2] is merged.
|
|
//
|
|
// This load is needed to prevent reordering of use of the data and
|
|
// deletion of the data. Because it is marked `Release`, the decreasing
|
|
// of the reference count synchronizes with this `Acquire` load. This
|
|
// means that use of the data happens before decreasing the reference
|
|
// count, which happens before this load, which happens before the
|
|
// deletion of the data.
|
|
//
|
|
// As explained in the [Boost documentation][1],
|
|
//
|
|
// > It is important to enforce any possible access to the object in one
|
|
// > thread (through an existing reference) to *happen before* deleting
|
|
// > the object in a different thread. This is achieved by a "release"
|
|
// > operation after dropping a reference (any access to the object
|
|
// > through this reference must obviously happened before), and an
|
|
// > "acquire" operation before deleting the object.
|
|
//
|
|
// [1]: (www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html)
|
|
// [2]: https://github.com/rust-lang/rust/pull/41714
|
|
self.inner().count.load(Acquire);
|
|
|
|
unsafe {
|
|
self.drop_slow();
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<T: ?Sized + PartialEq> PartialEq for Arc<T> {
|
|
fn eq(&self, other: &Arc<T>) -> bool {
|
|
Self::ptr_eq(self, other) || *(*self) == *(*other)
|
|
}
|
|
|
|
fn ne(&self, other: &Arc<T>) -> bool {
|
|
!Self::ptr_eq(self, other) && *(*self) != *(*other)
|
|
}
|
|
}
|
|
|
|
impl<T: ?Sized + PartialOrd> PartialOrd for Arc<T> {
|
|
fn partial_cmp(&self, other: &Arc<T>) -> Option<Ordering> {
|
|
(**self).partial_cmp(&**other)
|
|
}
|
|
|
|
fn lt(&self, other: &Arc<T>) -> bool {
|
|
*(*self) < *(*other)
|
|
}
|
|
|
|
fn le(&self, other: &Arc<T>) -> bool {
|
|
*(*self) <= *(*other)
|
|
}
|
|
|
|
fn gt(&self, other: &Arc<T>) -> bool {
|
|
*(*self) > *(*other)
|
|
}
|
|
|
|
fn ge(&self, other: &Arc<T>) -> bool {
|
|
*(*self) >= *(*other)
|
|
}
|
|
}
|
|
impl<T: ?Sized + Ord> Ord for Arc<T> {
|
|
fn cmp(&self, other: &Arc<T>) -> Ordering {
|
|
(**self).cmp(&**other)
|
|
}
|
|
}
|
|
impl<T: ?Sized + Eq> Eq for Arc<T> {}
|
|
|
|
impl<T: ?Sized + fmt::Display> fmt::Display for Arc<T> {
|
|
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
|
|
fmt::Display::fmt(&**self, f)
|
|
}
|
|
}
|
|
|
|
impl<T: ?Sized + fmt::Debug> fmt::Debug for Arc<T> {
|
|
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
|
|
fmt::Debug::fmt(&**self, f)
|
|
}
|
|
}
|
|
|
|
impl<T: ?Sized> fmt::Pointer for Arc<T> {
|
|
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
|
|
fmt::Pointer::fmt(&self.ptr(), f)
|
|
}
|
|
}
|
|
|
|
impl<T: Default> Default for Arc<T> {
|
|
fn default() -> Arc<T> {
|
|
Arc::new(Default::default())
|
|
}
|
|
}
|
|
|
|
impl<T: ?Sized + Hash> Hash for Arc<T> {
|
|
fn hash<H: Hasher>(&self, state: &mut H) {
|
|
(**self).hash(state)
|
|
}
|
|
}
|
|
|
|
impl<T> From<T> for Arc<T> {
|
|
#[inline]
|
|
fn from(t: T) -> Self {
|
|
Arc::new(t)
|
|
}
|
|
}
|
|
|
|
impl<T: ?Sized> borrow::Borrow<T> for Arc<T> {
|
|
#[inline]
|
|
fn borrow(&self) -> &T {
|
|
&**self
|
|
}
|
|
}
|
|
|
|
impl<T: ?Sized> AsRef<T> for Arc<T> {
|
|
#[inline]
|
|
fn as_ref(&self) -> &T {
|
|
&**self
|
|
}
|
|
}
|
|
|
|
unsafe impl<T: ?Sized> StableDeref for Arc<T> {}
|
|
unsafe impl<T: ?Sized> CloneStableDeref for Arc<T> {}
|
|
|
|
#[cfg(feature = "servo")]
|
|
impl<'de, T: Deserialize<'de>> Deserialize<'de> for Arc<T> {
|
|
fn deserialize<D>(deserializer: D) -> Result<Arc<T>, D::Error>
|
|
where
|
|
D: ::serde::de::Deserializer<'de>,
|
|
{
|
|
T::deserialize(deserializer).map(Arc::new)
|
|
}
|
|
}
|
|
|
|
#[cfg(feature = "servo")]
|
|
impl<T: Serialize> Serialize for Arc<T> {
|
|
fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
|
|
where
|
|
S: ::serde::ser::Serializer,
|
|
{
|
|
(**self).serialize(serializer)
|
|
}
|
|
}
|
|
|
|
/// Structure to allow Arc-managing some fixed-sized data and a variably-sized
|
|
/// slice in a single allocation.
|
|
///
|
|
/// cbindgen:derive-eq=false
|
|
/// cbindgen:derive-neq=false
|
|
#[derive(Eq)]
|
|
#[repr(C)]
|
|
pub struct HeaderSlice<H, T> {
|
|
/// The fixed-sized data.
|
|
pub header: H,
|
|
|
|
/// The length of the slice at our end.
|
|
len: usize,
|
|
|
|
/// The dynamically-sized data.
|
|
data: [T; 0],
|
|
}
|
|
|
|
impl<H: PartialEq, T: PartialEq> PartialEq for HeaderSlice<H, T> {
|
|
fn eq(&self, other: &Self) -> bool {
|
|
self.header == other.header && self.slice() == other.slice()
|
|
}
|
|
}
|
|
|
|
impl<H, T> Drop for HeaderSlice<H, T> {
|
|
fn drop(&mut self) {
|
|
unsafe {
|
|
let mut ptr = self.data_mut();
|
|
for _ in 0..self.len {
|
|
std::ptr::drop_in_place(ptr);
|
|
ptr = ptr.offset(1);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<H: fmt::Debug, T: fmt::Debug> fmt::Debug for HeaderSlice<H, T> {
|
|
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
|
|
f.debug_struct("HeaderSlice")
|
|
.field("header", &self.header)
|
|
.field("slice", &self.slice())
|
|
.finish()
|
|
}
|
|
}
|
|
|
|
impl<H, T> HeaderSlice<H, T> {
|
|
/// Returns the dynamically sized slice in this HeaderSlice.
|
|
#[inline(always)]
|
|
pub fn slice(&self) -> &[T] {
|
|
unsafe { std::slice::from_raw_parts(self.data(), self.len) }
|
|
}
|
|
|
|
#[inline(always)]
|
|
fn data(&self) -> *const T {
|
|
std::ptr::addr_of!(self.data) as *const _
|
|
}
|
|
|
|
#[inline(always)]
|
|
fn data_mut(&mut self) -> *mut T {
|
|
std::ptr::addr_of_mut!(self.data) as *mut _
|
|
}
|
|
|
|
/// Returns the dynamically sized slice in this HeaderSlice.
|
|
#[inline(always)]
|
|
pub fn slice_mut(&mut self) -> &mut [T] {
|
|
unsafe { std::slice::from_raw_parts_mut(self.data_mut(), self.len) }
|
|
}
|
|
|
|
/// Returns the len of the slice.
|
|
#[inline(always)]
|
|
pub fn len(&self) -> usize {
|
|
self.len
|
|
}
|
|
}
|
|
|
|
impl<H, T> Arc<HeaderSlice<H, T>> {
|
|
/// Creates an Arc for a HeaderSlice using the given header struct and
|
|
/// iterator to generate the slice.
|
|
///
|
|
/// `is_static` indicates whether to create a static Arc.
|
|
///
|
|
/// `alloc` is used to get a pointer to the memory into which the
|
|
/// dynamically sized ArcInner<HeaderSlice<H, T>> value will be
|
|
/// written. If `is_static` is true, then `alloc` must return a
|
|
/// pointer into some static memory allocation. If it is false,
|
|
/// then `alloc` must return an allocation that can be dellocated
|
|
/// by calling Box::from_raw::<ArcInner<HeaderSlice<H, T>>> on it.
|
|
#[inline]
|
|
pub fn from_header_and_iter_alloc<F, I>(
|
|
alloc: F,
|
|
header: H,
|
|
mut items: I,
|
|
num_items: usize,
|
|
is_static: bool,
|
|
) -> Self
|
|
where
|
|
F: FnOnce(Layout) -> *mut u8,
|
|
I: Iterator<Item = T>,
|
|
{
|
|
assert_ne!(size_of::<T>(), 0, "Need to think about ZST");
|
|
|
|
let layout = Layout::new::<ArcInner<HeaderSlice<H, T>>>();
|
|
debug_assert!(layout.align() >= align_of::<T>());
|
|
debug_assert!(layout.align() >= align_of::<usize>());
|
|
let array_layout = Layout::array::<T>(num_items).expect("Overflow");
|
|
let (layout, _offset) = layout.extend(array_layout).expect("Overflow");
|
|
let p = unsafe {
|
|
// Allocate the buffer.
|
|
let buffer = alloc(layout);
|
|
let mut p = ptr::NonNull::new(buffer)
|
|
.unwrap_or_else(|| alloc::handle_alloc_error(layout))
|
|
.cast::<ArcInner<HeaderSlice<H, T>>>();
|
|
|
|
// Write the data.
|
|
//
|
|
// Note that any panics here (i.e. from the iterator) are safe, since
|
|
// we'll just leak the uninitialized memory.
|
|
let count = if is_static {
|
|
atomic::AtomicUsize::new(STATIC_REFCOUNT)
|
|
} else {
|
|
atomic::AtomicUsize::new(1)
|
|
};
|
|
ptr::write(&mut p.as_mut().count, count);
|
|
#[cfg(feature = "track_alloc_size")]
|
|
ptr::write(&mut p.as_mut().alloc_size, layout.size());
|
|
ptr::write(&mut p.as_mut().data.header, header);
|
|
ptr::write(&mut p.as_mut().data.len, num_items);
|
|
if num_items != 0 {
|
|
let mut current = std::ptr::addr_of_mut!(p.as_mut().data.data) as *mut T;
|
|
for _ in 0..num_items {
|
|
ptr::write(
|
|
current,
|
|
items
|
|
.next()
|
|
.expect("ExactSizeIterator over-reported length"),
|
|
);
|
|
current = current.offset(1);
|
|
}
|
|
// We should have consumed the buffer exactly, maybe accounting
|
|
// for some padding from the alignment.
|
|
debug_assert!(
|
|
(buffer.add(layout.size()) as usize - current as *mut u8 as usize) < layout.align()
|
|
);
|
|
}
|
|
assert!(
|
|
items.next().is_none(),
|
|
"ExactSizeIterator under-reported length"
|
|
);
|
|
p
|
|
};
|
|
#[cfg(feature = "gecko_refcount_logging")]
|
|
unsafe {
|
|
if !is_static {
|
|
// FIXME(emilio): Would be so amazing to have
|
|
// std::intrinsics::type_name() around.
|
|
NS_LogCtor(p.as_ptr() as *mut _, b"ServoArc\0".as_ptr() as *const _, 8)
|
|
}
|
|
}
|
|
|
|
// Return the fat Arc.
|
|
assert_eq!(
|
|
size_of::<Self>(),
|
|
size_of::<usize>(),
|
|
"The Arc should be thin"
|
|
);
|
|
|
|
Arc {
|
|
p,
|
|
phantom: PhantomData,
|
|
}
|
|
}
|
|
|
|
/// Creates an Arc for a HeaderSlice using the given header struct and iterator to generate the
|
|
/// slice. Panics if num_items doesn't match the number of items.
|
|
#[inline]
|
|
pub fn from_header_and_iter_with_size<I>(header: H, items: I, num_items: usize) -> Self
|
|
where
|
|
I: Iterator<Item = T>,
|
|
{
|
|
Arc::from_header_and_iter_alloc(
|
|
|layout| unsafe { alloc::alloc(layout) },
|
|
header,
|
|
items,
|
|
num_items,
|
|
/* is_static = */ false,
|
|
)
|
|
}
|
|
|
|
/// Creates an Arc for a HeaderSlice using the given header struct and
|
|
/// iterator to generate the slice. The resulting Arc will be fat.
|
|
#[inline]
|
|
pub fn from_header_and_iter<I>(header: H, items: I) -> Self
|
|
where
|
|
I: Iterator<Item = T> + ExactSizeIterator,
|
|
{
|
|
let len = items.len();
|
|
Self::from_header_and_iter_with_size(header, items, len)
|
|
}
|
|
}
|
|
|
|
/// This is functionally equivalent to Arc<(H, [T])>
|
|
///
|
|
/// When you create an `Arc` containing a dynamically sized type like a slice, the `Arc` is
|
|
/// represented on the stack as a "fat pointer", where the length of the slice is stored alongside
|
|
/// the `Arc`'s pointer. In some situations you may wish to have a thin pointer instead, perhaps
|
|
/// for FFI compatibility or space efficiency. `ThinArc` solves this by storing the length in the
|
|
/// allocation itself, via `HeaderSlice`.
|
|
pub type ThinArc<H, T> = Arc<HeaderSlice<H, T>>;
|
|
|
|
/// See `ArcUnion`. This is a version that works for `ThinArc`s.
|
|
pub type ThinArcUnion<H1, T1, H2, T2> = ArcUnion<HeaderSlice<H1, T1>, HeaderSlice<H2, T2>>;
|
|
|
|
impl<H, T> UniqueArc<HeaderSlice<H, T>> {
|
|
#[inline]
|
|
pub fn from_header_and_iter<I>(header: H, items: I) -> Self
|
|
where
|
|
I: Iterator<Item = T> + ExactSizeIterator,
|
|
{
|
|
Self(Arc::from_header_and_iter(header, items))
|
|
}
|
|
|
|
#[inline]
|
|
pub fn from_header_and_iter_with_size<I>(header: H, items: I, num_items: usize) -> Self
|
|
where
|
|
I: Iterator<Item = T>,
|
|
{
|
|
Self(Arc::from_header_and_iter_with_size(
|
|
header, items, num_items,
|
|
))
|
|
}
|
|
|
|
/// Returns a mutable reference to the header.
|
|
pub fn header_mut(&mut self) -> &mut H {
|
|
// We know this to be uniquely owned
|
|
unsafe { &mut (*self.0.ptr()).data.header }
|
|
}
|
|
|
|
/// Returns a mutable reference to the slice.
|
|
pub fn data_mut(&mut self) -> &mut [T] {
|
|
// We know this to be uniquely owned
|
|
unsafe { (*self.0.ptr()).data.slice_mut() }
|
|
}
|
|
}
|
|
|
|
/// A "borrowed `Arc`". This is a pointer to
|
|
/// a T that is known to have been allocated within an
|
|
/// `Arc`.
|
|
///
|
|
/// This is equivalent in guarantees to `&Arc<T>`, however it is
|
|
/// a bit more flexible. To obtain an `&Arc<T>` you must have
|
|
/// an `Arc<T>` instance somewhere pinned down until we're done with it.
|
|
/// It's also a direct pointer to `T`, so using this involves less pointer-chasing
|
|
///
|
|
/// However, C++ code may hand us refcounted things as pointers to T directly,
|
|
/// so we have to conjure up a temporary `Arc` on the stack each time.
|
|
///
|
|
/// `ArcBorrow` lets us deal with borrows of known-refcounted objects
|
|
/// without needing to worry about where the `Arc<T>` is.
|
|
#[derive(Debug, Eq, PartialEq)]
|
|
pub struct ArcBorrow<'a, T: 'a>(&'a T);
|
|
|
|
impl<'a, T> Copy for ArcBorrow<'a, T> {}
|
|
impl<'a, T> Clone for ArcBorrow<'a, T> {
|
|
#[inline]
|
|
fn clone(&self) -> Self {
|
|
*self
|
|
}
|
|
}
|
|
|
|
impl<'a, T> ArcBorrow<'a, T> {
|
|
/// Clone this as an `Arc<T>`. This bumps the refcount.
|
|
#[inline]
|
|
pub fn clone_arc(&self) -> Arc<T> {
|
|
let arc = unsafe { Arc::from_raw(self.0) };
|
|
// addref it!
|
|
mem::forget(arc.clone());
|
|
arc
|
|
}
|
|
|
|
/// For constructing from a reference known to be Arc-backed,
|
|
/// e.g. if we obtain such a reference over FFI
|
|
#[inline]
|
|
pub unsafe fn from_ref(r: &'a T) -> Self {
|
|
ArcBorrow(r)
|
|
}
|
|
|
|
/// Compare two `ArcBorrow`s via pointer equality. Will only return
|
|
/// true if they come from the same allocation
|
|
pub fn ptr_eq(this: &Self, other: &Self) -> bool {
|
|
this.0 as *const T == other.0 as *const T
|
|
}
|
|
|
|
/// Temporarily converts |self| into a bonafide Arc and exposes it to the
|
|
/// provided callback. The refcount is not modified.
|
|
#[inline]
|
|
pub fn with_arc<F, U>(&self, f: F) -> U
|
|
where
|
|
F: FnOnce(&Arc<T>) -> U,
|
|
T: 'static,
|
|
{
|
|
// Synthesize transient Arc, which never touches the refcount.
|
|
let transient = unsafe { mem::ManuallyDrop::new(Arc::from_raw(self.0)) };
|
|
|
|
// Expose the transient Arc to the callback, which may clone it if it wants.
|
|
let result = f(&transient);
|
|
|
|
// Forward the result.
|
|
result
|
|
}
|
|
|
|
/// Similar to deref, but uses the lifetime |a| rather than the lifetime of
|
|
/// self, which is incompatible with the signature of the Deref trait.
|
|
#[inline]
|
|
pub fn get(&self) -> &'a T {
|
|
self.0
|
|
}
|
|
}
|
|
|
|
impl<'a, T> Deref for ArcBorrow<'a, T> {
|
|
type Target = T;
|
|
|
|
#[inline]
|
|
fn deref(&self) -> &T {
|
|
self.0
|
|
}
|
|
}
|
|
|
|
/// A tagged union that can represent `Arc<A>` or `Arc<B>` while only consuming a
|
|
/// single word. The type is also `NonNull`, and thus can be stored in an Option
|
|
/// without increasing size.
|
|
///
|
|
/// This is functionally equivalent to
|
|
/// `enum ArcUnion<A, B> { First(Arc<A>), Second(Arc<B>)` but only takes up
|
|
/// up a single word of stack space.
|
|
///
|
|
/// This could probably be extended to support four types if necessary.
|
|
pub struct ArcUnion<A, B> {
|
|
p: ptr::NonNull<()>,
|
|
phantom_a: PhantomData<A>,
|
|
phantom_b: PhantomData<B>,
|
|
}
|
|
|
|
unsafe impl<A: Sync + Send, B: Send + Sync> Send for ArcUnion<A, B> {}
|
|
unsafe impl<A: Sync + Send, B: Send + Sync> Sync for ArcUnion<A, B> {}
|
|
|
|
impl<A: PartialEq, B: PartialEq> PartialEq for ArcUnion<A, B> {
|
|
fn eq(&self, other: &Self) -> bool {
|
|
use crate::ArcUnionBorrow::*;
|
|
match (self.borrow(), other.borrow()) {
|
|
(First(x), First(y)) => x == y,
|
|
(Second(x), Second(y)) => x == y,
|
|
(_, _) => false,
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<A: Eq, B: Eq> Eq for ArcUnion<A, B> {}
|
|
|
|
/// This represents a borrow of an `ArcUnion`.
|
|
#[derive(Debug)]
|
|
pub enum ArcUnionBorrow<'a, A: 'a, B: 'a> {
|
|
First(ArcBorrow<'a, A>),
|
|
Second(ArcBorrow<'a, B>),
|
|
}
|
|
|
|
impl<A, B> ArcUnion<A, B> {
|
|
unsafe fn new(ptr: *mut ()) -> Self {
|
|
ArcUnion {
|
|
p: ptr::NonNull::new_unchecked(ptr),
|
|
phantom_a: PhantomData,
|
|
phantom_b: PhantomData,
|
|
}
|
|
}
|
|
|
|
/// Returns true if the two values are pointer-equal.
|
|
#[inline]
|
|
pub fn ptr_eq(this: &Self, other: &Self) -> bool {
|
|
this.p == other.p
|
|
}
|
|
|
|
#[inline]
|
|
pub fn ptr(&self) -> ptr::NonNull<()> {
|
|
self.p
|
|
}
|
|
|
|
/// Returns an enum representing a borrow of either A or B.
|
|
#[inline]
|
|
pub fn borrow(&self) -> ArcUnionBorrow<A, B> {
|
|
if self.is_first() {
|
|
let ptr = self.p.as_ptr() as *const ArcInner<A>;
|
|
let borrow = unsafe { ArcBorrow::from_ref(&(*ptr).data) };
|
|
ArcUnionBorrow::First(borrow)
|
|
} else {
|
|
let ptr = ((self.p.as_ptr() as usize) & !0x1) as *const ArcInner<B>;
|
|
let borrow = unsafe { ArcBorrow::from_ref(&(*ptr).data) };
|
|
ArcUnionBorrow::Second(borrow)
|
|
}
|
|
}
|
|
|
|
/// Creates an `ArcUnion` from an instance of the first type.
|
|
pub fn from_first(other: Arc<A>) -> Self {
|
|
let union = unsafe { Self::new(other.ptr() as *mut _) };
|
|
mem::forget(other);
|
|
union
|
|
}
|
|
|
|
/// Creates an `ArcUnion` from an instance of the second type.
|
|
pub fn from_second(other: Arc<B>) -> Self {
|
|
let union = unsafe { Self::new(((other.ptr() as usize) | 0x1) as *mut _) };
|
|
mem::forget(other);
|
|
union
|
|
}
|
|
|
|
/// Returns true if this `ArcUnion` contains the first type.
|
|
pub fn is_first(&self) -> bool {
|
|
self.p.as_ptr() as usize & 0x1 == 0
|
|
}
|
|
|
|
/// Returns true if this `ArcUnion` contains the second type.
|
|
pub fn is_second(&self) -> bool {
|
|
!self.is_first()
|
|
}
|
|
|
|
/// Returns a borrow of the first type if applicable, otherwise `None`.
|
|
pub fn as_first(&self) -> Option<ArcBorrow<A>> {
|
|
match self.borrow() {
|
|
ArcUnionBorrow::First(x) => Some(x),
|
|
ArcUnionBorrow::Second(_) => None,
|
|
}
|
|
}
|
|
|
|
/// Returns a borrow of the second type if applicable, otherwise None.
|
|
pub fn as_second(&self) -> Option<ArcBorrow<B>> {
|
|
match self.borrow() {
|
|
ArcUnionBorrow::First(_) => None,
|
|
ArcUnionBorrow::Second(x) => Some(x),
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<A, B> Clone for ArcUnion<A, B> {
|
|
fn clone(&self) -> Self {
|
|
match self.borrow() {
|
|
ArcUnionBorrow::First(x) => ArcUnion::from_first(x.clone_arc()),
|
|
ArcUnionBorrow::Second(x) => ArcUnion::from_second(x.clone_arc()),
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<A, B> Drop for ArcUnion<A, B> {
|
|
fn drop(&mut self) {
|
|
match self.borrow() {
|
|
ArcUnionBorrow::First(x) => unsafe {
|
|
let _ = Arc::from_raw(&*x);
|
|
},
|
|
ArcUnionBorrow::Second(x) => unsafe {
|
|
let _ = Arc::from_raw(&*x);
|
|
},
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<A: fmt::Debug, B: fmt::Debug> fmt::Debug for ArcUnion<A, B> {
|
|
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
|
|
fmt::Debug::fmt(&self.borrow(), f)
|
|
}
|
|
}
|
|
|
|
#[cfg(test)]
|
|
mod tests {
|
|
use super::{Arc, ThinArc};
|
|
use std::clone::Clone;
|
|
use std::ops::Drop;
|
|
use std::sync::atomic;
|
|
use std::sync::atomic::Ordering::{Acquire, SeqCst};
|
|
|
|
#[derive(PartialEq)]
|
|
struct Canary(*mut atomic::AtomicUsize);
|
|
|
|
impl Drop for Canary {
|
|
fn drop(&mut self) {
|
|
unsafe {
|
|
(*self.0).fetch_add(1, SeqCst);
|
|
}
|
|
}
|
|
}
|
|
|
|
#[test]
|
|
fn empty_thin() {
|
|
let x = Arc::from_header_and_iter(100u32, std::iter::empty::<i32>());
|
|
assert_eq!(x.header, 100);
|
|
assert!(x.slice().is_empty());
|
|
}
|
|
|
|
#[test]
|
|
fn thin_assert_padding() {
|
|
#[derive(Clone, Default)]
|
|
#[repr(C)]
|
|
struct Padded {
|
|
i: u16,
|
|
}
|
|
|
|
// The header will have more alignment than `Padded`
|
|
let items = vec![Padded { i: 0xdead }, Padded { i: 0xbeef }];
|
|
let a = ThinArc::from_header_and_iter(0i32, items.into_iter());
|
|
assert_eq!(a.len(), 2);
|
|
assert_eq!(a.slice()[0].i, 0xdead);
|
|
assert_eq!(a.slice()[1].i, 0xbeef);
|
|
}
|
|
|
|
#[test]
|
|
fn slices_and_thin() {
|
|
let mut canary = atomic::AtomicUsize::new(0);
|
|
let c = Canary(&mut canary as *mut atomic::AtomicUsize);
|
|
let v = vec![5, 6];
|
|
{
|
|
let x = Arc::from_header_and_iter(c, v.into_iter());
|
|
let _ = x.clone();
|
|
let _ = x == x;
|
|
}
|
|
assert_eq!(canary.load(Acquire), 1);
|
|
}
|
|
}
|