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85aaf69f | 1 | #![stable(feature = "rust1", since = "1.0.0")] |
1a4d82fc | 2 | |
c30ab7b3 | 3 | //! Thread-safe reference-counting pointers. |
1a4d82fc | 4 | //! |
3dfed10e | 5 | //! See the [`Arc<T>`][Arc] documentation for more details. |
1a4d82fc | 6 | |
94b46f34 | 7 | use core::any::Any; |
e9174d1e | 8 | use core::borrow; |
60c5eb7d | 9 | use core::cmp::Ordering; |
dfeec247 XL |
10 | use core::convert::{From, TryFrom}; |
11 | use core::fmt; | |
12 | use core::hash::{Hash, Hasher}; | |
29967ef6 | 13 | use core::hint; |
92a42be0 | 14 | use core::intrinsics::abort; |
dfeec247 XL |
15 | use core::iter; |
16 | use core::marker::{PhantomData, Unpin, Unsize}; | |
5869c6ff | 17 | use core::mem::{self, align_of_val_raw, size_of_val}; |
dfeec247 | 18 | use core::ops::{CoerceUnsized, Deref, DispatchFromDyn, Receiver}; |
0bf4aa26 | 19 | use core::pin::Pin; |
2c00a5a8 | 20 | use core::ptr::{self, NonNull}; |
f9f354fc | 21 | use core::slice::from_raw_parts_mut; |
dfeec247 XL |
22 | use core::sync::atomic; |
23 | use core::sync::atomic::Ordering::{Acquire, Relaxed, Release, SeqCst}; | |
041b39d2 | 24 | |
5869c6ff XL |
25 | use crate::alloc::{ |
26 | box_free, handle_alloc_error, AllocError, Allocator, Global, Layout, WriteCloneIntoRaw, | |
27 | }; | |
f9f354fc | 28 | use crate::borrow::{Cow, ToOwned}; |
9fa01778 XL |
29 | use crate::boxed::Box; |
30 | use crate::rc::is_dangling; | |
31 | use crate::string::String; | |
32 | use crate::vec::Vec; | |
1a4d82fc | 33 | |
416331ca XL |
34 | #[cfg(test)] |
35 | mod tests; | |
36 | ||
c30ab7b3 SL |
37 | /// A soft limit on the amount of references that may be made to an `Arc`. |
38 | /// | |
39 | /// Going above this limit will abort your program (although not | |
40 | /// necessarily) at _exactly_ `MAX_REFCOUNT + 1` references. | |
c1a9b12d SL |
41 | const MAX_REFCOUNT: usize = (isize::MAX) as usize; |
42 | ||
ba9703b0 XL |
43 | #[cfg(not(sanitize = "thread"))] |
44 | macro_rules! acquire { | |
45 | ($x:expr) => { | |
46 | atomic::fence(Acquire) | |
47 | }; | |
48 | } | |
49 | ||
50 | // ThreadSanitizer does not support memory fences. To avoid false positive | |
51 | // reports in Arc / Weak implementation use atomic loads for synchronization | |
52 | // instead. | |
53 | #[cfg(sanitize = "thread")] | |
54 | macro_rules! acquire { | |
55 | ($x:expr) => { | |
56 | $x.load(Acquire) | |
57 | }; | |
58 | } | |
59 | ||
041b39d2 XL |
60 | /// A thread-safe reference-counting pointer. 'Arc' stands for 'Atomically |
61 | /// Reference Counted'. | |
1a4d82fc | 62 | /// |
c30ab7b3 SL |
63 | /// The type `Arc<T>` provides shared ownership of a value of type `T`, |
64 | /// allocated in the heap. Invoking [`clone`][clone] on `Arc` produces | |
e74abb32 | 65 | /// a new `Arc` instance, which points to the same allocation on the heap as the |
b7449926 | 66 | /// source `Arc`, while increasing a reference count. When the last `Arc` |
e74abb32 XL |
67 | /// pointer to a given allocation is destroyed, the value stored in that allocation (often |
68 | /// referred to as "inner value") is also dropped. | |
1a4d82fc | 69 | /// |
c30ab7b3 | 70 | /// Shared references in Rust disallow mutation by default, and `Arc` is no |
ea8adc8c XL |
71 | /// exception: you cannot generally obtain a mutable reference to something |
72 | /// inside an `Arc`. If you need to mutate through an `Arc`, use | |
73 | /// [`Mutex`][mutex], [`RwLock`][rwlock], or one of the [`Atomic`][atomic] | |
74 | /// types. | |
9e0c209e | 75 | /// |
7cac9316 XL |
76 | /// ## Thread Safety |
77 | /// | |
78 | /// Unlike [`Rc<T>`], `Arc<T>` uses atomic operations for its reference | |
83c7162d | 79 | /// counting. This means that it is thread-safe. The disadvantage is that |
7cac9316 | 80 | /// atomic operations are more expensive than ordinary memory accesses. If you |
e74abb32 | 81 | /// are not sharing reference-counted allocations between threads, consider using |
7cac9316 XL |
82 | /// [`Rc<T>`] for lower overhead. [`Rc<T>`] is a safe default, because the |
83 | /// compiler will catch any attempt to send an [`Rc<T>`] between threads. | |
84 | /// However, a library might choose `Arc<T>` in order to give library consumers | |
c30ab7b3 | 85 | /// more flexibility. |
1a4d82fc | 86 | /// |
7cac9316 XL |
87 | /// `Arc<T>` will implement [`Send`] and [`Sync`] as long as the `T` implements |
88 | /// [`Send`] and [`Sync`]. Why can't you put a non-thread-safe type `T` in an | |
89 | /// `Arc<T>` to make it thread-safe? This may be a bit counter-intuitive at | |
90 | /// first: after all, isn't the point of `Arc<T>` thread safety? The key is | |
91 | /// this: `Arc<T>` makes it thread safe to have multiple ownership of the same | |
92 | /// data, but it doesn't add thread safety to its data. Consider | |
ea8adc8c XL |
93 | /// `Arc<`[`RefCell<T>`]`>`. [`RefCell<T>`] isn't [`Sync`], and if `Arc<T>` was always |
94 | /// [`Send`], `Arc<`[`RefCell<T>`]`>` would be as well. But then we'd have a problem: | |
95 | /// [`RefCell<T>`] is not thread safe; it keeps track of the borrowing count using | |
7cac9316 XL |
96 | /// non-atomic operations. |
97 | /// | |
98 | /// In the end, this means that you may need to pair `Arc<T>` with some sort of | |
ea8adc8c | 99 | /// [`std::sync`] type, usually [`Mutex<T>`][mutex]. |
7cac9316 XL |
100 | /// |
101 | /// ## Breaking cycles with `Weak` | |
102 | /// | |
c30ab7b3 | 103 | /// The [`downgrade`][downgrade] method can be used to create a non-owning |
3dfed10e | 104 | /// [`Weak`] pointer. A [`Weak`] pointer can be [`upgrade`][upgrade]d |
e74abb32 XL |
105 | /// to an `Arc`, but this will return [`None`] if the value stored in the allocation has |
106 | /// already been dropped. In other words, `Weak` pointers do not keep the value | |
107 | /// inside the allocation alive; however, they *do* keep the allocation | |
108 | /// (the backing store for the value) alive. | |
c30ab7b3 SL |
109 | /// |
110 | /// A cycle between `Arc` pointers will never be deallocated. For this reason, | |
3dfed10e XL |
111 | /// [`Weak`] is used to break cycles. For example, a tree could have |
112 | /// strong `Arc` pointers from parent nodes to children, and [`Weak`] | |
32a655c1 | 113 | /// pointers from children back to their parents. |
c30ab7b3 | 114 | /// |
7cac9316 XL |
115 | /// # Cloning references |
116 | /// | |
1b1a35ee | 117 | /// Creating a new reference from an existing reference-counted pointer is done using the |
3dfed10e | 118 | /// `Clone` trait implemented for [`Arc<T>`][Arc] and [`Weak<T>`][Weak]. |
7cac9316 XL |
119 | /// |
120 | /// ``` | |
121 | /// use std::sync::Arc; | |
122 | /// let foo = Arc::new(vec![1.0, 2.0, 3.0]); | |
123 | /// // The two syntaxes below are equivalent. | |
124 | /// let a = foo.clone(); | |
125 | /// let b = Arc::clone(&foo); | |
b7449926 | 126 | /// // a, b, and foo are all Arcs that point to the same memory location |
7cac9316 XL |
127 | /// ``` |
128 | /// | |
7cac9316 XL |
129 | /// ## `Deref` behavior |
130 | /// | |
c30ab7b3 SL |
131 | /// `Arc<T>` automatically dereferences to `T` (via the [`Deref`][deref] trait), |
132 | /// so you can call `T`'s methods on a value of type `Arc<T>`. To avoid name | |
13cf67c4 | 133 | /// clashes with `T`'s methods, the methods of `Arc<T>` itself are associated |
29967ef6 | 134 | /// functions, called using [fully qualified syntax]: |
c34b1796 AL |
135 | /// |
136 | /// ``` | |
1a4d82fc | 137 | /// use std::sync::Arc; |
1a4d82fc | 138 | /// |
29967ef6 | 139 | /// let my_arc = Arc::new(()); |
c30ab7b3 SL |
140 | /// Arc::downgrade(&my_arc); |
141 | /// ``` | |
1a4d82fc | 142 | /// |
29967ef6 XL |
143 | /// `Arc<T>`'s implementations of traits like `Clone` may also be called using |
144 | /// fully qualified syntax. Some people prefer to use fully qualified syntax, | |
145 | /// while others prefer using method-call syntax. | |
146 | /// | |
147 | /// ``` | |
148 | /// use std::sync::Arc; | |
149 | /// | |
150 | /// let arc = Arc::new(()); | |
151 | /// // Method-call syntax | |
152 | /// let arc2 = arc.clone(); | |
153 | /// // Fully qualified syntax | |
154 | /// let arc3 = Arc::clone(&arc); | |
155 | /// ``` | |
156 | /// | |
3dfed10e | 157 | /// [`Weak<T>`][Weak] does not auto-dereference to `T`, because the inner value may have |
e74abb32 | 158 | /// already been dropped. |
1a4d82fc | 159 | /// |
3dfed10e XL |
160 | /// [`Rc<T>`]: crate::rc::Rc |
161 | /// [clone]: Clone::clone | |
c30ab7b3 SL |
162 | /// [mutex]: ../../std/sync/struct.Mutex.html |
163 | /// [rwlock]: ../../std/sync/struct.RwLock.html | |
3dfed10e XL |
164 | /// [atomic]: core::sync::atomic |
165 | /// [`Send`]: core::marker::Send | |
166 | /// [`Sync`]: core::marker::Sync | |
167 | /// [deref]: core::ops::Deref | |
168 | /// [downgrade]: Arc::downgrade | |
169 | /// [upgrade]: Weak::upgrade | |
170 | /// [`RefCell<T>`]: core::cell::RefCell | |
ea8adc8c | 171 | /// [`std::sync`]: ../../std/sync/index.html |
1b1a35ee | 172 | /// [`Arc::clone(&from)`]: Arc::clone |
29967ef6 | 173 | /// [fully qualified syntax]: https://doc.rust-lang.org/book/ch19-03-advanced-traits.html#fully-qualified-syntax-for-disambiguation-calling-methods-with-the-same-name |
1a4d82fc | 174 | /// |
c30ab7b3 | 175 | /// # Examples |
5bcae85e | 176 | /// |
c30ab7b3 SL |
177 | /// Sharing some immutable data between threads: |
178 | /// | |
179 | // Note that we **do not** run these tests here. The windows builders get super | |
180 | // unhappy if a thread outlives the main thread and then exits at the same time | |
181 | // (something deadlocks) so we just avoid this entirely by not running these | |
182 | // tests. | |
5bcae85e | 183 | /// ```no_run |
c30ab7b3 | 184 | /// use std::sync::Arc; |
5bcae85e SL |
185 | /// use std::thread; |
186 | /// | |
c30ab7b3 | 187 | /// let five = Arc::new(5); |
5bcae85e SL |
188 | /// |
189 | /// for _ in 0..10 { | |
7cac9316 | 190 | /// let five = Arc::clone(&five); |
5bcae85e SL |
191 | /// |
192 | /// thread::spawn(move || { | |
c30ab7b3 SL |
193 | /// println!("{:?}", five); |
194 | /// }); | |
195 | /// } | |
196 | /// ``` | |
5bcae85e | 197 | /// |
32a655c1 SL |
198 | /// Sharing a mutable [`AtomicUsize`]: |
199 | /// | |
3dfed10e | 200 | /// [`AtomicUsize`]: core::sync::atomic::AtomicUsize |
5bcae85e | 201 | /// |
c30ab7b3 SL |
202 | /// ```no_run |
203 | /// use std::sync::Arc; | |
204 | /// use std::sync::atomic::{AtomicUsize, Ordering}; | |
205 | /// use std::thread; | |
206 | /// | |
207 | /// let val = Arc::new(AtomicUsize::new(5)); | |
208 | /// | |
209 | /// for _ in 0..10 { | |
7cac9316 | 210 | /// let val = Arc::clone(&val); |
c30ab7b3 SL |
211 | /// |
212 | /// thread::spawn(move || { | |
213 | /// let v = val.fetch_add(1, Ordering::SeqCst); | |
214 | /// println!("{:?}", v); | |
5bcae85e SL |
215 | /// }); |
216 | /// } | |
217 | /// ``` | |
c30ab7b3 SL |
218 | /// |
219 | /// See the [`rc` documentation][rc_examples] for more examples of reference | |
220 | /// counting in general. | |
221 | /// | |
1b1a35ee | 222 | /// [rc_examples]: crate::rc#examples |
ba9703b0 | 223 | #[cfg_attr(not(test), rustc_diagnostic_item = "Arc")] |
85aaf69f | 224 | #[stable(feature = "rust1", since = "1.0.0")] |
62682a34 | 225 | pub struct Arc<T: ?Sized> { |
2c00a5a8 | 226 | ptr: NonNull<ArcInner<T>>, |
60c5eb7d | 227 | phantom: PhantomData<ArcInner<T>>, |
1a4d82fc JJ |
228 | } |
229 | ||
92a42be0 SL |
230 | #[stable(feature = "rust1", since = "1.0.0")] |
231 | unsafe impl<T: ?Sized + Sync + Send> Send for Arc<T> {} | |
232 | #[stable(feature = "rust1", since = "1.0.0")] | |
233 | unsafe impl<T: ?Sized + Sync + Send> Sync for Arc<T> {} | |
1a4d82fc | 234 | |
92a42be0 | 235 | #[unstable(feature = "coerce_unsized", issue = "27732")] |
62682a34 | 236 | impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Arc<U>> for Arc<T> {} |
1a4d82fc | 237 | |
dfeec247 | 238 | #[unstable(feature = "dispatch_from_dyn", issue = "none")] |
a1dfa0c6 XL |
239 | impl<T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<Arc<U>> for Arc<T> {} |
240 | ||
416331ca XL |
241 | impl<T: ?Sized> Arc<T> { |
242 | fn from_inner(ptr: NonNull<ArcInner<T>>) -> Self { | |
dfeec247 | 243 | Self { ptr, phantom: PhantomData } |
416331ca XL |
244 | } |
245 | ||
246 | unsafe fn from_ptr(ptr: *mut ArcInner<T>) -> Self { | |
f035d41b | 247 | unsafe { Self::from_inner(NonNull::new_unchecked(ptr)) } |
416331ca XL |
248 | } |
249 | } | |
250 | ||
cc61c64b | 251 | /// `Weak` is a version of [`Arc`] that holds a non-owning reference to the |
e74abb32 | 252 | /// managed allocation. The allocation is accessed by calling [`upgrade`] on the `Weak` |
cc61c64b | 253 | /// pointer, which returns an [`Option`]`<`[`Arc`]`<T>>`. |
1a4d82fc | 254 | /// |
cc61c64b | 255 | /// Since a `Weak` reference does not count towards ownership, it will not |
e74abb32 XL |
256 | /// prevent the value stored in the allocation from being dropped, and `Weak` itself makes no |
257 | /// guarantees about the value still being present. Thus it may return [`None`] | |
258 | /// when [`upgrade`]d. Note however that a `Weak` reference *does* prevent the allocation | |
259 | /// itself (the backing store) from being deallocated. | |
5bcae85e | 260 | /// |
e74abb32 XL |
261 | /// A `Weak` pointer is useful for keeping a temporary reference to the allocation |
262 | /// managed by [`Arc`] without preventing its inner value from being dropped. It is also used to | |
263 | /// prevent circular references between [`Arc`] pointers, since mutual owning references | |
cc61c64b XL |
264 | /// would never allow either [`Arc`] to be dropped. For example, a tree could |
265 | /// have strong [`Arc`] pointers from parent nodes to children, and `Weak` | |
266 | /// pointers from children back to their parents. | |
5bcae85e | 267 | /// |
cc61c64b | 268 | /// The typical way to obtain a `Weak` pointer is to call [`Arc::downgrade`]. |
c30ab7b3 | 269 | /// |
3dfed10e | 270 | /// [`upgrade`]: Weak::upgrade |
e9174d1e | 271 | #[stable(feature = "arc_weak", since = "1.4.0")] |
62682a34 | 272 | pub struct Weak<T: ?Sized> { |
8faf50e0 XL |
273 | // This is a `NonNull` to allow optimizing the size of this type in enums, |
274 | // but it is not necessarily a valid pointer. | |
275 | // `Weak::new` sets this to `usize::MAX` so that it doesn’t need | |
276 | // to allocate space on the heap. That's not a value a real pointer | |
277 | // will ever have because RcBox has alignment at least 2. | |
f035d41b | 278 | // This is only possible when `T: Sized`; unsized `T` never dangle. |
2c00a5a8 | 279 | ptr: NonNull<ArcInner<T>>, |
1a4d82fc JJ |
280 | } |
281 | ||
7453a54e | 282 | #[stable(feature = "arc_weak", since = "1.4.0")] |
92a42be0 | 283 | unsafe impl<T: ?Sized + Sync + Send> Send for Weak<T> {} |
7453a54e | 284 | #[stable(feature = "arc_weak", since = "1.4.0")] |
92a42be0 | 285 | unsafe impl<T: ?Sized + Sync + Send> Sync for Weak<T> {} |
1a4d82fc | 286 | |
92a42be0 | 287 | #[unstable(feature = "coerce_unsized", issue = "27732")] |
c1a9b12d | 288 | impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Weak<U>> for Weak<T> {} |
dfeec247 | 289 | #[unstable(feature = "dispatch_from_dyn", issue = "none")] |
a1dfa0c6 | 290 | impl<T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<Weak<U>> for Weak<T> {} |
c1a9b12d | 291 | |
7453a54e | 292 | #[stable(feature = "arc_weak", since = "1.4.0")] |
62682a34 | 293 | impl<T: ?Sized + fmt::Debug> fmt::Debug for Weak<T> { |
9fa01778 | 294 | fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
c34b1796 AL |
295 | write!(f, "(Weak)") |
296 | } | |
297 | } | |
298 | ||
ba9703b0 XL |
299 | // This is repr(C) to future-proof against possible field-reordering, which |
300 | // would interfere with otherwise safe [into|from]_raw() of transmutable | |
301 | // inner types. | |
302 | #[repr(C)] | |
62682a34 | 303 | struct ArcInner<T: ?Sized> { |
85aaf69f | 304 | strong: atomic::AtomicUsize, |
c1a9b12d SL |
305 | |
306 | // the value usize::MAX acts as a sentinel for temporarily "locking" the | |
307 | // ability to upgrade weak pointers or downgrade strong ones; this is used | |
e9174d1e | 308 | // to avoid races in `make_mut` and `get_mut`. |
85aaf69f | 309 | weak: atomic::AtomicUsize, |
c1a9b12d | 310 | |
1a4d82fc JJ |
311 | data: T, |
312 | } | |
313 | ||
62682a34 SL |
314 | unsafe impl<T: ?Sized + Sync + Send> Send for ArcInner<T> {} |
315 | unsafe impl<T: ?Sized + Sync + Send> Sync for ArcInner<T> {} | |
1a4d82fc JJ |
316 | |
317 | impl<T> Arc<T> { | |
318 | /// Constructs a new `Arc<T>`. | |
319 | /// | |
320 | /// # Examples | |
321 | /// | |
322 | /// ``` | |
323 | /// use std::sync::Arc; | |
324 | /// | |
85aaf69f | 325 | /// let five = Arc::new(5); |
1a4d82fc JJ |
326 | /// ``` |
327 | #[inline] | |
85aaf69f | 328 | #[stable(feature = "rust1", since = "1.0.0")] |
1a4d82fc JJ |
329 | pub fn new(data: T) -> Arc<T> { |
330 | // Start the weak pointer count as 1 which is the weak pointer that's | |
331 | // held by all the strong pointers (kinda), see std/rc.rs for more info | |
c34b1796 | 332 | let x: Box<_> = box ArcInner { |
85aaf69f SL |
333 | strong: atomic::AtomicUsize::new(1), |
334 | weak: atomic::AtomicUsize::new(1), | |
3b2f2976 | 335 | data, |
1a4d82fc | 336 | }; |
f9f354fc | 337 | Self::from_inner(Box::leak(x).into()) |
e9174d1e SL |
338 | } |
339 | ||
3dfed10e XL |
340 | /// Constructs a new `Arc<T>` using a weak reference to itself. Attempting |
341 | /// to upgrade the weak reference before this function returns will result | |
342 | /// in a `None` value. However, the weak reference may be cloned freely and | |
343 | /// stored for use at a later time. | |
344 | /// | |
345 | /// # Examples | |
346 | /// ``` | |
347 | /// #![feature(arc_new_cyclic)] | |
348 | /// #![allow(dead_code)] | |
349 | /// | |
350 | /// use std::sync::{Arc, Weak}; | |
351 | /// | |
352 | /// struct Foo { | |
353 | /// me: Weak<Foo>, | |
354 | /// } | |
355 | /// | |
356 | /// let foo = Arc::new_cyclic(|me| Foo { | |
357 | /// me: me.clone(), | |
358 | /// }); | |
359 | /// ``` | |
360 | #[inline] | |
361 | #[unstable(feature = "arc_new_cyclic", issue = "75861")] | |
362 | pub fn new_cyclic(data_fn: impl FnOnce(&Weak<T>) -> T) -> Arc<T> { | |
363 | // Construct the inner in the "uninitialized" state with a single | |
364 | // weak reference. | |
365 | let uninit_ptr: NonNull<_> = Box::leak(box ArcInner { | |
366 | strong: atomic::AtomicUsize::new(0), | |
367 | weak: atomic::AtomicUsize::new(1), | |
368 | data: mem::MaybeUninit::<T>::uninit(), | |
369 | }) | |
370 | .into(); | |
371 | let init_ptr: NonNull<ArcInner<T>> = uninit_ptr.cast(); | |
372 | ||
373 | let weak = Weak { ptr: init_ptr }; | |
374 | ||
375 | // It's important we don't give up ownership of the weak pointer, or | |
376 | // else the memory might be freed by the time `data_fn` returns. If | |
377 | // we really wanted to pass ownership, we could create an additional | |
378 | // weak pointer for ourselves, but this would result in additional | |
379 | // updates to the weak reference count which might not be necessary | |
380 | // otherwise. | |
381 | let data = data_fn(&weak); | |
382 | ||
383 | // Now we can properly initialize the inner value and turn our weak | |
384 | // reference into a strong reference. | |
385 | unsafe { | |
386 | let inner = init_ptr.as_ptr(); | |
5869c6ff | 387 | ptr::write(ptr::addr_of_mut!((*inner).data), data); |
3dfed10e XL |
388 | |
389 | // The above write to the data field must be visible to any threads which | |
390 | // observe a non-zero strong count. Therefore we need at least "Release" ordering | |
391 | // in order to synchronize with the `compare_exchange_weak` in `Weak::upgrade`. | |
392 | // | |
393 | // "Acquire" ordering is not required. When considering the possible behaviours | |
394 | // of `data_fn` we only need to look at what it could do with a reference to a | |
395 | // non-upgradeable `Weak`: | |
396 | // - It can *clone* the `Weak`, increasing the weak reference count. | |
397 | // - It can drop those clones, decreasing the weak reference count (but never to zero). | |
398 | // | |
399 | // These side effects do not impact us in any way, and no other side effects are | |
400 | // possible with safe code alone. | |
401 | let prev_value = (*inner).strong.fetch_add(1, Release); | |
402 | debug_assert_eq!(prev_value, 0, "No prior strong references should exist"); | |
403 | } | |
404 | ||
405 | let strong = Arc::from_inner(init_ptr); | |
406 | ||
407 | // Strong references should collectively own a shared weak reference, | |
408 | // so don't run the destructor for our old weak reference. | |
409 | mem::forget(weak); | |
410 | strong | |
411 | } | |
412 | ||
e1599b0c XL |
413 | /// Constructs a new `Arc` with uninitialized contents. |
414 | /// | |
415 | /// # Examples | |
416 | /// | |
417 | /// ``` | |
418 | /// #![feature(new_uninit)] | |
419 | /// #![feature(get_mut_unchecked)] | |
420 | /// | |
421 | /// use std::sync::Arc; | |
422 | /// | |
423 | /// let mut five = Arc::<u32>::new_uninit(); | |
424 | /// | |
425 | /// let five = unsafe { | |
426 | /// // Deferred initialization: | |
427 | /// Arc::get_mut_unchecked(&mut five).as_mut_ptr().write(5); | |
428 | /// | |
429 | /// five.assume_init() | |
430 | /// }; | |
431 | /// | |
432 | /// assert_eq!(*five, 5) | |
433 | /// ``` | |
434 | #[unstable(feature = "new_uninit", issue = "63291")] | |
435 | pub fn new_uninit() -> Arc<mem::MaybeUninit<T>> { | |
436 | unsafe { | |
3dfed10e XL |
437 | Arc::from_ptr(Arc::allocate_for_layout( |
438 | Layout::new::<T>(), | |
fc512014 | 439 | |layout| Global.allocate(layout), |
3dfed10e XL |
440 | |mem| mem as *mut ArcInner<mem::MaybeUninit<T>>, |
441 | )) | |
e1599b0c XL |
442 | } |
443 | } | |
444 | ||
60c5eb7d XL |
445 | /// Constructs a new `Arc` with uninitialized contents, with the memory |
446 | /// being filled with `0` bytes. | |
447 | /// | |
448 | /// See [`MaybeUninit::zeroed`][zeroed] for examples of correct and incorrect usage | |
449 | /// of this method. | |
450 | /// | |
451 | /// # Examples | |
452 | /// | |
453 | /// ``` | |
454 | /// #![feature(new_uninit)] | |
455 | /// | |
456 | /// use std::sync::Arc; | |
457 | /// | |
458 | /// let zero = Arc::<u32>::new_zeroed(); | |
459 | /// let zero = unsafe { zero.assume_init() }; | |
460 | /// | |
461 | /// assert_eq!(*zero, 0) | |
462 | /// ``` | |
463 | /// | |
464 | /// [zeroed]: ../../std/mem/union.MaybeUninit.html#method.zeroed | |
465 | #[unstable(feature = "new_uninit", issue = "63291")] | |
466 | pub fn new_zeroed() -> Arc<mem::MaybeUninit<T>> { | |
467 | unsafe { | |
3dfed10e XL |
468 | Arc::from_ptr(Arc::allocate_for_layout( |
469 | Layout::new::<T>(), | |
fc512014 | 470 | |layout| Global.allocate_zeroed(layout), |
3dfed10e XL |
471 | |mem| mem as *mut ArcInner<mem::MaybeUninit<T>>, |
472 | )) | |
60c5eb7d XL |
473 | } |
474 | } | |
475 | ||
0731742a XL |
476 | /// Constructs a new `Pin<Arc<T>>`. If `T` does not implement `Unpin`, then |
477 | /// `data` will be pinned in memory and unable to be moved. | |
478 | #[stable(feature = "pin", since = "1.33.0")] | |
479 | pub fn pin(data: T) -> Pin<Arc<T>> { | |
0bf4aa26 XL |
480 | unsafe { Pin::new_unchecked(Arc::new(data)) } |
481 | } | |
482 | ||
5869c6ff XL |
483 | /// Constructs a new `Arc<T>`, returning an error if allocation fails. |
484 | /// | |
485 | /// # Examples | |
486 | /// | |
487 | /// ``` | |
488 | /// #![feature(allocator_api)] | |
489 | /// use std::sync::Arc; | |
490 | /// | |
491 | /// let five = Arc::try_new(5)?; | |
492 | /// # Ok::<(), std::alloc::AllocError>(()) | |
493 | /// ``` | |
494 | #[unstable(feature = "allocator_api", issue = "32838")] | |
495 | #[inline] | |
496 | pub fn try_new(data: T) -> Result<Arc<T>, AllocError> { | |
497 | // Start the weak pointer count as 1 which is the weak pointer that's | |
498 | // held by all the strong pointers (kinda), see std/rc.rs for more info | |
499 | let x: Box<_> = Box::try_new(ArcInner { | |
500 | strong: atomic::AtomicUsize::new(1), | |
501 | weak: atomic::AtomicUsize::new(1), | |
502 | data, | |
503 | })?; | |
504 | Ok(Self::from_inner(Box::leak(x).into())) | |
505 | } | |
506 | ||
507 | /// Constructs a new `Arc` with uninitialized contents, returning an error | |
508 | /// if allocation fails. | |
509 | /// | |
510 | /// # Examples | |
511 | /// | |
512 | /// ``` | |
513 | /// #![feature(new_uninit, allocator_api)] | |
514 | /// #![feature(get_mut_unchecked)] | |
515 | /// | |
516 | /// use std::sync::Arc; | |
517 | /// | |
518 | /// let mut five = Arc::<u32>::try_new_uninit()?; | |
519 | /// | |
520 | /// let five = unsafe { | |
521 | /// // Deferred initialization: | |
522 | /// Arc::get_mut_unchecked(&mut five).as_mut_ptr().write(5); | |
523 | /// | |
524 | /// five.assume_init() | |
525 | /// }; | |
526 | /// | |
527 | /// assert_eq!(*five, 5); | |
528 | /// # Ok::<(), std::alloc::AllocError>(()) | |
529 | /// ``` | |
530 | #[unstable(feature = "allocator_api", issue = "32838")] | |
531 | // #[unstable(feature = "new_uninit", issue = "63291")] | |
532 | pub fn try_new_uninit() -> Result<Arc<mem::MaybeUninit<T>>, AllocError> { | |
533 | unsafe { | |
534 | Ok(Arc::from_ptr(Arc::try_allocate_for_layout( | |
535 | Layout::new::<T>(), | |
536 | |layout| Global.allocate(layout), | |
537 | |mem| mem as *mut ArcInner<mem::MaybeUninit<T>>, | |
538 | )?)) | |
539 | } | |
540 | } | |
541 | ||
542 | /// Constructs a new `Arc` with uninitialized contents, with the memory | |
543 | /// being filled with `0` bytes, returning an error if allocation fails. | |
544 | /// | |
545 | /// See [`MaybeUninit::zeroed`][zeroed] for examples of correct and incorrect usage | |
546 | /// of this method. | |
547 | /// | |
548 | /// # Examples | |
549 | /// | |
550 | /// ``` | |
551 | /// #![feature(new_uninit, allocator_api)] | |
552 | /// | |
553 | /// use std::sync::Arc; | |
554 | /// | |
555 | /// let zero = Arc::<u32>::try_new_zeroed()?; | |
556 | /// let zero = unsafe { zero.assume_init() }; | |
557 | /// | |
558 | /// assert_eq!(*zero, 0); | |
559 | /// # Ok::<(), std::alloc::AllocError>(()) | |
560 | /// ``` | |
561 | /// | |
562 | /// [zeroed]: mem::MaybeUninit::zeroed | |
563 | #[unstable(feature = "allocator_api", issue = "32838")] | |
564 | // #[unstable(feature = "new_uninit", issue = "63291")] | |
565 | pub fn try_new_zeroed() -> Result<Arc<mem::MaybeUninit<T>>, AllocError> { | |
566 | unsafe { | |
567 | Ok(Arc::from_ptr(Arc::try_allocate_for_layout( | |
568 | Layout::new::<T>(), | |
569 | |layout| Global.allocate_zeroed(layout), | |
570 | |mem| mem as *mut ArcInner<mem::MaybeUninit<T>>, | |
571 | )?)) | |
572 | } | |
573 | } | |
e74abb32 | 574 | /// Returns the inner value, if the `Arc` has exactly one strong reference. |
e9174d1e | 575 | /// |
3dfed10e | 576 | /// Otherwise, an [`Err`] is returned with the same `Arc` that was |
c30ab7b3 | 577 | /// passed in. |
e9174d1e | 578 | /// |
54a0048b SL |
579 | /// This will succeed even if there are outstanding weak references. |
580 | /// | |
e9174d1e SL |
581 | /// # Examples |
582 | /// | |
583 | /// ``` | |
584 | /// use std::sync::Arc; | |
585 | /// | |
586 | /// let x = Arc::new(3); | |
587 | /// assert_eq!(Arc::try_unwrap(x), Ok(3)); | |
588 | /// | |
589 | /// let x = Arc::new(4); | |
7cac9316 | 590 | /// let _y = Arc::clone(&x); |
c30ab7b3 | 591 | /// assert_eq!(*Arc::try_unwrap(x).unwrap_err(), 4); |
e9174d1e SL |
592 | /// ``` |
593 | #[inline] | |
594 | #[stable(feature = "arc_unique", since = "1.4.0")] | |
595 | pub fn try_unwrap(this: Self) -> Result<T, Self> { | |
f035d41b | 596 | if this.inner().strong.compare_exchange(1, 0, Relaxed, Relaxed).is_err() { |
92a42be0 | 597 | return Err(this); |
b039eaaf | 598 | } |
e9174d1e | 599 | |
ba9703b0 | 600 | acquire!(this.inner().strong); |
e9174d1e SL |
601 | |
602 | unsafe { | |
7cac9316 | 603 | let elem = ptr::read(&this.ptr.as_ref().data); |
e9174d1e SL |
604 | |
605 | // Make a weak pointer to clean up the implicit strong-weak reference | |
54a0048b | 606 | let _weak = Weak { ptr: this.ptr }; |
e9174d1e SL |
607 | mem::forget(this); |
608 | ||
609 | Ok(elem) | |
610 | } | |
1a4d82fc | 611 | } |
ea8adc8c | 612 | } |
476ff2be | 613 | |
e1599b0c | 614 | impl<T> Arc<[T]> { |
3dfed10e | 615 | /// Constructs a new atomically reference-counted slice with uninitialized contents. |
e1599b0c XL |
616 | /// |
617 | /// # Examples | |
618 | /// | |
619 | /// ``` | |
620 | /// #![feature(new_uninit)] | |
621 | /// #![feature(get_mut_unchecked)] | |
622 | /// | |
623 | /// use std::sync::Arc; | |
624 | /// | |
625 | /// let mut values = Arc::<[u32]>::new_uninit_slice(3); | |
626 | /// | |
627 | /// let values = unsafe { | |
628 | /// // Deferred initialization: | |
629 | /// Arc::get_mut_unchecked(&mut values)[0].as_mut_ptr().write(1); | |
630 | /// Arc::get_mut_unchecked(&mut values)[1].as_mut_ptr().write(2); | |
631 | /// Arc::get_mut_unchecked(&mut values)[2].as_mut_ptr().write(3); | |
632 | /// | |
633 | /// values.assume_init() | |
634 | /// }; | |
635 | /// | |
636 | /// assert_eq!(*values, [1, 2, 3]) | |
637 | /// ``` | |
638 | #[unstable(feature = "new_uninit", issue = "63291")] | |
639 | pub fn new_uninit_slice(len: usize) -> Arc<[mem::MaybeUninit<T>]> { | |
dfeec247 | 640 | unsafe { Arc::from_ptr(Arc::allocate_for_slice(len)) } |
e1599b0c | 641 | } |
3dfed10e XL |
642 | |
643 | /// Constructs a new atomically reference-counted slice with uninitialized contents, with the memory being | |
644 | /// filled with `0` bytes. | |
645 | /// | |
646 | /// See [`MaybeUninit::zeroed`][zeroed] for examples of correct and | |
647 | /// incorrect usage of this method. | |
648 | /// | |
649 | /// # Examples | |
650 | /// | |
651 | /// ``` | |
652 | /// #![feature(new_uninit)] | |
653 | /// | |
654 | /// use std::sync::Arc; | |
655 | /// | |
656 | /// let values = Arc::<[u32]>::new_zeroed_slice(3); | |
657 | /// let values = unsafe { values.assume_init() }; | |
658 | /// | |
659 | /// assert_eq!(*values, [0, 0, 0]) | |
660 | /// ``` | |
661 | /// | |
662 | /// [zeroed]: ../../std/mem/union.MaybeUninit.html#method.zeroed | |
663 | #[unstable(feature = "new_uninit", issue = "63291")] | |
664 | pub fn new_zeroed_slice(len: usize) -> Arc<[mem::MaybeUninit<T>]> { | |
665 | unsafe { | |
666 | Arc::from_ptr(Arc::allocate_for_layout( | |
667 | Layout::array::<T>(len).unwrap(), | |
fc512014 | 668 | |layout| Global.allocate_zeroed(layout), |
3dfed10e XL |
669 | |mem| { |
670 | ptr::slice_from_raw_parts_mut(mem as *mut T, len) | |
671 | as *mut ArcInner<[mem::MaybeUninit<T>]> | |
672 | }, | |
673 | )) | |
674 | } | |
675 | } | |
e1599b0c XL |
676 | } |
677 | ||
678 | impl<T> Arc<mem::MaybeUninit<T>> { | |
679 | /// Converts to `Arc<T>`. | |
680 | /// | |
681 | /// # Safety | |
682 | /// | |
683 | /// As with [`MaybeUninit::assume_init`], | |
e74abb32 | 684 | /// it is up to the caller to guarantee that the inner value |
e1599b0c XL |
685 | /// really is in an initialized state. |
686 | /// Calling this when the content is not yet fully initialized | |
687 | /// causes immediate undefined behavior. | |
688 | /// | |
689 | /// [`MaybeUninit::assume_init`]: ../../std/mem/union.MaybeUninit.html#method.assume_init | |
690 | /// | |
691 | /// # Examples | |
692 | /// | |
693 | /// ``` | |
694 | /// #![feature(new_uninit)] | |
695 | /// #![feature(get_mut_unchecked)] | |
696 | /// | |
697 | /// use std::sync::Arc; | |
698 | /// | |
699 | /// let mut five = Arc::<u32>::new_uninit(); | |
700 | /// | |
701 | /// let five = unsafe { | |
702 | /// // Deferred initialization: | |
703 | /// Arc::get_mut_unchecked(&mut five).as_mut_ptr().write(5); | |
704 | /// | |
705 | /// five.assume_init() | |
706 | /// }; | |
707 | /// | |
708 | /// assert_eq!(*five, 5) | |
709 | /// ``` | |
710 | #[unstable(feature = "new_uninit", issue = "63291")] | |
711 | #[inline] | |
712 | pub unsafe fn assume_init(self) -> Arc<T> { | |
713 | Arc::from_inner(mem::ManuallyDrop::new(self).ptr.cast()) | |
714 | } | |
715 | } | |
716 | ||
717 | impl<T> Arc<[mem::MaybeUninit<T>]> { | |
718 | /// Converts to `Arc<[T]>`. | |
719 | /// | |
720 | /// # Safety | |
721 | /// | |
722 | /// As with [`MaybeUninit::assume_init`], | |
e74abb32 | 723 | /// it is up to the caller to guarantee that the inner value |
e1599b0c XL |
724 | /// really is in an initialized state. |
725 | /// Calling this when the content is not yet fully initialized | |
726 | /// causes immediate undefined behavior. | |
727 | /// | |
728 | /// [`MaybeUninit::assume_init`]: ../../std/mem/union.MaybeUninit.html#method.assume_init | |
729 | /// | |
730 | /// # Examples | |
731 | /// | |
732 | /// ``` | |
733 | /// #![feature(new_uninit)] | |
734 | /// #![feature(get_mut_unchecked)] | |
735 | /// | |
736 | /// use std::sync::Arc; | |
737 | /// | |
738 | /// let mut values = Arc::<[u32]>::new_uninit_slice(3); | |
739 | /// | |
740 | /// let values = unsafe { | |
741 | /// // Deferred initialization: | |
742 | /// Arc::get_mut_unchecked(&mut values)[0].as_mut_ptr().write(1); | |
743 | /// Arc::get_mut_unchecked(&mut values)[1].as_mut_ptr().write(2); | |
744 | /// Arc::get_mut_unchecked(&mut values)[2].as_mut_ptr().write(3); | |
745 | /// | |
746 | /// values.assume_init() | |
747 | /// }; | |
748 | /// | |
749 | /// assert_eq!(*values, [1, 2, 3]) | |
750 | /// ``` | |
751 | #[unstable(feature = "new_uninit", issue = "63291")] | |
752 | #[inline] | |
753 | pub unsafe fn assume_init(self) -> Arc<[T]> { | |
f035d41b | 754 | unsafe { Arc::from_ptr(mem::ManuallyDrop::new(self).ptr.as_ptr() as _) } |
e1599b0c XL |
755 | } |
756 | } | |
757 | ||
ea8adc8c | 758 | impl<T: ?Sized> Arc<T> { |
476ff2be SL |
759 | /// Consumes the `Arc`, returning the wrapped pointer. |
760 | /// | |
761 | /// To avoid a memory leak the pointer must be converted back to an `Arc` using | |
3dfed10e | 762 | /// [`Arc::from_raw`]. |
476ff2be SL |
763 | /// |
764 | /// # Examples | |
765 | /// | |
766 | /// ``` | |
476ff2be SL |
767 | /// use std::sync::Arc; |
768 | /// | |
dc9dc135 | 769 | /// let x = Arc::new("hello".to_owned()); |
476ff2be | 770 | /// let x_ptr = Arc::into_raw(x); |
dc9dc135 | 771 | /// assert_eq!(unsafe { &*x_ptr }, "hello"); |
476ff2be | 772 | /// ``` |
8bb4bdeb XL |
773 | #[stable(feature = "rc_raw", since = "1.17.0")] |
774 | pub fn into_raw(this: Self) -> *const T { | |
ba9703b0 XL |
775 | let ptr = Self::as_ptr(&this); |
776 | mem::forget(this); | |
777 | ptr | |
778 | } | |
779 | ||
780 | /// Provides a raw pointer to the data. | |
781 | /// | |
3dfed10e | 782 | /// The counts are not affected in any way and the `Arc` is not consumed. The pointer is valid for |
ba9703b0 XL |
783 | /// as long as there are strong counts in the `Arc`. |
784 | /// | |
785 | /// # Examples | |
786 | /// | |
787 | /// ``` | |
ba9703b0 XL |
788 | /// use std::sync::Arc; |
789 | /// | |
790 | /// let x = Arc::new("hello".to_owned()); | |
791 | /// let y = Arc::clone(&x); | |
792 | /// let x_ptr = Arc::as_ptr(&x); | |
793 | /// assert_eq!(x_ptr, Arc::as_ptr(&y)); | |
794 | /// assert_eq!(unsafe { &*x_ptr }, "hello"); | |
795 | /// ``` | |
f035d41b | 796 | #[stable(feature = "rc_as_ptr", since = "1.45.0")] |
ba9703b0 | 797 | pub fn as_ptr(this: &Self) -> *const T { |
dfeec247 | 798 | let ptr: *mut ArcInner<T> = NonNull::as_ptr(this.ptr); |
dfeec247 | 799 | |
f035d41b XL |
800 | // SAFETY: This cannot go through Deref::deref or RcBoxPtr::inner because |
801 | // this is required to retain raw/mut provenance such that e.g. `get_mut` can | |
802 | // write through the pointer after the Rc is recovered through `from_raw`. | |
5869c6ff | 803 | unsafe { ptr::addr_of_mut!((*ptr).data) } |
476ff2be SL |
804 | } |
805 | ||
ba9703b0 | 806 | /// Constructs an `Arc<T>` from a raw pointer. |
476ff2be | 807 | /// |
ba9703b0 XL |
808 | /// The raw pointer must have been previously returned by a call to |
809 | /// [`Arc<U>::into_raw`][into_raw] where `U` must have the same size and | |
810 | /// alignment as `T`. This is trivially true if `U` is `T`. | |
811 | /// Note that if `U` is not `T` but has the same size and alignment, this is | |
812 | /// basically like transmuting references of different types. See | |
813 | /// [`mem::transmute`][transmute] for more information on what | |
814 | /// restrictions apply in this case. | |
476ff2be | 815 | /// |
ba9703b0 XL |
816 | /// The user of `from_raw` has to make sure a specific value of `T` is only |
817 | /// dropped once. | |
818 | /// | |
819 | /// This function is unsafe because improper use may lead to memory unsafety, | |
820 | /// even if the returned `Arc<T>` is never accessed. | |
476ff2be | 821 | /// |
3dfed10e XL |
822 | /// [into_raw]: Arc::into_raw |
823 | /// [transmute]: core::mem::transmute | |
476ff2be SL |
824 | /// |
825 | /// # Examples | |
826 | /// | |
827 | /// ``` | |
476ff2be SL |
828 | /// use std::sync::Arc; |
829 | /// | |
dc9dc135 | 830 | /// let x = Arc::new("hello".to_owned()); |
476ff2be SL |
831 | /// let x_ptr = Arc::into_raw(x); |
832 | /// | |
833 | /// unsafe { | |
834 | /// // Convert back to an `Arc` to prevent leak. | |
835 | /// let x = Arc::from_raw(x_ptr); | |
dc9dc135 | 836 | /// assert_eq!(&*x, "hello"); |
476ff2be | 837 | /// |
e1599b0c | 838 | /// // Further calls to `Arc::from_raw(x_ptr)` would be memory-unsafe. |
476ff2be SL |
839 | /// } |
840 | /// | |
841 | /// // The memory was freed when `x` went out of scope above, so `x_ptr` is now dangling! | |
842 | /// ``` | |
8bb4bdeb XL |
843 | #[stable(feature = "rc_raw", since = "1.17.0")] |
844 | pub unsafe fn from_raw(ptr: *const T) -> Self { | |
f035d41b XL |
845 | unsafe { |
846 | let offset = data_offset(ptr); | |
ea8adc8c | 847 | |
f035d41b | 848 | // Reverse the offset to find the original ArcInner. |
5869c6ff | 849 | let arc_ptr = (ptr as *mut ArcInner<T>).set_ptr_value((ptr as *mut u8).offset(-offset)); |
ea8adc8c | 850 | |
f035d41b XL |
851 | Self::from_ptr(arc_ptr) |
852 | } | |
476ff2be | 853 | } |
1a4d82fc | 854 | |
3dfed10e | 855 | /// Creates a new [`Weak`] pointer to this allocation. |
1a4d82fc JJ |
856 | /// |
857 | /// # Examples | |
858 | /// | |
859 | /// ``` | |
860 | /// use std::sync::Arc; | |
861 | /// | |
85aaf69f | 862 | /// let five = Arc::new(5); |
1a4d82fc | 863 | /// |
e9174d1e | 864 | /// let weak_five = Arc::downgrade(&five); |
1a4d82fc | 865 | /// ``` |
e9174d1e SL |
866 | #[stable(feature = "arc_weak", since = "1.4.0")] |
867 | pub fn downgrade(this: &Self) -> Weak<T> { | |
54a0048b SL |
868 | // This Relaxed is OK because we're checking the value in the CAS |
869 | // below. | |
870 | let mut cur = this.inner().weak.load(Relaxed); | |
c1a9b12d | 871 | |
54a0048b | 872 | loop { |
c1a9b12d | 873 | // check if the weak counter is currently "locked"; if so, spin. |
b039eaaf | 874 | if cur == usize::MAX { |
29967ef6 | 875 | hint::spin_loop(); |
54a0048b | 876 | cur = this.inner().weak.load(Relaxed); |
92a42be0 | 877 | continue; |
b039eaaf | 878 | } |
c1a9b12d SL |
879 | |
880 | // NOTE: this code currently ignores the possibility of overflow | |
881 | // into usize::MAX; in general both Rc and Arc need to be adjusted | |
882 | // to deal with overflow. | |
883 | ||
884 | // Unlike with Clone(), we need this to be an Acquire read to | |
885 | // synchronize with the write coming from `is_unique`, so that the | |
886 | // events prior to that write happen before this read. | |
54a0048b | 887 | match this.inner().weak.compare_exchange_weak(cur, cur + 1, Acquire, Relaxed) { |
8faf50e0 XL |
888 | Ok(_) => { |
889 | // Make sure we do not create a dangling Weak | |
5869c6ff | 890 | debug_assert!(!is_dangling(this.ptr.as_ptr())); |
8faf50e0 XL |
891 | return Weak { ptr: this.ptr }; |
892 | } | |
54a0048b | 893 | Err(old) => cur = old, |
c1a9b12d SL |
894 | } |
895 | } | |
1a4d82fc | 896 | } |
1a4d82fc | 897 | |
3dfed10e | 898 | /// Gets the number of [`Weak`] pointers to this allocation. |
c30ab7b3 | 899 | /// |
476ff2be SL |
900 | /// # Safety |
901 | /// | |
902 | /// This method by itself is safe, but using it correctly requires extra care. | |
903 | /// Another thread can change the weak count at any time, | |
904 | /// including potentially between calling this method and acting on the result. | |
905 | /// | |
c30ab7b3 SL |
906 | /// # Examples |
907 | /// | |
908 | /// ``` | |
c30ab7b3 SL |
909 | /// use std::sync::Arc; |
910 | /// | |
911 | /// let five = Arc::new(5); | |
912 | /// let _weak_five = Arc::downgrade(&five); | |
913 | /// | |
914 | /// // This assertion is deterministic because we haven't shared | |
915 | /// // the `Arc` or `Weak` between threads. | |
916 | /// assert_eq!(1, Arc::weak_count(&five)); | |
917 | /// ``` | |
62682a34 | 918 | #[inline] |
476ff2be | 919 | #[stable(feature = "arc_counts", since = "1.15.0")] |
e9174d1e | 920 | pub fn weak_count(this: &Self) -> usize { |
3b2f2976 XL |
921 | let cnt = this.inner().weak.load(SeqCst); |
922 | // If the weak count is currently locked, the value of the | |
923 | // count was 0 just before taking the lock. | |
924 | if cnt == usize::MAX { 0 } else { cnt - 1 } | |
62682a34 SL |
925 | } |
926 | ||
e74abb32 | 927 | /// Gets the number of strong (`Arc`) pointers to this allocation. |
c30ab7b3 | 928 | /// |
476ff2be SL |
929 | /// # Safety |
930 | /// | |
931 | /// This method by itself is safe, but using it correctly requires extra care. | |
932 | /// Another thread can change the strong count at any time, | |
933 | /// including potentially between calling this method and acting on the result. | |
c30ab7b3 SL |
934 | /// |
935 | /// # Examples | |
936 | /// | |
937 | /// ``` | |
c30ab7b3 SL |
938 | /// use std::sync::Arc; |
939 | /// | |
940 | /// let five = Arc::new(5); | |
7cac9316 | 941 | /// let _also_five = Arc::clone(&five); |
c30ab7b3 SL |
942 | /// |
943 | /// // This assertion is deterministic because we haven't shared | |
944 | /// // the `Arc` between threads. | |
945 | /// assert_eq!(2, Arc::strong_count(&five)); | |
946 | /// ``` | |
62682a34 | 947 | #[inline] |
476ff2be | 948 | #[stable(feature = "arc_counts", since = "1.15.0")] |
e9174d1e | 949 | pub fn strong_count(this: &Self) -> usize { |
62682a34 SL |
950 | this.inner().strong.load(SeqCst) |
951 | } | |
952 | ||
f9f354fc XL |
953 | /// Increments the strong reference count on the `Arc<T>` associated with the |
954 | /// provided pointer by one. | |
955 | /// | |
956 | /// # Safety | |
957 | /// | |
958 | /// The pointer must have been obtained through `Arc::into_raw`, and the | |
959 | /// associated `Arc` instance must be valid (i.e. the strong count must be at | |
960 | /// least 1) for the duration of this method. | |
961 | /// | |
962 | /// # Examples | |
963 | /// | |
964 | /// ``` | |
f9f354fc XL |
965 | /// use std::sync::Arc; |
966 | /// | |
967 | /// let five = Arc::new(5); | |
968 | /// | |
969 | /// unsafe { | |
970 | /// let ptr = Arc::into_raw(five); | |
5869c6ff | 971 | /// Arc::increment_strong_count(ptr); |
f9f354fc XL |
972 | /// |
973 | /// // This assertion is deterministic because we haven't shared | |
974 | /// // the `Arc` between threads. | |
975 | /// let five = Arc::from_raw(ptr); | |
976 | /// assert_eq!(2, Arc::strong_count(&five)); | |
977 | /// } | |
978 | /// ``` | |
979 | #[inline] | |
5869c6ff XL |
980 | #[stable(feature = "arc_mutate_strong_count", since = "1.51.0")] |
981 | pub unsafe fn increment_strong_count(ptr: *const T) { | |
f9f354fc | 982 | // Retain Arc, but don't touch refcount by wrapping in ManuallyDrop |
f035d41b | 983 | let arc = unsafe { mem::ManuallyDrop::new(Arc::<T>::from_raw(ptr)) }; |
f9f354fc XL |
984 | // Now increase refcount, but don't drop new refcount either |
985 | let _arc_clone: mem::ManuallyDrop<_> = arc.clone(); | |
986 | } | |
987 | ||
988 | /// Decrements the strong reference count on the `Arc<T>` associated with the | |
989 | /// provided pointer by one. | |
990 | /// | |
991 | /// # Safety | |
992 | /// | |
993 | /// The pointer must have been obtained through `Arc::into_raw`, and the | |
994 | /// associated `Arc` instance must be valid (i.e. the strong count must be at | |
995 | /// least 1) when invoking this method. This method can be used to release the final | |
996 | /// `Arc` and backing storage, but **should not** be called after the final `Arc` has been | |
997 | /// released. | |
998 | /// | |
999 | /// # Examples | |
1000 | /// | |
1001 | /// ``` | |
f9f354fc XL |
1002 | /// use std::sync::Arc; |
1003 | /// | |
1004 | /// let five = Arc::new(5); | |
1005 | /// | |
1006 | /// unsafe { | |
1007 | /// let ptr = Arc::into_raw(five); | |
5869c6ff | 1008 | /// Arc::increment_strong_count(ptr); |
f9f354fc XL |
1009 | /// |
1010 | /// // Those assertions are deterministic because we haven't shared | |
1011 | /// // the `Arc` between threads. | |
1012 | /// let five = Arc::from_raw(ptr); | |
1013 | /// assert_eq!(2, Arc::strong_count(&five)); | |
5869c6ff | 1014 | /// Arc::decrement_strong_count(ptr); |
f9f354fc XL |
1015 | /// assert_eq!(1, Arc::strong_count(&five)); |
1016 | /// } | |
1017 | /// ``` | |
1018 | #[inline] | |
5869c6ff XL |
1019 | #[stable(feature = "arc_mutate_strong_count", since = "1.51.0")] |
1020 | pub unsafe fn decrement_strong_count(ptr: *const T) { | |
f035d41b | 1021 | unsafe { mem::drop(Arc::from_raw(ptr)) }; |
f9f354fc XL |
1022 | } |
1023 | ||
1a4d82fc JJ |
1024 | #[inline] |
1025 | fn inner(&self) -> &ArcInner<T> { | |
c34b1796 AL |
1026 | // This unsafety is ok because while this arc is alive we're guaranteed |
1027 | // that the inner pointer is valid. Furthermore, we know that the | |
1028 | // `ArcInner` structure itself is `Sync` because the inner data is | |
1029 | // `Sync` as well, so we're ok loaning out an immutable pointer to these | |
1030 | // contents. | |
7cac9316 | 1031 | unsafe { self.ptr.as_ref() } |
1a4d82fc | 1032 | } |
c34b1796 AL |
1033 | |
1034 | // Non-inlined part of `drop`. | |
1035 | #[inline(never)] | |
1036 | unsafe fn drop_slow(&mut self) { | |
c34b1796 AL |
1037 | // Destroy the data at this time, even though we may not free the box |
1038 | // allocation itself (there may still be weak pointers lying around). | |
f035d41b | 1039 | unsafe { ptr::drop_in_place(Self::get_mut_unchecked(self)) }; |
c34b1796 | 1040 | |
f9f354fc XL |
1041 | // Drop the weak ref collectively held by all strong references |
1042 | drop(Weak { ptr: self.ptr }); | |
c34b1796 | 1043 | } |
9e0c209e SL |
1044 | |
1045 | #[inline] | |
8bb4bdeb | 1046 | #[stable(feature = "ptr_eq", since = "1.17.0")] |
e74abb32 XL |
1047 | /// Returns `true` if the two `Arc`s point to the same allocation |
1048 | /// (in a vein similar to [`ptr::eq`]). | |
9e0c209e SL |
1049 | /// |
1050 | /// # Examples | |
1051 | /// | |
1052 | /// ``` | |
9e0c209e SL |
1053 | /// use std::sync::Arc; |
1054 | /// | |
1055 | /// let five = Arc::new(5); | |
7cac9316 | 1056 | /// let same_five = Arc::clone(&five); |
9e0c209e SL |
1057 | /// let other_five = Arc::new(5); |
1058 | /// | |
1059 | /// assert!(Arc::ptr_eq(&five, &same_five)); | |
1060 | /// assert!(!Arc::ptr_eq(&five, &other_five)); | |
1061 | /// ``` | |
e74abb32 | 1062 | /// |
3dfed10e | 1063 | /// [`ptr::eq`]: core::ptr::eq |
9e0c209e | 1064 | pub fn ptr_eq(this: &Self, other: &Self) -> bool { |
7cac9316 | 1065 | this.ptr.as_ptr() == other.ptr.as_ptr() |
9e0c209e | 1066 | } |
1a4d82fc JJ |
1067 | } |
1068 | ||
3b2f2976 | 1069 | impl<T: ?Sized> Arc<T> { |
416331ca | 1070 | /// Allocates an `ArcInner<T>` with sufficient space for |
e74abb32 | 1071 | /// a possibly-unsized inner value where the value has the layout provided. |
416331ca XL |
1072 | /// |
1073 | /// The function `mem_to_arcinner` is called with the data pointer | |
1074 | /// and must return back a (potentially fat)-pointer for the `ArcInner<T>`. | |
e1599b0c | 1075 | unsafe fn allocate_for_layout( |
416331ca | 1076 | value_layout: Layout, |
1b1a35ee | 1077 | allocate: impl FnOnce(Layout) -> Result<NonNull<[u8]>, AllocError>, |
dfeec247 | 1078 | mem_to_arcinner: impl FnOnce(*mut u8) -> *mut ArcInner<T>, |
416331ca XL |
1079 | ) -> *mut ArcInner<T> { |
1080 | // Calculate layout using the given value layout. | |
a1dfa0c6 XL |
1081 | // Previously, layout was calculated on the expression |
1082 | // `&*(ptr as *const ArcInner<T>)`, but this created a misaligned | |
1083 | // reference (see #54908). | |
dfeec247 | 1084 | let layout = Layout::new::<ArcInner<()>>().extend(value_layout).unwrap().0.pad_to_align(); |
5869c6ff XL |
1085 | unsafe { |
1086 | Arc::try_allocate_for_layout(value_layout, allocate, mem_to_arcinner) | |
1087 | .unwrap_or_else(|_| handle_alloc_error(layout)) | |
1088 | } | |
1089 | } | |
1090 | ||
1091 | /// Allocates an `ArcInner<T>` with sufficient space for | |
1092 | /// a possibly-unsized inner value where the value has the layout provided, | |
1093 | /// returning an error if allocation fails. | |
1094 | /// | |
1095 | /// The function `mem_to_arcinner` is called with the data pointer | |
1096 | /// and must return back a (potentially fat)-pointer for the `ArcInner<T>`. | |
1097 | unsafe fn try_allocate_for_layout( | |
1098 | value_layout: Layout, | |
1099 | allocate: impl FnOnce(Layout) -> Result<NonNull<[u8]>, AllocError>, | |
1100 | mem_to_arcinner: impl FnOnce(*mut u8) -> *mut ArcInner<T>, | |
1101 | ) -> Result<*mut ArcInner<T>, AllocError> { | |
1102 | // Calculate layout using the given value layout. | |
1103 | // Previously, layout was calculated on the expression | |
1104 | // `&*(ptr as *const ArcInner<T>)`, but this created a misaligned | |
1105 | // reference (see #54908). | |
1106 | let layout = Layout::new::<ArcInner<()>>().extend(value_layout).unwrap().0.pad_to_align(); | |
3b2f2976 | 1107 | |
5869c6ff | 1108 | let ptr = allocate(layout)?; |
3b2f2976 | 1109 | |
a1dfa0c6 | 1110 | // Initialize the ArcInner |
3dfed10e | 1111 | let inner = mem_to_arcinner(ptr.as_non_null_ptr().as_ptr()); |
f035d41b | 1112 | debug_assert_eq!(unsafe { Layout::for_value(&*inner) }, layout); |
3b2f2976 | 1113 | |
f035d41b XL |
1114 | unsafe { |
1115 | ptr::write(&mut (*inner).strong, atomic::AtomicUsize::new(1)); | |
1116 | ptr::write(&mut (*inner).weak, atomic::AtomicUsize::new(1)); | |
1117 | } | |
3b2f2976 | 1118 | |
5869c6ff | 1119 | Ok(inner) |
3b2f2976 XL |
1120 | } |
1121 | ||
e74abb32 | 1122 | /// Allocates an `ArcInner<T>` with sufficient space for an unsized inner value. |
416331ca XL |
1123 | unsafe fn allocate_for_ptr(ptr: *const T) -> *mut ArcInner<T> { |
1124 | // Allocate for the `ArcInner<T>` using the given value. | |
f035d41b | 1125 | unsafe { |
3dfed10e XL |
1126 | Self::allocate_for_layout( |
1127 | Layout::for_value(&*ptr), | |
fc512014 | 1128 | |layout| Global.allocate(layout), |
5869c6ff | 1129 | |mem| (ptr as *mut ArcInner<T>).set_ptr_value(mem) as *mut ArcInner<T>, |
3dfed10e | 1130 | ) |
f035d41b | 1131 | } |
416331ca XL |
1132 | } |
1133 | ||
3b2f2976 XL |
1134 | fn from_box(v: Box<T>) -> Arc<T> { |
1135 | unsafe { | |
29967ef6 | 1136 | let (box_unique, alloc) = Box::into_unique(v); |
83c7162d | 1137 | let bptr = box_unique.as_ptr(); |
3b2f2976 XL |
1138 | |
1139 | let value_size = size_of_val(&*bptr); | |
1140 | let ptr = Self::allocate_for_ptr(bptr); | |
1141 | ||
1142 | // Copy value as bytes | |
1143 | ptr::copy_nonoverlapping( | |
1144 | bptr as *const T as *const u8, | |
1145 | &mut (*ptr).data as *mut _ as *mut u8, | |
dfeec247 XL |
1146 | value_size, |
1147 | ); | |
3b2f2976 XL |
1148 | |
1149 | // Free the allocation without dropping its contents | |
29967ef6 | 1150 | box_free(box_unique, alloc); |
3b2f2976 | 1151 | |
416331ca | 1152 | Self::from_ptr(ptr) |
3b2f2976 XL |
1153 | } |
1154 | } | |
1155 | } | |
1156 | ||
416331ca XL |
1157 | impl<T> Arc<[T]> { |
1158 | /// Allocates an `ArcInner<[T]>` with the given length. | |
1159 | unsafe fn allocate_for_slice(len: usize) -> *mut ArcInner<[T]> { | |
f035d41b | 1160 | unsafe { |
3dfed10e XL |
1161 | Self::allocate_for_layout( |
1162 | Layout::array::<T>(len).unwrap(), | |
fc512014 | 1163 | |layout| Global.allocate(layout), |
3dfed10e XL |
1164 | |mem| ptr::slice_from_raw_parts_mut(mem as *mut T, len) as *mut ArcInner<[T]>, |
1165 | ) | |
f035d41b | 1166 | } |
416331ca | 1167 | } |
416331ca | 1168 | |
f9f354fc | 1169 | /// Copy elements from slice into newly allocated Arc<\[T\]> |
416331ca XL |
1170 | /// |
1171 | /// Unsafe because the caller must either take ownership or bind `T: Copy`. | |
3b2f2976 | 1172 | unsafe fn copy_from_slice(v: &[T]) -> Arc<[T]> { |
f035d41b XL |
1173 | unsafe { |
1174 | let ptr = Self::allocate_for_slice(v.len()); | |
3b2f2976 | 1175 | |
f035d41b | 1176 | ptr::copy_nonoverlapping(v.as_ptr(), &mut (*ptr).data as *mut [T] as *mut T, v.len()); |
3b2f2976 | 1177 | |
f035d41b XL |
1178 | Self::from_ptr(ptr) |
1179 | } | |
3b2f2976 | 1180 | } |
3b2f2976 | 1181 | |
416331ca XL |
1182 | /// Constructs an `Arc<[T]>` from an iterator known to be of a certain size. |
1183 | /// | |
1184 | /// Behavior is undefined should the size be wrong. | |
1185 | unsafe fn from_iter_exact(iter: impl iter::Iterator<Item = T>, len: usize) -> Arc<[T]> { | |
3b2f2976 XL |
1186 | // Panic guard while cloning T elements. |
1187 | // In the event of a panic, elements that have been written | |
1188 | // into the new ArcInner will be dropped, then the memory freed. | |
1189 | struct Guard<T> { | |
83c7162d | 1190 | mem: NonNull<u8>, |
3b2f2976 XL |
1191 | elems: *mut T, |
1192 | layout: Layout, | |
1193 | n_elems: usize, | |
1194 | } | |
1195 | ||
1196 | impl<T> Drop for Guard<T> { | |
1197 | fn drop(&mut self) { | |
3b2f2976 XL |
1198 | unsafe { |
1199 | let slice = from_raw_parts_mut(self.elems, self.n_elems); | |
1200 | ptr::drop_in_place(slice); | |
1201 | ||
fc512014 | 1202 | Global.deallocate(self.mem, self.layout); |
3b2f2976 XL |
1203 | } |
1204 | } | |
1205 | } | |
1206 | ||
f035d41b XL |
1207 | unsafe { |
1208 | let ptr = Self::allocate_for_slice(len); | |
3b2f2976 | 1209 | |
f035d41b XL |
1210 | let mem = ptr as *mut _ as *mut u8; |
1211 | let layout = Layout::for_value(&*ptr); | |
3b2f2976 | 1212 | |
f035d41b XL |
1213 | // Pointer to first element |
1214 | let elems = &mut (*ptr).data as *mut [T] as *mut T; | |
3b2f2976 | 1215 | |
f035d41b | 1216 | let mut guard = Guard { mem: NonNull::new_unchecked(mem), elems, layout, n_elems: 0 }; |
3b2f2976 | 1217 | |
f035d41b XL |
1218 | for (i, item) in iter.enumerate() { |
1219 | ptr::write(elems.add(i), item); | |
1220 | guard.n_elems += 1; | |
1221 | } | |
416331ca | 1222 | |
f035d41b XL |
1223 | // All clear. Forget the guard so it doesn't free the new ArcInner. |
1224 | mem::forget(guard); | |
416331ca | 1225 | |
f035d41b XL |
1226 | Self::from_ptr(ptr) |
1227 | } | |
416331ca XL |
1228 | } |
1229 | } | |
3b2f2976 | 1230 | |
416331ca XL |
1231 | /// Specialization trait used for `From<&[T]>`. |
1232 | trait ArcFromSlice<T> { | |
1233 | fn from_slice(slice: &[T]) -> Self; | |
1234 | } | |
3b2f2976 | 1235 | |
416331ca XL |
1236 | impl<T: Clone> ArcFromSlice<T> for Arc<[T]> { |
1237 | #[inline] | |
1238 | default fn from_slice(v: &[T]) -> Self { | |
dfeec247 | 1239 | unsafe { Self::from_iter_exact(v.iter().cloned(), v.len()) } |
3b2f2976 XL |
1240 | } |
1241 | } | |
1242 | ||
1243 | impl<T: Copy> ArcFromSlice<T> for Arc<[T]> { | |
1244 | #[inline] | |
1245 | fn from_slice(v: &[T]) -> Self { | |
1246 | unsafe { Arc::copy_from_slice(v) } | |
1247 | } | |
1248 | } | |
1249 | ||
85aaf69f | 1250 | #[stable(feature = "rust1", since = "1.0.0")] |
62682a34 | 1251 | impl<T: ?Sized> Clone for Arc<T> { |
c30ab7b3 | 1252 | /// Makes a clone of the `Arc` pointer. |
1a4d82fc | 1253 | /// |
e74abb32 | 1254 | /// This creates another pointer to the same allocation, increasing the |
c30ab7b3 | 1255 | /// strong reference count. |
1a4d82fc JJ |
1256 | /// |
1257 | /// # Examples | |
1258 | /// | |
1259 | /// ``` | |
1260 | /// use std::sync::Arc; | |
1261 | /// | |
85aaf69f | 1262 | /// let five = Arc::new(5); |
1a4d82fc | 1263 | /// |
0bf4aa26 | 1264 | /// let _ = Arc::clone(&five); |
1a4d82fc JJ |
1265 | /// ``` |
1266 | #[inline] | |
1267 | fn clone(&self) -> Arc<T> { | |
c34b1796 AL |
1268 | // Using a relaxed ordering is alright here, as knowledge of the |
1269 | // original reference prevents other threads from erroneously deleting | |
1270 | // the object. | |
1a4d82fc | 1271 | // |
c34b1796 AL |
1272 | // As explained in the [Boost documentation][1], Increasing the |
1273 | // reference counter can always be done with memory_order_relaxed: New | |
1274 | // references to an object can only be formed from an existing | |
1275 | // reference, and passing an existing reference from one thread to | |
1276 | // another must already provide any required synchronization. | |
1a4d82fc JJ |
1277 | // |
1278 | // [1]: (www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html) | |
c1a9b12d SL |
1279 | let old_size = self.inner().strong.fetch_add(1, Relaxed); |
1280 | ||
1281 | // However we need to guard against massive refcounts in case someone | |
1282 | // is `mem::forget`ing Arcs. If we don't do this the count can overflow | |
1283 | // and users will use-after free. We racily saturate to `isize::MAX` on | |
1284 | // the assumption that there aren't ~2 billion threads incrementing | |
1285 | // the reference count at once. This branch will never be taken in | |
1286 | // any realistic program. | |
1287 | // | |
1288 | // We abort because such a program is incredibly degenerate, and we | |
1289 | // don't care to support it. | |
1290 | if old_size > MAX_REFCOUNT { | |
f035d41b | 1291 | abort(); |
c1a9b12d SL |
1292 | } |
1293 | ||
416331ca | 1294 | Self::from_inner(self.ptr) |
1a4d82fc JJ |
1295 | } |
1296 | } | |
1297 | ||
85aaf69f | 1298 | #[stable(feature = "rust1", since = "1.0.0")] |
62682a34 | 1299 | impl<T: ?Sized> Deref for Arc<T> { |
1a4d82fc JJ |
1300 | type Target = T; |
1301 | ||
1302 | #[inline] | |
1303 | fn deref(&self) -> &T { | |
1304 | &self.inner().data | |
1305 | } | |
1306 | } | |
1307 | ||
dfeec247 | 1308 | #[unstable(feature = "receiver_trait", issue = "none")] |
0731742a XL |
1309 | impl<T: ?Sized> Receiver for Arc<T> {} |
1310 | ||
c34b1796 | 1311 | impl<T: Clone> Arc<T> { |
c30ab7b3 SL |
1312 | /// Makes a mutable reference into the given `Arc`. |
1313 | /// | |
3dfed10e | 1314 | /// If there are other `Arc` or [`Weak`] pointers to the same allocation, |
e74abb32 XL |
1315 | /// then `make_mut` will create a new allocation and invoke [`clone`][clone] on the inner value |
1316 | /// to ensure unique ownership. This is also referred to as clone-on-write. | |
1317 | /// | |
1318 | /// Note that this differs from the behavior of [`Rc::make_mut`] which disassociates | |
1319 | /// any remaining `Weak` pointers. | |
1a4d82fc | 1320 | /// |
c30ab7b3 SL |
1321 | /// See also [`get_mut`][get_mut], which will fail rather than cloning. |
1322 | /// | |
3dfed10e XL |
1323 | /// [clone]: Clone::clone |
1324 | /// [get_mut]: Arc::get_mut | |
1325 | /// [`Rc::make_mut`]: super::rc::Rc::make_mut | |
62682a34 | 1326 | /// |
1a4d82fc JJ |
1327 | /// # Examples |
1328 | /// | |
1329 | /// ``` | |
1330 | /// use std::sync::Arc; | |
1331 | /// | |
e9174d1e SL |
1332 | /// let mut data = Arc::new(5); |
1333 | /// | |
1334 | /// *Arc::make_mut(&mut data) += 1; // Won't clone anything | |
7cac9316 | 1335 | /// let mut other_data = Arc::clone(&data); // Won't clone inner data |
e9174d1e SL |
1336 | /// *Arc::make_mut(&mut data) += 1; // Clones inner data |
1337 | /// *Arc::make_mut(&mut data) += 1; // Won't clone anything | |
1338 | /// *Arc::make_mut(&mut other_data) *= 2; // Won't clone anything | |
1339 | /// | |
e74abb32 | 1340 | /// // Now `data` and `other_data` point to different allocations. |
e9174d1e SL |
1341 | /// assert_eq!(*data, 8); |
1342 | /// assert_eq!(*other_data, 12); | |
1a4d82fc JJ |
1343 | /// ``` |
1344 | #[inline] | |
e9174d1e SL |
1345 | #[stable(feature = "arc_unique", since = "1.4.0")] |
1346 | pub fn make_mut(this: &mut Self) -> &mut T { | |
c1a9b12d SL |
1347 | // Note that we hold both a strong reference and a weak reference. |
1348 | // Thus, releasing our strong reference only will not, by itself, cause | |
1349 | // the memory to be deallocated. | |
62682a34 | 1350 | // |
c1a9b12d SL |
1351 | // Use Acquire to ensure that we see any writes to `weak` that happen |
1352 | // before release writes (i.e., decrements) to `strong`. Since we hold a | |
1353 | // weak count, there's no chance the ArcInner itself could be | |
1354 | // deallocated. | |
54a0048b | 1355 | if this.inner().strong.compare_exchange(1, 0, Acquire, Relaxed).is_err() { |
5869c6ff XL |
1356 | // Another strong pointer exists, so we must clone. |
1357 | // Pre-allocate memory to allow writing the cloned value directly. | |
1358 | let mut arc = Self::new_uninit(); | |
1359 | unsafe { | |
1360 | let data = Arc::get_mut_unchecked(&mut arc); | |
1361 | (**this).write_clone_into_raw(data.as_mut_ptr()); | |
1362 | *this = arc.assume_init(); | |
1363 | } | |
c1a9b12d SL |
1364 | } else if this.inner().weak.load(Relaxed) != 1 { |
1365 | // Relaxed suffices in the above because this is fundamentally an | |
1366 | // optimization: we are always racing with weak pointers being | |
1367 | // dropped. Worst case, we end up allocated a new Arc unnecessarily. | |
1368 | ||
1369 | // We removed the last strong ref, but there are additional weak | |
1370 | // refs remaining. We'll move the contents to a new Arc, and | |
1371 | // invalidate the other weak refs. | |
1372 | ||
1373 | // Note that it is not possible for the read of `weak` to yield | |
1374 | // usize::MAX (i.e., locked), since the weak count can only be | |
1375 | // locked by a thread with a strong reference. | |
1376 | ||
1377 | // Materialize our own implicit weak pointer, so that it can clean | |
1378 | // up the ArcInner as needed. | |
5869c6ff | 1379 | let _weak = Weak { ptr: this.ptr }; |
c1a9b12d | 1380 | |
5869c6ff XL |
1381 | // Can just steal the data, all that's left is Weaks |
1382 | let mut arc = Self::new_uninit(); | |
c1a9b12d | 1383 | unsafe { |
5869c6ff XL |
1384 | let data = Arc::get_mut_unchecked(&mut arc); |
1385 | data.as_mut_ptr().copy_from_nonoverlapping(&**this, 1); | |
1386 | ptr::write(this, arc.assume_init()); | |
c1a9b12d SL |
1387 | } |
1388 | } else { | |
1389 | // We were the sole reference of either kind; bump back up the | |
1390 | // strong ref count. | |
1391 | this.inner().strong.store(1, Release); | |
1a4d82fc | 1392 | } |
c1a9b12d | 1393 | |
9346a6ac | 1394 | // As with `get_mut()`, the unsafety is ok because our reference was |
c34b1796 | 1395 | // either unique to begin with, or became one upon cloning the contents. |
f9f354fc | 1396 | unsafe { Self::get_mut_unchecked(this) } |
1a4d82fc JJ |
1397 | } |
1398 | } | |
1399 | ||
c1a9b12d | 1400 | impl<T: ?Sized> Arc<T> { |
e74abb32 | 1401 | /// Returns a mutable reference into the given `Arc`, if there are |
3dfed10e | 1402 | /// no other `Arc` or [`Weak`] pointers to the same allocation. |
c30ab7b3 | 1403 | /// |
3dfed10e | 1404 | /// Returns [`None`] otherwise, because it is not safe to |
c30ab7b3 SL |
1405 | /// mutate a shared value. |
1406 | /// | |
1407 | /// See also [`make_mut`][make_mut], which will [`clone`][clone] | |
e74abb32 | 1408 | /// the inner value when there are other pointers. |
c30ab7b3 | 1409 | /// |
3dfed10e XL |
1410 | /// [make_mut]: Arc::make_mut |
1411 | /// [clone]: Clone::clone | |
c1a9b12d SL |
1412 | /// |
1413 | /// # Examples | |
1414 | /// | |
1415 | /// ``` | |
e9174d1e | 1416 | /// use std::sync::Arc; |
c1a9b12d SL |
1417 | /// |
1418 | /// let mut x = Arc::new(3); | |
1419 | /// *Arc::get_mut(&mut x).unwrap() = 4; | |
1420 | /// assert_eq!(*x, 4); | |
1421 | /// | |
7cac9316 | 1422 | /// let _y = Arc::clone(&x); |
c1a9b12d | 1423 | /// assert!(Arc::get_mut(&mut x).is_none()); |
c1a9b12d SL |
1424 | /// ``` |
1425 | #[inline] | |
e9174d1e SL |
1426 | #[stable(feature = "arc_unique", since = "1.4.0")] |
1427 | pub fn get_mut(this: &mut Self) -> Option<&mut T> { | |
c1a9b12d SL |
1428 | if this.is_unique() { |
1429 | // This unsafety is ok because we're guaranteed that the pointer | |
1430 | // returned is the *only* pointer that will ever be returned to T. Our | |
1431 | // reference count is guaranteed to be 1 at this point, and we required | |
1432 | // the Arc itself to be `mut`, so we're returning the only possible | |
1433 | // reference to the inner data. | |
dfeec247 | 1434 | unsafe { Some(Arc::get_mut_unchecked(this)) } |
c1a9b12d SL |
1435 | } else { |
1436 | None | |
1437 | } | |
1438 | } | |
1439 | ||
e74abb32 | 1440 | /// Returns a mutable reference into the given `Arc`, |
e1599b0c XL |
1441 | /// without any check. |
1442 | /// | |
1443 | /// See also [`get_mut`], which is safe and does appropriate checks. | |
1444 | /// | |
3dfed10e | 1445 | /// [`get_mut`]: Arc::get_mut |
e1599b0c XL |
1446 | /// |
1447 | /// # Safety | |
1448 | /// | |
e74abb32 | 1449 | /// Any other `Arc` or [`Weak`] pointers to the same allocation must not be dereferenced |
e1599b0c XL |
1450 | /// for the duration of the returned borrow. |
1451 | /// This is trivially the case if no such pointers exist, | |
1452 | /// for example immediately after `Arc::new`. | |
1453 | /// | |
1454 | /// # Examples | |
1455 | /// | |
1456 | /// ``` | |
1457 | /// #![feature(get_mut_unchecked)] | |
1458 | /// | |
1459 | /// use std::sync::Arc; | |
1460 | /// | |
1461 | /// let mut x = Arc::new(String::new()); | |
1462 | /// unsafe { | |
1463 | /// Arc::get_mut_unchecked(&mut x).push_str("foo") | |
1464 | /// } | |
1465 | /// assert_eq!(*x, "foo"); | |
1466 | /// ``` | |
1467 | #[inline] | |
1468 | #[unstable(feature = "get_mut_unchecked", issue = "63292")] | |
1469 | pub unsafe fn get_mut_unchecked(this: &mut Self) -> &mut T { | |
f9f354fc XL |
1470 | // We are careful to *not* create a reference covering the "count" fields, as |
1471 | // this would alias with concurrent access to the reference counts (e.g. by `Weak`). | |
f035d41b | 1472 | unsafe { &mut (*this.ptr.as_ptr()).data } |
e1599b0c XL |
1473 | } |
1474 | ||
c1a9b12d SL |
1475 | /// Determine whether this is the unique reference (including weak refs) to |
1476 | /// the underlying data. | |
1477 | /// | |
1478 | /// Note that this requires locking the weak ref count. | |
1479 | fn is_unique(&mut self) -> bool { | |
1480 | // lock the weak pointer count if we appear to be the sole weak pointer | |
1481 | // holder. | |
1482 | // | |
1483 | // The acquire label here ensures a happens-before relationship with any | |
8faf50e0 XL |
1484 | // writes to `strong` (in particular in `Weak::upgrade`) prior to decrements |
1485 | // of the `weak` count (via `Weak::drop`, which uses release). If the upgraded | |
1486 | // weak ref was never dropped, the CAS here will fail so we do not care to synchronize. | |
54a0048b | 1487 | if self.inner().weak.compare_exchange(1, usize::MAX, Acquire, Relaxed).is_ok() { |
8faf50e0 XL |
1488 | // This needs to be an `Acquire` to synchronize with the decrement of the `strong` |
1489 | // counter in `drop` -- the only access that happens when any but the last reference | |
1490 | // is being dropped. | |
1491 | let unique = self.inner().strong.load(Acquire) == 1; | |
c1a9b12d SL |
1492 | |
1493 | // The release write here synchronizes with a read in `downgrade`, | |
1494 | // effectively preventing the above read of `strong` from happening | |
1495 | // after the write. | |
1496 | self.inner().weak.store(1, Release); // release the lock | |
1497 | unique | |
1498 | } else { | |
1499 | false | |
1500 | } | |
1501 | } | |
1502 | } | |
1503 | ||
85aaf69f | 1504 | #[stable(feature = "rust1", since = "1.0.0")] |
32a655c1 | 1505 | unsafe impl<#[may_dangle] T: ?Sized> Drop for Arc<T> { |
c30ab7b3 | 1506 | /// Drops the `Arc`. |
1a4d82fc | 1507 | /// |
c34b1796 | 1508 | /// This will decrement the strong reference count. If the strong reference |
c30ab7b3 | 1509 | /// count reaches zero then the only other references (if any) are |
b7449926 | 1510 | /// [`Weak`], so we `drop` the inner value. |
1a4d82fc JJ |
1511 | /// |
1512 | /// # Examples | |
1513 | /// | |
1514 | /// ``` | |
1515 | /// use std::sync::Arc; | |
1516 | /// | |
c30ab7b3 | 1517 | /// struct Foo; |
1a4d82fc | 1518 | /// |
c30ab7b3 SL |
1519 | /// impl Drop for Foo { |
1520 | /// fn drop(&mut self) { | |
1521 | /// println!("dropped!"); | |
1522 | /// } | |
1a4d82fc | 1523 | /// } |
1a4d82fc | 1524 | /// |
c30ab7b3 | 1525 | /// let foo = Arc::new(Foo); |
7cac9316 | 1526 | /// let foo2 = Arc::clone(&foo); |
1a4d82fc | 1527 | /// |
c30ab7b3 SL |
1528 | /// drop(foo); // Doesn't print anything |
1529 | /// drop(foo2); // Prints "dropped!" | |
1a4d82fc | 1530 | /// ``` |
c34b1796 | 1531 | #[inline] |
1a4d82fc | 1532 | fn drop(&mut self) { |
c34b1796 AL |
1533 | // Because `fetch_sub` is already atomic, we do not need to synchronize |
1534 | // with other threads unless we are going to delete the object. This | |
1535 | // same logic applies to the below `fetch_sub` to the `weak` count. | |
b039eaaf | 1536 | if self.inner().strong.fetch_sub(1, Release) != 1 { |
92a42be0 | 1537 | return; |
b039eaaf | 1538 | } |
1a4d82fc | 1539 | |
c34b1796 AL |
1540 | // This fence is needed to prevent reordering of use of the data and |
1541 | // deletion of the data. Because it is marked `Release`, the decreasing | |
1542 | // of the reference count synchronizes with this `Acquire` fence. This | |
1543 | // means that use of the data happens before decreasing the reference | |
1544 | // count, which happens before this fence, which happens before the | |
1545 | // deletion of the data. | |
1a4d82fc JJ |
1546 | // |
1547 | // As explained in the [Boost documentation][1], | |
1548 | // | |
c34b1796 AL |
1549 | // > It is important to enforce any possible access to the object in one |
1550 | // > thread (through an existing reference) to *happen before* deleting | |
1551 | // > the object in a different thread. This is achieved by a "release" | |
1552 | // > operation after dropping a reference (any access to the object | |
1553 | // > through this reference must obviously happened before), and an | |
1554 | // > "acquire" operation before deleting the object. | |
1a4d82fc | 1555 | // |
7cac9316 XL |
1556 | // In particular, while the contents of an Arc are usually immutable, it's |
1557 | // possible to have interior writes to something like a Mutex<T>. Since a | |
1558 | // Mutex is not acquired when it is deleted, we can't rely on its | |
1559 | // synchronization logic to make writes in thread A visible to a destructor | |
1560 | // running in thread B. | |
1561 | // | |
1562 | // Also note that the Acquire fence here could probably be replaced with an | |
1563 | // Acquire load, which could improve performance in highly-contended | |
1564 | // situations. See [2]. | |
1565 | // | |
1a4d82fc | 1566 | // [1]: (www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html) |
7cac9316 | 1567 | // [2]: (https://github.com/rust-lang/rust/pull/41714) |
ba9703b0 | 1568 | acquire!(self.inner().strong); |
1a4d82fc | 1569 | |
c34b1796 | 1570 | unsafe { |
b039eaaf | 1571 | self.drop_slow(); |
1a4d82fc JJ |
1572 | } |
1573 | } | |
1574 | } | |
1575 | ||
8faf50e0 | 1576 | impl Arc<dyn Any + Send + Sync> { |
94b46f34 | 1577 | #[inline] |
8faf50e0 XL |
1578 | #[stable(feature = "rc_downcast", since = "1.29.0")] |
1579 | /// Attempt to downcast the `Arc<dyn Any + Send + Sync>` to a concrete type. | |
94b46f34 XL |
1580 | /// |
1581 | /// # Examples | |
1582 | /// | |
1583 | /// ``` | |
94b46f34 XL |
1584 | /// use std::any::Any; |
1585 | /// use std::sync::Arc; | |
1586 | /// | |
8faf50e0 | 1587 | /// fn print_if_string(value: Arc<dyn Any + Send + Sync>) { |
94b46f34 XL |
1588 | /// if let Ok(string) = value.downcast::<String>() { |
1589 | /// println!("String ({}): {}", string.len(), string); | |
1590 | /// } | |
1591 | /// } | |
1592 | /// | |
e74abb32 XL |
1593 | /// let my_string = "Hello World".to_string(); |
1594 | /// print_if_string(Arc::new(my_string)); | |
1595 | /// print_if_string(Arc::new(0i8)); | |
94b46f34 XL |
1596 | /// ``` |
1597 | pub fn downcast<T>(self) -> Result<Arc<T>, Self> | |
1598 | where | |
1599 | T: Any + Send + Sync + 'static, | |
1600 | { | |
1601 | if (*self).is::<T>() { | |
1602 | let ptr = self.ptr.cast::<ArcInner<T>>(); | |
1603 | mem::forget(self); | |
416331ca | 1604 | Ok(Arc::from_inner(ptr)) |
94b46f34 XL |
1605 | } else { |
1606 | Err(self) | |
1607 | } | |
1608 | } | |
1609 | } | |
1610 | ||
a7813a04 | 1611 | impl<T> Weak<T> { |
8faf50e0 XL |
1612 | /// Constructs a new `Weak<T>`, without allocating any memory. |
1613 | /// Calling [`upgrade`] on the return value always gives [`None`]. | |
c30ab7b3 | 1614 | /// |
3dfed10e | 1615 | /// [`upgrade`]: Weak::upgrade |
a7813a04 XL |
1616 | /// |
1617 | /// # Examples | |
1618 | /// | |
1619 | /// ``` | |
1620 | /// use std::sync::Weak; | |
1621 | /// | |
1622 | /// let empty: Weak<i64> = Weak::new(); | |
c30ab7b3 | 1623 | /// assert!(empty.upgrade().is_none()); |
a7813a04 XL |
1624 | /// ``` |
1625 | #[stable(feature = "downgraded_weak", since = "1.10.0")] | |
1626 | pub fn new() -> Weak<T> { | |
dfeec247 | 1627 | Weak { ptr: NonNull::new(usize::MAX as *mut ArcInner<T>).expect("MAX is not 0") } |
a7813a04 | 1628 | } |
29967ef6 XL |
1629 | } |
1630 | ||
1631 | /// Helper type to allow accessing the reference counts without | |
1632 | /// making any assertions about the data field. | |
1633 | struct WeakInner<'a> { | |
1634 | weak: &'a atomic::AtomicUsize, | |
1635 | strong: &'a atomic::AtomicUsize, | |
1636 | } | |
dc9dc135 | 1637 | |
5869c6ff | 1638 | impl<T: ?Sized> Weak<T> { |
dc9dc135 XL |
1639 | /// Returns a raw pointer to the object `T` pointed to by this `Weak<T>`. |
1640 | /// | |
ba9703b0 XL |
1641 | /// The pointer is valid only if there are some strong references. The pointer may be dangling, |
1642 | /// unaligned or even [`null`] otherwise. | |
dc9dc135 XL |
1643 | /// |
1644 | /// # Examples | |
1645 | /// | |
1646 | /// ``` | |
416331ca | 1647 | /// use std::sync::Arc; |
dc9dc135 XL |
1648 | /// use std::ptr; |
1649 | /// | |
1650 | /// let strong = Arc::new("hello".to_owned()); | |
1651 | /// let weak = Arc::downgrade(&strong); | |
1652 | /// // Both point to the same object | |
ba9703b0 | 1653 | /// assert!(ptr::eq(&*strong, weak.as_ptr())); |
dc9dc135 | 1654 | /// // The strong here keeps it alive, so we can still access the object. |
ba9703b0 | 1655 | /// assert_eq!("hello", unsafe { &*weak.as_ptr() }); |
dc9dc135 XL |
1656 | /// |
1657 | /// drop(strong); | |
ba9703b0 | 1658 | /// // But not any more. We can do weak.as_ptr(), but accessing the pointer would lead to |
dc9dc135 | 1659 | /// // undefined behaviour. |
ba9703b0 | 1660 | /// // assert_eq!("hello", unsafe { &*weak.as_ptr() }); |
dc9dc135 XL |
1661 | /// ``` |
1662 | /// | |
3dfed10e | 1663 | /// [`null`]: core::ptr::null |
f9f354fc | 1664 | #[stable(feature = "weak_into_raw", since = "1.45.0")] |
ba9703b0 | 1665 | pub fn as_ptr(&self) -> *const T { |
f035d41b XL |
1666 | let ptr: *mut ArcInner<T> = NonNull::as_ptr(self.ptr); |
1667 | ||
5869c6ff XL |
1668 | if is_dangling(ptr) { |
1669 | // If the pointer is dangling, we return the sentinel directly. This cannot be | |
1670 | // a valid payload address, as the payload is at least as aligned as ArcInner (usize). | |
1671 | ptr as *const T | |
1672 | } else { | |
1673 | // SAFETY: if is_dangling returns false, then the pointer is dereferencable. | |
1674 | // The payload may be dropped at this point, and we have to maintain provenance, | |
1675 | // so use raw pointer manipulation. | |
1676 | unsafe { ptr::addr_of_mut!((*ptr).data) } | |
f035d41b | 1677 | } |
dc9dc135 XL |
1678 | } |
1679 | ||
1680 | /// Consumes the `Weak<T>` and turns it into a raw pointer. | |
1681 | /// | |
3dfed10e XL |
1682 | /// This converts the weak pointer into a raw pointer, while still preserving the ownership of |
1683 | /// one weak reference (the weak count is not modified by this operation). It can be turned | |
1684 | /// back into the `Weak<T>` with [`from_raw`]. | |
dc9dc135 XL |
1685 | /// |
1686 | /// The same restrictions of accessing the target of the pointer as with | |
ba9703b0 | 1687 | /// [`as_ptr`] apply. |
dc9dc135 XL |
1688 | /// |
1689 | /// # Examples | |
1690 | /// | |
1691 | /// ``` | |
dc9dc135 XL |
1692 | /// use std::sync::{Arc, Weak}; |
1693 | /// | |
1694 | /// let strong = Arc::new("hello".to_owned()); | |
1695 | /// let weak = Arc::downgrade(&strong); | |
416331ca | 1696 | /// let raw = weak.into_raw(); |
dc9dc135 XL |
1697 | /// |
1698 | /// assert_eq!(1, Arc::weak_count(&strong)); | |
1699 | /// assert_eq!("hello", unsafe { &*raw }); | |
1700 | /// | |
1701 | /// drop(unsafe { Weak::from_raw(raw) }); | |
1702 | /// assert_eq!(0, Arc::weak_count(&strong)); | |
1703 | /// ``` | |
1704 | /// | |
3dfed10e XL |
1705 | /// [`from_raw`]: Weak::from_raw |
1706 | /// [`as_ptr`]: Weak::as_ptr | |
f9f354fc | 1707 | #[stable(feature = "weak_into_raw", since = "1.45.0")] |
416331ca | 1708 | pub fn into_raw(self) -> *const T { |
ba9703b0 | 1709 | let result = self.as_ptr(); |
416331ca | 1710 | mem::forget(self); |
dc9dc135 XL |
1711 | result |
1712 | } | |
1713 | ||
3dfed10e | 1714 | /// Converts a raw pointer previously created by [`into_raw`] back into `Weak<T>`. |
dc9dc135 XL |
1715 | /// |
1716 | /// This can be used to safely get a strong reference (by calling [`upgrade`] | |
1717 | /// later) or to deallocate the weak count by dropping the `Weak<T>`. | |
1718 | /// | |
3dfed10e XL |
1719 | /// It takes ownership of one weak reference (with the exception of pointers created by [`new`], |
1720 | /// as these don't own anything; the method still works on them). | |
dc9dc135 XL |
1721 | /// |
1722 | /// # Safety | |
1723 | /// | |
ba9703b0 | 1724 | /// The pointer must have originated from the [`into_raw`] and must still own its potential |
3dfed10e | 1725 | /// weak reference. |
dc9dc135 | 1726 | /// |
3dfed10e XL |
1727 | /// It is allowed for the strong count to be 0 at the time of calling this. Nevertheless, this |
1728 | /// takes ownership of one weak reference currently represented as a raw pointer (the weak | |
1729 | /// count is not modified by this operation) and therefore it must be paired with a previous | |
1730 | /// call to [`into_raw`]. | |
dc9dc135 XL |
1731 | /// # Examples |
1732 | /// | |
1733 | /// ``` | |
dc9dc135 XL |
1734 | /// use std::sync::{Arc, Weak}; |
1735 | /// | |
1736 | /// let strong = Arc::new("hello".to_owned()); | |
1737 | /// | |
416331ca XL |
1738 | /// let raw_1 = Arc::downgrade(&strong).into_raw(); |
1739 | /// let raw_2 = Arc::downgrade(&strong).into_raw(); | |
dc9dc135 XL |
1740 | /// |
1741 | /// assert_eq!(2, Arc::weak_count(&strong)); | |
1742 | /// | |
416331ca | 1743 | /// assert_eq!("hello", &*unsafe { Weak::from_raw(raw_1) }.upgrade().unwrap()); |
dc9dc135 XL |
1744 | /// assert_eq!(1, Arc::weak_count(&strong)); |
1745 | /// | |
1746 | /// drop(strong); | |
1747 | /// | |
1748 | /// // Decrement the last weak count. | |
416331ca | 1749 | /// assert!(unsafe { Weak::from_raw(raw_2) }.upgrade().is_none()); |
dc9dc135 XL |
1750 | /// ``` |
1751 | /// | |
3dfed10e XL |
1752 | /// [`new`]: Weak::new |
1753 | /// [`into_raw`]: Weak::into_raw | |
1754 | /// [`upgrade`]: Weak::upgrade | |
1755 | /// [`forget`]: std::mem::forget | |
f9f354fc | 1756 | #[stable(feature = "weak_into_raw", since = "1.45.0")] |
dc9dc135 | 1757 | pub unsafe fn from_raw(ptr: *const T) -> Self { |
29967ef6 | 1758 | // See Weak::as_ptr for context on how the input pointer is derived. |
29967ef6 | 1759 | |
5869c6ff XL |
1760 | let ptr = if is_dangling(ptr as *mut T) { |
1761 | // This is a dangling Weak. | |
1762 | ptr as *mut ArcInner<T> | |
1763 | } else { | |
1764 | // Otherwise, we're guaranteed the pointer came from a nondangling Weak. | |
1765 | // SAFETY: data_offset is safe to call, as ptr references a real (potentially dropped) T. | |
1766 | let offset = unsafe { data_offset(ptr) }; | |
1767 | // Thus, we reverse the offset to get the whole RcBox. | |
1768 | // SAFETY: the pointer originated from a Weak, so this offset is safe. | |
1769 | unsafe { (ptr as *mut ArcInner<T>).set_ptr_value((ptr as *mut u8).offset(-offset)) } | |
29967ef6 | 1770 | }; |
a7813a04 | 1771 | |
29967ef6 | 1772 | // SAFETY: we now have recovered the original Weak pointer, so can create the Weak. |
5869c6ff | 1773 | Weak { ptr: unsafe { NonNull::new_unchecked(ptr) } } |
29967ef6 | 1774 | } |
b9856134 | 1775 | } |
f9f354fc | 1776 | |
b9856134 | 1777 | impl<T: ?Sized> Weak<T> { |
e74abb32 XL |
1778 | /// Attempts to upgrade the `Weak` pointer to an [`Arc`], delaying |
1779 | /// dropping of the inner value if successful. | |
1a4d82fc | 1780 | /// |
e74abb32 | 1781 | /// Returns [`None`] if the inner value has since been dropped. |
1a4d82fc | 1782 | /// |
1a4d82fc JJ |
1783 | /// # Examples |
1784 | /// | |
1785 | /// ``` | |
1786 | /// use std::sync::Arc; | |
1787 | /// | |
85aaf69f | 1788 | /// let five = Arc::new(5); |
1a4d82fc | 1789 | /// |
e9174d1e | 1790 | /// let weak_five = Arc::downgrade(&five); |
1a4d82fc JJ |
1791 | /// |
1792 | /// let strong_five: Option<Arc<_>> = weak_five.upgrade(); | |
c30ab7b3 SL |
1793 | /// assert!(strong_five.is_some()); |
1794 | /// | |
1795 | /// // Destroy all strong pointers. | |
1796 | /// drop(strong_five); | |
1797 | /// drop(five); | |
1798 | /// | |
1799 | /// assert!(weak_five.upgrade().is_none()); | |
1a4d82fc | 1800 | /// ``` |
e9174d1e | 1801 | #[stable(feature = "arc_weak", since = "1.4.0")] |
1a4d82fc | 1802 | pub fn upgrade(&self) -> Option<Arc<T>> { |
c34b1796 | 1803 | // We use a CAS loop to increment the strong count instead of a |
3dfed10e XL |
1804 | // fetch_add as this function should never take the reference count |
1805 | // from zero to one. | |
8faf50e0 | 1806 | let inner = self.inner()?; |
54a0048b SL |
1807 | |
1808 | // Relaxed load because any write of 0 that we can observe | |
1809 | // leaves the field in a permanently zero state (so a | |
1810 | // "stale" read of 0 is fine), and any other value is | |
1811 | // confirmed via the CAS below. | |
1812 | let mut n = inner.strong.load(Relaxed); | |
1813 | ||
1a4d82fc | 1814 | loop { |
b039eaaf | 1815 | if n == 0 { |
92a42be0 SL |
1816 | return None; |
1817 | } | |
1818 | ||
1819 | // See comments in `Arc::clone` for why we do this (for `mem::forget`). | |
1820 | if n > MAX_REFCOUNT { | |
f035d41b | 1821 | abort(); |
b039eaaf | 1822 | } |
c1a9b12d | 1823 | |
3dfed10e XL |
1824 | // Relaxed is fine for the failure case because we don't have any expectations about the new state. |
1825 | // Acquire is necessary for the success case to synchronise with `Arc::new_cyclic`, when the inner | |
1826 | // value can be initialized after `Weak` references have already been created. In that case, we | |
1827 | // expect to observe the fully initialized value. | |
1828 | match inner.strong.compare_exchange_weak(n, n + 1, Acquire, Relaxed) { | |
416331ca | 1829 | Ok(_) => return Some(Arc::from_inner(self.ptr)), // null checked above |
54a0048b | 1830 | Err(old) => n = old, |
b039eaaf | 1831 | } |
1a4d82fc JJ |
1832 | } |
1833 | } | |
1834 | ||
e74abb32 | 1835 | /// Gets the number of strong (`Arc`) pointers pointing to this allocation. |
9fa01778 XL |
1836 | /// |
1837 | /// If `self` was created using [`Weak::new`], this will return 0. | |
60c5eb7d | 1838 | #[stable(feature = "weak_counts", since = "1.41.0")] |
9fa01778 | 1839 | pub fn strong_count(&self) -> usize { |
dfeec247 | 1840 | if let Some(inner) = self.inner() { inner.strong.load(SeqCst) } else { 0 } |
9fa01778 XL |
1841 | } |
1842 | ||
1843 | /// Gets an approximation of the number of `Weak` pointers pointing to this | |
e74abb32 | 1844 | /// allocation. |
9fa01778 | 1845 | /// |
60c5eb7d XL |
1846 | /// If `self` was created using [`Weak::new`], or if there are no remaining |
1847 | /// strong pointers, this will return 0. | |
9fa01778 XL |
1848 | /// |
1849 | /// # Accuracy | |
1850 | /// | |
1851 | /// Due to implementation details, the returned value can be off by 1 in | |
1852 | /// either direction when other threads are manipulating any `Arc`s or | |
e74abb32 | 1853 | /// `Weak`s pointing to the same allocation. |
60c5eb7d XL |
1854 | #[stable(feature = "weak_counts", since = "1.41.0")] |
1855 | pub fn weak_count(&self) -> usize { | |
dfeec247 XL |
1856 | self.inner() |
1857 | .map(|inner| { | |
1858 | let weak = inner.weak.load(SeqCst); | |
1859 | let strong = inner.strong.load(SeqCst); | |
1860 | if strong == 0 { | |
1861 | 0 | |
1862 | } else { | |
1863 | // Since we observed that there was at least one strong pointer | |
1864 | // after reading the weak count, we know that the implicit weak | |
1865 | // reference (present whenever any strong references are alive) | |
1866 | // was still around when we observed the weak count, and can | |
1867 | // therefore safely subtract it. | |
1868 | weak - 1 | |
1869 | } | |
1870 | }) | |
1871 | .unwrap_or(0) | |
9fa01778 XL |
1872 | } |
1873 | ||
1874 | /// Returns `None` when the pointer is dangling and there is no allocated `ArcInner`, | |
1875 | /// (i.e., when this `Weak` was created by `Weak::new`). | |
1a4d82fc | 1876 | #[inline] |
f9f354fc | 1877 | fn inner(&self) -> Option<WeakInner<'_>> { |
5869c6ff | 1878 | if is_dangling(self.ptr.as_ptr()) { |
f9f354fc XL |
1879 | None |
1880 | } else { | |
1881 | // We are careful to *not* create a reference covering the "data" field, as | |
1882 | // the field may be mutated concurrently (for example, if the last `Arc` | |
1883 | // is dropped, the data field will be dropped in-place). | |
1884 | Some(unsafe { | |
1885 | let ptr = self.ptr.as_ptr(); | |
1886 | WeakInner { strong: &(*ptr).strong, weak: &(*ptr).weak } | |
1887 | }) | |
1888 | } | |
1a4d82fc | 1889 | } |
0731742a | 1890 | |
e74abb32 XL |
1891 | /// Returns `true` if the two `Weak`s point to the same allocation (similar to |
1892 | /// [`ptr::eq`]), or if both don't point to any allocation | |
e1599b0c | 1893 | /// (because they were created with `Weak::new()`). |
0731742a XL |
1894 | /// |
1895 | /// # Notes | |
1896 | /// | |
1897 | /// Since this compares pointers it means that `Weak::new()` will equal each | |
e74abb32 | 1898 | /// other, even though they don't point to any allocation. |
0731742a | 1899 | /// |
0731742a XL |
1900 | /// # Examples |
1901 | /// | |
1902 | /// ``` | |
dc9dc135 | 1903 | /// use std::sync::Arc; |
0731742a XL |
1904 | /// |
1905 | /// let first_rc = Arc::new(5); | |
1906 | /// let first = Arc::downgrade(&first_rc); | |
1907 | /// let second = Arc::downgrade(&first_rc); | |
1908 | /// | |
dc9dc135 | 1909 | /// assert!(first.ptr_eq(&second)); |
0731742a XL |
1910 | /// |
1911 | /// let third_rc = Arc::new(5); | |
1912 | /// let third = Arc::downgrade(&third_rc); | |
1913 | /// | |
dc9dc135 | 1914 | /// assert!(!first.ptr_eq(&third)); |
0731742a XL |
1915 | /// ``` |
1916 | /// | |
1917 | /// Comparing `Weak::new`. | |
1918 | /// | |
1919 | /// ``` | |
0731742a XL |
1920 | /// use std::sync::{Arc, Weak}; |
1921 | /// | |
1922 | /// let first = Weak::new(); | |
1923 | /// let second = Weak::new(); | |
dc9dc135 | 1924 | /// assert!(first.ptr_eq(&second)); |
0731742a XL |
1925 | /// |
1926 | /// let third_rc = Arc::new(()); | |
1927 | /// let third = Arc::downgrade(&third_rc); | |
dc9dc135 | 1928 | /// assert!(!first.ptr_eq(&third)); |
0731742a | 1929 | /// ``` |
e74abb32 | 1930 | /// |
3dfed10e | 1931 | /// [`ptr::eq`]: core::ptr::eq |
0731742a | 1932 | #[inline] |
e1599b0c | 1933 | #[stable(feature = "weak_ptr_eq", since = "1.39.0")] |
dc9dc135 XL |
1934 | pub fn ptr_eq(&self, other: &Self) -> bool { |
1935 | self.ptr.as_ptr() == other.ptr.as_ptr() | |
0731742a | 1936 | } |
1a4d82fc JJ |
1937 | } |
1938 | ||
e9174d1e | 1939 | #[stable(feature = "arc_weak", since = "1.4.0")] |
62682a34 | 1940 | impl<T: ?Sized> Clone for Weak<T> { |
e74abb32 | 1941 | /// Makes a clone of the `Weak` pointer that points to the same allocation. |
1a4d82fc JJ |
1942 | /// |
1943 | /// # Examples | |
1944 | /// | |
1945 | /// ``` | |
7cac9316 | 1946 | /// use std::sync::{Arc, Weak}; |
1a4d82fc | 1947 | /// |
e9174d1e | 1948 | /// let weak_five = Arc::downgrade(&Arc::new(5)); |
1a4d82fc | 1949 | /// |
0bf4aa26 | 1950 | /// let _ = Weak::clone(&weak_five); |
1a4d82fc JJ |
1951 | /// ``` |
1952 | #[inline] | |
1953 | fn clone(&self) -> Weak<T> { | |
8faf50e0 XL |
1954 | let inner = if let Some(inner) = self.inner() { |
1955 | inner | |
1956 | } else { | |
1957 | return Weak { ptr: self.ptr }; | |
1958 | }; | |
c1a9b12d SL |
1959 | // See comments in Arc::clone() for why this is relaxed. This can use a |
1960 | // fetch_add (ignoring the lock) because the weak count is only locked | |
1961 | // where are *no other* weak pointers in existence. (So we can't be | |
1962 | // running this code in that case). | |
8faf50e0 | 1963 | let old_size = inner.weak.fetch_add(1, Relaxed); |
c1a9b12d SL |
1964 | |
1965 | // See comments in Arc::clone() for why we do this (for mem::forget). | |
1966 | if old_size > MAX_REFCOUNT { | |
f035d41b | 1967 | abort(); |
c1a9b12d SL |
1968 | } |
1969 | ||
e74abb32 | 1970 | Weak { ptr: self.ptr } |
1a4d82fc JJ |
1971 | } |
1972 | } | |
1973 | ||
a7813a04 XL |
1974 | #[stable(feature = "downgraded_weak", since = "1.10.0")] |
1975 | impl<T> Default for Weak<T> { | |
8faf50e0 | 1976 | /// Constructs a new `Weak<T>`, without allocating memory. |
0731742a | 1977 | /// Calling [`upgrade`] on the return value always |
b7449926 | 1978 | /// gives [`None`]. |
c30ab7b3 | 1979 | /// |
3dfed10e | 1980 | /// [`upgrade`]: Weak::upgrade |
c30ab7b3 SL |
1981 | /// |
1982 | /// # Examples | |
1983 | /// | |
1984 | /// ``` | |
1985 | /// use std::sync::Weak; | |
1986 | /// | |
1987 | /// let empty: Weak<i64> = Default::default(); | |
1988 | /// assert!(empty.upgrade().is_none()); | |
1989 | /// ``` | |
a7813a04 XL |
1990 | fn default() -> Weak<T> { |
1991 | Weak::new() | |
1992 | } | |
1993 | } | |
1994 | ||
7453a54e | 1995 | #[stable(feature = "arc_weak", since = "1.4.0")] |
62682a34 | 1996 | impl<T: ?Sized> Drop for Weak<T> { |
c30ab7b3 | 1997 | /// Drops the `Weak` pointer. |
1a4d82fc | 1998 | /// |
1a4d82fc JJ |
1999 | /// # Examples |
2000 | /// | |
2001 | /// ``` | |
7cac9316 | 2002 | /// use std::sync::{Arc, Weak}; |
1a4d82fc | 2003 | /// |
c30ab7b3 | 2004 | /// struct Foo; |
1a4d82fc | 2005 | /// |
c30ab7b3 SL |
2006 | /// impl Drop for Foo { |
2007 | /// fn drop(&mut self) { | |
2008 | /// println!("dropped!"); | |
2009 | /// } | |
1a4d82fc | 2010 | /// } |
1a4d82fc | 2011 | /// |
c30ab7b3 SL |
2012 | /// let foo = Arc::new(Foo); |
2013 | /// let weak_foo = Arc::downgrade(&foo); | |
7cac9316 | 2014 | /// let other_weak_foo = Weak::clone(&weak_foo); |
1a4d82fc | 2015 | /// |
c30ab7b3 SL |
2016 | /// drop(weak_foo); // Doesn't print anything |
2017 | /// drop(foo); // Prints "dropped!" | |
2018 | /// | |
2019 | /// assert!(other_weak_foo.upgrade().is_none()); | |
1a4d82fc JJ |
2020 | /// ``` |
2021 | fn drop(&mut self) { | |
c34b1796 AL |
2022 | // If we find out that we were the last weak pointer, then its time to |
2023 | // deallocate the data entirely. See the discussion in Arc::drop() about | |
2024 | // the memory orderings | |
c1a9b12d SL |
2025 | // |
2026 | // It's not necessary to check for the locked state here, because the | |
2027 | // weak count can only be locked if there was precisely one weak ref, | |
2028 | // meaning that drop could only subsequently run ON that remaining weak | |
2029 | // ref, which can only happen after the lock is released. | |
dfeec247 | 2030 | let inner = if let Some(inner) = self.inner() { inner } else { return }; |
8faf50e0 XL |
2031 | |
2032 | if inner.weak.fetch_sub(1, Release) == 1 { | |
ba9703b0 | 2033 | acquire!(inner.weak); |
5869c6ff | 2034 | unsafe { Global.deallocate(self.ptr.cast(), Layout::for_value_raw(self.ptr.as_ptr())) } |
1a4d82fc JJ |
2035 | } |
2036 | } | |
2037 | } | |
2038 | ||
0731742a XL |
2039 | #[stable(feature = "rust1", since = "1.0.0")] |
2040 | trait ArcEqIdent<T: ?Sized + PartialEq> { | |
2041 | fn eq(&self, other: &Arc<T>) -> bool; | |
2042 | fn ne(&self, other: &Arc<T>) -> bool; | |
2043 | } | |
2044 | ||
2045 | #[stable(feature = "rust1", since = "1.0.0")] | |
2046 | impl<T: ?Sized + PartialEq> ArcEqIdent<T> for Arc<T> { | |
2047 | #[inline] | |
2048 | default fn eq(&self, other: &Arc<T>) -> bool { | |
2049 | **self == **other | |
2050 | } | |
2051 | #[inline] | |
2052 | default fn ne(&self, other: &Arc<T>) -> bool { | |
2053 | **self != **other | |
2054 | } | |
2055 | } | |
2056 | ||
48663c56 XL |
2057 | /// We're doing this specialization here, and not as a more general optimization on `&T`, because it |
2058 | /// would otherwise add a cost to all equality checks on refs. We assume that `Arc`s are used to | |
2059 | /// store large values, that are slow to clone, but also heavy to check for equality, causing this | |
2060 | /// cost to pay off more easily. It's also more likely to have two `Arc` clones, that point to | |
2061 | /// the same value, than two `&T`s. | |
e74abb32 XL |
2062 | /// |
2063 | /// We can only do this when `T: Eq` as a `PartialEq` might be deliberately irreflexive. | |
0731742a | 2064 | #[stable(feature = "rust1", since = "1.0.0")] |
f9f354fc | 2065 | impl<T: ?Sized + crate::rc::MarkerEq> ArcEqIdent<T> for Arc<T> { |
0731742a XL |
2066 | #[inline] |
2067 | fn eq(&self, other: &Arc<T>) -> bool { | |
2068 | Arc::ptr_eq(self, other) || **self == **other | |
2069 | } | |
2070 | ||
2071 | #[inline] | |
2072 | fn ne(&self, other: &Arc<T>) -> bool { | |
2073 | !Arc::ptr_eq(self, other) && **self != **other | |
2074 | } | |
2075 | } | |
2076 | ||
85aaf69f | 2077 | #[stable(feature = "rust1", since = "1.0.0")] |
62682a34 | 2078 | impl<T: ?Sized + PartialEq> PartialEq for Arc<T> { |
c30ab7b3 | 2079 | /// Equality for two `Arc`s. |
1a4d82fc | 2080 | /// |
e74abb32 XL |
2081 | /// Two `Arc`s are equal if their inner values are equal, even if they are |
2082 | /// stored in different allocation. | |
1a4d82fc | 2083 | /// |
e74abb32 XL |
2084 | /// If `T` also implements `Eq` (implying reflexivity of equality), |
2085 | /// two `Arc`s that point to the same allocation are always equal. | |
0731742a | 2086 | /// |
1a4d82fc JJ |
2087 | /// # Examples |
2088 | /// | |
2089 | /// ``` | |
2090 | /// use std::sync::Arc; | |
2091 | /// | |
85aaf69f | 2092 | /// let five = Arc::new(5); |
1a4d82fc | 2093 | /// |
c30ab7b3 | 2094 | /// assert!(five == Arc::new(5)); |
1a4d82fc | 2095 | /// ``` |
0731742a | 2096 | #[inline] |
b039eaaf | 2097 | fn eq(&self, other: &Arc<T>) -> bool { |
0731742a | 2098 | ArcEqIdent::eq(self, other) |
b039eaaf | 2099 | } |
1a4d82fc | 2100 | |
c30ab7b3 | 2101 | /// Inequality for two `Arc`s. |
1a4d82fc | 2102 | /// |
c30ab7b3 | 2103 | /// Two `Arc`s are unequal if their inner values are unequal. |
1a4d82fc | 2104 | /// |
e74abb32 XL |
2105 | /// If `T` also implements `Eq` (implying reflexivity of equality), |
2106 | /// two `Arc`s that point to the same value are never unequal. | |
0731742a | 2107 | /// |
1a4d82fc JJ |
2108 | /// # Examples |
2109 | /// | |
2110 | /// ``` | |
2111 | /// use std::sync::Arc; | |
2112 | /// | |
85aaf69f | 2113 | /// let five = Arc::new(5); |
1a4d82fc | 2114 | /// |
c30ab7b3 | 2115 | /// assert!(five != Arc::new(6)); |
1a4d82fc | 2116 | /// ``` |
0731742a | 2117 | #[inline] |
b039eaaf | 2118 | fn ne(&self, other: &Arc<T>) -> bool { |
0731742a | 2119 | ArcEqIdent::ne(self, other) |
b039eaaf | 2120 | } |
1a4d82fc | 2121 | } |
0731742a | 2122 | |
85aaf69f | 2123 | #[stable(feature = "rust1", since = "1.0.0")] |
62682a34 | 2124 | impl<T: ?Sized + PartialOrd> PartialOrd for Arc<T> { |
c30ab7b3 | 2125 | /// Partial comparison for two `Arc`s. |
1a4d82fc JJ |
2126 | /// |
2127 | /// The two are compared by calling `partial_cmp()` on their inner values. | |
2128 | /// | |
2129 | /// # Examples | |
2130 | /// | |
2131 | /// ``` | |
2132 | /// use std::sync::Arc; | |
c30ab7b3 | 2133 | /// use std::cmp::Ordering; |
1a4d82fc | 2134 | /// |
85aaf69f | 2135 | /// let five = Arc::new(5); |
1a4d82fc | 2136 | /// |
c30ab7b3 | 2137 | /// assert_eq!(Some(Ordering::Less), five.partial_cmp(&Arc::new(6))); |
1a4d82fc JJ |
2138 | /// ``` |
2139 | fn partial_cmp(&self, other: &Arc<T>) -> Option<Ordering> { | |
2140 | (**self).partial_cmp(&**other) | |
2141 | } | |
2142 | ||
c30ab7b3 | 2143 | /// Less-than comparison for two `Arc`s. |
1a4d82fc JJ |
2144 | /// |
2145 | /// The two are compared by calling `<` on their inner values. | |
2146 | /// | |
2147 | /// # Examples | |
2148 | /// | |
2149 | /// ``` | |
2150 | /// use std::sync::Arc; | |
2151 | /// | |
85aaf69f | 2152 | /// let five = Arc::new(5); |
1a4d82fc | 2153 | /// |
c30ab7b3 | 2154 | /// assert!(five < Arc::new(6)); |
1a4d82fc | 2155 | /// ``` |
b039eaaf SL |
2156 | fn lt(&self, other: &Arc<T>) -> bool { |
2157 | *(*self) < *(*other) | |
2158 | } | |
1a4d82fc | 2159 | |
c30ab7b3 | 2160 | /// 'Less than or equal to' comparison for two `Arc`s. |
1a4d82fc JJ |
2161 | /// |
2162 | /// The two are compared by calling `<=` on their inner values. | |
2163 | /// | |
2164 | /// # Examples | |
2165 | /// | |
2166 | /// ``` | |
2167 | /// use std::sync::Arc; | |
2168 | /// | |
85aaf69f | 2169 | /// let five = Arc::new(5); |
1a4d82fc | 2170 | /// |
c30ab7b3 | 2171 | /// assert!(five <= Arc::new(5)); |
1a4d82fc | 2172 | /// ``` |
b039eaaf SL |
2173 | fn le(&self, other: &Arc<T>) -> bool { |
2174 | *(*self) <= *(*other) | |
2175 | } | |
1a4d82fc | 2176 | |
c30ab7b3 | 2177 | /// Greater-than comparison for two `Arc`s. |
1a4d82fc JJ |
2178 | /// |
2179 | /// The two are compared by calling `>` on their inner values. | |
2180 | /// | |
2181 | /// # Examples | |
2182 | /// | |
2183 | /// ``` | |
2184 | /// use std::sync::Arc; | |
2185 | /// | |
85aaf69f | 2186 | /// let five = Arc::new(5); |
1a4d82fc | 2187 | /// |
c30ab7b3 | 2188 | /// assert!(five > Arc::new(4)); |
1a4d82fc | 2189 | /// ``` |
b039eaaf SL |
2190 | fn gt(&self, other: &Arc<T>) -> bool { |
2191 | *(*self) > *(*other) | |
2192 | } | |
1a4d82fc | 2193 | |
c30ab7b3 | 2194 | /// 'Greater than or equal to' comparison for two `Arc`s. |
1a4d82fc JJ |
2195 | /// |
2196 | /// The two are compared by calling `>=` on their inner values. | |
2197 | /// | |
2198 | /// # Examples | |
2199 | /// | |
2200 | /// ``` | |
2201 | /// use std::sync::Arc; | |
2202 | /// | |
85aaf69f | 2203 | /// let five = Arc::new(5); |
1a4d82fc | 2204 | /// |
c30ab7b3 | 2205 | /// assert!(five >= Arc::new(5)); |
1a4d82fc | 2206 | /// ``` |
b039eaaf SL |
2207 | fn ge(&self, other: &Arc<T>) -> bool { |
2208 | *(*self) >= *(*other) | |
2209 | } | |
1a4d82fc | 2210 | } |
85aaf69f | 2211 | #[stable(feature = "rust1", since = "1.0.0")] |
62682a34 | 2212 | impl<T: ?Sized + Ord> Ord for Arc<T> { |
c30ab7b3 SL |
2213 | /// Comparison for two `Arc`s. |
2214 | /// | |
2215 | /// The two are compared by calling `cmp()` on their inner values. | |
2216 | /// | |
2217 | /// # Examples | |
2218 | /// | |
2219 | /// ``` | |
2220 | /// use std::sync::Arc; | |
2221 | /// use std::cmp::Ordering; | |
2222 | /// | |
2223 | /// let five = Arc::new(5); | |
2224 | /// | |
2225 | /// assert_eq!(Ordering::Less, five.cmp(&Arc::new(6))); | |
2226 | /// ``` | |
b039eaaf SL |
2227 | fn cmp(&self, other: &Arc<T>) -> Ordering { |
2228 | (**self).cmp(&**other) | |
2229 | } | |
1a4d82fc | 2230 | } |
85aaf69f | 2231 | #[stable(feature = "rust1", since = "1.0.0")] |
62682a34 | 2232 | impl<T: ?Sized + Eq> Eq for Arc<T> {} |
1a4d82fc | 2233 | |
85aaf69f | 2234 | #[stable(feature = "rust1", since = "1.0.0")] |
62682a34 | 2235 | impl<T: ?Sized + fmt::Display> fmt::Display for Arc<T> { |
9fa01778 | 2236 | fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
85aaf69f | 2237 | fmt::Display::fmt(&**self, f) |
1a4d82fc JJ |
2238 | } |
2239 | } | |
2240 | ||
85aaf69f | 2241 | #[stable(feature = "rust1", since = "1.0.0")] |
62682a34 | 2242 | impl<T: ?Sized + fmt::Debug> fmt::Debug for Arc<T> { |
9fa01778 | 2243 | fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
85aaf69f | 2244 | fmt::Debug::fmt(&**self, f) |
1a4d82fc JJ |
2245 | } |
2246 | } | |
2247 | ||
9346a6ac | 2248 | #[stable(feature = "rust1", since = "1.0.0")] |
7453a54e | 2249 | impl<T: ?Sized> fmt::Pointer for Arc<T> { |
9fa01778 | 2250 | fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
ff7c6d11 | 2251 | fmt::Pointer::fmt(&(&**self as *const T), f) |
9346a6ac AL |
2252 | } |
2253 | } | |
2254 | ||
85aaf69f | 2255 | #[stable(feature = "rust1", since = "1.0.0")] |
d9579d0f | 2256 | impl<T: Default> Default for Arc<T> { |
c30ab7b3 SL |
2257 | /// Creates a new `Arc<T>`, with the `Default` value for `T`. |
2258 | /// | |
2259 | /// # Examples | |
2260 | /// | |
2261 | /// ``` | |
2262 | /// use std::sync::Arc; | |
2263 | /// | |
2264 | /// let x: Arc<i32> = Default::default(); | |
2265 | /// assert_eq!(*x, 0); | |
2266 | /// ``` | |
b039eaaf SL |
2267 | fn default() -> Arc<T> { |
2268 | Arc::new(Default::default()) | |
2269 | } | |
1a4d82fc JJ |
2270 | } |
2271 | ||
85aaf69f | 2272 | #[stable(feature = "rust1", since = "1.0.0")] |
62682a34 | 2273 | impl<T: ?Sized + Hash> Hash for Arc<T> { |
85aaf69f SL |
2274 | fn hash<H: Hasher>(&self, state: &mut H) { |
2275 | (**self).hash(state) | |
2276 | } | |
2277 | } | |
1a4d82fc | 2278 | |
92a42be0 SL |
2279 | #[stable(feature = "from_for_ptrs", since = "1.6.0")] |
2280 | impl<T> From<T> for Arc<T> { | |
2281 | fn from(t: T) -> Self { | |
2282 | Arc::new(t) | |
2283 | } | |
2284 | } | |
2285 | ||
3b2f2976 | 2286 | #[stable(feature = "shared_from_slice", since = "1.21.0")] |
9fa01778 | 2287 | impl<T: Clone> From<&[T]> for Arc<[T]> { |
6a06907d XL |
2288 | /// Allocate a reference-counted slice and fill it by cloning `v`'s items. |
2289 | /// | |
2290 | /// # Example | |
2291 | /// | |
2292 | /// ``` | |
2293 | /// # use std::sync::Arc; | |
2294 | /// let original: &[i32] = &[1, 2, 3]; | |
2295 | /// let shared: Arc<[i32]> = Arc::from(original); | |
2296 | /// assert_eq!(&[1, 2, 3], &shared[..]); | |
2297 | /// ``` | |
3b2f2976 XL |
2298 | #[inline] |
2299 | fn from(v: &[T]) -> Arc<[T]> { | |
2300 | <Self as ArcFromSlice<T>>::from_slice(v) | |
2301 | } | |
2302 | } | |
2303 | ||
2304 | #[stable(feature = "shared_from_slice", since = "1.21.0")] | |
9fa01778 | 2305 | impl From<&str> for Arc<str> { |
6a06907d XL |
2306 | /// Allocate a reference-counted `str` and copy `v` into it. |
2307 | /// | |
2308 | /// # Example | |
2309 | /// | |
2310 | /// ``` | |
2311 | /// # use std::sync::Arc; | |
2312 | /// let shared: Arc<str> = Arc::from("eggplant"); | |
2313 | /// assert_eq!("eggplant", &shared[..]); | |
2314 | /// ``` | |
3b2f2976 XL |
2315 | #[inline] |
2316 | fn from(v: &str) -> Arc<str> { | |
ff7c6d11 XL |
2317 | let arc = Arc::<[u8]>::from(v.as_bytes()); |
2318 | unsafe { Arc::from_raw(Arc::into_raw(arc) as *const str) } | |
3b2f2976 XL |
2319 | } |
2320 | } | |
2321 | ||
2322 | #[stable(feature = "shared_from_slice", since = "1.21.0")] | |
2323 | impl From<String> for Arc<str> { | |
6a06907d XL |
2324 | /// Allocate a reference-counted `str` and copy `v` into it. |
2325 | /// | |
2326 | /// # Example | |
2327 | /// | |
2328 | /// ``` | |
2329 | /// # use std::sync::Arc; | |
2330 | /// let unique: String = "eggplant".to_owned(); | |
2331 | /// let shared: Arc<str> = Arc::from(unique); | |
2332 | /// assert_eq!("eggplant", &shared[..]); | |
2333 | /// ``` | |
3b2f2976 XL |
2334 | #[inline] |
2335 | fn from(v: String) -> Arc<str> { | |
2336 | Arc::from(&v[..]) | |
2337 | } | |
2338 | } | |
2339 | ||
2340 | #[stable(feature = "shared_from_slice", since = "1.21.0")] | |
2341 | impl<T: ?Sized> From<Box<T>> for Arc<T> { | |
6a06907d XL |
2342 | /// Move a boxed object to a new, reference-counted allocation. |
2343 | /// | |
2344 | /// # Example | |
2345 | /// | |
2346 | /// ``` | |
2347 | /// # use std::sync::Arc; | |
2348 | /// let unique: Box<str> = Box::from("eggplant"); | |
2349 | /// let shared: Arc<str> = Arc::from(unique); | |
2350 | /// assert_eq!("eggplant", &shared[..]); | |
2351 | /// ``` | |
3b2f2976 XL |
2352 | #[inline] |
2353 | fn from(v: Box<T>) -> Arc<T> { | |
2354 | Arc::from_box(v) | |
2355 | } | |
2356 | } | |
2357 | ||
2358 | #[stable(feature = "shared_from_slice", since = "1.21.0")] | |
2359 | impl<T> From<Vec<T>> for Arc<[T]> { | |
6a06907d XL |
2360 | /// Allocate a reference-counted slice and move `v`'s items into it. |
2361 | /// | |
2362 | /// # Example | |
2363 | /// | |
2364 | /// ``` | |
2365 | /// # use std::sync::Arc; | |
2366 | /// let unique: Vec<i32> = vec![1, 2, 3]; | |
2367 | /// let shared: Arc<[i32]> = Arc::from(unique); | |
2368 | /// assert_eq!(&[1, 2, 3], &shared[..]); | |
2369 | /// ``` | |
3b2f2976 XL |
2370 | #[inline] |
2371 | fn from(mut v: Vec<T>) -> Arc<[T]> { | |
2372 | unsafe { | |
2373 | let arc = Arc::copy_from_slice(&v); | |
2374 | ||
2375 | // Allow the Vec to free its memory, but not destroy its contents | |
2376 | v.set_len(0); | |
2377 | ||
2378 | arc | |
2379 | } | |
2380 | } | |
2381 | } | |
2382 | ||
f9f354fc XL |
2383 | #[stable(feature = "shared_from_cow", since = "1.45.0")] |
2384 | impl<'a, B> From<Cow<'a, B>> for Arc<B> | |
2385 | where | |
2386 | B: ToOwned + ?Sized, | |
2387 | Arc<B>: From<&'a B> + From<B::Owned>, | |
2388 | { | |
2389 | #[inline] | |
2390 | fn from(cow: Cow<'a, B>) -> Arc<B> { | |
2391 | match cow { | |
2392 | Cow::Borrowed(s) => Arc::from(s), | |
2393 | Cow::Owned(s) => Arc::from(s), | |
2394 | } | |
2395 | } | |
2396 | } | |
2397 | ||
74b04a01 | 2398 | #[stable(feature = "boxed_slice_try_from", since = "1.43.0")] |
3dfed10e | 2399 | impl<T, const N: usize> TryFrom<Arc<[T]>> for Arc<[T; N]> { |
416331ca | 2400 | type Error = Arc<[T]>; |
1a4d82fc | 2401 | |
416331ca XL |
2402 | fn try_from(boxed_slice: Arc<[T]>) -> Result<Self, Self::Error> { |
2403 | if boxed_slice.len() == N { | |
2404 | Ok(unsafe { Arc::from_raw(Arc::into_raw(boxed_slice) as *mut [T; N]) }) | |
2405 | } else { | |
2406 | Err(boxed_slice) | |
3b2f2976 | 2407 | } |
3b2f2976 | 2408 | } |
416331ca | 2409 | } |
3b2f2976 | 2410 | |
416331ca XL |
2411 | #[stable(feature = "shared_from_iter", since = "1.37.0")] |
2412 | impl<T> iter::FromIterator<T> for Arc<[T]> { | |
2413 | /// Takes each element in the `Iterator` and collects it into an `Arc<[T]>`. | |
2414 | /// | |
2415 | /// # Performance characteristics | |
2416 | /// | |
2417 | /// ## The general case | |
2418 | /// | |
2419 | /// In the general case, collecting into `Arc<[T]>` is done by first | |
2420 | /// collecting into a `Vec<T>`. That is, when writing the following: | |
2421 | /// | |
2422 | /// ```rust | |
2423 | /// # use std::sync::Arc; | |
2424 | /// let evens: Arc<[u8]> = (0..10).filter(|&x| x % 2 == 0).collect(); | |
2425 | /// # assert_eq!(&*evens, &[0, 2, 4, 6, 8]); | |
2426 | /// ``` | |
2427 | /// | |
2428 | /// this behaves as if we wrote: | |
2429 | /// | |
2430 | /// ```rust | |
2431 | /// # use std::sync::Arc; | |
2432 | /// let evens: Arc<[u8]> = (0..10).filter(|&x| x % 2 == 0) | |
2433 | /// .collect::<Vec<_>>() // The first set of allocations happens here. | |
2434 | /// .into(); // A second allocation for `Arc<[T]>` happens here. | |
2435 | /// # assert_eq!(&*evens, &[0, 2, 4, 6, 8]); | |
2436 | /// ``` | |
2437 | /// | |
2438 | /// This will allocate as many times as needed for constructing the `Vec<T>` | |
2439 | /// and then it will allocate once for turning the `Vec<T>` into the `Arc<[T]>`. | |
2440 | /// | |
2441 | /// ## Iterators of known length | |
2442 | /// | |
2443 | /// When your `Iterator` implements `TrustedLen` and is of an exact size, | |
2444 | /// a single allocation will be made for the `Arc<[T]>`. For example: | |
2445 | /// | |
2446 | /// ```rust | |
2447 | /// # use std::sync::Arc; | |
2448 | /// let evens: Arc<[u8]> = (0..10).collect(); // Just a single allocation happens here. | |
2449 | /// # assert_eq!(&*evens, &*(0..10).collect::<Vec<_>>()); | |
2450 | /// ``` | |
2451 | fn from_iter<I: iter::IntoIterator<Item = T>>(iter: I) -> Self { | |
f9f354fc | 2452 | ToArcSlice::to_arc_slice(iter.into_iter()) |
3b2f2976 | 2453 | } |
416331ca | 2454 | } |
3b2f2976 | 2455 | |
416331ca | 2456 | /// Specialization trait used for collecting into `Arc<[T]>`. |
f9f354fc XL |
2457 | trait ToArcSlice<T>: Iterator<Item = T> + Sized { |
2458 | fn to_arc_slice(self) -> Arc<[T]>; | |
416331ca | 2459 | } |
3b2f2976 | 2460 | |
f9f354fc XL |
2461 | impl<T, I: Iterator<Item = T>> ToArcSlice<T> for I { |
2462 | default fn to_arc_slice(self) -> Arc<[T]> { | |
2463 | self.collect::<Vec<T>>().into() | |
3b2f2976 | 2464 | } |
416331ca | 2465 | } |
3b2f2976 | 2466 | |
f9f354fc XL |
2467 | impl<T, I: iter::TrustedLen<Item = T>> ToArcSlice<T> for I { |
2468 | fn to_arc_slice(self) -> Arc<[T]> { | |
416331ca | 2469 | // This is the case for a `TrustedLen` iterator. |
f9f354fc | 2470 | let (low, high) = self.size_hint(); |
416331ca XL |
2471 | if let Some(high) = high { |
2472 | debug_assert_eq!( | |
dfeec247 XL |
2473 | low, |
2474 | high, | |
416331ca XL |
2475 | "TrustedLen iterator's size hint is not exact: {:?}", |
2476 | (low, high) | |
2477 | ); | |
3b2f2976 | 2478 | |
416331ca XL |
2479 | unsafe { |
2480 | // SAFETY: We need to ensure that the iterator has an exact length and we have. | |
f9f354fc | 2481 | Arc::from_iter_exact(self, low) |
3b2f2976 | 2482 | } |
416331ca XL |
2483 | } else { |
2484 | // Fall back to normal implementation. | |
f9f354fc | 2485 | self.collect::<Vec<T>>().into() |
3b2f2976 | 2486 | } |
3b2f2976 | 2487 | } |
416331ca | 2488 | } |
3b2f2976 | 2489 | |
92a42be0 | 2490 | #[stable(feature = "rust1", since = "1.0.0")] |
e9174d1e | 2491 | impl<T: ?Sized> borrow::Borrow<T> for Arc<T> { |
b039eaaf SL |
2492 | fn borrow(&self) -> &T { |
2493 | &**self | |
2494 | } | |
2495 | } | |
2496 | ||
2497 | #[stable(since = "1.5.0", feature = "smart_ptr_as_ref")] | |
2498 | impl<T: ?Sized> AsRef<T> for Arc<T> { | |
2499 | fn as_ref(&self) -> &T { | |
2500 | &**self | |
2501 | } | |
e9174d1e | 2502 | } |
b7449926 | 2503 | |
0731742a | 2504 | #[stable(feature = "pin", since = "1.33.0")] |
dfeec247 | 2505 | impl<T: ?Sized> Unpin for Arc<T> {} |
dc9dc135 | 2506 | |
5869c6ff | 2507 | /// Get the offset within an `ArcInner` for the payload behind a pointer. |
f035d41b XL |
2508 | /// |
2509 | /// # Safety | |
2510 | /// | |
5869c6ff XL |
2511 | /// The pointer must point to (and have valid metadata for) a previously |
2512 | /// valid instance of T, but the T is allowed to be dropped. | |
dc9dc135 | 2513 | unsafe fn data_offset<T: ?Sized>(ptr: *const T) -> isize { |
5869c6ff XL |
2514 | // Align the unsized value to the end of the ArcInner. |
2515 | // Because RcBox is repr(C), it will always be the last field in memory. | |
2516 | // SAFETY: since the only unsized types possible are slices, trait objects, | |
2517 | // and extern types, the input safety requirement is currently enough to | |
2518 | // satisfy the requirements of align_of_val_raw; this is an implementation | |
2519 | // detail of the language that may not be relied upon outside of std. | |
2520 | unsafe { data_offset_align(align_of_val_raw(ptr)) } | |
416331ca XL |
2521 | } |
2522 | ||
2523 | #[inline] | |
2524 | fn data_offset_align(align: usize) -> isize { | |
dc9dc135 XL |
2525 | let layout = Layout::new::<ArcInner<()>>(); |
2526 | (layout.size() + layout.padding_needed_for(align)) as isize | |
2527 | } |