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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; |
17df50a5 | 15 | #[cfg(not(no_global_oom_handling))] |
dfeec247 XL |
16 | use core::iter; |
17 | use core::marker::{PhantomData, Unpin, Unsize}; | |
17df50a5 XL |
18 | #[cfg(not(no_global_oom_handling))] |
19 | use core::mem::size_of_val; | |
20 | use core::mem::{self, align_of_val_raw}; | |
dfeec247 | 21 | use core::ops::{CoerceUnsized, Deref, DispatchFromDyn, Receiver}; |
0bf4aa26 | 22 | use core::pin::Pin; |
2c00a5a8 | 23 | use core::ptr::{self, NonNull}; |
17df50a5 | 24 | #[cfg(not(no_global_oom_handling))] |
f9f354fc | 25 | use core::slice::from_raw_parts_mut; |
dfeec247 XL |
26 | use core::sync::atomic; |
27 | use core::sync::atomic::Ordering::{Acquire, Relaxed, Release, SeqCst}; | |
041b39d2 | 28 | |
17df50a5 XL |
29 | #[cfg(not(no_global_oom_handling))] |
30 | use crate::alloc::handle_alloc_error; | |
31 | #[cfg(not(no_global_oom_handling))] | |
32 | use crate::alloc::{box_free, WriteCloneIntoRaw}; | |
33 | use crate::alloc::{AllocError, Allocator, Global, Layout}; | |
f9f354fc | 34 | use crate::borrow::{Cow, ToOwned}; |
9fa01778 XL |
35 | use crate::boxed::Box; |
36 | use crate::rc::is_dangling; | |
17df50a5 | 37 | #[cfg(not(no_global_oom_handling))] |
9fa01778 | 38 | use crate::string::String; |
17df50a5 | 39 | #[cfg(not(no_global_oom_handling))] |
9fa01778 | 40 | use crate::vec::Vec; |
1a4d82fc | 41 | |
416331ca XL |
42 | #[cfg(test)] |
43 | mod tests; | |
44 | ||
c30ab7b3 SL |
45 | /// A soft limit on the amount of references that may be made to an `Arc`. |
46 | /// | |
47 | /// Going above this limit will abort your program (although not | |
48 | /// necessarily) at _exactly_ `MAX_REFCOUNT + 1` references. | |
c1a9b12d SL |
49 | const MAX_REFCOUNT: usize = (isize::MAX) as usize; |
50 | ||
ba9703b0 XL |
51 | #[cfg(not(sanitize = "thread"))] |
52 | macro_rules! acquire { | |
53 | ($x:expr) => { | |
54 | atomic::fence(Acquire) | |
55 | }; | |
56 | } | |
57 | ||
58 | // ThreadSanitizer does not support memory fences. To avoid false positive | |
59 | // reports in Arc / Weak implementation use atomic loads for synchronization | |
60 | // instead. | |
61 | #[cfg(sanitize = "thread")] | |
62 | macro_rules! acquire { | |
63 | ($x:expr) => { | |
64 | $x.load(Acquire) | |
65 | }; | |
66 | } | |
67 | ||
041b39d2 XL |
68 | /// A thread-safe reference-counting pointer. 'Arc' stands for 'Atomically |
69 | /// Reference Counted'. | |
1a4d82fc | 70 | /// |
c30ab7b3 SL |
71 | /// The type `Arc<T>` provides shared ownership of a value of type `T`, |
72 | /// allocated in the heap. Invoking [`clone`][clone] on `Arc` produces | |
e74abb32 | 73 | /// a new `Arc` instance, which points to the same allocation on the heap as the |
b7449926 | 74 | /// source `Arc`, while increasing a reference count. When the last `Arc` |
e74abb32 XL |
75 | /// pointer to a given allocation is destroyed, the value stored in that allocation (often |
76 | /// referred to as "inner value") is also dropped. | |
1a4d82fc | 77 | /// |
c30ab7b3 | 78 | /// Shared references in Rust disallow mutation by default, and `Arc` is no |
ea8adc8c XL |
79 | /// exception: you cannot generally obtain a mutable reference to something |
80 | /// inside an `Arc`. If you need to mutate through an `Arc`, use | |
81 | /// [`Mutex`][mutex], [`RwLock`][rwlock], or one of the [`Atomic`][atomic] | |
82 | /// types. | |
9e0c209e | 83 | /// |
7cac9316 XL |
84 | /// ## Thread Safety |
85 | /// | |
86 | /// Unlike [`Rc<T>`], `Arc<T>` uses atomic operations for its reference | |
83c7162d | 87 | /// counting. This means that it is thread-safe. The disadvantage is that |
7cac9316 | 88 | /// atomic operations are more expensive than ordinary memory accesses. If you |
e74abb32 | 89 | /// are not sharing reference-counted allocations between threads, consider using |
7cac9316 XL |
90 | /// [`Rc<T>`] for lower overhead. [`Rc<T>`] is a safe default, because the |
91 | /// compiler will catch any attempt to send an [`Rc<T>`] between threads. | |
92 | /// However, a library might choose `Arc<T>` in order to give library consumers | |
c30ab7b3 | 93 | /// more flexibility. |
1a4d82fc | 94 | /// |
7cac9316 XL |
95 | /// `Arc<T>` will implement [`Send`] and [`Sync`] as long as the `T` implements |
96 | /// [`Send`] and [`Sync`]. Why can't you put a non-thread-safe type `T` in an | |
97 | /// `Arc<T>` to make it thread-safe? This may be a bit counter-intuitive at | |
98 | /// first: after all, isn't the point of `Arc<T>` thread safety? The key is | |
99 | /// this: `Arc<T>` makes it thread safe to have multiple ownership of the same | |
100 | /// data, but it doesn't add thread safety to its data. Consider | |
ea8adc8c XL |
101 | /// `Arc<`[`RefCell<T>`]`>`. [`RefCell<T>`] isn't [`Sync`], and if `Arc<T>` was always |
102 | /// [`Send`], `Arc<`[`RefCell<T>`]`>` would be as well. But then we'd have a problem: | |
103 | /// [`RefCell<T>`] is not thread safe; it keeps track of the borrowing count using | |
7cac9316 XL |
104 | /// non-atomic operations. |
105 | /// | |
106 | /// In the end, this means that you may need to pair `Arc<T>` with some sort of | |
ea8adc8c | 107 | /// [`std::sync`] type, usually [`Mutex<T>`][mutex]. |
7cac9316 XL |
108 | /// |
109 | /// ## Breaking cycles with `Weak` | |
110 | /// | |
c30ab7b3 | 111 | /// The [`downgrade`][downgrade] method can be used to create a non-owning |
3dfed10e | 112 | /// [`Weak`] pointer. A [`Weak`] pointer can be [`upgrade`][upgrade]d |
e74abb32 XL |
113 | /// to an `Arc`, but this will return [`None`] if the value stored in the allocation has |
114 | /// already been dropped. In other words, `Weak` pointers do not keep the value | |
115 | /// inside the allocation alive; however, they *do* keep the allocation | |
116 | /// (the backing store for the value) alive. | |
c30ab7b3 SL |
117 | /// |
118 | /// A cycle between `Arc` pointers will never be deallocated. For this reason, | |
3dfed10e XL |
119 | /// [`Weak`] is used to break cycles. For example, a tree could have |
120 | /// strong `Arc` pointers from parent nodes to children, and [`Weak`] | |
32a655c1 | 121 | /// pointers from children back to their parents. |
c30ab7b3 | 122 | /// |
7cac9316 XL |
123 | /// # Cloning references |
124 | /// | |
1b1a35ee | 125 | /// Creating a new reference from an existing reference-counted pointer is done using the |
3dfed10e | 126 | /// `Clone` trait implemented for [`Arc<T>`][Arc] and [`Weak<T>`][Weak]. |
7cac9316 XL |
127 | /// |
128 | /// ``` | |
129 | /// use std::sync::Arc; | |
130 | /// let foo = Arc::new(vec![1.0, 2.0, 3.0]); | |
131 | /// // The two syntaxes below are equivalent. | |
132 | /// let a = foo.clone(); | |
133 | /// let b = Arc::clone(&foo); | |
b7449926 | 134 | /// // a, b, and foo are all Arcs that point to the same memory location |
7cac9316 XL |
135 | /// ``` |
136 | /// | |
7cac9316 XL |
137 | /// ## `Deref` behavior |
138 | /// | |
c30ab7b3 SL |
139 | /// `Arc<T>` automatically dereferences to `T` (via the [`Deref`][deref] trait), |
140 | /// so you can call `T`'s methods on a value of type `Arc<T>`. To avoid name | |
13cf67c4 | 141 | /// clashes with `T`'s methods, the methods of `Arc<T>` itself are associated |
29967ef6 | 142 | /// functions, called using [fully qualified syntax]: |
c34b1796 AL |
143 | /// |
144 | /// ``` | |
1a4d82fc | 145 | /// use std::sync::Arc; |
1a4d82fc | 146 | /// |
29967ef6 | 147 | /// let my_arc = Arc::new(()); |
c30ab7b3 SL |
148 | /// Arc::downgrade(&my_arc); |
149 | /// ``` | |
1a4d82fc | 150 | /// |
29967ef6 XL |
151 | /// `Arc<T>`'s implementations of traits like `Clone` may also be called using |
152 | /// fully qualified syntax. Some people prefer to use fully qualified syntax, | |
153 | /// while others prefer using method-call syntax. | |
154 | /// | |
155 | /// ``` | |
156 | /// use std::sync::Arc; | |
157 | /// | |
158 | /// let arc = Arc::new(()); | |
159 | /// // Method-call syntax | |
160 | /// let arc2 = arc.clone(); | |
161 | /// // Fully qualified syntax | |
162 | /// let arc3 = Arc::clone(&arc); | |
163 | /// ``` | |
164 | /// | |
3dfed10e | 165 | /// [`Weak<T>`][Weak] does not auto-dereference to `T`, because the inner value may have |
e74abb32 | 166 | /// already been dropped. |
1a4d82fc | 167 | /// |
3dfed10e XL |
168 | /// [`Rc<T>`]: crate::rc::Rc |
169 | /// [clone]: Clone::clone | |
c30ab7b3 SL |
170 | /// [mutex]: ../../std/sync/struct.Mutex.html |
171 | /// [rwlock]: ../../std/sync/struct.RwLock.html | |
3dfed10e XL |
172 | /// [atomic]: core::sync::atomic |
173 | /// [`Send`]: core::marker::Send | |
174 | /// [`Sync`]: core::marker::Sync | |
175 | /// [deref]: core::ops::Deref | |
176 | /// [downgrade]: Arc::downgrade | |
177 | /// [upgrade]: Weak::upgrade | |
178 | /// [`RefCell<T>`]: core::cell::RefCell | |
ea8adc8c | 179 | /// [`std::sync`]: ../../std/sync/index.html |
1b1a35ee | 180 | /// [`Arc::clone(&from)`]: Arc::clone |
29967ef6 | 181 | /// [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 | 182 | /// |
c30ab7b3 | 183 | /// # Examples |
5bcae85e | 184 | /// |
c30ab7b3 SL |
185 | /// Sharing some immutable data between threads: |
186 | /// | |
187 | // Note that we **do not** run these tests here. The windows builders get super | |
188 | // unhappy if a thread outlives the main thread and then exits at the same time | |
189 | // (something deadlocks) so we just avoid this entirely by not running these | |
190 | // tests. | |
5bcae85e | 191 | /// ```no_run |
c30ab7b3 | 192 | /// use std::sync::Arc; |
5bcae85e SL |
193 | /// use std::thread; |
194 | /// | |
c30ab7b3 | 195 | /// let five = Arc::new(5); |
5bcae85e SL |
196 | /// |
197 | /// for _ in 0..10 { | |
7cac9316 | 198 | /// let five = Arc::clone(&five); |
5bcae85e SL |
199 | /// |
200 | /// thread::spawn(move || { | |
c30ab7b3 SL |
201 | /// println!("{:?}", five); |
202 | /// }); | |
203 | /// } | |
204 | /// ``` | |
5bcae85e | 205 | /// |
32a655c1 SL |
206 | /// Sharing a mutable [`AtomicUsize`]: |
207 | /// | |
3dfed10e | 208 | /// [`AtomicUsize`]: core::sync::atomic::AtomicUsize |
5bcae85e | 209 | /// |
c30ab7b3 SL |
210 | /// ```no_run |
211 | /// use std::sync::Arc; | |
212 | /// use std::sync::atomic::{AtomicUsize, Ordering}; | |
213 | /// use std::thread; | |
214 | /// | |
215 | /// let val = Arc::new(AtomicUsize::new(5)); | |
216 | /// | |
217 | /// for _ in 0..10 { | |
7cac9316 | 218 | /// let val = Arc::clone(&val); |
c30ab7b3 SL |
219 | /// |
220 | /// thread::spawn(move || { | |
221 | /// let v = val.fetch_add(1, Ordering::SeqCst); | |
222 | /// println!("{:?}", v); | |
5bcae85e SL |
223 | /// }); |
224 | /// } | |
225 | /// ``` | |
c30ab7b3 SL |
226 | /// |
227 | /// See the [`rc` documentation][rc_examples] for more examples of reference | |
228 | /// counting in general. | |
229 | /// | |
1b1a35ee | 230 | /// [rc_examples]: crate::rc#examples |
ba9703b0 | 231 | #[cfg_attr(not(test), rustc_diagnostic_item = "Arc")] |
85aaf69f | 232 | #[stable(feature = "rust1", since = "1.0.0")] |
62682a34 | 233 | pub struct Arc<T: ?Sized> { |
2c00a5a8 | 234 | ptr: NonNull<ArcInner<T>>, |
60c5eb7d | 235 | phantom: PhantomData<ArcInner<T>>, |
1a4d82fc JJ |
236 | } |
237 | ||
92a42be0 SL |
238 | #[stable(feature = "rust1", since = "1.0.0")] |
239 | unsafe impl<T: ?Sized + Sync + Send> Send for Arc<T> {} | |
240 | #[stable(feature = "rust1", since = "1.0.0")] | |
241 | unsafe impl<T: ?Sized + Sync + Send> Sync for Arc<T> {} | |
1a4d82fc | 242 | |
92a42be0 | 243 | #[unstable(feature = "coerce_unsized", issue = "27732")] |
62682a34 | 244 | impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Arc<U>> for Arc<T> {} |
1a4d82fc | 245 | |
dfeec247 | 246 | #[unstable(feature = "dispatch_from_dyn", issue = "none")] |
a1dfa0c6 XL |
247 | impl<T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<Arc<U>> for Arc<T> {} |
248 | ||
416331ca XL |
249 | impl<T: ?Sized> Arc<T> { |
250 | fn from_inner(ptr: NonNull<ArcInner<T>>) -> Self { | |
dfeec247 | 251 | Self { ptr, phantom: PhantomData } |
416331ca XL |
252 | } |
253 | ||
254 | unsafe fn from_ptr(ptr: *mut ArcInner<T>) -> Self { | |
f035d41b | 255 | unsafe { Self::from_inner(NonNull::new_unchecked(ptr)) } |
416331ca XL |
256 | } |
257 | } | |
258 | ||
cc61c64b | 259 | /// `Weak` is a version of [`Arc`] that holds a non-owning reference to the |
e74abb32 | 260 | /// managed allocation. The allocation is accessed by calling [`upgrade`] on the `Weak` |
cc61c64b | 261 | /// pointer, which returns an [`Option`]`<`[`Arc`]`<T>>`. |
1a4d82fc | 262 | /// |
cc61c64b | 263 | /// Since a `Weak` reference does not count towards ownership, it will not |
e74abb32 XL |
264 | /// prevent the value stored in the allocation from being dropped, and `Weak` itself makes no |
265 | /// guarantees about the value still being present. Thus it may return [`None`] | |
266 | /// when [`upgrade`]d. Note however that a `Weak` reference *does* prevent the allocation | |
267 | /// itself (the backing store) from being deallocated. | |
5bcae85e | 268 | /// |
e74abb32 XL |
269 | /// A `Weak` pointer is useful for keeping a temporary reference to the allocation |
270 | /// managed by [`Arc`] without preventing its inner value from being dropped. It is also used to | |
271 | /// prevent circular references between [`Arc`] pointers, since mutual owning references | |
cc61c64b XL |
272 | /// would never allow either [`Arc`] to be dropped. For example, a tree could |
273 | /// have strong [`Arc`] pointers from parent nodes to children, and `Weak` | |
274 | /// pointers from children back to their parents. | |
5bcae85e | 275 | /// |
cc61c64b | 276 | /// The typical way to obtain a `Weak` pointer is to call [`Arc::downgrade`]. |
c30ab7b3 | 277 | /// |
3dfed10e | 278 | /// [`upgrade`]: Weak::upgrade |
e9174d1e | 279 | #[stable(feature = "arc_weak", since = "1.4.0")] |
62682a34 | 280 | pub struct Weak<T: ?Sized> { |
8faf50e0 XL |
281 | // This is a `NonNull` to allow optimizing the size of this type in enums, |
282 | // but it is not necessarily a valid pointer. | |
283 | // `Weak::new` sets this to `usize::MAX` so that it doesn’t need | |
284 | // to allocate space on the heap. That's not a value a real pointer | |
285 | // will ever have because RcBox has alignment at least 2. | |
f035d41b | 286 | // This is only possible when `T: Sized`; unsized `T` never dangle. |
2c00a5a8 | 287 | ptr: NonNull<ArcInner<T>>, |
1a4d82fc JJ |
288 | } |
289 | ||
7453a54e | 290 | #[stable(feature = "arc_weak", since = "1.4.0")] |
92a42be0 | 291 | unsafe impl<T: ?Sized + Sync + Send> Send for Weak<T> {} |
7453a54e | 292 | #[stable(feature = "arc_weak", since = "1.4.0")] |
92a42be0 | 293 | unsafe impl<T: ?Sized + Sync + Send> Sync for Weak<T> {} |
1a4d82fc | 294 | |
92a42be0 | 295 | #[unstable(feature = "coerce_unsized", issue = "27732")] |
c1a9b12d | 296 | impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Weak<U>> for Weak<T> {} |
dfeec247 | 297 | #[unstable(feature = "dispatch_from_dyn", issue = "none")] |
a1dfa0c6 | 298 | impl<T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<Weak<U>> for Weak<T> {} |
c1a9b12d | 299 | |
7453a54e | 300 | #[stable(feature = "arc_weak", since = "1.4.0")] |
62682a34 | 301 | impl<T: ?Sized + fmt::Debug> fmt::Debug for Weak<T> { |
9fa01778 | 302 | fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
c34b1796 AL |
303 | write!(f, "(Weak)") |
304 | } | |
305 | } | |
306 | ||
ba9703b0 XL |
307 | // This is repr(C) to future-proof against possible field-reordering, which |
308 | // would interfere with otherwise safe [into|from]_raw() of transmutable | |
309 | // inner types. | |
310 | #[repr(C)] | |
62682a34 | 311 | struct ArcInner<T: ?Sized> { |
85aaf69f | 312 | strong: atomic::AtomicUsize, |
c1a9b12d SL |
313 | |
314 | // the value usize::MAX acts as a sentinel for temporarily "locking" the | |
315 | // ability to upgrade weak pointers or downgrade strong ones; this is used | |
e9174d1e | 316 | // to avoid races in `make_mut` and `get_mut`. |
85aaf69f | 317 | weak: atomic::AtomicUsize, |
c1a9b12d | 318 | |
1a4d82fc JJ |
319 | data: T, |
320 | } | |
321 | ||
62682a34 SL |
322 | unsafe impl<T: ?Sized + Sync + Send> Send for ArcInner<T> {} |
323 | unsafe impl<T: ?Sized + Sync + Send> Sync for ArcInner<T> {} | |
1a4d82fc JJ |
324 | |
325 | impl<T> Arc<T> { | |
326 | /// Constructs a new `Arc<T>`. | |
327 | /// | |
328 | /// # Examples | |
329 | /// | |
330 | /// ``` | |
331 | /// use std::sync::Arc; | |
332 | /// | |
85aaf69f | 333 | /// let five = Arc::new(5); |
1a4d82fc JJ |
334 | /// ``` |
335 | #[inline] | |
85aaf69f | 336 | #[stable(feature = "rust1", since = "1.0.0")] |
1a4d82fc JJ |
337 | pub fn new(data: T) -> Arc<T> { |
338 | // Start the weak pointer count as 1 which is the weak pointer that's | |
339 | // held by all the strong pointers (kinda), see std/rc.rs for more info | |
c34b1796 | 340 | let x: Box<_> = box ArcInner { |
85aaf69f SL |
341 | strong: atomic::AtomicUsize::new(1), |
342 | weak: atomic::AtomicUsize::new(1), | |
3b2f2976 | 343 | data, |
1a4d82fc | 344 | }; |
f9f354fc | 345 | Self::from_inner(Box::leak(x).into()) |
e9174d1e SL |
346 | } |
347 | ||
3dfed10e XL |
348 | /// Constructs a new `Arc<T>` using a weak reference to itself. Attempting |
349 | /// to upgrade the weak reference before this function returns will result | |
350 | /// in a `None` value. However, the weak reference may be cloned freely and | |
351 | /// stored for use at a later time. | |
352 | /// | |
353 | /// # Examples | |
354 | /// ``` | |
355 | /// #![feature(arc_new_cyclic)] | |
356 | /// #![allow(dead_code)] | |
357 | /// | |
358 | /// use std::sync::{Arc, Weak}; | |
359 | /// | |
360 | /// struct Foo { | |
361 | /// me: Weak<Foo>, | |
362 | /// } | |
363 | /// | |
364 | /// let foo = Arc::new_cyclic(|me| Foo { | |
365 | /// me: me.clone(), | |
366 | /// }); | |
367 | /// ``` | |
368 | #[inline] | |
369 | #[unstable(feature = "arc_new_cyclic", issue = "75861")] | |
370 | pub fn new_cyclic(data_fn: impl FnOnce(&Weak<T>) -> T) -> Arc<T> { | |
371 | // Construct the inner in the "uninitialized" state with a single | |
372 | // weak reference. | |
373 | let uninit_ptr: NonNull<_> = Box::leak(box ArcInner { | |
374 | strong: atomic::AtomicUsize::new(0), | |
375 | weak: atomic::AtomicUsize::new(1), | |
376 | data: mem::MaybeUninit::<T>::uninit(), | |
377 | }) | |
378 | .into(); | |
379 | let init_ptr: NonNull<ArcInner<T>> = uninit_ptr.cast(); | |
380 | ||
381 | let weak = Weak { ptr: init_ptr }; | |
382 | ||
383 | // It's important we don't give up ownership of the weak pointer, or | |
384 | // else the memory might be freed by the time `data_fn` returns. If | |
385 | // we really wanted to pass ownership, we could create an additional | |
386 | // weak pointer for ourselves, but this would result in additional | |
387 | // updates to the weak reference count which might not be necessary | |
388 | // otherwise. | |
389 | let data = data_fn(&weak); | |
390 | ||
391 | // Now we can properly initialize the inner value and turn our weak | |
392 | // reference into a strong reference. | |
393 | unsafe { | |
394 | let inner = init_ptr.as_ptr(); | |
5869c6ff | 395 | ptr::write(ptr::addr_of_mut!((*inner).data), data); |
3dfed10e XL |
396 | |
397 | // The above write to the data field must be visible to any threads which | |
398 | // observe a non-zero strong count. Therefore we need at least "Release" ordering | |
399 | // in order to synchronize with the `compare_exchange_weak` in `Weak::upgrade`. | |
400 | // | |
401 | // "Acquire" ordering is not required. When considering the possible behaviours | |
402 | // of `data_fn` we only need to look at what it could do with a reference to a | |
403 | // non-upgradeable `Weak`: | |
404 | // - It can *clone* the `Weak`, increasing the weak reference count. | |
405 | // - It can drop those clones, decreasing the weak reference count (but never to zero). | |
406 | // | |
407 | // These side effects do not impact us in any way, and no other side effects are | |
408 | // possible with safe code alone. | |
409 | let prev_value = (*inner).strong.fetch_add(1, Release); | |
410 | debug_assert_eq!(prev_value, 0, "No prior strong references should exist"); | |
411 | } | |
412 | ||
413 | let strong = Arc::from_inner(init_ptr); | |
414 | ||
415 | // Strong references should collectively own a shared weak reference, | |
416 | // so don't run the destructor for our old weak reference. | |
417 | mem::forget(weak); | |
418 | strong | |
419 | } | |
420 | ||
e1599b0c XL |
421 | /// Constructs a new `Arc` with uninitialized contents. |
422 | /// | |
423 | /// # Examples | |
424 | /// | |
425 | /// ``` | |
426 | /// #![feature(new_uninit)] | |
427 | /// #![feature(get_mut_unchecked)] | |
428 | /// | |
429 | /// use std::sync::Arc; | |
430 | /// | |
431 | /// let mut five = Arc::<u32>::new_uninit(); | |
432 | /// | |
433 | /// let five = unsafe { | |
434 | /// // Deferred initialization: | |
435 | /// Arc::get_mut_unchecked(&mut five).as_mut_ptr().write(5); | |
436 | /// | |
437 | /// five.assume_init() | |
438 | /// }; | |
439 | /// | |
440 | /// assert_eq!(*five, 5) | |
441 | /// ``` | |
17df50a5 | 442 | #[cfg(not(no_global_oom_handling))] |
e1599b0c XL |
443 | #[unstable(feature = "new_uninit", issue = "63291")] |
444 | pub fn new_uninit() -> Arc<mem::MaybeUninit<T>> { | |
445 | unsafe { | |
3dfed10e XL |
446 | Arc::from_ptr(Arc::allocate_for_layout( |
447 | Layout::new::<T>(), | |
fc512014 | 448 | |layout| Global.allocate(layout), |
3dfed10e XL |
449 | |mem| mem as *mut ArcInner<mem::MaybeUninit<T>>, |
450 | )) | |
e1599b0c XL |
451 | } |
452 | } | |
453 | ||
60c5eb7d XL |
454 | /// Constructs a new `Arc` with uninitialized contents, with the memory |
455 | /// being filled with `0` bytes. | |
456 | /// | |
457 | /// See [`MaybeUninit::zeroed`][zeroed] for examples of correct and incorrect usage | |
458 | /// of this method. | |
459 | /// | |
460 | /// # Examples | |
461 | /// | |
462 | /// ``` | |
463 | /// #![feature(new_uninit)] | |
464 | /// | |
465 | /// use std::sync::Arc; | |
466 | /// | |
467 | /// let zero = Arc::<u32>::new_zeroed(); | |
468 | /// let zero = unsafe { zero.assume_init() }; | |
469 | /// | |
470 | /// assert_eq!(*zero, 0) | |
471 | /// ``` | |
472 | /// | |
473 | /// [zeroed]: ../../std/mem/union.MaybeUninit.html#method.zeroed | |
17df50a5 | 474 | #[cfg(not(no_global_oom_handling))] |
60c5eb7d XL |
475 | #[unstable(feature = "new_uninit", issue = "63291")] |
476 | pub fn new_zeroed() -> Arc<mem::MaybeUninit<T>> { | |
477 | unsafe { | |
3dfed10e XL |
478 | Arc::from_ptr(Arc::allocate_for_layout( |
479 | Layout::new::<T>(), | |
fc512014 | 480 | |layout| Global.allocate_zeroed(layout), |
3dfed10e XL |
481 | |mem| mem as *mut ArcInner<mem::MaybeUninit<T>>, |
482 | )) | |
60c5eb7d XL |
483 | } |
484 | } | |
485 | ||
0731742a XL |
486 | /// Constructs a new `Pin<Arc<T>>`. If `T` does not implement `Unpin`, then |
487 | /// `data` will be pinned in memory and unable to be moved. | |
488 | #[stable(feature = "pin", since = "1.33.0")] | |
489 | pub fn pin(data: T) -> Pin<Arc<T>> { | |
0bf4aa26 XL |
490 | unsafe { Pin::new_unchecked(Arc::new(data)) } |
491 | } | |
492 | ||
5869c6ff XL |
493 | /// Constructs a new `Arc<T>`, returning an error if allocation fails. |
494 | /// | |
495 | /// # Examples | |
496 | /// | |
497 | /// ``` | |
498 | /// #![feature(allocator_api)] | |
499 | /// use std::sync::Arc; | |
500 | /// | |
501 | /// let five = Arc::try_new(5)?; | |
502 | /// # Ok::<(), std::alloc::AllocError>(()) | |
503 | /// ``` | |
504 | #[unstable(feature = "allocator_api", issue = "32838")] | |
505 | #[inline] | |
506 | pub fn try_new(data: T) -> Result<Arc<T>, AllocError> { | |
507 | // Start the weak pointer count as 1 which is the weak pointer that's | |
508 | // held by all the strong pointers (kinda), see std/rc.rs for more info | |
509 | let x: Box<_> = Box::try_new(ArcInner { | |
510 | strong: atomic::AtomicUsize::new(1), | |
511 | weak: atomic::AtomicUsize::new(1), | |
512 | data, | |
513 | })?; | |
514 | Ok(Self::from_inner(Box::leak(x).into())) | |
515 | } | |
516 | ||
517 | /// Constructs a new `Arc` with uninitialized contents, returning an error | |
518 | /// if allocation fails. | |
519 | /// | |
520 | /// # Examples | |
521 | /// | |
522 | /// ``` | |
523 | /// #![feature(new_uninit, allocator_api)] | |
524 | /// #![feature(get_mut_unchecked)] | |
525 | /// | |
526 | /// use std::sync::Arc; | |
527 | /// | |
528 | /// let mut five = Arc::<u32>::try_new_uninit()?; | |
529 | /// | |
530 | /// let five = unsafe { | |
531 | /// // Deferred initialization: | |
532 | /// Arc::get_mut_unchecked(&mut five).as_mut_ptr().write(5); | |
533 | /// | |
534 | /// five.assume_init() | |
535 | /// }; | |
536 | /// | |
537 | /// assert_eq!(*five, 5); | |
538 | /// # Ok::<(), std::alloc::AllocError>(()) | |
539 | /// ``` | |
540 | #[unstable(feature = "allocator_api", issue = "32838")] | |
541 | // #[unstable(feature = "new_uninit", issue = "63291")] | |
542 | pub fn try_new_uninit() -> Result<Arc<mem::MaybeUninit<T>>, AllocError> { | |
543 | unsafe { | |
544 | Ok(Arc::from_ptr(Arc::try_allocate_for_layout( | |
545 | Layout::new::<T>(), | |
546 | |layout| Global.allocate(layout), | |
547 | |mem| mem as *mut ArcInner<mem::MaybeUninit<T>>, | |
548 | )?)) | |
549 | } | |
550 | } | |
551 | ||
552 | /// Constructs a new `Arc` with uninitialized contents, with the memory | |
553 | /// being filled with `0` bytes, returning an error if allocation fails. | |
554 | /// | |
555 | /// See [`MaybeUninit::zeroed`][zeroed] for examples of correct and incorrect usage | |
556 | /// of this method. | |
557 | /// | |
558 | /// # Examples | |
559 | /// | |
560 | /// ``` | |
561 | /// #![feature(new_uninit, allocator_api)] | |
562 | /// | |
563 | /// use std::sync::Arc; | |
564 | /// | |
565 | /// let zero = Arc::<u32>::try_new_zeroed()?; | |
566 | /// let zero = unsafe { zero.assume_init() }; | |
567 | /// | |
568 | /// assert_eq!(*zero, 0); | |
569 | /// # Ok::<(), std::alloc::AllocError>(()) | |
570 | /// ``` | |
571 | /// | |
572 | /// [zeroed]: mem::MaybeUninit::zeroed | |
573 | #[unstable(feature = "allocator_api", issue = "32838")] | |
574 | // #[unstable(feature = "new_uninit", issue = "63291")] | |
575 | pub fn try_new_zeroed() -> Result<Arc<mem::MaybeUninit<T>>, AllocError> { | |
576 | unsafe { | |
577 | Ok(Arc::from_ptr(Arc::try_allocate_for_layout( | |
578 | Layout::new::<T>(), | |
579 | |layout| Global.allocate_zeroed(layout), | |
580 | |mem| mem as *mut ArcInner<mem::MaybeUninit<T>>, | |
581 | )?)) | |
582 | } | |
583 | } | |
e74abb32 | 584 | /// Returns the inner value, if the `Arc` has exactly one strong reference. |
e9174d1e | 585 | /// |
3dfed10e | 586 | /// Otherwise, an [`Err`] is returned with the same `Arc` that was |
c30ab7b3 | 587 | /// passed in. |
e9174d1e | 588 | /// |
54a0048b SL |
589 | /// This will succeed even if there are outstanding weak references. |
590 | /// | |
e9174d1e SL |
591 | /// # Examples |
592 | /// | |
593 | /// ``` | |
594 | /// use std::sync::Arc; | |
595 | /// | |
596 | /// let x = Arc::new(3); | |
597 | /// assert_eq!(Arc::try_unwrap(x), Ok(3)); | |
598 | /// | |
599 | /// let x = Arc::new(4); | |
7cac9316 | 600 | /// let _y = Arc::clone(&x); |
c30ab7b3 | 601 | /// assert_eq!(*Arc::try_unwrap(x).unwrap_err(), 4); |
e9174d1e SL |
602 | /// ``` |
603 | #[inline] | |
604 | #[stable(feature = "arc_unique", since = "1.4.0")] | |
605 | pub fn try_unwrap(this: Self) -> Result<T, Self> { | |
f035d41b | 606 | if this.inner().strong.compare_exchange(1, 0, Relaxed, Relaxed).is_err() { |
92a42be0 | 607 | return Err(this); |
b039eaaf | 608 | } |
e9174d1e | 609 | |
ba9703b0 | 610 | acquire!(this.inner().strong); |
e9174d1e SL |
611 | |
612 | unsafe { | |
7cac9316 | 613 | let elem = ptr::read(&this.ptr.as_ref().data); |
e9174d1e SL |
614 | |
615 | // Make a weak pointer to clean up the implicit strong-weak reference | |
54a0048b | 616 | let _weak = Weak { ptr: this.ptr }; |
e9174d1e SL |
617 | mem::forget(this); |
618 | ||
619 | Ok(elem) | |
620 | } | |
1a4d82fc | 621 | } |
ea8adc8c | 622 | } |
476ff2be | 623 | |
e1599b0c | 624 | impl<T> Arc<[T]> { |
3dfed10e | 625 | /// Constructs a new atomically reference-counted slice with uninitialized contents. |
e1599b0c XL |
626 | /// |
627 | /// # Examples | |
628 | /// | |
629 | /// ``` | |
630 | /// #![feature(new_uninit)] | |
631 | /// #![feature(get_mut_unchecked)] | |
632 | /// | |
633 | /// use std::sync::Arc; | |
634 | /// | |
635 | /// let mut values = Arc::<[u32]>::new_uninit_slice(3); | |
636 | /// | |
637 | /// let values = unsafe { | |
638 | /// // Deferred initialization: | |
639 | /// Arc::get_mut_unchecked(&mut values)[0].as_mut_ptr().write(1); | |
640 | /// Arc::get_mut_unchecked(&mut values)[1].as_mut_ptr().write(2); | |
641 | /// Arc::get_mut_unchecked(&mut values)[2].as_mut_ptr().write(3); | |
642 | /// | |
643 | /// values.assume_init() | |
644 | /// }; | |
645 | /// | |
646 | /// assert_eq!(*values, [1, 2, 3]) | |
647 | /// ``` | |
17df50a5 | 648 | #[cfg(not(no_global_oom_handling))] |
e1599b0c XL |
649 | #[unstable(feature = "new_uninit", issue = "63291")] |
650 | pub fn new_uninit_slice(len: usize) -> Arc<[mem::MaybeUninit<T>]> { | |
dfeec247 | 651 | unsafe { Arc::from_ptr(Arc::allocate_for_slice(len)) } |
e1599b0c | 652 | } |
3dfed10e XL |
653 | |
654 | /// Constructs a new atomically reference-counted slice with uninitialized contents, with the memory being | |
655 | /// filled with `0` bytes. | |
656 | /// | |
657 | /// See [`MaybeUninit::zeroed`][zeroed] for examples of correct and | |
658 | /// incorrect usage of this method. | |
659 | /// | |
660 | /// # Examples | |
661 | /// | |
662 | /// ``` | |
663 | /// #![feature(new_uninit)] | |
664 | /// | |
665 | /// use std::sync::Arc; | |
666 | /// | |
667 | /// let values = Arc::<[u32]>::new_zeroed_slice(3); | |
668 | /// let values = unsafe { values.assume_init() }; | |
669 | /// | |
670 | /// assert_eq!(*values, [0, 0, 0]) | |
671 | /// ``` | |
672 | /// | |
673 | /// [zeroed]: ../../std/mem/union.MaybeUninit.html#method.zeroed | |
17df50a5 | 674 | #[cfg(not(no_global_oom_handling))] |
3dfed10e XL |
675 | #[unstable(feature = "new_uninit", issue = "63291")] |
676 | pub fn new_zeroed_slice(len: usize) -> Arc<[mem::MaybeUninit<T>]> { | |
677 | unsafe { | |
678 | Arc::from_ptr(Arc::allocate_for_layout( | |
679 | Layout::array::<T>(len).unwrap(), | |
fc512014 | 680 | |layout| Global.allocate_zeroed(layout), |
3dfed10e XL |
681 | |mem| { |
682 | ptr::slice_from_raw_parts_mut(mem as *mut T, len) | |
683 | as *mut ArcInner<[mem::MaybeUninit<T>]> | |
684 | }, | |
685 | )) | |
686 | } | |
687 | } | |
e1599b0c XL |
688 | } |
689 | ||
690 | impl<T> Arc<mem::MaybeUninit<T>> { | |
691 | /// Converts to `Arc<T>`. | |
692 | /// | |
693 | /// # Safety | |
694 | /// | |
695 | /// As with [`MaybeUninit::assume_init`], | |
e74abb32 | 696 | /// it is up to the caller to guarantee that the inner value |
e1599b0c XL |
697 | /// really is in an initialized state. |
698 | /// Calling this when the content is not yet fully initialized | |
699 | /// causes immediate undefined behavior. | |
700 | /// | |
701 | /// [`MaybeUninit::assume_init`]: ../../std/mem/union.MaybeUninit.html#method.assume_init | |
702 | /// | |
703 | /// # Examples | |
704 | /// | |
705 | /// ``` | |
706 | /// #![feature(new_uninit)] | |
707 | /// #![feature(get_mut_unchecked)] | |
708 | /// | |
709 | /// use std::sync::Arc; | |
710 | /// | |
711 | /// let mut five = Arc::<u32>::new_uninit(); | |
712 | /// | |
713 | /// let five = unsafe { | |
714 | /// // Deferred initialization: | |
715 | /// Arc::get_mut_unchecked(&mut five).as_mut_ptr().write(5); | |
716 | /// | |
717 | /// five.assume_init() | |
718 | /// }; | |
719 | /// | |
720 | /// assert_eq!(*five, 5) | |
721 | /// ``` | |
722 | #[unstable(feature = "new_uninit", issue = "63291")] | |
723 | #[inline] | |
724 | pub unsafe fn assume_init(self) -> Arc<T> { | |
725 | Arc::from_inner(mem::ManuallyDrop::new(self).ptr.cast()) | |
726 | } | |
727 | } | |
728 | ||
729 | impl<T> Arc<[mem::MaybeUninit<T>]> { | |
730 | /// Converts to `Arc<[T]>`. | |
731 | /// | |
732 | /// # Safety | |
733 | /// | |
734 | /// As with [`MaybeUninit::assume_init`], | |
e74abb32 | 735 | /// it is up to the caller to guarantee that the inner value |
e1599b0c XL |
736 | /// really is in an initialized state. |
737 | /// Calling this when the content is not yet fully initialized | |
738 | /// causes immediate undefined behavior. | |
739 | /// | |
740 | /// [`MaybeUninit::assume_init`]: ../../std/mem/union.MaybeUninit.html#method.assume_init | |
741 | /// | |
742 | /// # Examples | |
743 | /// | |
744 | /// ``` | |
745 | /// #![feature(new_uninit)] | |
746 | /// #![feature(get_mut_unchecked)] | |
747 | /// | |
748 | /// use std::sync::Arc; | |
749 | /// | |
750 | /// let mut values = Arc::<[u32]>::new_uninit_slice(3); | |
751 | /// | |
752 | /// let values = unsafe { | |
753 | /// // Deferred initialization: | |
754 | /// Arc::get_mut_unchecked(&mut values)[0].as_mut_ptr().write(1); | |
755 | /// Arc::get_mut_unchecked(&mut values)[1].as_mut_ptr().write(2); | |
756 | /// Arc::get_mut_unchecked(&mut values)[2].as_mut_ptr().write(3); | |
757 | /// | |
758 | /// values.assume_init() | |
759 | /// }; | |
760 | /// | |
761 | /// assert_eq!(*values, [1, 2, 3]) | |
762 | /// ``` | |
763 | #[unstable(feature = "new_uninit", issue = "63291")] | |
764 | #[inline] | |
765 | pub unsafe fn assume_init(self) -> Arc<[T]> { | |
f035d41b | 766 | unsafe { Arc::from_ptr(mem::ManuallyDrop::new(self).ptr.as_ptr() as _) } |
e1599b0c XL |
767 | } |
768 | } | |
769 | ||
ea8adc8c | 770 | impl<T: ?Sized> Arc<T> { |
476ff2be SL |
771 | /// Consumes the `Arc`, returning the wrapped pointer. |
772 | /// | |
773 | /// To avoid a memory leak the pointer must be converted back to an `Arc` using | |
3dfed10e | 774 | /// [`Arc::from_raw`]. |
476ff2be SL |
775 | /// |
776 | /// # Examples | |
777 | /// | |
778 | /// ``` | |
476ff2be SL |
779 | /// use std::sync::Arc; |
780 | /// | |
dc9dc135 | 781 | /// let x = Arc::new("hello".to_owned()); |
476ff2be | 782 | /// let x_ptr = Arc::into_raw(x); |
dc9dc135 | 783 | /// assert_eq!(unsafe { &*x_ptr }, "hello"); |
476ff2be | 784 | /// ``` |
8bb4bdeb XL |
785 | #[stable(feature = "rc_raw", since = "1.17.0")] |
786 | pub fn into_raw(this: Self) -> *const T { | |
ba9703b0 XL |
787 | let ptr = Self::as_ptr(&this); |
788 | mem::forget(this); | |
789 | ptr | |
790 | } | |
791 | ||
792 | /// Provides a raw pointer to the data. | |
793 | /// | |
3dfed10e | 794 | /// The counts are not affected in any way and the `Arc` is not consumed. The pointer is valid for |
ba9703b0 XL |
795 | /// as long as there are strong counts in the `Arc`. |
796 | /// | |
797 | /// # Examples | |
798 | /// | |
799 | /// ``` | |
ba9703b0 XL |
800 | /// use std::sync::Arc; |
801 | /// | |
802 | /// let x = Arc::new("hello".to_owned()); | |
803 | /// let y = Arc::clone(&x); | |
804 | /// let x_ptr = Arc::as_ptr(&x); | |
805 | /// assert_eq!(x_ptr, Arc::as_ptr(&y)); | |
806 | /// assert_eq!(unsafe { &*x_ptr }, "hello"); | |
807 | /// ``` | |
f035d41b | 808 | #[stable(feature = "rc_as_ptr", since = "1.45.0")] |
ba9703b0 | 809 | pub fn as_ptr(this: &Self) -> *const T { |
dfeec247 | 810 | let ptr: *mut ArcInner<T> = NonNull::as_ptr(this.ptr); |
dfeec247 | 811 | |
f035d41b XL |
812 | // SAFETY: This cannot go through Deref::deref or RcBoxPtr::inner because |
813 | // this is required to retain raw/mut provenance such that e.g. `get_mut` can | |
814 | // write through the pointer after the Rc is recovered through `from_raw`. | |
5869c6ff | 815 | unsafe { ptr::addr_of_mut!((*ptr).data) } |
476ff2be SL |
816 | } |
817 | ||
ba9703b0 | 818 | /// Constructs an `Arc<T>` from a raw pointer. |
476ff2be | 819 | /// |
ba9703b0 XL |
820 | /// The raw pointer must have been previously returned by a call to |
821 | /// [`Arc<U>::into_raw`][into_raw] where `U` must have the same size and | |
822 | /// alignment as `T`. This is trivially true if `U` is `T`. | |
823 | /// Note that if `U` is not `T` but has the same size and alignment, this is | |
824 | /// basically like transmuting references of different types. See | |
825 | /// [`mem::transmute`][transmute] for more information on what | |
826 | /// restrictions apply in this case. | |
476ff2be | 827 | /// |
ba9703b0 XL |
828 | /// The user of `from_raw` has to make sure a specific value of `T` is only |
829 | /// dropped once. | |
830 | /// | |
831 | /// This function is unsafe because improper use may lead to memory unsafety, | |
832 | /// even if the returned `Arc<T>` is never accessed. | |
476ff2be | 833 | /// |
3dfed10e XL |
834 | /// [into_raw]: Arc::into_raw |
835 | /// [transmute]: core::mem::transmute | |
476ff2be SL |
836 | /// |
837 | /// # Examples | |
838 | /// | |
839 | /// ``` | |
476ff2be SL |
840 | /// use std::sync::Arc; |
841 | /// | |
dc9dc135 | 842 | /// let x = Arc::new("hello".to_owned()); |
476ff2be SL |
843 | /// let x_ptr = Arc::into_raw(x); |
844 | /// | |
845 | /// unsafe { | |
846 | /// // Convert back to an `Arc` to prevent leak. | |
847 | /// let x = Arc::from_raw(x_ptr); | |
dc9dc135 | 848 | /// assert_eq!(&*x, "hello"); |
476ff2be | 849 | /// |
e1599b0c | 850 | /// // Further calls to `Arc::from_raw(x_ptr)` would be memory-unsafe. |
476ff2be SL |
851 | /// } |
852 | /// | |
853 | /// // The memory was freed when `x` went out of scope above, so `x_ptr` is now dangling! | |
854 | /// ``` | |
8bb4bdeb XL |
855 | #[stable(feature = "rc_raw", since = "1.17.0")] |
856 | pub unsafe fn from_raw(ptr: *const T) -> Self { | |
f035d41b XL |
857 | unsafe { |
858 | let offset = data_offset(ptr); | |
ea8adc8c | 859 | |
f035d41b | 860 | // Reverse the offset to find the original ArcInner. |
5869c6ff | 861 | let arc_ptr = (ptr as *mut ArcInner<T>).set_ptr_value((ptr as *mut u8).offset(-offset)); |
ea8adc8c | 862 | |
f035d41b XL |
863 | Self::from_ptr(arc_ptr) |
864 | } | |
476ff2be | 865 | } |
1a4d82fc | 866 | |
3dfed10e | 867 | /// Creates a new [`Weak`] pointer to this allocation. |
1a4d82fc JJ |
868 | /// |
869 | /// # Examples | |
870 | /// | |
871 | /// ``` | |
872 | /// use std::sync::Arc; | |
873 | /// | |
85aaf69f | 874 | /// let five = Arc::new(5); |
1a4d82fc | 875 | /// |
e9174d1e | 876 | /// let weak_five = Arc::downgrade(&five); |
1a4d82fc | 877 | /// ``` |
e9174d1e SL |
878 | #[stable(feature = "arc_weak", since = "1.4.0")] |
879 | pub fn downgrade(this: &Self) -> Weak<T> { | |
54a0048b SL |
880 | // This Relaxed is OK because we're checking the value in the CAS |
881 | // below. | |
882 | let mut cur = this.inner().weak.load(Relaxed); | |
c1a9b12d | 883 | |
54a0048b | 884 | loop { |
c1a9b12d | 885 | // check if the weak counter is currently "locked"; if so, spin. |
b039eaaf | 886 | if cur == usize::MAX { |
29967ef6 | 887 | hint::spin_loop(); |
54a0048b | 888 | cur = this.inner().weak.load(Relaxed); |
92a42be0 | 889 | continue; |
b039eaaf | 890 | } |
c1a9b12d SL |
891 | |
892 | // NOTE: this code currently ignores the possibility of overflow | |
893 | // into usize::MAX; in general both Rc and Arc need to be adjusted | |
894 | // to deal with overflow. | |
895 | ||
896 | // Unlike with Clone(), we need this to be an Acquire read to | |
897 | // synchronize with the write coming from `is_unique`, so that the | |
898 | // events prior to that write happen before this read. | |
54a0048b | 899 | match this.inner().weak.compare_exchange_weak(cur, cur + 1, Acquire, Relaxed) { |
8faf50e0 XL |
900 | Ok(_) => { |
901 | // Make sure we do not create a dangling Weak | |
5869c6ff | 902 | debug_assert!(!is_dangling(this.ptr.as_ptr())); |
8faf50e0 XL |
903 | return Weak { ptr: this.ptr }; |
904 | } | |
54a0048b | 905 | Err(old) => cur = old, |
c1a9b12d SL |
906 | } |
907 | } | |
1a4d82fc | 908 | } |
1a4d82fc | 909 | |
3dfed10e | 910 | /// Gets the number of [`Weak`] pointers to this allocation. |
c30ab7b3 | 911 | /// |
476ff2be SL |
912 | /// # Safety |
913 | /// | |
914 | /// This method by itself is safe, but using it correctly requires extra care. | |
915 | /// Another thread can change the weak count at any time, | |
916 | /// including potentially between calling this method and acting on the result. | |
917 | /// | |
c30ab7b3 SL |
918 | /// # Examples |
919 | /// | |
920 | /// ``` | |
c30ab7b3 SL |
921 | /// use std::sync::Arc; |
922 | /// | |
923 | /// let five = Arc::new(5); | |
924 | /// let _weak_five = Arc::downgrade(&five); | |
925 | /// | |
926 | /// // This assertion is deterministic because we haven't shared | |
927 | /// // the `Arc` or `Weak` between threads. | |
928 | /// assert_eq!(1, Arc::weak_count(&five)); | |
929 | /// ``` | |
62682a34 | 930 | #[inline] |
476ff2be | 931 | #[stable(feature = "arc_counts", since = "1.15.0")] |
e9174d1e | 932 | pub fn weak_count(this: &Self) -> usize { |
3b2f2976 XL |
933 | let cnt = this.inner().weak.load(SeqCst); |
934 | // If the weak count is currently locked, the value of the | |
935 | // count was 0 just before taking the lock. | |
936 | if cnt == usize::MAX { 0 } else { cnt - 1 } | |
62682a34 SL |
937 | } |
938 | ||
e74abb32 | 939 | /// Gets the number of strong (`Arc`) pointers to this allocation. |
c30ab7b3 | 940 | /// |
476ff2be SL |
941 | /// # Safety |
942 | /// | |
943 | /// This method by itself is safe, but using it correctly requires extra care. | |
944 | /// Another thread can change the strong count at any time, | |
945 | /// including potentially between calling this method and acting on the result. | |
c30ab7b3 SL |
946 | /// |
947 | /// # Examples | |
948 | /// | |
949 | /// ``` | |
c30ab7b3 SL |
950 | /// use std::sync::Arc; |
951 | /// | |
952 | /// let five = Arc::new(5); | |
7cac9316 | 953 | /// let _also_five = Arc::clone(&five); |
c30ab7b3 SL |
954 | /// |
955 | /// // This assertion is deterministic because we haven't shared | |
956 | /// // the `Arc` between threads. | |
957 | /// assert_eq!(2, Arc::strong_count(&five)); | |
958 | /// ``` | |
62682a34 | 959 | #[inline] |
476ff2be | 960 | #[stable(feature = "arc_counts", since = "1.15.0")] |
e9174d1e | 961 | pub fn strong_count(this: &Self) -> usize { |
62682a34 SL |
962 | this.inner().strong.load(SeqCst) |
963 | } | |
964 | ||
f9f354fc XL |
965 | /// Increments the strong reference count on the `Arc<T>` associated with the |
966 | /// provided pointer by one. | |
967 | /// | |
968 | /// # Safety | |
969 | /// | |
970 | /// The pointer must have been obtained through `Arc::into_raw`, and the | |
971 | /// associated `Arc` instance must be valid (i.e. the strong count must be at | |
972 | /// least 1) for the duration of this method. | |
973 | /// | |
974 | /// # Examples | |
975 | /// | |
976 | /// ``` | |
f9f354fc XL |
977 | /// use std::sync::Arc; |
978 | /// | |
979 | /// let five = Arc::new(5); | |
980 | /// | |
981 | /// unsafe { | |
982 | /// let ptr = Arc::into_raw(five); | |
5869c6ff | 983 | /// Arc::increment_strong_count(ptr); |
f9f354fc XL |
984 | /// |
985 | /// // This assertion is deterministic because we haven't shared | |
986 | /// // the `Arc` between threads. | |
987 | /// let five = Arc::from_raw(ptr); | |
988 | /// assert_eq!(2, Arc::strong_count(&five)); | |
989 | /// } | |
990 | /// ``` | |
991 | #[inline] | |
5869c6ff XL |
992 | #[stable(feature = "arc_mutate_strong_count", since = "1.51.0")] |
993 | pub unsafe fn increment_strong_count(ptr: *const T) { | |
f9f354fc | 994 | // Retain Arc, but don't touch refcount by wrapping in ManuallyDrop |
f035d41b | 995 | let arc = unsafe { mem::ManuallyDrop::new(Arc::<T>::from_raw(ptr)) }; |
f9f354fc XL |
996 | // Now increase refcount, but don't drop new refcount either |
997 | let _arc_clone: mem::ManuallyDrop<_> = arc.clone(); | |
998 | } | |
999 | ||
1000 | /// Decrements the strong reference count on the `Arc<T>` associated with the | |
1001 | /// provided pointer by one. | |
1002 | /// | |
1003 | /// # Safety | |
1004 | /// | |
1005 | /// The pointer must have been obtained through `Arc::into_raw`, and the | |
1006 | /// associated `Arc` instance must be valid (i.e. the strong count must be at | |
1007 | /// least 1) when invoking this method. This method can be used to release the final | |
1008 | /// `Arc` and backing storage, but **should not** be called after the final `Arc` has been | |
1009 | /// released. | |
1010 | /// | |
1011 | /// # Examples | |
1012 | /// | |
1013 | /// ``` | |
f9f354fc XL |
1014 | /// use std::sync::Arc; |
1015 | /// | |
1016 | /// let five = Arc::new(5); | |
1017 | /// | |
1018 | /// unsafe { | |
1019 | /// let ptr = Arc::into_raw(five); | |
5869c6ff | 1020 | /// Arc::increment_strong_count(ptr); |
f9f354fc XL |
1021 | /// |
1022 | /// // Those assertions are deterministic because we haven't shared | |
1023 | /// // the `Arc` between threads. | |
1024 | /// let five = Arc::from_raw(ptr); | |
1025 | /// assert_eq!(2, Arc::strong_count(&five)); | |
5869c6ff | 1026 | /// Arc::decrement_strong_count(ptr); |
f9f354fc XL |
1027 | /// assert_eq!(1, Arc::strong_count(&five)); |
1028 | /// } | |
1029 | /// ``` | |
1030 | #[inline] | |
5869c6ff XL |
1031 | #[stable(feature = "arc_mutate_strong_count", since = "1.51.0")] |
1032 | pub unsafe fn decrement_strong_count(ptr: *const T) { | |
f035d41b | 1033 | unsafe { mem::drop(Arc::from_raw(ptr)) }; |
f9f354fc XL |
1034 | } |
1035 | ||
1a4d82fc JJ |
1036 | #[inline] |
1037 | fn inner(&self) -> &ArcInner<T> { | |
c34b1796 AL |
1038 | // This unsafety is ok because while this arc is alive we're guaranteed |
1039 | // that the inner pointer is valid. Furthermore, we know that the | |
1040 | // `ArcInner` structure itself is `Sync` because the inner data is | |
1041 | // `Sync` as well, so we're ok loaning out an immutable pointer to these | |
1042 | // contents. | |
7cac9316 | 1043 | unsafe { self.ptr.as_ref() } |
1a4d82fc | 1044 | } |
c34b1796 AL |
1045 | |
1046 | // Non-inlined part of `drop`. | |
1047 | #[inline(never)] | |
1048 | unsafe fn drop_slow(&mut self) { | |
c34b1796 AL |
1049 | // Destroy the data at this time, even though we may not free the box |
1050 | // allocation itself (there may still be weak pointers lying around). | |
f035d41b | 1051 | unsafe { ptr::drop_in_place(Self::get_mut_unchecked(self)) }; |
c34b1796 | 1052 | |
f9f354fc XL |
1053 | // Drop the weak ref collectively held by all strong references |
1054 | drop(Weak { ptr: self.ptr }); | |
c34b1796 | 1055 | } |
9e0c209e SL |
1056 | |
1057 | #[inline] | |
8bb4bdeb | 1058 | #[stable(feature = "ptr_eq", since = "1.17.0")] |
e74abb32 XL |
1059 | /// Returns `true` if the two `Arc`s point to the same allocation |
1060 | /// (in a vein similar to [`ptr::eq`]). | |
9e0c209e SL |
1061 | /// |
1062 | /// # Examples | |
1063 | /// | |
1064 | /// ``` | |
9e0c209e SL |
1065 | /// use std::sync::Arc; |
1066 | /// | |
1067 | /// let five = Arc::new(5); | |
7cac9316 | 1068 | /// let same_five = Arc::clone(&five); |
9e0c209e SL |
1069 | /// let other_five = Arc::new(5); |
1070 | /// | |
1071 | /// assert!(Arc::ptr_eq(&five, &same_five)); | |
1072 | /// assert!(!Arc::ptr_eq(&five, &other_five)); | |
1073 | /// ``` | |
e74abb32 | 1074 | /// |
3dfed10e | 1075 | /// [`ptr::eq`]: core::ptr::eq |
9e0c209e | 1076 | pub fn ptr_eq(this: &Self, other: &Self) -> bool { |
7cac9316 | 1077 | this.ptr.as_ptr() == other.ptr.as_ptr() |
9e0c209e | 1078 | } |
1a4d82fc JJ |
1079 | } |
1080 | ||
3b2f2976 | 1081 | impl<T: ?Sized> Arc<T> { |
416331ca | 1082 | /// Allocates an `ArcInner<T>` with sufficient space for |
e74abb32 | 1083 | /// a possibly-unsized inner value where the value has the layout provided. |
416331ca XL |
1084 | /// |
1085 | /// The function `mem_to_arcinner` is called with the data pointer | |
1086 | /// and must return back a (potentially fat)-pointer for the `ArcInner<T>`. | |
17df50a5 | 1087 | #[cfg(not(no_global_oom_handling))] |
e1599b0c | 1088 | unsafe fn allocate_for_layout( |
416331ca | 1089 | value_layout: Layout, |
1b1a35ee | 1090 | allocate: impl FnOnce(Layout) -> Result<NonNull<[u8]>, AllocError>, |
dfeec247 | 1091 | mem_to_arcinner: impl FnOnce(*mut u8) -> *mut ArcInner<T>, |
416331ca XL |
1092 | ) -> *mut ArcInner<T> { |
1093 | // Calculate layout using the given value layout. | |
a1dfa0c6 XL |
1094 | // Previously, layout was calculated on the expression |
1095 | // `&*(ptr as *const ArcInner<T>)`, but this created a misaligned | |
1096 | // reference (see #54908). | |
dfeec247 | 1097 | let layout = Layout::new::<ArcInner<()>>().extend(value_layout).unwrap().0.pad_to_align(); |
5869c6ff XL |
1098 | unsafe { |
1099 | Arc::try_allocate_for_layout(value_layout, allocate, mem_to_arcinner) | |
1100 | .unwrap_or_else(|_| handle_alloc_error(layout)) | |
1101 | } | |
1102 | } | |
1103 | ||
1104 | /// Allocates an `ArcInner<T>` with sufficient space for | |
1105 | /// a possibly-unsized inner value where the value has the layout provided, | |
1106 | /// returning an error if allocation fails. | |
1107 | /// | |
1108 | /// The function `mem_to_arcinner` is called with the data pointer | |
1109 | /// and must return back a (potentially fat)-pointer for the `ArcInner<T>`. | |
1110 | unsafe fn try_allocate_for_layout( | |
1111 | value_layout: Layout, | |
1112 | allocate: impl FnOnce(Layout) -> Result<NonNull<[u8]>, AllocError>, | |
1113 | mem_to_arcinner: impl FnOnce(*mut u8) -> *mut ArcInner<T>, | |
1114 | ) -> Result<*mut ArcInner<T>, AllocError> { | |
1115 | // Calculate layout using the given value layout. | |
1116 | // Previously, layout was calculated on the expression | |
1117 | // `&*(ptr as *const ArcInner<T>)`, but this created a misaligned | |
1118 | // reference (see #54908). | |
1119 | let layout = Layout::new::<ArcInner<()>>().extend(value_layout).unwrap().0.pad_to_align(); | |
3b2f2976 | 1120 | |
5869c6ff | 1121 | let ptr = allocate(layout)?; |
3b2f2976 | 1122 | |
a1dfa0c6 | 1123 | // Initialize the ArcInner |
3dfed10e | 1124 | let inner = mem_to_arcinner(ptr.as_non_null_ptr().as_ptr()); |
f035d41b | 1125 | debug_assert_eq!(unsafe { Layout::for_value(&*inner) }, layout); |
3b2f2976 | 1126 | |
f035d41b XL |
1127 | unsafe { |
1128 | ptr::write(&mut (*inner).strong, atomic::AtomicUsize::new(1)); | |
1129 | ptr::write(&mut (*inner).weak, atomic::AtomicUsize::new(1)); | |
1130 | } | |
3b2f2976 | 1131 | |
5869c6ff | 1132 | Ok(inner) |
3b2f2976 XL |
1133 | } |
1134 | ||
e74abb32 | 1135 | /// Allocates an `ArcInner<T>` with sufficient space for an unsized inner value. |
17df50a5 | 1136 | #[cfg(not(no_global_oom_handling))] |
416331ca XL |
1137 | unsafe fn allocate_for_ptr(ptr: *const T) -> *mut ArcInner<T> { |
1138 | // Allocate for the `ArcInner<T>` using the given value. | |
f035d41b | 1139 | unsafe { |
3dfed10e XL |
1140 | Self::allocate_for_layout( |
1141 | Layout::for_value(&*ptr), | |
fc512014 | 1142 | |layout| Global.allocate(layout), |
5869c6ff | 1143 | |mem| (ptr as *mut ArcInner<T>).set_ptr_value(mem) as *mut ArcInner<T>, |
3dfed10e | 1144 | ) |
f035d41b | 1145 | } |
416331ca XL |
1146 | } |
1147 | ||
17df50a5 | 1148 | #[cfg(not(no_global_oom_handling))] |
3b2f2976 XL |
1149 | fn from_box(v: Box<T>) -> Arc<T> { |
1150 | unsafe { | |
29967ef6 | 1151 | let (box_unique, alloc) = Box::into_unique(v); |
83c7162d | 1152 | let bptr = box_unique.as_ptr(); |
3b2f2976 XL |
1153 | |
1154 | let value_size = size_of_val(&*bptr); | |
1155 | let ptr = Self::allocate_for_ptr(bptr); | |
1156 | ||
1157 | // Copy value as bytes | |
1158 | ptr::copy_nonoverlapping( | |
1159 | bptr as *const T as *const u8, | |
1160 | &mut (*ptr).data as *mut _ as *mut u8, | |
dfeec247 XL |
1161 | value_size, |
1162 | ); | |
3b2f2976 XL |
1163 | |
1164 | // Free the allocation without dropping its contents | |
29967ef6 | 1165 | box_free(box_unique, alloc); |
3b2f2976 | 1166 | |
416331ca | 1167 | Self::from_ptr(ptr) |
3b2f2976 XL |
1168 | } |
1169 | } | |
1170 | } | |
1171 | ||
416331ca XL |
1172 | impl<T> Arc<[T]> { |
1173 | /// Allocates an `ArcInner<[T]>` with the given length. | |
17df50a5 | 1174 | #[cfg(not(no_global_oom_handling))] |
416331ca | 1175 | unsafe fn allocate_for_slice(len: usize) -> *mut ArcInner<[T]> { |
f035d41b | 1176 | unsafe { |
3dfed10e XL |
1177 | Self::allocate_for_layout( |
1178 | Layout::array::<T>(len).unwrap(), | |
fc512014 | 1179 | |layout| Global.allocate(layout), |
3dfed10e XL |
1180 | |mem| ptr::slice_from_raw_parts_mut(mem as *mut T, len) as *mut ArcInner<[T]>, |
1181 | ) | |
f035d41b | 1182 | } |
416331ca | 1183 | } |
416331ca | 1184 | |
f9f354fc | 1185 | /// Copy elements from slice into newly allocated Arc<\[T\]> |
416331ca XL |
1186 | /// |
1187 | /// Unsafe because the caller must either take ownership or bind `T: Copy`. | |
17df50a5 | 1188 | #[cfg(not(no_global_oom_handling))] |
3b2f2976 | 1189 | unsafe fn copy_from_slice(v: &[T]) -> Arc<[T]> { |
f035d41b XL |
1190 | unsafe { |
1191 | let ptr = Self::allocate_for_slice(v.len()); | |
3b2f2976 | 1192 | |
f035d41b | 1193 | ptr::copy_nonoverlapping(v.as_ptr(), &mut (*ptr).data as *mut [T] as *mut T, v.len()); |
3b2f2976 | 1194 | |
f035d41b XL |
1195 | Self::from_ptr(ptr) |
1196 | } | |
3b2f2976 | 1197 | } |
3b2f2976 | 1198 | |
416331ca XL |
1199 | /// Constructs an `Arc<[T]>` from an iterator known to be of a certain size. |
1200 | /// | |
1201 | /// Behavior is undefined should the size be wrong. | |
17df50a5 | 1202 | #[cfg(not(no_global_oom_handling))] |
416331ca | 1203 | unsafe fn from_iter_exact(iter: impl iter::Iterator<Item = T>, len: usize) -> Arc<[T]> { |
3b2f2976 XL |
1204 | // Panic guard while cloning T elements. |
1205 | // In the event of a panic, elements that have been written | |
1206 | // into the new ArcInner will be dropped, then the memory freed. | |
1207 | struct Guard<T> { | |
83c7162d | 1208 | mem: NonNull<u8>, |
3b2f2976 XL |
1209 | elems: *mut T, |
1210 | layout: Layout, | |
1211 | n_elems: usize, | |
1212 | } | |
1213 | ||
1214 | impl<T> Drop for Guard<T> { | |
1215 | fn drop(&mut self) { | |
3b2f2976 XL |
1216 | unsafe { |
1217 | let slice = from_raw_parts_mut(self.elems, self.n_elems); | |
1218 | ptr::drop_in_place(slice); | |
1219 | ||
fc512014 | 1220 | Global.deallocate(self.mem, self.layout); |
3b2f2976 XL |
1221 | } |
1222 | } | |
1223 | } | |
1224 | ||
f035d41b XL |
1225 | unsafe { |
1226 | let ptr = Self::allocate_for_slice(len); | |
3b2f2976 | 1227 | |
f035d41b XL |
1228 | let mem = ptr as *mut _ as *mut u8; |
1229 | let layout = Layout::for_value(&*ptr); | |
3b2f2976 | 1230 | |
f035d41b XL |
1231 | // Pointer to first element |
1232 | let elems = &mut (*ptr).data as *mut [T] as *mut T; | |
3b2f2976 | 1233 | |
f035d41b | 1234 | let mut guard = Guard { mem: NonNull::new_unchecked(mem), elems, layout, n_elems: 0 }; |
3b2f2976 | 1235 | |
f035d41b XL |
1236 | for (i, item) in iter.enumerate() { |
1237 | ptr::write(elems.add(i), item); | |
1238 | guard.n_elems += 1; | |
1239 | } | |
416331ca | 1240 | |
f035d41b XL |
1241 | // All clear. Forget the guard so it doesn't free the new ArcInner. |
1242 | mem::forget(guard); | |
416331ca | 1243 | |
f035d41b XL |
1244 | Self::from_ptr(ptr) |
1245 | } | |
416331ca XL |
1246 | } |
1247 | } | |
3b2f2976 | 1248 | |
416331ca | 1249 | /// Specialization trait used for `From<&[T]>`. |
17df50a5 | 1250 | #[cfg(not(no_global_oom_handling))] |
416331ca XL |
1251 | trait ArcFromSlice<T> { |
1252 | fn from_slice(slice: &[T]) -> Self; | |
1253 | } | |
3b2f2976 | 1254 | |
17df50a5 | 1255 | #[cfg(not(no_global_oom_handling))] |
416331ca XL |
1256 | impl<T: Clone> ArcFromSlice<T> for Arc<[T]> { |
1257 | #[inline] | |
1258 | default fn from_slice(v: &[T]) -> Self { | |
dfeec247 | 1259 | unsafe { Self::from_iter_exact(v.iter().cloned(), v.len()) } |
3b2f2976 XL |
1260 | } |
1261 | } | |
1262 | ||
17df50a5 | 1263 | #[cfg(not(no_global_oom_handling))] |
3b2f2976 XL |
1264 | impl<T: Copy> ArcFromSlice<T> for Arc<[T]> { |
1265 | #[inline] | |
1266 | fn from_slice(v: &[T]) -> Self { | |
1267 | unsafe { Arc::copy_from_slice(v) } | |
1268 | } | |
1269 | } | |
1270 | ||
85aaf69f | 1271 | #[stable(feature = "rust1", since = "1.0.0")] |
62682a34 | 1272 | impl<T: ?Sized> Clone for Arc<T> { |
c30ab7b3 | 1273 | /// Makes a clone of the `Arc` pointer. |
1a4d82fc | 1274 | /// |
e74abb32 | 1275 | /// This creates another pointer to the same allocation, increasing the |
c30ab7b3 | 1276 | /// strong reference count. |
1a4d82fc JJ |
1277 | /// |
1278 | /// # Examples | |
1279 | /// | |
1280 | /// ``` | |
1281 | /// use std::sync::Arc; | |
1282 | /// | |
85aaf69f | 1283 | /// let five = Arc::new(5); |
1a4d82fc | 1284 | /// |
0bf4aa26 | 1285 | /// let _ = Arc::clone(&five); |
1a4d82fc JJ |
1286 | /// ``` |
1287 | #[inline] | |
1288 | fn clone(&self) -> Arc<T> { | |
c34b1796 AL |
1289 | // Using a relaxed ordering is alright here, as knowledge of the |
1290 | // original reference prevents other threads from erroneously deleting | |
1291 | // the object. | |
1a4d82fc | 1292 | // |
c34b1796 AL |
1293 | // As explained in the [Boost documentation][1], Increasing the |
1294 | // reference counter can always be done with memory_order_relaxed: New | |
1295 | // references to an object can only be formed from an existing | |
1296 | // reference, and passing an existing reference from one thread to | |
1297 | // another must already provide any required synchronization. | |
1a4d82fc JJ |
1298 | // |
1299 | // [1]: (www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html) | |
c1a9b12d SL |
1300 | let old_size = self.inner().strong.fetch_add(1, Relaxed); |
1301 | ||
1302 | // However we need to guard against massive refcounts in case someone | |
1303 | // is `mem::forget`ing Arcs. If we don't do this the count can overflow | |
1304 | // and users will use-after free. We racily saturate to `isize::MAX` on | |
1305 | // the assumption that there aren't ~2 billion threads incrementing | |
1306 | // the reference count at once. This branch will never be taken in | |
1307 | // any realistic program. | |
1308 | // | |
1309 | // We abort because such a program is incredibly degenerate, and we | |
1310 | // don't care to support it. | |
1311 | if old_size > MAX_REFCOUNT { | |
f035d41b | 1312 | abort(); |
c1a9b12d SL |
1313 | } |
1314 | ||
416331ca | 1315 | Self::from_inner(self.ptr) |
1a4d82fc JJ |
1316 | } |
1317 | } | |
1318 | ||
85aaf69f | 1319 | #[stable(feature = "rust1", since = "1.0.0")] |
62682a34 | 1320 | impl<T: ?Sized> Deref for Arc<T> { |
1a4d82fc JJ |
1321 | type Target = T; |
1322 | ||
1323 | #[inline] | |
1324 | fn deref(&self) -> &T { | |
1325 | &self.inner().data | |
1326 | } | |
1327 | } | |
1328 | ||
dfeec247 | 1329 | #[unstable(feature = "receiver_trait", issue = "none")] |
0731742a XL |
1330 | impl<T: ?Sized> Receiver for Arc<T> {} |
1331 | ||
c34b1796 | 1332 | impl<T: Clone> Arc<T> { |
c30ab7b3 SL |
1333 | /// Makes a mutable reference into the given `Arc`. |
1334 | /// | |
3dfed10e | 1335 | /// If there are other `Arc` or [`Weak`] pointers to the same allocation, |
e74abb32 XL |
1336 | /// then `make_mut` will create a new allocation and invoke [`clone`][clone] on the inner value |
1337 | /// to ensure unique ownership. This is also referred to as clone-on-write. | |
1338 | /// | |
1339 | /// Note that this differs from the behavior of [`Rc::make_mut`] which disassociates | |
1340 | /// any remaining `Weak` pointers. | |
1a4d82fc | 1341 | /// |
c30ab7b3 SL |
1342 | /// See also [`get_mut`][get_mut], which will fail rather than cloning. |
1343 | /// | |
3dfed10e XL |
1344 | /// [clone]: Clone::clone |
1345 | /// [get_mut]: Arc::get_mut | |
1346 | /// [`Rc::make_mut`]: super::rc::Rc::make_mut | |
62682a34 | 1347 | /// |
1a4d82fc JJ |
1348 | /// # Examples |
1349 | /// | |
1350 | /// ``` | |
1351 | /// use std::sync::Arc; | |
1352 | /// | |
e9174d1e SL |
1353 | /// let mut data = Arc::new(5); |
1354 | /// | |
1355 | /// *Arc::make_mut(&mut data) += 1; // Won't clone anything | |
7cac9316 | 1356 | /// let mut other_data = Arc::clone(&data); // Won't clone inner data |
e9174d1e SL |
1357 | /// *Arc::make_mut(&mut data) += 1; // Clones inner data |
1358 | /// *Arc::make_mut(&mut data) += 1; // Won't clone anything | |
1359 | /// *Arc::make_mut(&mut other_data) *= 2; // Won't clone anything | |
1360 | /// | |
e74abb32 | 1361 | /// // Now `data` and `other_data` point to different allocations. |
e9174d1e SL |
1362 | /// assert_eq!(*data, 8); |
1363 | /// assert_eq!(*other_data, 12); | |
1a4d82fc | 1364 | /// ``` |
17df50a5 | 1365 | #[cfg(not(no_global_oom_handling))] |
1a4d82fc | 1366 | #[inline] |
e9174d1e SL |
1367 | #[stable(feature = "arc_unique", since = "1.4.0")] |
1368 | pub fn make_mut(this: &mut Self) -> &mut T { | |
c1a9b12d SL |
1369 | // Note that we hold both a strong reference and a weak reference. |
1370 | // Thus, releasing our strong reference only will not, by itself, cause | |
1371 | // the memory to be deallocated. | |
62682a34 | 1372 | // |
c1a9b12d SL |
1373 | // Use Acquire to ensure that we see any writes to `weak` that happen |
1374 | // before release writes (i.e., decrements) to `strong`. Since we hold a | |
1375 | // weak count, there's no chance the ArcInner itself could be | |
1376 | // deallocated. | |
54a0048b | 1377 | if this.inner().strong.compare_exchange(1, 0, Acquire, Relaxed).is_err() { |
5869c6ff XL |
1378 | // Another strong pointer exists, so we must clone. |
1379 | // Pre-allocate memory to allow writing the cloned value directly. | |
1380 | let mut arc = Self::new_uninit(); | |
1381 | unsafe { | |
1382 | let data = Arc::get_mut_unchecked(&mut arc); | |
1383 | (**this).write_clone_into_raw(data.as_mut_ptr()); | |
1384 | *this = arc.assume_init(); | |
1385 | } | |
c1a9b12d SL |
1386 | } else if this.inner().weak.load(Relaxed) != 1 { |
1387 | // Relaxed suffices in the above because this is fundamentally an | |
1388 | // optimization: we are always racing with weak pointers being | |
1389 | // dropped. Worst case, we end up allocated a new Arc unnecessarily. | |
1390 | ||
1391 | // We removed the last strong ref, but there are additional weak | |
1392 | // refs remaining. We'll move the contents to a new Arc, and | |
1393 | // invalidate the other weak refs. | |
1394 | ||
1395 | // Note that it is not possible for the read of `weak` to yield | |
1396 | // usize::MAX (i.e., locked), since the weak count can only be | |
1397 | // locked by a thread with a strong reference. | |
1398 | ||
1399 | // Materialize our own implicit weak pointer, so that it can clean | |
1400 | // up the ArcInner as needed. | |
5869c6ff | 1401 | let _weak = Weak { ptr: this.ptr }; |
c1a9b12d | 1402 | |
5869c6ff XL |
1403 | // Can just steal the data, all that's left is Weaks |
1404 | let mut arc = Self::new_uninit(); | |
c1a9b12d | 1405 | unsafe { |
5869c6ff XL |
1406 | let data = Arc::get_mut_unchecked(&mut arc); |
1407 | data.as_mut_ptr().copy_from_nonoverlapping(&**this, 1); | |
1408 | ptr::write(this, arc.assume_init()); | |
c1a9b12d SL |
1409 | } |
1410 | } else { | |
1411 | // We were the sole reference of either kind; bump back up the | |
1412 | // strong ref count. | |
1413 | this.inner().strong.store(1, Release); | |
1a4d82fc | 1414 | } |
c1a9b12d | 1415 | |
9346a6ac | 1416 | // As with `get_mut()`, the unsafety is ok because our reference was |
c34b1796 | 1417 | // either unique to begin with, or became one upon cloning the contents. |
f9f354fc | 1418 | unsafe { Self::get_mut_unchecked(this) } |
1a4d82fc JJ |
1419 | } |
1420 | } | |
1421 | ||
c1a9b12d | 1422 | impl<T: ?Sized> Arc<T> { |
e74abb32 | 1423 | /// Returns a mutable reference into the given `Arc`, if there are |
3dfed10e | 1424 | /// no other `Arc` or [`Weak`] pointers to the same allocation. |
c30ab7b3 | 1425 | /// |
3dfed10e | 1426 | /// Returns [`None`] otherwise, because it is not safe to |
c30ab7b3 SL |
1427 | /// mutate a shared value. |
1428 | /// | |
1429 | /// See also [`make_mut`][make_mut], which will [`clone`][clone] | |
e74abb32 | 1430 | /// the inner value when there are other pointers. |
c30ab7b3 | 1431 | /// |
3dfed10e XL |
1432 | /// [make_mut]: Arc::make_mut |
1433 | /// [clone]: Clone::clone | |
c1a9b12d SL |
1434 | /// |
1435 | /// # Examples | |
1436 | /// | |
1437 | /// ``` | |
e9174d1e | 1438 | /// use std::sync::Arc; |
c1a9b12d SL |
1439 | /// |
1440 | /// let mut x = Arc::new(3); | |
1441 | /// *Arc::get_mut(&mut x).unwrap() = 4; | |
1442 | /// assert_eq!(*x, 4); | |
1443 | /// | |
7cac9316 | 1444 | /// let _y = Arc::clone(&x); |
c1a9b12d | 1445 | /// assert!(Arc::get_mut(&mut x).is_none()); |
c1a9b12d SL |
1446 | /// ``` |
1447 | #[inline] | |
e9174d1e SL |
1448 | #[stable(feature = "arc_unique", since = "1.4.0")] |
1449 | pub fn get_mut(this: &mut Self) -> Option<&mut T> { | |
c1a9b12d SL |
1450 | if this.is_unique() { |
1451 | // This unsafety is ok because we're guaranteed that the pointer | |
1452 | // returned is the *only* pointer that will ever be returned to T. Our | |
1453 | // reference count is guaranteed to be 1 at this point, and we required | |
1454 | // the Arc itself to be `mut`, so we're returning the only possible | |
1455 | // reference to the inner data. | |
dfeec247 | 1456 | unsafe { Some(Arc::get_mut_unchecked(this)) } |
c1a9b12d SL |
1457 | } else { |
1458 | None | |
1459 | } | |
1460 | } | |
1461 | ||
e74abb32 | 1462 | /// Returns a mutable reference into the given `Arc`, |
e1599b0c XL |
1463 | /// without any check. |
1464 | /// | |
1465 | /// See also [`get_mut`], which is safe and does appropriate checks. | |
1466 | /// | |
3dfed10e | 1467 | /// [`get_mut`]: Arc::get_mut |
e1599b0c XL |
1468 | /// |
1469 | /// # Safety | |
1470 | /// | |
e74abb32 | 1471 | /// Any other `Arc` or [`Weak`] pointers to the same allocation must not be dereferenced |
e1599b0c XL |
1472 | /// for the duration of the returned borrow. |
1473 | /// This is trivially the case if no such pointers exist, | |
1474 | /// for example immediately after `Arc::new`. | |
1475 | /// | |
1476 | /// # Examples | |
1477 | /// | |
1478 | /// ``` | |
1479 | /// #![feature(get_mut_unchecked)] | |
1480 | /// | |
1481 | /// use std::sync::Arc; | |
1482 | /// | |
1483 | /// let mut x = Arc::new(String::new()); | |
1484 | /// unsafe { | |
1485 | /// Arc::get_mut_unchecked(&mut x).push_str("foo") | |
1486 | /// } | |
1487 | /// assert_eq!(*x, "foo"); | |
1488 | /// ``` | |
1489 | #[inline] | |
1490 | #[unstable(feature = "get_mut_unchecked", issue = "63292")] | |
1491 | pub unsafe fn get_mut_unchecked(this: &mut Self) -> &mut T { | |
f9f354fc XL |
1492 | // We are careful to *not* create a reference covering the "count" fields, as |
1493 | // this would alias with concurrent access to the reference counts (e.g. by `Weak`). | |
f035d41b | 1494 | unsafe { &mut (*this.ptr.as_ptr()).data } |
e1599b0c XL |
1495 | } |
1496 | ||
c1a9b12d SL |
1497 | /// Determine whether this is the unique reference (including weak refs) to |
1498 | /// the underlying data. | |
1499 | /// | |
1500 | /// Note that this requires locking the weak ref count. | |
1501 | fn is_unique(&mut self) -> bool { | |
1502 | // lock the weak pointer count if we appear to be the sole weak pointer | |
1503 | // holder. | |
1504 | // | |
1505 | // The acquire label here ensures a happens-before relationship with any | |
8faf50e0 XL |
1506 | // writes to `strong` (in particular in `Weak::upgrade`) prior to decrements |
1507 | // of the `weak` count (via `Weak::drop`, which uses release). If the upgraded | |
1508 | // weak ref was never dropped, the CAS here will fail so we do not care to synchronize. | |
54a0048b | 1509 | if self.inner().weak.compare_exchange(1, usize::MAX, Acquire, Relaxed).is_ok() { |
8faf50e0 XL |
1510 | // This needs to be an `Acquire` to synchronize with the decrement of the `strong` |
1511 | // counter in `drop` -- the only access that happens when any but the last reference | |
1512 | // is being dropped. | |
1513 | let unique = self.inner().strong.load(Acquire) == 1; | |
c1a9b12d SL |
1514 | |
1515 | // The release write here synchronizes with a read in `downgrade`, | |
1516 | // effectively preventing the above read of `strong` from happening | |
1517 | // after the write. | |
1518 | self.inner().weak.store(1, Release); // release the lock | |
1519 | unique | |
1520 | } else { | |
1521 | false | |
1522 | } | |
1523 | } | |
1524 | } | |
1525 | ||
85aaf69f | 1526 | #[stable(feature = "rust1", since = "1.0.0")] |
32a655c1 | 1527 | unsafe impl<#[may_dangle] T: ?Sized> Drop for Arc<T> { |
c30ab7b3 | 1528 | /// Drops the `Arc`. |
1a4d82fc | 1529 | /// |
c34b1796 | 1530 | /// This will decrement the strong reference count. If the strong reference |
c30ab7b3 | 1531 | /// count reaches zero then the only other references (if any) are |
b7449926 | 1532 | /// [`Weak`], so we `drop` the inner value. |
1a4d82fc JJ |
1533 | /// |
1534 | /// # Examples | |
1535 | /// | |
1536 | /// ``` | |
1537 | /// use std::sync::Arc; | |
1538 | /// | |
c30ab7b3 | 1539 | /// struct Foo; |
1a4d82fc | 1540 | /// |
c30ab7b3 SL |
1541 | /// impl Drop for Foo { |
1542 | /// fn drop(&mut self) { | |
1543 | /// println!("dropped!"); | |
1544 | /// } | |
1a4d82fc | 1545 | /// } |
1a4d82fc | 1546 | /// |
c30ab7b3 | 1547 | /// let foo = Arc::new(Foo); |
7cac9316 | 1548 | /// let foo2 = Arc::clone(&foo); |
1a4d82fc | 1549 | /// |
c30ab7b3 SL |
1550 | /// drop(foo); // Doesn't print anything |
1551 | /// drop(foo2); // Prints "dropped!" | |
1a4d82fc | 1552 | /// ``` |
c34b1796 | 1553 | #[inline] |
1a4d82fc | 1554 | fn drop(&mut self) { |
c34b1796 AL |
1555 | // Because `fetch_sub` is already atomic, we do not need to synchronize |
1556 | // with other threads unless we are going to delete the object. This | |
1557 | // same logic applies to the below `fetch_sub` to the `weak` count. | |
b039eaaf | 1558 | if self.inner().strong.fetch_sub(1, Release) != 1 { |
92a42be0 | 1559 | return; |
b039eaaf | 1560 | } |
1a4d82fc | 1561 | |
c34b1796 AL |
1562 | // This fence is needed to prevent reordering of use of the data and |
1563 | // deletion of the data. Because it is marked `Release`, the decreasing | |
1564 | // of the reference count synchronizes with this `Acquire` fence. This | |
1565 | // means that use of the data happens before decreasing the reference | |
1566 | // count, which happens before this fence, which happens before the | |
1567 | // deletion of the data. | |
1a4d82fc JJ |
1568 | // |
1569 | // As explained in the [Boost documentation][1], | |
1570 | // | |
c34b1796 AL |
1571 | // > It is important to enforce any possible access to the object in one |
1572 | // > thread (through an existing reference) to *happen before* deleting | |
1573 | // > the object in a different thread. This is achieved by a "release" | |
1574 | // > operation after dropping a reference (any access to the object | |
1575 | // > through this reference must obviously happened before), and an | |
1576 | // > "acquire" operation before deleting the object. | |
1a4d82fc | 1577 | // |
7cac9316 XL |
1578 | // In particular, while the contents of an Arc are usually immutable, it's |
1579 | // possible to have interior writes to something like a Mutex<T>. Since a | |
1580 | // Mutex is not acquired when it is deleted, we can't rely on its | |
1581 | // synchronization logic to make writes in thread A visible to a destructor | |
1582 | // running in thread B. | |
1583 | // | |
1584 | // Also note that the Acquire fence here could probably be replaced with an | |
1585 | // Acquire load, which could improve performance in highly-contended | |
1586 | // situations. See [2]. | |
1587 | // | |
1a4d82fc | 1588 | // [1]: (www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html) |
7cac9316 | 1589 | // [2]: (https://github.com/rust-lang/rust/pull/41714) |
ba9703b0 | 1590 | acquire!(self.inner().strong); |
1a4d82fc | 1591 | |
c34b1796 | 1592 | unsafe { |
b039eaaf | 1593 | self.drop_slow(); |
1a4d82fc JJ |
1594 | } |
1595 | } | |
1596 | } | |
1597 | ||
8faf50e0 | 1598 | impl Arc<dyn Any + Send + Sync> { |
94b46f34 | 1599 | #[inline] |
8faf50e0 XL |
1600 | #[stable(feature = "rc_downcast", since = "1.29.0")] |
1601 | /// Attempt to downcast the `Arc<dyn Any + Send + Sync>` to a concrete type. | |
94b46f34 XL |
1602 | /// |
1603 | /// # Examples | |
1604 | /// | |
1605 | /// ``` | |
94b46f34 XL |
1606 | /// use std::any::Any; |
1607 | /// use std::sync::Arc; | |
1608 | /// | |
8faf50e0 | 1609 | /// fn print_if_string(value: Arc<dyn Any + Send + Sync>) { |
94b46f34 XL |
1610 | /// if let Ok(string) = value.downcast::<String>() { |
1611 | /// println!("String ({}): {}", string.len(), string); | |
1612 | /// } | |
1613 | /// } | |
1614 | /// | |
e74abb32 XL |
1615 | /// let my_string = "Hello World".to_string(); |
1616 | /// print_if_string(Arc::new(my_string)); | |
1617 | /// print_if_string(Arc::new(0i8)); | |
94b46f34 XL |
1618 | /// ``` |
1619 | pub fn downcast<T>(self) -> Result<Arc<T>, Self> | |
1620 | where | |
1621 | T: Any + Send + Sync + 'static, | |
1622 | { | |
1623 | if (*self).is::<T>() { | |
1624 | let ptr = self.ptr.cast::<ArcInner<T>>(); | |
1625 | mem::forget(self); | |
416331ca | 1626 | Ok(Arc::from_inner(ptr)) |
94b46f34 XL |
1627 | } else { |
1628 | Err(self) | |
1629 | } | |
1630 | } | |
1631 | } | |
1632 | ||
a7813a04 | 1633 | impl<T> Weak<T> { |
8faf50e0 XL |
1634 | /// Constructs a new `Weak<T>`, without allocating any memory. |
1635 | /// Calling [`upgrade`] on the return value always gives [`None`]. | |
c30ab7b3 | 1636 | /// |
3dfed10e | 1637 | /// [`upgrade`]: Weak::upgrade |
a7813a04 XL |
1638 | /// |
1639 | /// # Examples | |
1640 | /// | |
1641 | /// ``` | |
1642 | /// use std::sync::Weak; | |
1643 | /// | |
1644 | /// let empty: Weak<i64> = Weak::new(); | |
c30ab7b3 | 1645 | /// assert!(empty.upgrade().is_none()); |
a7813a04 XL |
1646 | /// ``` |
1647 | #[stable(feature = "downgraded_weak", since = "1.10.0")] | |
1648 | pub fn new() -> Weak<T> { | |
dfeec247 | 1649 | Weak { ptr: NonNull::new(usize::MAX as *mut ArcInner<T>).expect("MAX is not 0") } |
a7813a04 | 1650 | } |
29967ef6 XL |
1651 | } |
1652 | ||
1653 | /// Helper type to allow accessing the reference counts without | |
1654 | /// making any assertions about the data field. | |
1655 | struct WeakInner<'a> { | |
1656 | weak: &'a atomic::AtomicUsize, | |
1657 | strong: &'a atomic::AtomicUsize, | |
1658 | } | |
dc9dc135 | 1659 | |
5869c6ff | 1660 | impl<T: ?Sized> Weak<T> { |
dc9dc135 XL |
1661 | /// Returns a raw pointer to the object `T` pointed to by this `Weak<T>`. |
1662 | /// | |
ba9703b0 XL |
1663 | /// The pointer is valid only if there are some strong references. The pointer may be dangling, |
1664 | /// unaligned or even [`null`] otherwise. | |
dc9dc135 XL |
1665 | /// |
1666 | /// # Examples | |
1667 | /// | |
1668 | /// ``` | |
416331ca | 1669 | /// use std::sync::Arc; |
dc9dc135 XL |
1670 | /// use std::ptr; |
1671 | /// | |
1672 | /// let strong = Arc::new("hello".to_owned()); | |
1673 | /// let weak = Arc::downgrade(&strong); | |
1674 | /// // Both point to the same object | |
ba9703b0 | 1675 | /// assert!(ptr::eq(&*strong, weak.as_ptr())); |
dc9dc135 | 1676 | /// // The strong here keeps it alive, so we can still access the object. |
ba9703b0 | 1677 | /// assert_eq!("hello", unsafe { &*weak.as_ptr() }); |
dc9dc135 XL |
1678 | /// |
1679 | /// drop(strong); | |
ba9703b0 | 1680 | /// // But not any more. We can do weak.as_ptr(), but accessing the pointer would lead to |
dc9dc135 | 1681 | /// // undefined behaviour. |
ba9703b0 | 1682 | /// // assert_eq!("hello", unsafe { &*weak.as_ptr() }); |
dc9dc135 XL |
1683 | /// ``` |
1684 | /// | |
3dfed10e | 1685 | /// [`null`]: core::ptr::null |
f9f354fc | 1686 | #[stable(feature = "weak_into_raw", since = "1.45.0")] |
ba9703b0 | 1687 | pub fn as_ptr(&self) -> *const T { |
f035d41b XL |
1688 | let ptr: *mut ArcInner<T> = NonNull::as_ptr(self.ptr); |
1689 | ||
5869c6ff XL |
1690 | if is_dangling(ptr) { |
1691 | // If the pointer is dangling, we return the sentinel directly. This cannot be | |
1692 | // a valid payload address, as the payload is at least as aligned as ArcInner (usize). | |
1693 | ptr as *const T | |
1694 | } else { | |
1695 | // SAFETY: if is_dangling returns false, then the pointer is dereferencable. | |
1696 | // The payload may be dropped at this point, and we have to maintain provenance, | |
1697 | // so use raw pointer manipulation. | |
1698 | unsafe { ptr::addr_of_mut!((*ptr).data) } | |
f035d41b | 1699 | } |
dc9dc135 XL |
1700 | } |
1701 | ||
1702 | /// Consumes the `Weak<T>` and turns it into a raw pointer. | |
1703 | /// | |
3dfed10e XL |
1704 | /// This converts the weak pointer into a raw pointer, while still preserving the ownership of |
1705 | /// one weak reference (the weak count is not modified by this operation). It can be turned | |
1706 | /// back into the `Weak<T>` with [`from_raw`]. | |
dc9dc135 XL |
1707 | /// |
1708 | /// The same restrictions of accessing the target of the pointer as with | |
ba9703b0 | 1709 | /// [`as_ptr`] apply. |
dc9dc135 XL |
1710 | /// |
1711 | /// # Examples | |
1712 | /// | |
1713 | /// ``` | |
dc9dc135 XL |
1714 | /// use std::sync::{Arc, Weak}; |
1715 | /// | |
1716 | /// let strong = Arc::new("hello".to_owned()); | |
1717 | /// let weak = Arc::downgrade(&strong); | |
416331ca | 1718 | /// let raw = weak.into_raw(); |
dc9dc135 XL |
1719 | /// |
1720 | /// assert_eq!(1, Arc::weak_count(&strong)); | |
1721 | /// assert_eq!("hello", unsafe { &*raw }); | |
1722 | /// | |
1723 | /// drop(unsafe { Weak::from_raw(raw) }); | |
1724 | /// assert_eq!(0, Arc::weak_count(&strong)); | |
1725 | /// ``` | |
1726 | /// | |
3dfed10e XL |
1727 | /// [`from_raw`]: Weak::from_raw |
1728 | /// [`as_ptr`]: Weak::as_ptr | |
f9f354fc | 1729 | #[stable(feature = "weak_into_raw", since = "1.45.0")] |
416331ca | 1730 | pub fn into_raw(self) -> *const T { |
ba9703b0 | 1731 | let result = self.as_ptr(); |
416331ca | 1732 | mem::forget(self); |
dc9dc135 XL |
1733 | result |
1734 | } | |
1735 | ||
3dfed10e | 1736 | /// Converts a raw pointer previously created by [`into_raw`] back into `Weak<T>`. |
dc9dc135 XL |
1737 | /// |
1738 | /// This can be used to safely get a strong reference (by calling [`upgrade`] | |
1739 | /// later) or to deallocate the weak count by dropping the `Weak<T>`. | |
1740 | /// | |
3dfed10e XL |
1741 | /// It takes ownership of one weak reference (with the exception of pointers created by [`new`], |
1742 | /// as these don't own anything; the method still works on them). | |
dc9dc135 XL |
1743 | /// |
1744 | /// # Safety | |
1745 | /// | |
ba9703b0 | 1746 | /// The pointer must have originated from the [`into_raw`] and must still own its potential |
3dfed10e | 1747 | /// weak reference. |
dc9dc135 | 1748 | /// |
3dfed10e XL |
1749 | /// It is allowed for the strong count to be 0 at the time of calling this. Nevertheless, this |
1750 | /// takes ownership of one weak reference currently represented as a raw pointer (the weak | |
1751 | /// count is not modified by this operation) and therefore it must be paired with a previous | |
1752 | /// call to [`into_raw`]. | |
dc9dc135 XL |
1753 | /// # Examples |
1754 | /// | |
1755 | /// ``` | |
dc9dc135 XL |
1756 | /// use std::sync::{Arc, Weak}; |
1757 | /// | |
1758 | /// let strong = Arc::new("hello".to_owned()); | |
1759 | /// | |
416331ca XL |
1760 | /// let raw_1 = Arc::downgrade(&strong).into_raw(); |
1761 | /// let raw_2 = Arc::downgrade(&strong).into_raw(); | |
dc9dc135 XL |
1762 | /// |
1763 | /// assert_eq!(2, Arc::weak_count(&strong)); | |
1764 | /// | |
416331ca | 1765 | /// assert_eq!("hello", &*unsafe { Weak::from_raw(raw_1) }.upgrade().unwrap()); |
dc9dc135 XL |
1766 | /// assert_eq!(1, Arc::weak_count(&strong)); |
1767 | /// | |
1768 | /// drop(strong); | |
1769 | /// | |
1770 | /// // Decrement the last weak count. | |
416331ca | 1771 | /// assert!(unsafe { Weak::from_raw(raw_2) }.upgrade().is_none()); |
dc9dc135 XL |
1772 | /// ``` |
1773 | /// | |
3dfed10e XL |
1774 | /// [`new`]: Weak::new |
1775 | /// [`into_raw`]: Weak::into_raw | |
1776 | /// [`upgrade`]: Weak::upgrade | |
1777 | /// [`forget`]: std::mem::forget | |
f9f354fc | 1778 | #[stable(feature = "weak_into_raw", since = "1.45.0")] |
dc9dc135 | 1779 | pub unsafe fn from_raw(ptr: *const T) -> Self { |
29967ef6 | 1780 | // See Weak::as_ptr for context on how the input pointer is derived. |
29967ef6 | 1781 | |
5869c6ff XL |
1782 | let ptr = if is_dangling(ptr as *mut T) { |
1783 | // This is a dangling Weak. | |
1784 | ptr as *mut ArcInner<T> | |
1785 | } else { | |
1786 | // Otherwise, we're guaranteed the pointer came from a nondangling Weak. | |
1787 | // SAFETY: data_offset is safe to call, as ptr references a real (potentially dropped) T. | |
1788 | let offset = unsafe { data_offset(ptr) }; | |
1789 | // Thus, we reverse the offset to get the whole RcBox. | |
1790 | // SAFETY: the pointer originated from a Weak, so this offset is safe. | |
1791 | unsafe { (ptr as *mut ArcInner<T>).set_ptr_value((ptr as *mut u8).offset(-offset)) } | |
29967ef6 | 1792 | }; |
a7813a04 | 1793 | |
29967ef6 | 1794 | // SAFETY: we now have recovered the original Weak pointer, so can create the Weak. |
5869c6ff | 1795 | Weak { ptr: unsafe { NonNull::new_unchecked(ptr) } } |
29967ef6 | 1796 | } |
b9856134 | 1797 | } |
f9f354fc | 1798 | |
b9856134 | 1799 | impl<T: ?Sized> Weak<T> { |
e74abb32 XL |
1800 | /// Attempts to upgrade the `Weak` pointer to an [`Arc`], delaying |
1801 | /// dropping of the inner value if successful. | |
1a4d82fc | 1802 | /// |
e74abb32 | 1803 | /// Returns [`None`] if the inner value has since been dropped. |
1a4d82fc | 1804 | /// |
1a4d82fc JJ |
1805 | /// # Examples |
1806 | /// | |
1807 | /// ``` | |
1808 | /// use std::sync::Arc; | |
1809 | /// | |
85aaf69f | 1810 | /// let five = Arc::new(5); |
1a4d82fc | 1811 | /// |
e9174d1e | 1812 | /// let weak_five = Arc::downgrade(&five); |
1a4d82fc JJ |
1813 | /// |
1814 | /// let strong_five: Option<Arc<_>> = weak_five.upgrade(); | |
c30ab7b3 SL |
1815 | /// assert!(strong_five.is_some()); |
1816 | /// | |
1817 | /// // Destroy all strong pointers. | |
1818 | /// drop(strong_five); | |
1819 | /// drop(five); | |
1820 | /// | |
1821 | /// assert!(weak_five.upgrade().is_none()); | |
1a4d82fc | 1822 | /// ``` |
e9174d1e | 1823 | #[stable(feature = "arc_weak", since = "1.4.0")] |
1a4d82fc | 1824 | pub fn upgrade(&self) -> Option<Arc<T>> { |
c34b1796 | 1825 | // We use a CAS loop to increment the strong count instead of a |
3dfed10e XL |
1826 | // fetch_add as this function should never take the reference count |
1827 | // from zero to one. | |
8faf50e0 | 1828 | let inner = self.inner()?; |
54a0048b SL |
1829 | |
1830 | // Relaxed load because any write of 0 that we can observe | |
1831 | // leaves the field in a permanently zero state (so a | |
1832 | // "stale" read of 0 is fine), and any other value is | |
1833 | // confirmed via the CAS below. | |
1834 | let mut n = inner.strong.load(Relaxed); | |
1835 | ||
1a4d82fc | 1836 | loop { |
b039eaaf | 1837 | if n == 0 { |
92a42be0 SL |
1838 | return None; |
1839 | } | |
1840 | ||
1841 | // See comments in `Arc::clone` for why we do this (for `mem::forget`). | |
1842 | if n > MAX_REFCOUNT { | |
f035d41b | 1843 | abort(); |
b039eaaf | 1844 | } |
c1a9b12d | 1845 | |
3dfed10e XL |
1846 | // Relaxed is fine for the failure case because we don't have any expectations about the new state. |
1847 | // Acquire is necessary for the success case to synchronise with `Arc::new_cyclic`, when the inner | |
1848 | // value can be initialized after `Weak` references have already been created. In that case, we | |
1849 | // expect to observe the fully initialized value. | |
1850 | match inner.strong.compare_exchange_weak(n, n + 1, Acquire, Relaxed) { | |
416331ca | 1851 | Ok(_) => return Some(Arc::from_inner(self.ptr)), // null checked above |
54a0048b | 1852 | Err(old) => n = old, |
b039eaaf | 1853 | } |
1a4d82fc JJ |
1854 | } |
1855 | } | |
1856 | ||
e74abb32 | 1857 | /// Gets the number of strong (`Arc`) pointers pointing to this allocation. |
9fa01778 XL |
1858 | /// |
1859 | /// If `self` was created using [`Weak::new`], this will return 0. | |
60c5eb7d | 1860 | #[stable(feature = "weak_counts", since = "1.41.0")] |
9fa01778 | 1861 | pub fn strong_count(&self) -> usize { |
dfeec247 | 1862 | if let Some(inner) = self.inner() { inner.strong.load(SeqCst) } else { 0 } |
9fa01778 XL |
1863 | } |
1864 | ||
1865 | /// Gets an approximation of the number of `Weak` pointers pointing to this | |
e74abb32 | 1866 | /// allocation. |
9fa01778 | 1867 | /// |
60c5eb7d XL |
1868 | /// If `self` was created using [`Weak::new`], or if there are no remaining |
1869 | /// strong pointers, this will return 0. | |
9fa01778 XL |
1870 | /// |
1871 | /// # Accuracy | |
1872 | /// | |
1873 | /// Due to implementation details, the returned value can be off by 1 in | |
1874 | /// either direction when other threads are manipulating any `Arc`s or | |
e74abb32 | 1875 | /// `Weak`s pointing to the same allocation. |
60c5eb7d XL |
1876 | #[stable(feature = "weak_counts", since = "1.41.0")] |
1877 | pub fn weak_count(&self) -> usize { | |
dfeec247 XL |
1878 | self.inner() |
1879 | .map(|inner| { | |
1880 | let weak = inner.weak.load(SeqCst); | |
1881 | let strong = inner.strong.load(SeqCst); | |
1882 | if strong == 0 { | |
1883 | 0 | |
1884 | } else { | |
1885 | // Since we observed that there was at least one strong pointer | |
1886 | // after reading the weak count, we know that the implicit weak | |
1887 | // reference (present whenever any strong references are alive) | |
1888 | // was still around when we observed the weak count, and can | |
1889 | // therefore safely subtract it. | |
1890 | weak - 1 | |
1891 | } | |
1892 | }) | |
1893 | .unwrap_or(0) | |
9fa01778 XL |
1894 | } |
1895 | ||
1896 | /// Returns `None` when the pointer is dangling and there is no allocated `ArcInner`, | |
1897 | /// (i.e., when this `Weak` was created by `Weak::new`). | |
1a4d82fc | 1898 | #[inline] |
f9f354fc | 1899 | fn inner(&self) -> Option<WeakInner<'_>> { |
5869c6ff | 1900 | if is_dangling(self.ptr.as_ptr()) { |
f9f354fc XL |
1901 | None |
1902 | } else { | |
1903 | // We are careful to *not* create a reference covering the "data" field, as | |
1904 | // the field may be mutated concurrently (for example, if the last `Arc` | |
1905 | // is dropped, the data field will be dropped in-place). | |
1906 | Some(unsafe { | |
1907 | let ptr = self.ptr.as_ptr(); | |
1908 | WeakInner { strong: &(*ptr).strong, weak: &(*ptr).weak } | |
1909 | }) | |
1910 | } | |
1a4d82fc | 1911 | } |
0731742a | 1912 | |
e74abb32 XL |
1913 | /// Returns `true` if the two `Weak`s point to the same allocation (similar to |
1914 | /// [`ptr::eq`]), or if both don't point to any allocation | |
e1599b0c | 1915 | /// (because they were created with `Weak::new()`). |
0731742a XL |
1916 | /// |
1917 | /// # Notes | |
1918 | /// | |
1919 | /// Since this compares pointers it means that `Weak::new()` will equal each | |
e74abb32 | 1920 | /// other, even though they don't point to any allocation. |
0731742a | 1921 | /// |
0731742a XL |
1922 | /// # Examples |
1923 | /// | |
1924 | /// ``` | |
dc9dc135 | 1925 | /// use std::sync::Arc; |
0731742a XL |
1926 | /// |
1927 | /// let first_rc = Arc::new(5); | |
1928 | /// let first = Arc::downgrade(&first_rc); | |
1929 | /// let second = Arc::downgrade(&first_rc); | |
1930 | /// | |
dc9dc135 | 1931 | /// assert!(first.ptr_eq(&second)); |
0731742a XL |
1932 | /// |
1933 | /// let third_rc = Arc::new(5); | |
1934 | /// let third = Arc::downgrade(&third_rc); | |
1935 | /// | |
dc9dc135 | 1936 | /// assert!(!first.ptr_eq(&third)); |
0731742a XL |
1937 | /// ``` |
1938 | /// | |
1939 | /// Comparing `Weak::new`. | |
1940 | /// | |
1941 | /// ``` | |
0731742a XL |
1942 | /// use std::sync::{Arc, Weak}; |
1943 | /// | |
1944 | /// let first = Weak::new(); | |
1945 | /// let second = Weak::new(); | |
dc9dc135 | 1946 | /// assert!(first.ptr_eq(&second)); |
0731742a XL |
1947 | /// |
1948 | /// let third_rc = Arc::new(()); | |
1949 | /// let third = Arc::downgrade(&third_rc); | |
dc9dc135 | 1950 | /// assert!(!first.ptr_eq(&third)); |
0731742a | 1951 | /// ``` |
e74abb32 | 1952 | /// |
3dfed10e | 1953 | /// [`ptr::eq`]: core::ptr::eq |
0731742a | 1954 | #[inline] |
e1599b0c | 1955 | #[stable(feature = "weak_ptr_eq", since = "1.39.0")] |
dc9dc135 XL |
1956 | pub fn ptr_eq(&self, other: &Self) -> bool { |
1957 | self.ptr.as_ptr() == other.ptr.as_ptr() | |
0731742a | 1958 | } |
1a4d82fc JJ |
1959 | } |
1960 | ||
e9174d1e | 1961 | #[stable(feature = "arc_weak", since = "1.4.0")] |
62682a34 | 1962 | impl<T: ?Sized> Clone for Weak<T> { |
e74abb32 | 1963 | /// Makes a clone of the `Weak` pointer that points to the same allocation. |
1a4d82fc JJ |
1964 | /// |
1965 | /// # Examples | |
1966 | /// | |
1967 | /// ``` | |
7cac9316 | 1968 | /// use std::sync::{Arc, Weak}; |
1a4d82fc | 1969 | /// |
e9174d1e | 1970 | /// let weak_five = Arc::downgrade(&Arc::new(5)); |
1a4d82fc | 1971 | /// |
0bf4aa26 | 1972 | /// let _ = Weak::clone(&weak_five); |
1a4d82fc JJ |
1973 | /// ``` |
1974 | #[inline] | |
1975 | fn clone(&self) -> Weak<T> { | |
8faf50e0 XL |
1976 | let inner = if let Some(inner) = self.inner() { |
1977 | inner | |
1978 | } else { | |
1979 | return Weak { ptr: self.ptr }; | |
1980 | }; | |
c1a9b12d SL |
1981 | // See comments in Arc::clone() for why this is relaxed. This can use a |
1982 | // fetch_add (ignoring the lock) because the weak count is only locked | |
1983 | // where are *no other* weak pointers in existence. (So we can't be | |
1984 | // running this code in that case). | |
8faf50e0 | 1985 | let old_size = inner.weak.fetch_add(1, Relaxed); |
c1a9b12d SL |
1986 | |
1987 | // See comments in Arc::clone() for why we do this (for mem::forget). | |
1988 | if old_size > MAX_REFCOUNT { | |
f035d41b | 1989 | abort(); |
c1a9b12d SL |
1990 | } |
1991 | ||
e74abb32 | 1992 | Weak { ptr: self.ptr } |
1a4d82fc JJ |
1993 | } |
1994 | } | |
1995 | ||
a7813a04 XL |
1996 | #[stable(feature = "downgraded_weak", since = "1.10.0")] |
1997 | impl<T> Default for Weak<T> { | |
8faf50e0 | 1998 | /// Constructs a new `Weak<T>`, without allocating memory. |
0731742a | 1999 | /// Calling [`upgrade`] on the return value always |
b7449926 | 2000 | /// gives [`None`]. |
c30ab7b3 | 2001 | /// |
3dfed10e | 2002 | /// [`upgrade`]: Weak::upgrade |
c30ab7b3 SL |
2003 | /// |
2004 | /// # Examples | |
2005 | /// | |
2006 | /// ``` | |
2007 | /// use std::sync::Weak; | |
2008 | /// | |
2009 | /// let empty: Weak<i64> = Default::default(); | |
2010 | /// assert!(empty.upgrade().is_none()); | |
2011 | /// ``` | |
a7813a04 XL |
2012 | fn default() -> Weak<T> { |
2013 | Weak::new() | |
2014 | } | |
2015 | } | |
2016 | ||
7453a54e | 2017 | #[stable(feature = "arc_weak", since = "1.4.0")] |
17df50a5 | 2018 | unsafe impl<#[may_dangle] T: ?Sized> Drop for Weak<T> { |
c30ab7b3 | 2019 | /// Drops the `Weak` pointer. |
1a4d82fc | 2020 | /// |
1a4d82fc JJ |
2021 | /// # Examples |
2022 | /// | |
2023 | /// ``` | |
7cac9316 | 2024 | /// use std::sync::{Arc, Weak}; |
1a4d82fc | 2025 | /// |
c30ab7b3 | 2026 | /// struct Foo; |
1a4d82fc | 2027 | /// |
c30ab7b3 SL |
2028 | /// impl Drop for Foo { |
2029 | /// fn drop(&mut self) { | |
2030 | /// println!("dropped!"); | |
2031 | /// } | |
1a4d82fc | 2032 | /// } |
1a4d82fc | 2033 | /// |
c30ab7b3 SL |
2034 | /// let foo = Arc::new(Foo); |
2035 | /// let weak_foo = Arc::downgrade(&foo); | |
7cac9316 | 2036 | /// let other_weak_foo = Weak::clone(&weak_foo); |
1a4d82fc | 2037 | /// |
c30ab7b3 SL |
2038 | /// drop(weak_foo); // Doesn't print anything |
2039 | /// drop(foo); // Prints "dropped!" | |
2040 | /// | |
2041 | /// assert!(other_weak_foo.upgrade().is_none()); | |
1a4d82fc JJ |
2042 | /// ``` |
2043 | fn drop(&mut self) { | |
c34b1796 AL |
2044 | // If we find out that we were the last weak pointer, then its time to |
2045 | // deallocate the data entirely. See the discussion in Arc::drop() about | |
2046 | // the memory orderings | |
c1a9b12d SL |
2047 | // |
2048 | // It's not necessary to check for the locked state here, because the | |
2049 | // weak count can only be locked if there was precisely one weak ref, | |
2050 | // meaning that drop could only subsequently run ON that remaining weak | |
2051 | // ref, which can only happen after the lock is released. | |
dfeec247 | 2052 | let inner = if let Some(inner) = self.inner() { inner } else { return }; |
8faf50e0 XL |
2053 | |
2054 | if inner.weak.fetch_sub(1, Release) == 1 { | |
ba9703b0 | 2055 | acquire!(inner.weak); |
5869c6ff | 2056 | unsafe { Global.deallocate(self.ptr.cast(), Layout::for_value_raw(self.ptr.as_ptr())) } |
1a4d82fc JJ |
2057 | } |
2058 | } | |
2059 | } | |
2060 | ||
0731742a XL |
2061 | #[stable(feature = "rust1", since = "1.0.0")] |
2062 | trait ArcEqIdent<T: ?Sized + PartialEq> { | |
2063 | fn eq(&self, other: &Arc<T>) -> bool; | |
2064 | fn ne(&self, other: &Arc<T>) -> bool; | |
2065 | } | |
2066 | ||
2067 | #[stable(feature = "rust1", since = "1.0.0")] | |
2068 | impl<T: ?Sized + PartialEq> ArcEqIdent<T> for Arc<T> { | |
2069 | #[inline] | |
2070 | default fn eq(&self, other: &Arc<T>) -> bool { | |
2071 | **self == **other | |
2072 | } | |
2073 | #[inline] | |
2074 | default fn ne(&self, other: &Arc<T>) -> bool { | |
2075 | **self != **other | |
2076 | } | |
2077 | } | |
2078 | ||
48663c56 XL |
2079 | /// We're doing this specialization here, and not as a more general optimization on `&T`, because it |
2080 | /// would otherwise add a cost to all equality checks on refs. We assume that `Arc`s are used to | |
2081 | /// store large values, that are slow to clone, but also heavy to check for equality, causing this | |
2082 | /// cost to pay off more easily. It's also more likely to have two `Arc` clones, that point to | |
2083 | /// the same value, than two `&T`s. | |
e74abb32 XL |
2084 | /// |
2085 | /// We can only do this when `T: Eq` as a `PartialEq` might be deliberately irreflexive. | |
0731742a | 2086 | #[stable(feature = "rust1", since = "1.0.0")] |
f9f354fc | 2087 | impl<T: ?Sized + crate::rc::MarkerEq> ArcEqIdent<T> for Arc<T> { |
0731742a XL |
2088 | #[inline] |
2089 | fn eq(&self, other: &Arc<T>) -> bool { | |
2090 | Arc::ptr_eq(self, other) || **self == **other | |
2091 | } | |
2092 | ||
2093 | #[inline] | |
2094 | fn ne(&self, other: &Arc<T>) -> bool { | |
2095 | !Arc::ptr_eq(self, other) && **self != **other | |
2096 | } | |
2097 | } | |
2098 | ||
85aaf69f | 2099 | #[stable(feature = "rust1", since = "1.0.0")] |
62682a34 | 2100 | impl<T: ?Sized + PartialEq> PartialEq for Arc<T> { |
c30ab7b3 | 2101 | /// Equality for two `Arc`s. |
1a4d82fc | 2102 | /// |
e74abb32 XL |
2103 | /// Two `Arc`s are equal if their inner values are equal, even if they are |
2104 | /// stored in different allocation. | |
1a4d82fc | 2105 | /// |
e74abb32 XL |
2106 | /// If `T` also implements `Eq` (implying reflexivity of equality), |
2107 | /// two `Arc`s that point to the same allocation are always equal. | |
0731742a | 2108 | /// |
1a4d82fc JJ |
2109 | /// # Examples |
2110 | /// | |
2111 | /// ``` | |
2112 | /// use std::sync::Arc; | |
2113 | /// | |
85aaf69f | 2114 | /// let five = Arc::new(5); |
1a4d82fc | 2115 | /// |
c30ab7b3 | 2116 | /// assert!(five == Arc::new(5)); |
1a4d82fc | 2117 | /// ``` |
0731742a | 2118 | #[inline] |
b039eaaf | 2119 | fn eq(&self, other: &Arc<T>) -> bool { |
0731742a | 2120 | ArcEqIdent::eq(self, other) |
b039eaaf | 2121 | } |
1a4d82fc | 2122 | |
c30ab7b3 | 2123 | /// Inequality for two `Arc`s. |
1a4d82fc | 2124 | /// |
c30ab7b3 | 2125 | /// Two `Arc`s are unequal if their inner values are unequal. |
1a4d82fc | 2126 | /// |
e74abb32 XL |
2127 | /// If `T` also implements `Eq` (implying reflexivity of equality), |
2128 | /// two `Arc`s that point to the same value are never unequal. | |
0731742a | 2129 | /// |
1a4d82fc JJ |
2130 | /// # Examples |
2131 | /// | |
2132 | /// ``` | |
2133 | /// use std::sync::Arc; | |
2134 | /// | |
85aaf69f | 2135 | /// let five = Arc::new(5); |
1a4d82fc | 2136 | /// |
c30ab7b3 | 2137 | /// assert!(five != Arc::new(6)); |
1a4d82fc | 2138 | /// ``` |
0731742a | 2139 | #[inline] |
b039eaaf | 2140 | fn ne(&self, other: &Arc<T>) -> bool { |
0731742a | 2141 | ArcEqIdent::ne(self, other) |
b039eaaf | 2142 | } |
1a4d82fc | 2143 | } |
0731742a | 2144 | |
85aaf69f | 2145 | #[stable(feature = "rust1", since = "1.0.0")] |
62682a34 | 2146 | impl<T: ?Sized + PartialOrd> PartialOrd for Arc<T> { |
c30ab7b3 | 2147 | /// Partial comparison for two `Arc`s. |
1a4d82fc JJ |
2148 | /// |
2149 | /// The two are compared by calling `partial_cmp()` on their inner values. | |
2150 | /// | |
2151 | /// # Examples | |
2152 | /// | |
2153 | /// ``` | |
2154 | /// use std::sync::Arc; | |
c30ab7b3 | 2155 | /// use std::cmp::Ordering; |
1a4d82fc | 2156 | /// |
85aaf69f | 2157 | /// let five = Arc::new(5); |
1a4d82fc | 2158 | /// |
c30ab7b3 | 2159 | /// assert_eq!(Some(Ordering::Less), five.partial_cmp(&Arc::new(6))); |
1a4d82fc JJ |
2160 | /// ``` |
2161 | fn partial_cmp(&self, other: &Arc<T>) -> Option<Ordering> { | |
2162 | (**self).partial_cmp(&**other) | |
2163 | } | |
2164 | ||
c30ab7b3 | 2165 | /// Less-than comparison for two `Arc`s. |
1a4d82fc JJ |
2166 | /// |
2167 | /// The two are compared by calling `<` on their inner values. | |
2168 | /// | |
2169 | /// # Examples | |
2170 | /// | |
2171 | /// ``` | |
2172 | /// use std::sync::Arc; | |
2173 | /// | |
85aaf69f | 2174 | /// let five = Arc::new(5); |
1a4d82fc | 2175 | /// |
c30ab7b3 | 2176 | /// assert!(five < Arc::new(6)); |
1a4d82fc | 2177 | /// ``` |
b039eaaf SL |
2178 | fn lt(&self, other: &Arc<T>) -> bool { |
2179 | *(*self) < *(*other) | |
2180 | } | |
1a4d82fc | 2181 | |
c30ab7b3 | 2182 | /// 'Less than or equal to' comparison for two `Arc`s. |
1a4d82fc JJ |
2183 | /// |
2184 | /// The two are compared by calling `<=` on their inner values. | |
2185 | /// | |
2186 | /// # Examples | |
2187 | /// | |
2188 | /// ``` | |
2189 | /// use std::sync::Arc; | |
2190 | /// | |
85aaf69f | 2191 | /// let five = Arc::new(5); |
1a4d82fc | 2192 | /// |
c30ab7b3 | 2193 | /// assert!(five <= Arc::new(5)); |
1a4d82fc | 2194 | /// ``` |
b039eaaf SL |
2195 | fn le(&self, other: &Arc<T>) -> bool { |
2196 | *(*self) <= *(*other) | |
2197 | } | |
1a4d82fc | 2198 | |
c30ab7b3 | 2199 | /// Greater-than comparison for two `Arc`s. |
1a4d82fc JJ |
2200 | /// |
2201 | /// The two are compared by calling `>` on their inner values. | |
2202 | /// | |
2203 | /// # Examples | |
2204 | /// | |
2205 | /// ``` | |
2206 | /// use std::sync::Arc; | |
2207 | /// | |
85aaf69f | 2208 | /// let five = Arc::new(5); |
1a4d82fc | 2209 | /// |
c30ab7b3 | 2210 | /// assert!(five > Arc::new(4)); |
1a4d82fc | 2211 | /// ``` |
b039eaaf SL |
2212 | fn gt(&self, other: &Arc<T>) -> bool { |
2213 | *(*self) > *(*other) | |
2214 | } | |
1a4d82fc | 2215 | |
c30ab7b3 | 2216 | /// 'Greater than or equal to' comparison for two `Arc`s. |
1a4d82fc JJ |
2217 | /// |
2218 | /// The two are compared by calling `>=` on their inner values. | |
2219 | /// | |
2220 | /// # Examples | |
2221 | /// | |
2222 | /// ``` | |
2223 | /// use std::sync::Arc; | |
2224 | /// | |
85aaf69f | 2225 | /// let five = Arc::new(5); |
1a4d82fc | 2226 | /// |
c30ab7b3 | 2227 | /// assert!(five >= Arc::new(5)); |
1a4d82fc | 2228 | /// ``` |
b039eaaf SL |
2229 | fn ge(&self, other: &Arc<T>) -> bool { |
2230 | *(*self) >= *(*other) | |
2231 | } | |
1a4d82fc | 2232 | } |
85aaf69f | 2233 | #[stable(feature = "rust1", since = "1.0.0")] |
62682a34 | 2234 | impl<T: ?Sized + Ord> Ord for Arc<T> { |
c30ab7b3 SL |
2235 | /// Comparison for two `Arc`s. |
2236 | /// | |
2237 | /// The two are compared by calling `cmp()` on their inner values. | |
2238 | /// | |
2239 | /// # Examples | |
2240 | /// | |
2241 | /// ``` | |
2242 | /// use std::sync::Arc; | |
2243 | /// use std::cmp::Ordering; | |
2244 | /// | |
2245 | /// let five = Arc::new(5); | |
2246 | /// | |
2247 | /// assert_eq!(Ordering::Less, five.cmp(&Arc::new(6))); | |
2248 | /// ``` | |
b039eaaf SL |
2249 | fn cmp(&self, other: &Arc<T>) -> Ordering { |
2250 | (**self).cmp(&**other) | |
2251 | } | |
1a4d82fc | 2252 | } |
85aaf69f | 2253 | #[stable(feature = "rust1", since = "1.0.0")] |
62682a34 | 2254 | impl<T: ?Sized + Eq> Eq for Arc<T> {} |
1a4d82fc | 2255 | |
85aaf69f | 2256 | #[stable(feature = "rust1", since = "1.0.0")] |
62682a34 | 2257 | impl<T: ?Sized + fmt::Display> fmt::Display for Arc<T> { |
9fa01778 | 2258 | fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
85aaf69f | 2259 | fmt::Display::fmt(&**self, f) |
1a4d82fc JJ |
2260 | } |
2261 | } | |
2262 | ||
85aaf69f | 2263 | #[stable(feature = "rust1", since = "1.0.0")] |
62682a34 | 2264 | impl<T: ?Sized + fmt::Debug> fmt::Debug for Arc<T> { |
9fa01778 | 2265 | fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
85aaf69f | 2266 | fmt::Debug::fmt(&**self, f) |
1a4d82fc JJ |
2267 | } |
2268 | } | |
2269 | ||
9346a6ac | 2270 | #[stable(feature = "rust1", since = "1.0.0")] |
7453a54e | 2271 | impl<T: ?Sized> fmt::Pointer for Arc<T> { |
9fa01778 | 2272 | fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
ff7c6d11 | 2273 | fmt::Pointer::fmt(&(&**self as *const T), f) |
9346a6ac AL |
2274 | } |
2275 | } | |
2276 | ||
85aaf69f | 2277 | #[stable(feature = "rust1", since = "1.0.0")] |
d9579d0f | 2278 | impl<T: Default> Default for Arc<T> { |
c30ab7b3 SL |
2279 | /// Creates a new `Arc<T>`, with the `Default` value for `T`. |
2280 | /// | |
2281 | /// # Examples | |
2282 | /// | |
2283 | /// ``` | |
2284 | /// use std::sync::Arc; | |
2285 | /// | |
2286 | /// let x: Arc<i32> = Default::default(); | |
2287 | /// assert_eq!(*x, 0); | |
2288 | /// ``` | |
b039eaaf SL |
2289 | fn default() -> Arc<T> { |
2290 | Arc::new(Default::default()) | |
2291 | } | |
1a4d82fc JJ |
2292 | } |
2293 | ||
85aaf69f | 2294 | #[stable(feature = "rust1", since = "1.0.0")] |
62682a34 | 2295 | impl<T: ?Sized + Hash> Hash for Arc<T> { |
85aaf69f SL |
2296 | fn hash<H: Hasher>(&self, state: &mut H) { |
2297 | (**self).hash(state) | |
2298 | } | |
2299 | } | |
1a4d82fc | 2300 | |
92a42be0 SL |
2301 | #[stable(feature = "from_for_ptrs", since = "1.6.0")] |
2302 | impl<T> From<T> for Arc<T> { | |
2303 | fn from(t: T) -> Self { | |
2304 | Arc::new(t) | |
2305 | } | |
2306 | } | |
2307 | ||
17df50a5 | 2308 | #[cfg(not(no_global_oom_handling))] |
3b2f2976 | 2309 | #[stable(feature = "shared_from_slice", since = "1.21.0")] |
9fa01778 | 2310 | impl<T: Clone> From<&[T]> for Arc<[T]> { |
6a06907d XL |
2311 | /// Allocate a reference-counted slice and fill it by cloning `v`'s items. |
2312 | /// | |
2313 | /// # Example | |
2314 | /// | |
2315 | /// ``` | |
2316 | /// # use std::sync::Arc; | |
2317 | /// let original: &[i32] = &[1, 2, 3]; | |
2318 | /// let shared: Arc<[i32]> = Arc::from(original); | |
2319 | /// assert_eq!(&[1, 2, 3], &shared[..]); | |
2320 | /// ``` | |
3b2f2976 XL |
2321 | #[inline] |
2322 | fn from(v: &[T]) -> Arc<[T]> { | |
2323 | <Self as ArcFromSlice<T>>::from_slice(v) | |
2324 | } | |
2325 | } | |
2326 | ||
17df50a5 | 2327 | #[cfg(not(no_global_oom_handling))] |
3b2f2976 | 2328 | #[stable(feature = "shared_from_slice", since = "1.21.0")] |
9fa01778 | 2329 | impl From<&str> for Arc<str> { |
6a06907d XL |
2330 | /// Allocate a reference-counted `str` and copy `v` into it. |
2331 | /// | |
2332 | /// # Example | |
2333 | /// | |
2334 | /// ``` | |
2335 | /// # use std::sync::Arc; | |
2336 | /// let shared: Arc<str> = Arc::from("eggplant"); | |
2337 | /// assert_eq!("eggplant", &shared[..]); | |
2338 | /// ``` | |
3b2f2976 XL |
2339 | #[inline] |
2340 | fn from(v: &str) -> Arc<str> { | |
ff7c6d11 XL |
2341 | let arc = Arc::<[u8]>::from(v.as_bytes()); |
2342 | unsafe { Arc::from_raw(Arc::into_raw(arc) as *const str) } | |
3b2f2976 XL |
2343 | } |
2344 | } | |
2345 | ||
17df50a5 | 2346 | #[cfg(not(no_global_oom_handling))] |
3b2f2976 XL |
2347 | #[stable(feature = "shared_from_slice", since = "1.21.0")] |
2348 | impl From<String> for Arc<str> { | |
6a06907d XL |
2349 | /// Allocate a reference-counted `str` and copy `v` into it. |
2350 | /// | |
2351 | /// # Example | |
2352 | /// | |
2353 | /// ``` | |
2354 | /// # use std::sync::Arc; | |
2355 | /// let unique: String = "eggplant".to_owned(); | |
2356 | /// let shared: Arc<str> = Arc::from(unique); | |
2357 | /// assert_eq!("eggplant", &shared[..]); | |
2358 | /// ``` | |
3b2f2976 XL |
2359 | #[inline] |
2360 | fn from(v: String) -> Arc<str> { | |
2361 | Arc::from(&v[..]) | |
2362 | } | |
2363 | } | |
2364 | ||
17df50a5 | 2365 | #[cfg(not(no_global_oom_handling))] |
3b2f2976 XL |
2366 | #[stable(feature = "shared_from_slice", since = "1.21.0")] |
2367 | impl<T: ?Sized> From<Box<T>> for Arc<T> { | |
6a06907d XL |
2368 | /// Move a boxed object to a new, reference-counted allocation. |
2369 | /// | |
2370 | /// # Example | |
2371 | /// | |
2372 | /// ``` | |
2373 | /// # use std::sync::Arc; | |
2374 | /// let unique: Box<str> = Box::from("eggplant"); | |
2375 | /// let shared: Arc<str> = Arc::from(unique); | |
2376 | /// assert_eq!("eggplant", &shared[..]); | |
2377 | /// ``` | |
3b2f2976 XL |
2378 | #[inline] |
2379 | fn from(v: Box<T>) -> Arc<T> { | |
2380 | Arc::from_box(v) | |
2381 | } | |
2382 | } | |
2383 | ||
17df50a5 | 2384 | #[cfg(not(no_global_oom_handling))] |
3b2f2976 XL |
2385 | #[stable(feature = "shared_from_slice", since = "1.21.0")] |
2386 | impl<T> From<Vec<T>> for Arc<[T]> { | |
6a06907d XL |
2387 | /// Allocate a reference-counted slice and move `v`'s items into it. |
2388 | /// | |
2389 | /// # Example | |
2390 | /// | |
2391 | /// ``` | |
2392 | /// # use std::sync::Arc; | |
2393 | /// let unique: Vec<i32> = vec![1, 2, 3]; | |
2394 | /// let shared: Arc<[i32]> = Arc::from(unique); | |
2395 | /// assert_eq!(&[1, 2, 3], &shared[..]); | |
2396 | /// ``` | |
3b2f2976 XL |
2397 | #[inline] |
2398 | fn from(mut v: Vec<T>) -> Arc<[T]> { | |
2399 | unsafe { | |
2400 | let arc = Arc::copy_from_slice(&v); | |
2401 | ||
2402 | // Allow the Vec to free its memory, but not destroy its contents | |
2403 | v.set_len(0); | |
2404 | ||
2405 | arc | |
2406 | } | |
2407 | } | |
2408 | } | |
2409 | ||
f9f354fc XL |
2410 | #[stable(feature = "shared_from_cow", since = "1.45.0")] |
2411 | impl<'a, B> From<Cow<'a, B>> for Arc<B> | |
2412 | where | |
2413 | B: ToOwned + ?Sized, | |
2414 | Arc<B>: From<&'a B> + From<B::Owned>, | |
2415 | { | |
17df50a5 XL |
2416 | /// Create an atomically reference-counted pointer from |
2417 | /// a clone-on-write pointer by copying its content. | |
2418 | /// | |
2419 | /// # Example | |
2420 | /// | |
2421 | /// ```rust | |
2422 | /// # use std::sync::Arc; | |
2423 | /// # use std::borrow::Cow; | |
2424 | /// let cow: Cow<str> = Cow::Borrowed("eggplant"); | |
2425 | /// let shared: Arc<str> = Arc::from(cow); | |
2426 | /// assert_eq!("eggplant", &shared[..]); | |
2427 | /// ``` | |
f9f354fc XL |
2428 | #[inline] |
2429 | fn from(cow: Cow<'a, B>) -> Arc<B> { | |
2430 | match cow { | |
2431 | Cow::Borrowed(s) => Arc::from(s), | |
2432 | Cow::Owned(s) => Arc::from(s), | |
2433 | } | |
2434 | } | |
2435 | } | |
2436 | ||
74b04a01 | 2437 | #[stable(feature = "boxed_slice_try_from", since = "1.43.0")] |
3dfed10e | 2438 | impl<T, const N: usize> TryFrom<Arc<[T]>> for Arc<[T; N]> { |
416331ca | 2439 | type Error = Arc<[T]>; |
1a4d82fc | 2440 | |
416331ca XL |
2441 | fn try_from(boxed_slice: Arc<[T]>) -> Result<Self, Self::Error> { |
2442 | if boxed_slice.len() == N { | |
2443 | Ok(unsafe { Arc::from_raw(Arc::into_raw(boxed_slice) as *mut [T; N]) }) | |
2444 | } else { | |
2445 | Err(boxed_slice) | |
3b2f2976 | 2446 | } |
3b2f2976 | 2447 | } |
416331ca | 2448 | } |
3b2f2976 | 2449 | |
17df50a5 | 2450 | #[cfg(not(no_global_oom_handling))] |
416331ca XL |
2451 | #[stable(feature = "shared_from_iter", since = "1.37.0")] |
2452 | impl<T> iter::FromIterator<T> for Arc<[T]> { | |
2453 | /// Takes each element in the `Iterator` and collects it into an `Arc<[T]>`. | |
2454 | /// | |
2455 | /// # Performance characteristics | |
2456 | /// | |
2457 | /// ## The general case | |
2458 | /// | |
2459 | /// In the general case, collecting into `Arc<[T]>` is done by first | |
2460 | /// collecting into a `Vec<T>`. That is, when writing the following: | |
2461 | /// | |
2462 | /// ```rust | |
2463 | /// # use std::sync::Arc; | |
2464 | /// let evens: Arc<[u8]> = (0..10).filter(|&x| x % 2 == 0).collect(); | |
2465 | /// # assert_eq!(&*evens, &[0, 2, 4, 6, 8]); | |
2466 | /// ``` | |
2467 | /// | |
2468 | /// this behaves as if we wrote: | |
2469 | /// | |
2470 | /// ```rust | |
2471 | /// # use std::sync::Arc; | |
2472 | /// let evens: Arc<[u8]> = (0..10).filter(|&x| x % 2 == 0) | |
2473 | /// .collect::<Vec<_>>() // The first set of allocations happens here. | |
2474 | /// .into(); // A second allocation for `Arc<[T]>` happens here. | |
2475 | /// # assert_eq!(&*evens, &[0, 2, 4, 6, 8]); | |
2476 | /// ``` | |
2477 | /// | |
2478 | /// This will allocate as many times as needed for constructing the `Vec<T>` | |
2479 | /// and then it will allocate once for turning the `Vec<T>` into the `Arc<[T]>`. | |
2480 | /// | |
2481 | /// ## Iterators of known length | |
2482 | /// | |
2483 | /// When your `Iterator` implements `TrustedLen` and is of an exact size, | |
2484 | /// a single allocation will be made for the `Arc<[T]>`. For example: | |
2485 | /// | |
2486 | /// ```rust | |
2487 | /// # use std::sync::Arc; | |
2488 | /// let evens: Arc<[u8]> = (0..10).collect(); // Just a single allocation happens here. | |
2489 | /// # assert_eq!(&*evens, &*(0..10).collect::<Vec<_>>()); | |
2490 | /// ``` | |
2491 | fn from_iter<I: iter::IntoIterator<Item = T>>(iter: I) -> Self { | |
f9f354fc | 2492 | ToArcSlice::to_arc_slice(iter.into_iter()) |
3b2f2976 | 2493 | } |
416331ca | 2494 | } |
3b2f2976 | 2495 | |
416331ca | 2496 | /// Specialization trait used for collecting into `Arc<[T]>`. |
f9f354fc XL |
2497 | trait ToArcSlice<T>: Iterator<Item = T> + Sized { |
2498 | fn to_arc_slice(self) -> Arc<[T]>; | |
416331ca | 2499 | } |
3b2f2976 | 2500 | |
17df50a5 | 2501 | #[cfg(not(no_global_oom_handling))] |
f9f354fc XL |
2502 | impl<T, I: Iterator<Item = T>> ToArcSlice<T> for I { |
2503 | default fn to_arc_slice(self) -> Arc<[T]> { | |
2504 | self.collect::<Vec<T>>().into() | |
3b2f2976 | 2505 | } |
416331ca | 2506 | } |
3b2f2976 | 2507 | |
17df50a5 | 2508 | #[cfg(not(no_global_oom_handling))] |
f9f354fc XL |
2509 | impl<T, I: iter::TrustedLen<Item = T>> ToArcSlice<T> for I { |
2510 | fn to_arc_slice(self) -> Arc<[T]> { | |
416331ca | 2511 | // This is the case for a `TrustedLen` iterator. |
f9f354fc | 2512 | let (low, high) = self.size_hint(); |
416331ca XL |
2513 | if let Some(high) = high { |
2514 | debug_assert_eq!( | |
dfeec247 XL |
2515 | low, |
2516 | high, | |
416331ca XL |
2517 | "TrustedLen iterator's size hint is not exact: {:?}", |
2518 | (low, high) | |
2519 | ); | |
3b2f2976 | 2520 | |
416331ca XL |
2521 | unsafe { |
2522 | // SAFETY: We need to ensure that the iterator has an exact length and we have. | |
f9f354fc | 2523 | Arc::from_iter_exact(self, low) |
3b2f2976 | 2524 | } |
416331ca | 2525 | } else { |
cdc7bbd5 XL |
2526 | // TrustedLen contract guarantees that `upper_bound == `None` implies an iterator |
2527 | // length exceeding `usize::MAX`. | |
2528 | // The default implementation would collect into a vec which would panic. | |
2529 | // Thus we panic here immediately without invoking `Vec` code. | |
2530 | panic!("capacity overflow"); | |
3b2f2976 | 2531 | } |
3b2f2976 | 2532 | } |
416331ca | 2533 | } |
3b2f2976 | 2534 | |
92a42be0 | 2535 | #[stable(feature = "rust1", since = "1.0.0")] |
e9174d1e | 2536 | impl<T: ?Sized> borrow::Borrow<T> for Arc<T> { |
b039eaaf SL |
2537 | fn borrow(&self) -> &T { |
2538 | &**self | |
2539 | } | |
2540 | } | |
2541 | ||
2542 | #[stable(since = "1.5.0", feature = "smart_ptr_as_ref")] | |
2543 | impl<T: ?Sized> AsRef<T> for Arc<T> { | |
2544 | fn as_ref(&self) -> &T { | |
2545 | &**self | |
2546 | } | |
e9174d1e | 2547 | } |
b7449926 | 2548 | |
0731742a | 2549 | #[stable(feature = "pin", since = "1.33.0")] |
dfeec247 | 2550 | impl<T: ?Sized> Unpin for Arc<T> {} |
dc9dc135 | 2551 | |
5869c6ff | 2552 | /// Get the offset within an `ArcInner` for the payload behind a pointer. |
f035d41b XL |
2553 | /// |
2554 | /// # Safety | |
2555 | /// | |
5869c6ff XL |
2556 | /// The pointer must point to (and have valid metadata for) a previously |
2557 | /// valid instance of T, but the T is allowed to be dropped. | |
dc9dc135 | 2558 | unsafe fn data_offset<T: ?Sized>(ptr: *const T) -> isize { |
5869c6ff XL |
2559 | // Align the unsized value to the end of the ArcInner. |
2560 | // Because RcBox is repr(C), it will always be the last field in memory. | |
2561 | // SAFETY: since the only unsized types possible are slices, trait objects, | |
2562 | // and extern types, the input safety requirement is currently enough to | |
2563 | // satisfy the requirements of align_of_val_raw; this is an implementation | |
2564 | // detail of the language that may not be relied upon outside of std. | |
2565 | unsafe { data_offset_align(align_of_val_raw(ptr)) } | |
416331ca XL |
2566 | } |
2567 | ||
2568 | #[inline] | |
2569 | fn data_offset_align(align: usize) -> isize { | |
dc9dc135 XL |
2570 | let layout = Layout::new::<ArcInner<()>>(); |
2571 | (layout.size() + layout.padding_needed_for(align)) as isize | |
2572 | } |