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1// SPDX-License-Identifier: GPL-2.0
2
3//! A reference-counted pointer.
4//!
5//! This module implements a way for users to create reference-counted objects and pointers to
6//! them. Such a pointer automatically increments and decrements the count, and drops the
7//! underlying object when it reaches zero. It is also safe to use concurrently from multiple
8//! threads.
9//!
10//! It is different from the standard library's [`Arc`] in a few ways:
11//! 1. It is backed by the kernel's `refcount_t` type.
12//! 2. It does not support weak references, which allows it to be half the size.
13//! 3. It saturates the reference count instead of aborting when it goes over a threshold.
14//! 4. It does not provide a `get_mut` method, so the ref counted object is pinned.
15//!
16//! [`Arc`]: https://doc.rust-lang.org/std/sync/struct.Arc.html
17
18use crate::{
19 bindings,
20 error::{self, Error},
21 init::{self, InPlaceInit, Init, PinInit},
22 try_init,
23 types::{ForeignOwnable, Opaque},
24};
25use alloc::boxed::Box;
26use core::{
27 alloc::{AllocError, Layout},
28 fmt,
29 marker::{PhantomData, Unsize},
30 mem::{ManuallyDrop, MaybeUninit},
31 ops::{Deref, DerefMut},
32 pin::Pin,
33 ptr::NonNull,
34};
35use macros::pin_data;
36
37mod std_vendor;
38
39/// A reference-counted pointer to an instance of `T`.
40///
41/// The reference count is incremented when new instances of [`Arc`] are created, and decremented
42/// when they are dropped. When the count reaches zero, the underlying `T` is also dropped.
43///
44/// # Invariants
45///
46/// The reference count on an instance of [`Arc`] is always non-zero.
47/// The object pointed to by [`Arc`] is always pinned.
48///
49/// # Examples
50///
51/// ```
52/// use kernel::sync::Arc;
53///
54/// struct Example {
55/// a: u32,
56/// b: u32,
57/// }
58///
59/// // Create a refcounted instance of `Example`.
60/// let obj = Arc::try_new(Example { a: 10, b: 20 })?;
61///
62/// // Get a new pointer to `obj` and increment the refcount.
63/// let cloned = obj.clone();
64///
65/// // Assert that both `obj` and `cloned` point to the same underlying object.
66/// assert!(core::ptr::eq(&*obj, &*cloned));
67///
68/// // Destroy `obj` and decrement its refcount.
69/// drop(obj);
70///
71/// // Check that the values are still accessible through `cloned`.
72/// assert_eq!(cloned.a, 10);
73/// assert_eq!(cloned.b, 20);
74///
75/// // The refcount drops to zero when `cloned` goes out of scope, and the memory is freed.
76/// # Ok::<(), Error>(())
77/// ```
78///
79/// Using `Arc<T>` as the type of `self`:
80///
81/// ```
82/// use kernel::sync::Arc;
83///
84/// struct Example {
85/// a: u32,
86/// b: u32,
87/// }
88///
89/// impl Example {
90/// fn take_over(self: Arc<Self>) {
91/// // ...
92/// }
93///
94/// fn use_reference(self: &Arc<Self>) {
95/// // ...
96/// }
97/// }
98///
99/// let obj = Arc::try_new(Example { a: 10, b: 20 })?;
100/// obj.use_reference();
101/// obj.take_over();
102/// # Ok::<(), Error>(())
103/// ```
104///
105/// Coercion from `Arc<Example>` to `Arc<dyn MyTrait>`:
106///
107/// ```
108/// use kernel::sync::{Arc, ArcBorrow};
109///
110/// trait MyTrait {
111/// // Trait has a function whose `self` type is `Arc<Self>`.
112/// fn example1(self: Arc<Self>) {}
113///
114/// // Trait has a function whose `self` type is `ArcBorrow<'_, Self>`.
115/// fn example2(self: ArcBorrow<'_, Self>) {}
116/// }
117///
118/// struct Example;
119/// impl MyTrait for Example {}
120///
121/// // `obj` has type `Arc<Example>`.
122/// let obj: Arc<Example> = Arc::try_new(Example)?;
123///
124/// // `coerced` has type `Arc<dyn MyTrait>`.
125/// let coerced: Arc<dyn MyTrait> = obj;
126/// # Ok::<(), Error>(())
127/// ```
128pub struct Arc<T: ?Sized> {
129 ptr: NonNull<ArcInner<T>>,
130 _p: PhantomData<ArcInner<T>>,
131}
132
133#[pin_data]
134#[repr(C)]
135struct ArcInner<T: ?Sized> {
136 refcount: Opaque<bindings::refcount_t>,
137 data: T,
138}
139
140// This is to allow [`Arc`] (and variants) to be used as the type of `self`.
141impl<T: ?Sized> core::ops::Receiver for Arc<T> {}
142
143// This is to allow coercion from `Arc<T>` to `Arc<U>` if `T` can be converted to the
144// dynamically-sized type (DST) `U`.
145impl<T: ?Sized + Unsize<U>, U: ?Sized> core::ops::CoerceUnsized<Arc<U>> for Arc<T> {}
146
147// This is to allow `Arc<U>` to be dispatched on when `Arc<T>` can be coerced into `Arc<U>`.
148impl<T: ?Sized + Unsize<U>, U: ?Sized> core::ops::DispatchFromDyn<Arc<U>> for Arc<T> {}
149
150// SAFETY: It is safe to send `Arc<T>` to another thread when the underlying `T` is `Sync` because
151// it effectively means sharing `&T` (which is safe because `T` is `Sync`); additionally, it needs
152// `T` to be `Send` because any thread that has an `Arc<T>` may ultimately access `T` using a
153// mutable reference when the reference count reaches zero and `T` is dropped.
154unsafe impl<T: ?Sized + Sync + Send> Send for Arc<T> {}
155
156// SAFETY: It is safe to send `&Arc<T>` to another thread when the underlying `T` is `Sync`
157// because it effectively means sharing `&T` (which is safe because `T` is `Sync`); additionally,
158// it needs `T` to be `Send` because any thread that has a `&Arc<T>` may clone it and get an
159// `Arc<T>` on that thread, so the thread may ultimately access `T` using a mutable reference when
160// the reference count reaches zero and `T` is dropped.
161unsafe impl<T: ?Sized + Sync + Send> Sync for Arc<T> {}
162
163impl<T> Arc<T> {
164 /// Constructs a new reference counted instance of `T`.
165 pub fn try_new(contents: T) -> Result<Self, AllocError> {
166 // INVARIANT: The refcount is initialised to a non-zero value.
167 let value = ArcInner {
168 // SAFETY: There are no safety requirements for this FFI call.
169 refcount: Opaque::new(unsafe { bindings::REFCOUNT_INIT(1) }),
170 data: contents,
171 };
172
173 let inner = Box::try_new(value)?;
174
175 // SAFETY: We just created `inner` with a reference count of 1, which is owned by the new
176 // `Arc` object.
177 Ok(unsafe { Self::from_inner(Box::leak(inner).into()) })
178 }
179
180 /// Use the given initializer to in-place initialize a `T`.
181 ///
182 /// If `T: !Unpin` it will not be able to move afterwards.
183 #[inline]
184 pub fn pin_init<E>(init: impl PinInit<T, E>) -> error::Result<Self>
185 where
186 Error: From<E>,
187 {
188 UniqueArc::pin_init(init).map(|u| u.into())
189 }
190
191 /// Use the given initializer to in-place initialize a `T`.
192 ///
193 /// This is equivalent to [`Arc<T>::pin_init`], since an [`Arc`] is always pinned.
194 #[inline]
195 pub fn init<E>(init: impl Init<T, E>) -> error::Result<Self>
196 where
197 Error: From<E>,
198 {
199 UniqueArc::init(init).map(|u| u.into())
200 }
201}
202
203impl<T: ?Sized> Arc<T> {
204 /// Constructs a new [`Arc`] from an existing [`ArcInner`].
205 ///
206 /// # Safety
207 ///
208 /// The caller must ensure that `inner` points to a valid location and has a non-zero reference
209 /// count, one of which will be owned by the new [`Arc`] instance.
210 unsafe fn from_inner(inner: NonNull<ArcInner<T>>) -> Self {
211 // INVARIANT: By the safety requirements, the invariants hold.
212 Arc {
213 ptr: inner,
214 _p: PhantomData,
215 }
216 }
217
218 /// Convert the [`Arc`] into a raw pointer.
219 ///
220 /// The raw pointer has ownership of the refcount that this Arc object owned.
221 pub fn into_raw(self) -> *const T {
222 let ptr = self.ptr.as_ptr();
223 core::mem::forget(self);
224 // SAFETY: The pointer is valid.
225 unsafe { core::ptr::addr_of!((*ptr).data) }
226 }
227
228 /// Recreates an [`Arc`] instance previously deconstructed via [`Arc::into_raw`].
229 ///
230 /// # Safety
231 ///
232 /// `ptr` must have been returned by a previous call to [`Arc::into_raw`]. Additionally, it
233 /// must not be called more than once for each previous call to [`Arc::into_raw`].
234 pub unsafe fn from_raw(ptr: *const T) -> Self {
235 let refcount_layout = Layout::new::<bindings::refcount_t>();
236 // SAFETY: The caller guarantees that the pointer is valid.
237 let val_layout = Layout::for_value(unsafe { &*ptr });
238 // SAFETY: We're computing the layout of a real struct that existed when compiling this
239 // binary, so its layout is not so large that it can trigger arithmetic overflow.
240 let val_offset = unsafe { refcount_layout.extend(val_layout).unwrap_unchecked().1 };
241
242 // Pointer casts leave the metadata unchanged. This is okay because the metadata of `T` and
243 // `ArcInner<T>` is the same since `ArcInner` is a struct with `T` as its last field.
244 //
245 // This is documented at:
246 // <https://doc.rust-lang.org/std/ptr/trait.Pointee.html>.
247 let ptr = ptr as *const ArcInner<T>;
248
249 // SAFETY: The pointer is in-bounds of an allocation both before and after offsetting the
250 // pointer, since it originates from a previous call to `Arc::into_raw` and is still valid.
251 let ptr = unsafe { ptr.byte_sub(val_offset) };
252
253 // SAFETY: By the safety requirements we know that `ptr` came from `Arc::into_raw`, so the
254 // reference count held then will be owned by the new `Arc` object.
255 unsafe { Self::from_inner(NonNull::new_unchecked(ptr.cast_mut())) }
256 }
257
258 /// Returns an [`ArcBorrow`] from the given [`Arc`].
259 ///
260 /// This is useful when the argument of a function call is an [`ArcBorrow`] (e.g., in a method
261 /// receiver), but we have an [`Arc`] instead. Getting an [`ArcBorrow`] is free when optimised.
262 #[inline]
263 pub fn as_arc_borrow(&self) -> ArcBorrow<'_, T> {
264 // SAFETY: The constraint that the lifetime of the shared reference must outlive that of
265 // the returned `ArcBorrow` ensures that the object remains alive and that no mutable
266 // reference can be created.
267 unsafe { ArcBorrow::new(self.ptr) }
268 }
269
270 /// Compare whether two [`Arc`] pointers reference the same underlying object.
271 pub fn ptr_eq(this: &Self, other: &Self) -> bool {
272 core::ptr::eq(this.ptr.as_ptr(), other.ptr.as_ptr())
273 }
274}
275
276impl<T: 'static> ForeignOwnable for Arc<T> {
277 type Borrowed<'a> = ArcBorrow<'a, T>;
278
279 fn into_foreign(self) -> *const core::ffi::c_void {
280 ManuallyDrop::new(self).ptr.as_ptr() as _
281 }
282
283 unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> ArcBorrow<'a, T> {
284 // SAFETY: By the safety requirement of this function, we know that `ptr` came from
285 // a previous call to `Arc::into_foreign`.
286 let inner = NonNull::new(ptr as *mut ArcInner<T>).unwrap();
287
288 // SAFETY: The safety requirements of `from_foreign` ensure that the object remains alive
289 // for the lifetime of the returned value.
290 unsafe { ArcBorrow::new(inner) }
291 }
292
293 unsafe fn from_foreign(ptr: *const core::ffi::c_void) -> Self {
294 // SAFETY: By the safety requirement of this function, we know that `ptr` came from
295 // a previous call to `Arc::into_foreign`, which guarantees that `ptr` is valid and
296 // holds a reference count increment that is transferrable to us.
297 unsafe { Self::from_inner(NonNull::new(ptr as _).unwrap()) }
298 }
299}
300
301impl<T: ?Sized> Deref for Arc<T> {
302 type Target = T;
303
304 fn deref(&self) -> &Self::Target {
305 // SAFETY: By the type invariant, there is necessarily a reference to the object, so it is
306 // safe to dereference it.
307 unsafe { &self.ptr.as_ref().data }
308 }
309}
310
311impl<T: ?Sized> AsRef<T> for Arc<T> {
312 fn as_ref(&self) -> &T {
313 self.deref()
314 }
315}
316
317impl<T: ?Sized> Clone for Arc<T> {
318 fn clone(&self) -> Self {
319 // INVARIANT: C `refcount_inc` saturates the refcount, so it cannot overflow to zero.
320 // SAFETY: By the type invariant, there is necessarily a reference to the object, so it is
321 // safe to increment the refcount.
322 unsafe { bindings::refcount_inc(self.ptr.as_ref().refcount.get()) };
323
324 // SAFETY: We just incremented the refcount. This increment is now owned by the new `Arc`.
325 unsafe { Self::from_inner(self.ptr) }
326 }
327}
328
329impl<T: ?Sized> Drop for Arc<T> {
330 fn drop(&mut self) {
331 // SAFETY: By the type invariant, there is necessarily a reference to the object. We cannot
332 // touch `refcount` after it's decremented to a non-zero value because another thread/CPU
333 // may concurrently decrement it to zero and free it. It is ok to have a raw pointer to
334 // freed/invalid memory as long as it is never dereferenced.
335 let refcount = unsafe { self.ptr.as_ref() }.refcount.get();
336
337 // INVARIANT: If the refcount reaches zero, there are no other instances of `Arc`, and
338 // this instance is being dropped, so the broken invariant is not observable.
339 // SAFETY: Also by the type invariant, we are allowed to decrement the refcount.
340 let is_zero = unsafe { bindings::refcount_dec_and_test(refcount) };
341 if is_zero {
342 // The count reached zero, we must free the memory.
343 //
344 // SAFETY: The pointer was initialised from the result of `Box::leak`.
345 unsafe { drop(Box::from_raw(self.ptr.as_ptr())) };
346 }
347 }
348}
349
350impl<T: ?Sized> From<UniqueArc<T>> for Arc<T> {
351 fn from(item: UniqueArc<T>) -> Self {
352 item.inner
353 }
354}
355
356impl<T: ?Sized> From<Pin<UniqueArc<T>>> for Arc<T> {
357 fn from(item: Pin<UniqueArc<T>>) -> Self {
358 // SAFETY: The type invariants of `Arc` guarantee that the data is pinned.
359 unsafe { Pin::into_inner_unchecked(item).inner }
360 }
361}
362
363/// A borrowed reference to an [`Arc`] instance.
364///
365/// For cases when one doesn't ever need to increment the refcount on the allocation, it is simpler
366/// to use just `&T`, which we can trivially get from an [`Arc<T>`] instance.
367///
368/// However, when one may need to increment the refcount, it is preferable to use an `ArcBorrow<T>`
369/// over `&Arc<T>` because the latter results in a double-indirection: a pointer (shared reference)
370/// to a pointer ([`Arc<T>`]) to the object (`T`). An [`ArcBorrow`] eliminates this double
371/// indirection while still allowing one to increment the refcount and getting an [`Arc<T>`] when/if
372/// needed.
373///
374/// # Invariants
375///
376/// There are no mutable references to the underlying [`Arc`], and it remains valid for the
377/// lifetime of the [`ArcBorrow`] instance.
378///
379/// # Example
380///
381/// ```
382/// use kernel::sync::{Arc, ArcBorrow};
383///
384/// struct Example;
385///
386/// fn do_something(e: ArcBorrow<'_, Example>) -> Arc<Example> {
387/// e.into()
388/// }
389///
390/// let obj = Arc::try_new(Example)?;
391/// let cloned = do_something(obj.as_arc_borrow());
392///
393/// // Assert that both `obj` and `cloned` point to the same underlying object.
394/// assert!(core::ptr::eq(&*obj, &*cloned));
395/// # Ok::<(), Error>(())
396/// ```
397///
398/// Using `ArcBorrow<T>` as the type of `self`:
399///
400/// ```
401/// use kernel::sync::{Arc, ArcBorrow};
402///
403/// struct Example {
404/// a: u32,
405/// b: u32,
406/// }
407///
408/// impl Example {
409/// fn use_reference(self: ArcBorrow<'_, Self>) {
410/// // ...
411/// }
412/// }
413///
414/// let obj = Arc::try_new(Example { a: 10, b: 20 })?;
415/// obj.as_arc_borrow().use_reference();
416/// # Ok::<(), Error>(())
417/// ```
418pub struct ArcBorrow<'a, T: ?Sized + 'a> {
419 inner: NonNull<ArcInner<T>>,
420 _p: PhantomData<&'a ()>,
421}
422
423// This is to allow [`ArcBorrow`] (and variants) to be used as the type of `self`.
424impl<T: ?Sized> core::ops::Receiver for ArcBorrow<'_, T> {}
425
426// This is to allow `ArcBorrow<U>` to be dispatched on when `ArcBorrow<T>` can be coerced into
427// `ArcBorrow<U>`.
428impl<T: ?Sized + Unsize<U>, U: ?Sized> core::ops::DispatchFromDyn<ArcBorrow<'_, U>>
429 for ArcBorrow<'_, T>
430{
431}
432
433impl<T: ?Sized> Clone for ArcBorrow<'_, T> {
434 fn clone(&self) -> Self {
435 *self
436 }
437}
438
439impl<T: ?Sized> Copy for ArcBorrow<'_, T> {}
440
441impl<T: ?Sized> ArcBorrow<'_, T> {
442 /// Creates a new [`ArcBorrow`] instance.
443 ///
444 /// # Safety
445 ///
446 /// Callers must ensure the following for the lifetime of the returned [`ArcBorrow`] instance:
447 /// 1. That `inner` remains valid;
448 /// 2. That no mutable references to `inner` are created.
449 unsafe fn new(inner: NonNull<ArcInner<T>>) -> Self {
450 // INVARIANT: The safety requirements guarantee the invariants.
451 Self {
452 inner,
453 _p: PhantomData,
454 }
455 }
456}
457
458impl<T: ?Sized> From<ArcBorrow<'_, T>> for Arc<T> {
459 fn from(b: ArcBorrow<'_, T>) -> Self {
460 // SAFETY: The existence of `b` guarantees that the refcount is non-zero. `ManuallyDrop`
461 // guarantees that `drop` isn't called, so it's ok that the temporary `Arc` doesn't own the
462 // increment.
463 ManuallyDrop::new(unsafe { Arc::from_inner(b.inner) })
464 .deref()
465 .clone()
466 }
467}
468
469impl<T: ?Sized> Deref for ArcBorrow<'_, T> {
470 type Target = T;
471
472 fn deref(&self) -> &Self::Target {
473 // SAFETY: By the type invariant, the underlying object is still alive with no mutable
474 // references to it, so it is safe to create a shared reference.
475 unsafe { &self.inner.as_ref().data }
476 }
477}
478
479/// A refcounted object that is known to have a refcount of 1.
480///
481/// It is mutable and can be converted to an [`Arc`] so that it can be shared.
482///
483/// # Invariants
484///
485/// `inner` always has a reference count of 1.
486///
487/// # Examples
488///
489/// In the following example, we make changes to the inner object before turning it into an
490/// `Arc<Test>` object (after which point, it cannot be mutated directly). Note that `x.into()`
491/// cannot fail.
492///
493/// ```
494/// use kernel::sync::{Arc, UniqueArc};
495///
496/// struct Example {
497/// a: u32,
498/// b: u32,
499/// }
500///
501/// fn test() -> Result<Arc<Example>> {
502/// let mut x = UniqueArc::try_new(Example { a: 10, b: 20 })?;
503/// x.a += 1;
504/// x.b += 1;
505/// Ok(x.into())
506/// }
507///
508/// # test().unwrap();
509/// ```
510///
511/// In the following example we first allocate memory for a refcounted `Example` but we don't
512/// initialise it on allocation. We do initialise it later with a call to [`UniqueArc::write`],
513/// followed by a conversion to `Arc<Example>`. This is particularly useful when allocation happens
514/// in one context (e.g., sleepable) and initialisation in another (e.g., atomic):
515///
516/// ```
517/// use kernel::sync::{Arc, UniqueArc};
518///
519/// struct Example {
520/// a: u32,
521/// b: u32,
522/// }
523///
524/// fn test() -> Result<Arc<Example>> {
525/// let x = UniqueArc::try_new_uninit()?;
526/// Ok(x.write(Example { a: 10, b: 20 }).into())
527/// }
528///
529/// # test().unwrap();
530/// ```
531///
532/// In the last example below, the caller gets a pinned instance of `Example` while converting to
533/// `Arc<Example>`; this is useful in scenarios where one needs a pinned reference during
534/// initialisation, for example, when initialising fields that are wrapped in locks.
535///
536/// ```
537/// use kernel::sync::{Arc, UniqueArc};
538///
539/// struct Example {
540/// a: u32,
541/// b: u32,
542/// }
543///
544/// fn test() -> Result<Arc<Example>> {
545/// let mut pinned = Pin::from(UniqueArc::try_new(Example { a: 10, b: 20 })?);
546/// // We can modify `pinned` because it is `Unpin`.
547/// pinned.as_mut().a += 1;
548/// Ok(pinned.into())
549/// }
550///
551/// # test().unwrap();
552/// ```
553pub struct UniqueArc<T: ?Sized> {
554 inner: Arc<T>,
555}
556
557impl<T> UniqueArc<T> {
558 /// Tries to allocate a new [`UniqueArc`] instance.
559 pub fn try_new(value: T) -> Result<Self, AllocError> {
560 Ok(Self {
561 // INVARIANT: The newly-created object has a refcount of 1.
562 inner: Arc::try_new(value)?,
563 })
564 }
565
566 /// Tries to allocate a new [`UniqueArc`] instance whose contents are not initialised yet.
567 pub fn try_new_uninit() -> Result<UniqueArc<MaybeUninit<T>>, AllocError> {
568 // INVARIANT: The refcount is initialised to a non-zero value.
569 let inner = Box::try_init::<AllocError>(try_init!(ArcInner {
570 // SAFETY: There are no safety requirements for this FFI call.
571 refcount: Opaque::new(unsafe { bindings::REFCOUNT_INIT(1) }),
572 data <- init::uninit::<T, AllocError>(),
573 }? AllocError))?;
574 Ok(UniqueArc {
575 // INVARIANT: The newly-created object has a refcount of 1.
576 // SAFETY: The pointer from the `Box` is valid.
577 inner: unsafe { Arc::from_inner(Box::leak(inner).into()) },
578 })
579 }
580}
581
582impl<T> UniqueArc<MaybeUninit<T>> {
583 /// Converts a `UniqueArc<MaybeUninit<T>>` into a `UniqueArc<T>` by writing a value into it.
584 pub fn write(mut self, value: T) -> UniqueArc<T> {
585 self.deref_mut().write(value);
586 // SAFETY: We just wrote the value to be initialized.
587 unsafe { self.assume_init() }
588 }
589
590 /// Unsafely assume that `self` is initialized.
591 ///
592 /// # Safety
593 ///
594 /// The caller guarantees that the value behind this pointer has been initialized. It is
595 /// *immediate* UB to call this when the value is not initialized.
596 pub unsafe fn assume_init(self) -> UniqueArc<T> {
597 let inner = ManuallyDrop::new(self).inner.ptr;
598 UniqueArc {
599 // SAFETY: The new `Arc` is taking over `ptr` from `self.inner` (which won't be
600 // dropped). The types are compatible because `MaybeUninit<T>` is compatible with `T`.
601 inner: unsafe { Arc::from_inner(inner.cast()) },
602 }
603 }
604
605 /// Initialize `self` using the given initializer.
606 pub fn init_with<E>(mut self, init: impl Init<T, E>) -> core::result::Result<UniqueArc<T>, E> {
607 // SAFETY: The supplied pointer is valid for initialization.
608 match unsafe { init.__init(self.as_mut_ptr()) } {
609 // SAFETY: Initialization completed successfully.
610 Ok(()) => Ok(unsafe { self.assume_init() }),
611 Err(err) => Err(err),
612 }
613 }
614
615 /// Pin-initialize `self` using the given pin-initializer.
616 pub fn pin_init_with<E>(
617 mut self,
618 init: impl PinInit<T, E>,
619 ) -> core::result::Result<Pin<UniqueArc<T>>, E> {
620 // SAFETY: The supplied pointer is valid for initialization and we will later pin the value
621 // to ensure it does not move.
622 match unsafe { init.__pinned_init(self.as_mut_ptr()) } {
623 // SAFETY: Initialization completed successfully.
624 Ok(()) => Ok(unsafe { self.assume_init() }.into()),
625 Err(err) => Err(err),
626 }
627 }
628}
629
630impl<T: ?Sized> From<UniqueArc<T>> for Pin<UniqueArc<T>> {
631 fn from(obj: UniqueArc<T>) -> Self {
632 // SAFETY: It is not possible to move/replace `T` inside a `Pin<UniqueArc<T>>` (unless `T`
633 // is `Unpin`), so it is ok to convert it to `Pin<UniqueArc<T>>`.
634 unsafe { Pin::new_unchecked(obj) }
635 }
636}
637
638impl<T: ?Sized> Deref for UniqueArc<T> {
639 type Target = T;
640
641 fn deref(&self) -> &Self::Target {
642 self.inner.deref()
643 }
644}
645
646impl<T: ?Sized> DerefMut for UniqueArc<T> {
647 fn deref_mut(&mut self) -> &mut Self::Target {
648 // SAFETY: By the `Arc` type invariant, there is necessarily a reference to the object, so
649 // it is safe to dereference it. Additionally, we know there is only one reference when
650 // it's inside a `UniqueArc`, so it is safe to get a mutable reference.
651 unsafe { &mut self.inner.ptr.as_mut().data }
652 }
653}
654
655impl<T: fmt::Display + ?Sized> fmt::Display for UniqueArc<T> {
656 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
657 fmt::Display::fmt(self.deref(), f)
658 }
659}
660
661impl<T: fmt::Display + ?Sized> fmt::Display for Arc<T> {
662 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
663 fmt::Display::fmt(self.deref(), f)
664 }
665}
666
667impl<T: fmt::Debug + ?Sized> fmt::Debug for UniqueArc<T> {
668 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
669 fmt::Debug::fmt(self.deref(), f)
670 }
671}
672
673impl<T: fmt::Debug + ?Sized> fmt::Debug for Arc<T> {
674 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
675 fmt::Debug::fmt(self.deref(), f)
676 }
677}