]>
Commit | Line | Data |
---|---|---|
85aaf69f | 1 | #![stable(feature = "rust1", since = "1.0.0")] |
1a4d82fc | 2 | |
c30ab7b3 | 3 | //! Thread-safe reference-counting pointers. |
1a4d82fc | 4 | //! |
c30ab7b3 | 5 | //! See the [`Arc<T>`][arc] documentation for more details. |
1a4d82fc | 6 | //! |
c30ab7b3 | 7 | //! [arc]: struct.Arc.html |
1a4d82fc | 8 | |
94b46f34 | 9 | use core::any::Any; |
416331ca | 10 | use core::array::LengthAtMost32; |
e9174d1e | 11 | use core::borrow; |
60c5eb7d | 12 | use core::cmp::Ordering; |
dfeec247 XL |
13 | use core::convert::{From, TryFrom}; |
14 | use core::fmt; | |
15 | use core::hash::{Hash, Hasher}; | |
92a42be0 | 16 | use core::intrinsics::abort; |
dfeec247 XL |
17 | use core::iter; |
18 | use core::marker::{PhantomData, Unpin, Unsize}; | |
dc9dc135 | 19 | use core::mem::{self, align_of, align_of_val, size_of_val}; |
dfeec247 | 20 | use core::ops::{CoerceUnsized, Deref, DispatchFromDyn, Receiver}; |
0bf4aa26 | 21 | use core::pin::Pin; |
2c00a5a8 | 22 | use core::ptr::{self, NonNull}; |
416331ca | 23 | use core::slice::{self, from_raw_parts_mut}; |
dfeec247 XL |
24 | use core::sync::atomic; |
25 | use core::sync::atomic::Ordering::{Acquire, Relaxed, Release, SeqCst}; | |
041b39d2 | 26 | |
ba9703b0 | 27 | use crate::alloc::{box_free, handle_alloc_error, AllocInit, AllocRef, Global, Layout}; |
9fa01778 XL |
28 | use crate::boxed::Box; |
29 | use crate::rc::is_dangling; | |
30 | use crate::string::String; | |
31 | use crate::vec::Vec; | |
1a4d82fc | 32 | |
416331ca XL |
33 | #[cfg(test)] |
34 | mod tests; | |
35 | ||
c30ab7b3 SL |
36 | /// A soft limit on the amount of references that may be made to an `Arc`. |
37 | /// | |
38 | /// Going above this limit will abort your program (although not | |
39 | /// necessarily) at _exactly_ `MAX_REFCOUNT + 1` references. | |
c1a9b12d SL |
40 | const MAX_REFCOUNT: usize = (isize::MAX) as usize; |
41 | ||
ba9703b0 XL |
42 | #[cfg(not(sanitize = "thread"))] |
43 | macro_rules! acquire { | |
44 | ($x:expr) => { | |
45 | atomic::fence(Acquire) | |
46 | }; | |
47 | } | |
48 | ||
49 | // ThreadSanitizer does not support memory fences. To avoid false positive | |
50 | // reports in Arc / Weak implementation use atomic loads for synchronization | |
51 | // instead. | |
52 | #[cfg(sanitize = "thread")] | |
53 | macro_rules! acquire { | |
54 | ($x:expr) => { | |
55 | $x.load(Acquire) | |
56 | }; | |
57 | } | |
58 | ||
041b39d2 XL |
59 | /// A thread-safe reference-counting pointer. 'Arc' stands for 'Atomically |
60 | /// Reference Counted'. | |
1a4d82fc | 61 | /// |
c30ab7b3 SL |
62 | /// The type `Arc<T>` provides shared ownership of a value of type `T`, |
63 | /// allocated in the heap. Invoking [`clone`][clone] on `Arc` produces | |
e74abb32 | 64 | /// a new `Arc` instance, which points to the same allocation on the heap as the |
b7449926 | 65 | /// source `Arc`, while increasing a reference count. When the last `Arc` |
e74abb32 XL |
66 | /// pointer to a given allocation is destroyed, the value stored in that allocation (often |
67 | /// referred to as "inner value") is also dropped. | |
1a4d82fc | 68 | /// |
c30ab7b3 | 69 | /// Shared references in Rust disallow mutation by default, and `Arc` is no |
ea8adc8c XL |
70 | /// exception: you cannot generally obtain a mutable reference to something |
71 | /// inside an `Arc`. If you need to mutate through an `Arc`, use | |
72 | /// [`Mutex`][mutex], [`RwLock`][rwlock], or one of the [`Atomic`][atomic] | |
73 | /// types. | |
9e0c209e | 74 | /// |
7cac9316 XL |
75 | /// ## Thread Safety |
76 | /// | |
77 | /// Unlike [`Rc<T>`], `Arc<T>` uses atomic operations for its reference | |
83c7162d | 78 | /// counting. This means that it is thread-safe. The disadvantage is that |
7cac9316 | 79 | /// atomic operations are more expensive than ordinary memory accesses. If you |
e74abb32 | 80 | /// are not sharing reference-counted allocations between threads, consider using |
7cac9316 XL |
81 | /// [`Rc<T>`] for lower overhead. [`Rc<T>`] is a safe default, because the |
82 | /// compiler will catch any attempt to send an [`Rc<T>`] between threads. | |
83 | /// However, a library might choose `Arc<T>` in order to give library consumers | |
c30ab7b3 | 84 | /// more flexibility. |
1a4d82fc | 85 | /// |
7cac9316 XL |
86 | /// `Arc<T>` will implement [`Send`] and [`Sync`] as long as the `T` implements |
87 | /// [`Send`] and [`Sync`]. Why can't you put a non-thread-safe type `T` in an | |
88 | /// `Arc<T>` to make it thread-safe? This may be a bit counter-intuitive at | |
89 | /// first: after all, isn't the point of `Arc<T>` thread safety? The key is | |
90 | /// this: `Arc<T>` makes it thread safe to have multiple ownership of the same | |
91 | /// data, but it doesn't add thread safety to its data. Consider | |
ea8adc8c XL |
92 | /// `Arc<`[`RefCell<T>`]`>`. [`RefCell<T>`] isn't [`Sync`], and if `Arc<T>` was always |
93 | /// [`Send`], `Arc<`[`RefCell<T>`]`>` would be as well. But then we'd have a problem: | |
94 | /// [`RefCell<T>`] is not thread safe; it keeps track of the borrowing count using | |
7cac9316 XL |
95 | /// non-atomic operations. |
96 | /// | |
97 | /// In the end, this means that you may need to pair `Arc<T>` with some sort of | |
ea8adc8c | 98 | /// [`std::sync`] type, usually [`Mutex<T>`][mutex]. |
7cac9316 XL |
99 | /// |
100 | /// ## Breaking cycles with `Weak` | |
101 | /// | |
c30ab7b3 | 102 | /// The [`downgrade`][downgrade] method can be used to create a non-owning |
32a655c1 | 103 | /// [`Weak`][weak] pointer. A [`Weak`][weak] pointer can be [`upgrade`][upgrade]d |
e74abb32 XL |
104 | /// to an `Arc`, but this will return [`None`] if the value stored in the allocation has |
105 | /// already been dropped. In other words, `Weak` pointers do not keep the value | |
106 | /// inside the allocation alive; however, they *do* keep the allocation | |
107 | /// (the backing store for the value) alive. | |
c30ab7b3 SL |
108 | /// |
109 | /// A cycle between `Arc` pointers will never be deallocated. For this reason, | |
32a655c1 SL |
110 | /// [`Weak`][weak] is used to break cycles. For example, a tree could have |
111 | /// strong `Arc` pointers from parent nodes to children, and [`Weak`][weak] | |
112 | /// pointers from children back to their parents. | |
c30ab7b3 | 113 | /// |
7cac9316 XL |
114 | /// # Cloning references |
115 | /// | |
116 | /// Creating a new reference from an existing reference counted pointer is done using the | |
3b2f2976 | 117 | /// `Clone` trait implemented for [`Arc<T>`][arc] and [`Weak<T>`][weak]. |
7cac9316 XL |
118 | /// |
119 | /// ``` | |
120 | /// use std::sync::Arc; | |
121 | /// let foo = Arc::new(vec![1.0, 2.0, 3.0]); | |
122 | /// // The two syntaxes below are equivalent. | |
123 | /// let a = foo.clone(); | |
124 | /// let b = Arc::clone(&foo); | |
b7449926 | 125 | /// // a, b, and foo are all Arcs that point to the same memory location |
7cac9316 XL |
126 | /// ``` |
127 | /// | |
7cac9316 XL |
128 | /// ## `Deref` behavior |
129 | /// | |
c30ab7b3 SL |
130 | /// `Arc<T>` automatically dereferences to `T` (via the [`Deref`][deref] trait), |
131 | /// so you can call `T`'s methods on a value of type `Arc<T>`. To avoid name | |
13cf67c4 XL |
132 | /// clashes with `T`'s methods, the methods of `Arc<T>` itself are associated |
133 | /// functions, called using function-like syntax: | |
c34b1796 AL |
134 | /// |
135 | /// ``` | |
1a4d82fc | 136 | /// use std::sync::Arc; |
c30ab7b3 | 137 | /// let my_arc = Arc::new(()); |
1a4d82fc | 138 | /// |
c30ab7b3 SL |
139 | /// Arc::downgrade(&my_arc); |
140 | /// ``` | |
1a4d82fc | 141 | /// |
e74abb32 XL |
142 | /// [`Weak<T>`][weak] does not auto-dereference to `T`, because the inner value may have |
143 | /// already been dropped. | |
1a4d82fc | 144 | /// |
c30ab7b3 SL |
145 | /// [arc]: struct.Arc.html |
146 | /// [weak]: struct.Weak.html | |
7cac9316 | 147 | /// [`Rc<T>`]: ../../std/rc/struct.Rc.html |
c30ab7b3 SL |
148 | /// [clone]: ../../std/clone/trait.Clone.html#tymethod.clone |
149 | /// [mutex]: ../../std/sync/struct.Mutex.html | |
150 | /// [rwlock]: ../../std/sync/struct.RwLock.html | |
151 | /// [atomic]: ../../std/sync/atomic/index.html | |
32a655c1 | 152 | /// [`Send`]: ../../std/marker/trait.Send.html |
7cac9316 | 153 | /// [`Sync`]: ../../std/marker/trait.Sync.html |
c30ab7b3 SL |
154 | /// [deref]: ../../std/ops/trait.Deref.html |
155 | /// [downgrade]: struct.Arc.html#method.downgrade | |
156 | /// [upgrade]: struct.Weak.html#method.upgrade | |
32a655c1 | 157 | /// [`None`]: ../../std/option/enum.Option.html#variant.None |
ea8adc8c XL |
158 | /// [`RefCell<T>`]: ../../std/cell/struct.RefCell.html |
159 | /// [`std::sync`]: ../../std/sync/index.html | |
160 | /// [`Arc::clone(&from)`]: #method.clone | |
1a4d82fc | 161 | /// |
c30ab7b3 | 162 | /// # Examples |
5bcae85e | 163 | /// |
c30ab7b3 SL |
164 | /// Sharing some immutable data between threads: |
165 | /// | |
166 | // Note that we **do not** run these tests here. The windows builders get super | |
167 | // unhappy if a thread outlives the main thread and then exits at the same time | |
168 | // (something deadlocks) so we just avoid this entirely by not running these | |
169 | // tests. | |
5bcae85e | 170 | /// ```no_run |
c30ab7b3 | 171 | /// use std::sync::Arc; |
5bcae85e SL |
172 | /// use std::thread; |
173 | /// | |
c30ab7b3 | 174 | /// let five = Arc::new(5); |
5bcae85e SL |
175 | /// |
176 | /// for _ in 0..10 { | |
7cac9316 | 177 | /// let five = Arc::clone(&five); |
5bcae85e SL |
178 | /// |
179 | /// thread::spawn(move || { | |
c30ab7b3 SL |
180 | /// println!("{:?}", five); |
181 | /// }); | |
182 | /// } | |
183 | /// ``` | |
5bcae85e | 184 | /// |
32a655c1 SL |
185 | /// Sharing a mutable [`AtomicUsize`]: |
186 | /// | |
187 | /// [`AtomicUsize`]: ../../std/sync/atomic/struct.AtomicUsize.html | |
5bcae85e | 188 | /// |
c30ab7b3 SL |
189 | /// ```no_run |
190 | /// use std::sync::Arc; | |
191 | /// use std::sync::atomic::{AtomicUsize, Ordering}; | |
192 | /// use std::thread; | |
193 | /// | |
194 | /// let val = Arc::new(AtomicUsize::new(5)); | |
195 | /// | |
196 | /// for _ in 0..10 { | |
7cac9316 | 197 | /// let val = Arc::clone(&val); |
c30ab7b3 SL |
198 | /// |
199 | /// thread::spawn(move || { | |
200 | /// let v = val.fetch_add(1, Ordering::SeqCst); | |
201 | /// println!("{:?}", v); | |
5bcae85e SL |
202 | /// }); |
203 | /// } | |
204 | /// ``` | |
c30ab7b3 SL |
205 | /// |
206 | /// See the [`rc` documentation][rc_examples] for more examples of reference | |
207 | /// counting in general. | |
208 | /// | |
209 | /// [rc_examples]: ../../std/rc/index.html#examples | |
ba9703b0 XL |
210 | #[cfg_attr(all(bootstrap, not(test)), lang = "arc")] |
211 | #[cfg_attr(not(test), rustc_diagnostic_item = "Arc")] | |
85aaf69f | 212 | #[stable(feature = "rust1", since = "1.0.0")] |
62682a34 | 213 | pub struct Arc<T: ?Sized> { |
2c00a5a8 | 214 | ptr: NonNull<ArcInner<T>>, |
60c5eb7d | 215 | phantom: PhantomData<ArcInner<T>>, |
1a4d82fc JJ |
216 | } |
217 | ||
92a42be0 SL |
218 | #[stable(feature = "rust1", since = "1.0.0")] |
219 | unsafe impl<T: ?Sized + Sync + Send> Send for Arc<T> {} | |
220 | #[stable(feature = "rust1", since = "1.0.0")] | |
221 | unsafe impl<T: ?Sized + Sync + Send> Sync for Arc<T> {} | |
1a4d82fc | 222 | |
92a42be0 | 223 | #[unstable(feature = "coerce_unsized", issue = "27732")] |
62682a34 | 224 | impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Arc<U>> for Arc<T> {} |
1a4d82fc | 225 | |
dfeec247 | 226 | #[unstable(feature = "dispatch_from_dyn", issue = "none")] |
a1dfa0c6 XL |
227 | impl<T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<Arc<U>> for Arc<T> {} |
228 | ||
416331ca XL |
229 | impl<T: ?Sized> Arc<T> { |
230 | fn from_inner(ptr: NonNull<ArcInner<T>>) -> Self { | |
dfeec247 | 231 | Self { ptr, phantom: PhantomData } |
416331ca XL |
232 | } |
233 | ||
234 | unsafe fn from_ptr(ptr: *mut ArcInner<T>) -> Self { | |
235 | Self::from_inner(NonNull::new_unchecked(ptr)) | |
236 | } | |
237 | } | |
238 | ||
cc61c64b | 239 | /// `Weak` is a version of [`Arc`] that holds a non-owning reference to the |
e74abb32 | 240 | /// managed allocation. The allocation is accessed by calling [`upgrade`] on the `Weak` |
cc61c64b | 241 | /// pointer, which returns an [`Option`]`<`[`Arc`]`<T>>`. |
1a4d82fc | 242 | /// |
cc61c64b | 243 | /// Since a `Weak` reference does not count towards ownership, it will not |
e74abb32 XL |
244 | /// prevent the value stored in the allocation from being dropped, and `Weak` itself makes no |
245 | /// guarantees about the value still being present. Thus it may return [`None`] | |
246 | /// when [`upgrade`]d. Note however that a `Weak` reference *does* prevent the allocation | |
247 | /// itself (the backing store) from being deallocated. | |
5bcae85e | 248 | /// |
e74abb32 XL |
249 | /// A `Weak` pointer is useful for keeping a temporary reference to the allocation |
250 | /// managed by [`Arc`] without preventing its inner value from being dropped. It is also used to | |
251 | /// prevent circular references between [`Arc`] pointers, since mutual owning references | |
cc61c64b XL |
252 | /// would never allow either [`Arc`] to be dropped. For example, a tree could |
253 | /// have strong [`Arc`] pointers from parent nodes to children, and `Weak` | |
254 | /// pointers from children back to their parents. | |
5bcae85e | 255 | /// |
cc61c64b | 256 | /// The typical way to obtain a `Weak` pointer is to call [`Arc::downgrade`]. |
c30ab7b3 | 257 | /// |
cc61c64b XL |
258 | /// [`Arc`]: struct.Arc.html |
259 | /// [`Arc::downgrade`]: struct.Arc.html#method.downgrade | |
260 | /// [`upgrade`]: struct.Weak.html#method.upgrade | |
261 | /// [`Option`]: ../../std/option/enum.Option.html | |
262 | /// [`None`]: ../../std/option/enum.Option.html#variant.None | |
e9174d1e | 263 | #[stable(feature = "arc_weak", since = "1.4.0")] |
62682a34 | 264 | pub struct Weak<T: ?Sized> { |
8faf50e0 XL |
265 | // This is a `NonNull` to allow optimizing the size of this type in enums, |
266 | // but it is not necessarily a valid pointer. | |
267 | // `Weak::new` sets this to `usize::MAX` so that it doesn’t need | |
268 | // to allocate space on the heap. That's not a value a real pointer | |
269 | // will ever have because RcBox has alignment at least 2. | |
2c00a5a8 | 270 | ptr: NonNull<ArcInner<T>>, |
1a4d82fc JJ |
271 | } |
272 | ||
7453a54e | 273 | #[stable(feature = "arc_weak", since = "1.4.0")] |
92a42be0 | 274 | unsafe impl<T: ?Sized + Sync + Send> Send for Weak<T> {} |
7453a54e | 275 | #[stable(feature = "arc_weak", since = "1.4.0")] |
92a42be0 | 276 | unsafe impl<T: ?Sized + Sync + Send> Sync for Weak<T> {} |
1a4d82fc | 277 | |
92a42be0 | 278 | #[unstable(feature = "coerce_unsized", issue = "27732")] |
c1a9b12d | 279 | impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Weak<U>> for Weak<T> {} |
dfeec247 | 280 | #[unstable(feature = "dispatch_from_dyn", issue = "none")] |
a1dfa0c6 | 281 | impl<T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<Weak<U>> for Weak<T> {} |
c1a9b12d | 282 | |
7453a54e | 283 | #[stable(feature = "arc_weak", since = "1.4.0")] |
62682a34 | 284 | impl<T: ?Sized + fmt::Debug> fmt::Debug for Weak<T> { |
9fa01778 | 285 | fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
c34b1796 AL |
286 | write!(f, "(Weak)") |
287 | } | |
288 | } | |
289 | ||
ba9703b0 XL |
290 | // This is repr(C) to future-proof against possible field-reordering, which |
291 | // would interfere with otherwise safe [into|from]_raw() of transmutable | |
292 | // inner types. | |
293 | #[repr(C)] | |
62682a34 | 294 | struct ArcInner<T: ?Sized> { |
85aaf69f | 295 | strong: atomic::AtomicUsize, |
c1a9b12d SL |
296 | |
297 | // the value usize::MAX acts as a sentinel for temporarily "locking" the | |
298 | // ability to upgrade weak pointers or downgrade strong ones; this is used | |
e9174d1e | 299 | // to avoid races in `make_mut` and `get_mut`. |
85aaf69f | 300 | weak: atomic::AtomicUsize, |
c1a9b12d | 301 | |
1a4d82fc JJ |
302 | data: T, |
303 | } | |
304 | ||
62682a34 SL |
305 | unsafe impl<T: ?Sized + Sync + Send> Send for ArcInner<T> {} |
306 | unsafe impl<T: ?Sized + Sync + Send> Sync for ArcInner<T> {} | |
1a4d82fc JJ |
307 | |
308 | impl<T> Arc<T> { | |
309 | /// Constructs a new `Arc<T>`. | |
310 | /// | |
311 | /// # Examples | |
312 | /// | |
313 | /// ``` | |
314 | /// use std::sync::Arc; | |
315 | /// | |
85aaf69f | 316 | /// let five = Arc::new(5); |
1a4d82fc JJ |
317 | /// ``` |
318 | #[inline] | |
85aaf69f | 319 | #[stable(feature = "rust1", since = "1.0.0")] |
1a4d82fc JJ |
320 | pub fn new(data: T) -> Arc<T> { |
321 | // Start the weak pointer count as 1 which is the weak pointer that's | |
322 | // held by all the strong pointers (kinda), see std/rc.rs for more info | |
c34b1796 | 323 | let x: Box<_> = box ArcInner { |
85aaf69f SL |
324 | strong: atomic::AtomicUsize::new(1), |
325 | weak: atomic::AtomicUsize::new(1), | |
3b2f2976 | 326 | data, |
1a4d82fc | 327 | }; |
416331ca | 328 | Self::from_inner(Box::into_raw_non_null(x)) |
e9174d1e SL |
329 | } |
330 | ||
e1599b0c XL |
331 | /// Constructs a new `Arc` with uninitialized contents. |
332 | /// | |
333 | /// # Examples | |
334 | /// | |
335 | /// ``` | |
336 | /// #![feature(new_uninit)] | |
337 | /// #![feature(get_mut_unchecked)] | |
338 | /// | |
339 | /// use std::sync::Arc; | |
340 | /// | |
341 | /// let mut five = Arc::<u32>::new_uninit(); | |
342 | /// | |
343 | /// let five = unsafe { | |
344 | /// // Deferred initialization: | |
345 | /// Arc::get_mut_unchecked(&mut five).as_mut_ptr().write(5); | |
346 | /// | |
347 | /// five.assume_init() | |
348 | /// }; | |
349 | /// | |
350 | /// assert_eq!(*five, 5) | |
351 | /// ``` | |
352 | #[unstable(feature = "new_uninit", issue = "63291")] | |
353 | pub fn new_uninit() -> Arc<mem::MaybeUninit<T>> { | |
354 | unsafe { | |
dfeec247 XL |
355 | Arc::from_ptr(Arc::allocate_for_layout(Layout::new::<T>(), |mem| { |
356 | mem as *mut ArcInner<mem::MaybeUninit<T>> | |
357 | })) | |
e1599b0c XL |
358 | } |
359 | } | |
360 | ||
60c5eb7d XL |
361 | /// Constructs a new `Arc` with uninitialized contents, with the memory |
362 | /// being filled with `0` bytes. | |
363 | /// | |
364 | /// See [`MaybeUninit::zeroed`][zeroed] for examples of correct and incorrect usage | |
365 | /// of this method. | |
366 | /// | |
367 | /// # Examples | |
368 | /// | |
369 | /// ``` | |
370 | /// #![feature(new_uninit)] | |
371 | /// | |
372 | /// use std::sync::Arc; | |
373 | /// | |
374 | /// let zero = Arc::<u32>::new_zeroed(); | |
375 | /// let zero = unsafe { zero.assume_init() }; | |
376 | /// | |
377 | /// assert_eq!(*zero, 0) | |
378 | /// ``` | |
379 | /// | |
380 | /// [zeroed]: ../../std/mem/union.MaybeUninit.html#method.zeroed | |
381 | #[unstable(feature = "new_uninit", issue = "63291")] | |
382 | pub fn new_zeroed() -> Arc<mem::MaybeUninit<T>> { | |
383 | unsafe { | |
384 | let mut uninit = Self::new_uninit(); | |
385 | ptr::write_bytes::<T>(Arc::get_mut_unchecked(&mut uninit).as_mut_ptr(), 0, 1); | |
386 | uninit | |
387 | } | |
388 | } | |
389 | ||
0731742a XL |
390 | /// Constructs a new `Pin<Arc<T>>`. If `T` does not implement `Unpin`, then |
391 | /// `data` will be pinned in memory and unable to be moved. | |
392 | #[stable(feature = "pin", since = "1.33.0")] | |
393 | pub fn pin(data: T) -> Pin<Arc<T>> { | |
0bf4aa26 XL |
394 | unsafe { Pin::new_unchecked(Arc::new(data)) } |
395 | } | |
396 | ||
e74abb32 | 397 | /// Returns the inner value, if the `Arc` has exactly one strong reference. |
e9174d1e | 398 | /// |
c30ab7b3 SL |
399 | /// Otherwise, an [`Err`][result] is returned with the same `Arc` that was |
400 | /// passed in. | |
e9174d1e | 401 | /// |
54a0048b SL |
402 | /// This will succeed even if there are outstanding weak references. |
403 | /// | |
c30ab7b3 SL |
404 | /// [result]: ../../std/result/enum.Result.html |
405 | /// | |
e9174d1e SL |
406 | /// # Examples |
407 | /// | |
408 | /// ``` | |
409 | /// use std::sync::Arc; | |
410 | /// | |
411 | /// let x = Arc::new(3); | |
412 | /// assert_eq!(Arc::try_unwrap(x), Ok(3)); | |
413 | /// | |
414 | /// let x = Arc::new(4); | |
7cac9316 | 415 | /// let _y = Arc::clone(&x); |
c30ab7b3 | 416 | /// assert_eq!(*Arc::try_unwrap(x).unwrap_err(), 4); |
e9174d1e SL |
417 | /// ``` |
418 | #[inline] | |
419 | #[stable(feature = "arc_unique", since = "1.4.0")] | |
420 | pub fn try_unwrap(this: Self) -> Result<T, Self> { | |
421 | // See `drop` for why all these atomics are like this | |
54a0048b | 422 | if this.inner().strong.compare_exchange(1, 0, Release, Relaxed).is_err() { |
92a42be0 | 423 | return Err(this); |
b039eaaf | 424 | } |
e9174d1e | 425 | |
ba9703b0 | 426 | acquire!(this.inner().strong); |
e9174d1e SL |
427 | |
428 | unsafe { | |
7cac9316 | 429 | let elem = ptr::read(&this.ptr.as_ref().data); |
e9174d1e SL |
430 | |
431 | // Make a weak pointer to clean up the implicit strong-weak reference | |
54a0048b | 432 | let _weak = Weak { ptr: this.ptr }; |
e9174d1e SL |
433 | mem::forget(this); |
434 | ||
435 | Ok(elem) | |
436 | } | |
1a4d82fc | 437 | } |
ea8adc8c | 438 | } |
476ff2be | 439 | |
e1599b0c XL |
440 | impl<T> Arc<[T]> { |
441 | /// Constructs a new reference-counted slice with uninitialized contents. | |
442 | /// | |
443 | /// # Examples | |
444 | /// | |
445 | /// ``` | |
446 | /// #![feature(new_uninit)] | |
447 | /// #![feature(get_mut_unchecked)] | |
448 | /// | |
449 | /// use std::sync::Arc; | |
450 | /// | |
451 | /// let mut values = Arc::<[u32]>::new_uninit_slice(3); | |
452 | /// | |
453 | /// let values = unsafe { | |
454 | /// // Deferred initialization: | |
455 | /// Arc::get_mut_unchecked(&mut values)[0].as_mut_ptr().write(1); | |
456 | /// Arc::get_mut_unchecked(&mut values)[1].as_mut_ptr().write(2); | |
457 | /// Arc::get_mut_unchecked(&mut values)[2].as_mut_ptr().write(3); | |
458 | /// | |
459 | /// values.assume_init() | |
460 | /// }; | |
461 | /// | |
462 | /// assert_eq!(*values, [1, 2, 3]) | |
463 | /// ``` | |
464 | #[unstable(feature = "new_uninit", issue = "63291")] | |
465 | pub fn new_uninit_slice(len: usize) -> Arc<[mem::MaybeUninit<T>]> { | |
dfeec247 | 466 | unsafe { Arc::from_ptr(Arc::allocate_for_slice(len)) } |
e1599b0c XL |
467 | } |
468 | } | |
469 | ||
470 | impl<T> Arc<mem::MaybeUninit<T>> { | |
471 | /// Converts to `Arc<T>`. | |
472 | /// | |
473 | /// # Safety | |
474 | /// | |
475 | /// As with [`MaybeUninit::assume_init`], | |
e74abb32 | 476 | /// it is up to the caller to guarantee that the inner value |
e1599b0c XL |
477 | /// really is in an initialized state. |
478 | /// Calling this when the content is not yet fully initialized | |
479 | /// causes immediate undefined behavior. | |
480 | /// | |
481 | /// [`MaybeUninit::assume_init`]: ../../std/mem/union.MaybeUninit.html#method.assume_init | |
482 | /// | |
483 | /// # Examples | |
484 | /// | |
485 | /// ``` | |
486 | /// #![feature(new_uninit)] | |
487 | /// #![feature(get_mut_unchecked)] | |
488 | /// | |
489 | /// use std::sync::Arc; | |
490 | /// | |
491 | /// let mut five = Arc::<u32>::new_uninit(); | |
492 | /// | |
493 | /// let five = unsafe { | |
494 | /// // Deferred initialization: | |
495 | /// Arc::get_mut_unchecked(&mut five).as_mut_ptr().write(5); | |
496 | /// | |
497 | /// five.assume_init() | |
498 | /// }; | |
499 | /// | |
500 | /// assert_eq!(*five, 5) | |
501 | /// ``` | |
502 | #[unstable(feature = "new_uninit", issue = "63291")] | |
503 | #[inline] | |
504 | pub unsafe fn assume_init(self) -> Arc<T> { | |
505 | Arc::from_inner(mem::ManuallyDrop::new(self).ptr.cast()) | |
506 | } | |
507 | } | |
508 | ||
509 | impl<T> Arc<[mem::MaybeUninit<T>]> { | |
510 | /// Converts to `Arc<[T]>`. | |
511 | /// | |
512 | /// # Safety | |
513 | /// | |
514 | /// As with [`MaybeUninit::assume_init`], | |
e74abb32 | 515 | /// it is up to the caller to guarantee that the inner value |
e1599b0c XL |
516 | /// really is in an initialized state. |
517 | /// Calling this when the content is not yet fully initialized | |
518 | /// causes immediate undefined behavior. | |
519 | /// | |
520 | /// [`MaybeUninit::assume_init`]: ../../std/mem/union.MaybeUninit.html#method.assume_init | |
521 | /// | |
522 | /// # Examples | |
523 | /// | |
524 | /// ``` | |
525 | /// #![feature(new_uninit)] | |
526 | /// #![feature(get_mut_unchecked)] | |
527 | /// | |
528 | /// use std::sync::Arc; | |
529 | /// | |
530 | /// let mut values = Arc::<[u32]>::new_uninit_slice(3); | |
531 | /// | |
532 | /// let values = unsafe { | |
533 | /// // Deferred initialization: | |
534 | /// Arc::get_mut_unchecked(&mut values)[0].as_mut_ptr().write(1); | |
535 | /// Arc::get_mut_unchecked(&mut values)[1].as_mut_ptr().write(2); | |
536 | /// Arc::get_mut_unchecked(&mut values)[2].as_mut_ptr().write(3); | |
537 | /// | |
538 | /// values.assume_init() | |
539 | /// }; | |
540 | /// | |
541 | /// assert_eq!(*values, [1, 2, 3]) | |
542 | /// ``` | |
543 | #[unstable(feature = "new_uninit", issue = "63291")] | |
544 | #[inline] | |
545 | pub unsafe fn assume_init(self) -> Arc<[T]> { | |
546 | Arc::from_ptr(mem::ManuallyDrop::new(self).ptr.as_ptr() as _) | |
547 | } | |
548 | } | |
549 | ||
ea8adc8c | 550 | impl<T: ?Sized> Arc<T> { |
476ff2be SL |
551 | /// Consumes the `Arc`, returning the wrapped pointer. |
552 | /// | |
553 | /// To avoid a memory leak the pointer must be converted back to an `Arc` using | |
554 | /// [`Arc::from_raw`][from_raw]. | |
555 | /// | |
556 | /// [from_raw]: struct.Arc.html#method.from_raw | |
557 | /// | |
558 | /// # Examples | |
559 | /// | |
560 | /// ``` | |
476ff2be SL |
561 | /// use std::sync::Arc; |
562 | /// | |
dc9dc135 | 563 | /// let x = Arc::new("hello".to_owned()); |
476ff2be | 564 | /// let x_ptr = Arc::into_raw(x); |
dc9dc135 | 565 | /// assert_eq!(unsafe { &*x_ptr }, "hello"); |
476ff2be | 566 | /// ``` |
8bb4bdeb XL |
567 | #[stable(feature = "rc_raw", since = "1.17.0")] |
568 | pub fn into_raw(this: Self) -> *const T { | |
ba9703b0 XL |
569 | let ptr = Self::as_ptr(&this); |
570 | mem::forget(this); | |
571 | ptr | |
572 | } | |
573 | ||
574 | /// Provides a raw pointer to the data. | |
575 | /// | |
576 | /// The counts are not affected in way and the `Arc` is not consumed. The pointer is valid for | |
577 | /// as long as there are strong counts in the `Arc`. | |
578 | /// | |
579 | /// # Examples | |
580 | /// | |
581 | /// ``` | |
582 | /// #![feature(weak_into_raw)] | |
583 | /// | |
584 | /// use std::sync::Arc; | |
585 | /// | |
586 | /// let x = Arc::new("hello".to_owned()); | |
587 | /// let y = Arc::clone(&x); | |
588 | /// let x_ptr = Arc::as_ptr(&x); | |
589 | /// assert_eq!(x_ptr, Arc::as_ptr(&y)); | |
590 | /// assert_eq!(unsafe { &*x_ptr }, "hello"); | |
591 | /// ``` | |
592 | #[unstable(feature = "weak_into_raw", issue = "60728")] | |
593 | pub fn as_ptr(this: &Self) -> *const T { | |
dfeec247 XL |
594 | let ptr: *mut ArcInner<T> = NonNull::as_ptr(this.ptr); |
595 | let fake_ptr = ptr as *mut T; | |
dfeec247 XL |
596 | |
597 | // SAFETY: This cannot go through Deref::deref. | |
598 | // Instead, we manually offset the pointer rather than manifesting a reference. | |
599 | // This is so that the returned pointer retains the same provenance as our pointer. | |
600 | // This is required so that e.g. `get_mut` can write through the pointer | |
601 | // after the Arc is recovered through `from_raw`. | |
602 | unsafe { | |
603 | let offset = data_offset(&(*ptr).data); | |
604 | set_data_ptr(fake_ptr, (ptr as *mut u8).offset(offset)) | |
605 | } | |
476ff2be SL |
606 | } |
607 | ||
ba9703b0 | 608 | /// Constructs an `Arc<T>` from a raw pointer. |
476ff2be | 609 | /// |
ba9703b0 XL |
610 | /// The raw pointer must have been previously returned by a call to |
611 | /// [`Arc<U>::into_raw`][into_raw] where `U` must have the same size and | |
612 | /// alignment as `T`. This is trivially true if `U` is `T`. | |
613 | /// Note that if `U` is not `T` but has the same size and alignment, this is | |
614 | /// basically like transmuting references of different types. See | |
615 | /// [`mem::transmute`][transmute] for more information on what | |
616 | /// restrictions apply in this case. | |
476ff2be | 617 | /// |
ba9703b0 XL |
618 | /// The user of `from_raw` has to make sure a specific value of `T` is only |
619 | /// dropped once. | |
620 | /// | |
621 | /// This function is unsafe because improper use may lead to memory unsafety, | |
622 | /// even if the returned `Arc<T>` is never accessed. | |
476ff2be SL |
623 | /// |
624 | /// [into_raw]: struct.Arc.html#method.into_raw | |
ba9703b0 | 625 | /// [transmute]: ../../std/mem/fn.transmute.html |
476ff2be SL |
626 | /// |
627 | /// # Examples | |
628 | /// | |
629 | /// ``` | |
476ff2be SL |
630 | /// use std::sync::Arc; |
631 | /// | |
dc9dc135 | 632 | /// let x = Arc::new("hello".to_owned()); |
476ff2be SL |
633 | /// let x_ptr = Arc::into_raw(x); |
634 | /// | |
635 | /// unsafe { | |
636 | /// // Convert back to an `Arc` to prevent leak. | |
637 | /// let x = Arc::from_raw(x_ptr); | |
dc9dc135 | 638 | /// assert_eq!(&*x, "hello"); |
476ff2be | 639 | /// |
e1599b0c | 640 | /// // Further calls to `Arc::from_raw(x_ptr)` would be memory-unsafe. |
476ff2be SL |
641 | /// } |
642 | /// | |
643 | /// // The memory was freed when `x` went out of scope above, so `x_ptr` is now dangling! | |
644 | /// ``` | |
8bb4bdeb XL |
645 | #[stable(feature = "rc_raw", since = "1.17.0")] |
646 | pub unsafe fn from_raw(ptr: *const T) -> Self { | |
dc9dc135 | 647 | let offset = data_offset(ptr); |
ea8adc8c XL |
648 | |
649 | // Reverse the offset to find the original ArcInner. | |
650 | let fake_ptr = ptr as *mut ArcInner<T>; | |
651 | let arc_ptr = set_data_ptr(fake_ptr, (ptr as *mut u8).offset(-offset)); | |
652 | ||
416331ca | 653 | Self::from_ptr(arc_ptr) |
476ff2be | 654 | } |
1a4d82fc | 655 | |
9fa01778 XL |
656 | /// Consumes the `Arc`, returning the wrapped pointer as `NonNull<T>`. |
657 | /// | |
658 | /// # Examples | |
659 | /// | |
660 | /// ``` | |
661 | /// #![feature(rc_into_raw_non_null)] | |
662 | /// | |
663 | /// use std::sync::Arc; | |
664 | /// | |
dc9dc135 | 665 | /// let x = Arc::new("hello".to_owned()); |
9fa01778 | 666 | /// let ptr = Arc::into_raw_non_null(x); |
dc9dc135 XL |
667 | /// let deref = unsafe { ptr.as_ref() }; |
668 | /// assert_eq!(deref, "hello"); | |
9fa01778 XL |
669 | /// ``` |
670 | #[unstable(feature = "rc_into_raw_non_null", issue = "47336")] | |
671 | #[inline] | |
672 | pub fn into_raw_non_null(this: Self) -> NonNull<T> { | |
673 | // safe because Arc guarantees its pointer is non-null | |
674 | unsafe { NonNull::new_unchecked(Arc::into_raw(this) as *mut _) } | |
675 | } | |
676 | ||
e74abb32 | 677 | /// Creates a new [`Weak`][weak] pointer to this allocation. |
c30ab7b3 SL |
678 | /// |
679 | /// [weak]: struct.Weak.html | |
1a4d82fc JJ |
680 | /// |
681 | /// # Examples | |
682 | /// | |
683 | /// ``` | |
684 | /// use std::sync::Arc; | |
685 | /// | |
85aaf69f | 686 | /// let five = Arc::new(5); |
1a4d82fc | 687 | /// |
e9174d1e | 688 | /// let weak_five = Arc::downgrade(&five); |
1a4d82fc | 689 | /// ``` |
e9174d1e SL |
690 | #[stable(feature = "arc_weak", since = "1.4.0")] |
691 | pub fn downgrade(this: &Self) -> Weak<T> { | |
54a0048b SL |
692 | // This Relaxed is OK because we're checking the value in the CAS |
693 | // below. | |
694 | let mut cur = this.inner().weak.load(Relaxed); | |
c1a9b12d | 695 | |
54a0048b | 696 | loop { |
c1a9b12d | 697 | // check if the weak counter is currently "locked"; if so, spin. |
b039eaaf | 698 | if cur == usize::MAX { |
54a0048b | 699 | cur = this.inner().weak.load(Relaxed); |
92a42be0 | 700 | continue; |
b039eaaf | 701 | } |
c1a9b12d SL |
702 | |
703 | // NOTE: this code currently ignores the possibility of overflow | |
704 | // into usize::MAX; in general both Rc and Arc need to be adjusted | |
705 | // to deal with overflow. | |
706 | ||
707 | // Unlike with Clone(), we need this to be an Acquire read to | |
708 | // synchronize with the write coming from `is_unique`, so that the | |
709 | // events prior to that write happen before this read. | |
54a0048b | 710 | match this.inner().weak.compare_exchange_weak(cur, cur + 1, Acquire, Relaxed) { |
8faf50e0 XL |
711 | Ok(_) => { |
712 | // Make sure we do not create a dangling Weak | |
713 | debug_assert!(!is_dangling(this.ptr)); | |
714 | return Weak { ptr: this.ptr }; | |
715 | } | |
54a0048b | 716 | Err(old) => cur = old, |
c1a9b12d SL |
717 | } |
718 | } | |
1a4d82fc | 719 | } |
1a4d82fc | 720 | |
e74abb32 | 721 | /// Gets the number of [`Weak`][weak] pointers to this allocation. |
c30ab7b3 | 722 | /// |
c30ab7b3 SL |
723 | /// [weak]: struct.Weak.html |
724 | /// | |
476ff2be SL |
725 | /// # Safety |
726 | /// | |
727 | /// This method by itself is safe, but using it correctly requires extra care. | |
728 | /// Another thread can change the weak count at any time, | |
729 | /// including potentially between calling this method and acting on the result. | |
730 | /// | |
c30ab7b3 SL |
731 | /// # Examples |
732 | /// | |
733 | /// ``` | |
c30ab7b3 SL |
734 | /// use std::sync::Arc; |
735 | /// | |
736 | /// let five = Arc::new(5); | |
737 | /// let _weak_five = Arc::downgrade(&five); | |
738 | /// | |
739 | /// // This assertion is deterministic because we haven't shared | |
740 | /// // the `Arc` or `Weak` between threads. | |
741 | /// assert_eq!(1, Arc::weak_count(&five)); | |
742 | /// ``` | |
62682a34 | 743 | #[inline] |
476ff2be | 744 | #[stable(feature = "arc_counts", since = "1.15.0")] |
e9174d1e | 745 | pub fn weak_count(this: &Self) -> usize { |
3b2f2976 XL |
746 | let cnt = this.inner().weak.load(SeqCst); |
747 | // If the weak count is currently locked, the value of the | |
748 | // count was 0 just before taking the lock. | |
749 | if cnt == usize::MAX { 0 } else { cnt - 1 } | |
62682a34 SL |
750 | } |
751 | ||
e74abb32 | 752 | /// Gets the number of strong (`Arc`) pointers to this allocation. |
c30ab7b3 | 753 | /// |
476ff2be SL |
754 | /// # Safety |
755 | /// | |
756 | /// This method by itself is safe, but using it correctly requires extra care. | |
757 | /// Another thread can change the strong count at any time, | |
758 | /// including potentially between calling this method and acting on the result. | |
c30ab7b3 SL |
759 | /// |
760 | /// # Examples | |
761 | /// | |
762 | /// ``` | |
c30ab7b3 SL |
763 | /// use std::sync::Arc; |
764 | /// | |
765 | /// let five = Arc::new(5); | |
7cac9316 | 766 | /// let _also_five = Arc::clone(&five); |
c30ab7b3 SL |
767 | /// |
768 | /// // This assertion is deterministic because we haven't shared | |
769 | /// // the `Arc` between threads. | |
770 | /// assert_eq!(2, Arc::strong_count(&five)); | |
771 | /// ``` | |
62682a34 | 772 | #[inline] |
476ff2be | 773 | #[stable(feature = "arc_counts", since = "1.15.0")] |
e9174d1e | 774 | pub fn strong_count(this: &Self) -> usize { |
62682a34 SL |
775 | this.inner().strong.load(SeqCst) |
776 | } | |
777 | ||
1a4d82fc JJ |
778 | #[inline] |
779 | fn inner(&self) -> &ArcInner<T> { | |
c34b1796 AL |
780 | // This unsafety is ok because while this arc is alive we're guaranteed |
781 | // that the inner pointer is valid. Furthermore, we know that the | |
782 | // `ArcInner` structure itself is `Sync` because the inner data is | |
783 | // `Sync` as well, so we're ok loaning out an immutable pointer to these | |
784 | // contents. | |
7cac9316 | 785 | unsafe { self.ptr.as_ref() } |
1a4d82fc | 786 | } |
c34b1796 AL |
787 | |
788 | // Non-inlined part of `drop`. | |
789 | #[inline(never)] | |
790 | unsafe fn drop_slow(&mut self) { | |
c34b1796 AL |
791 | // Destroy the data at this time, even though we may not free the box |
792 | // allocation itself (there may still be weak pointers lying around). | |
7cac9316 | 793 | ptr::drop_in_place(&mut self.ptr.as_mut().data); |
c34b1796 AL |
794 | |
795 | if self.inner().weak.fetch_sub(1, Release) == 1 { | |
ba9703b0 | 796 | acquire!(self.inner().weak); |
94b46f34 | 797 | Global.dealloc(self.ptr.cast(), Layout::for_value(self.ptr.as_ref())) |
c34b1796 AL |
798 | } |
799 | } | |
9e0c209e SL |
800 | |
801 | #[inline] | |
8bb4bdeb | 802 | #[stable(feature = "ptr_eq", since = "1.17.0")] |
e74abb32 XL |
803 | /// Returns `true` if the two `Arc`s point to the same allocation |
804 | /// (in a vein similar to [`ptr::eq`]). | |
9e0c209e SL |
805 | /// |
806 | /// # Examples | |
807 | /// | |
808 | /// ``` | |
9e0c209e SL |
809 | /// use std::sync::Arc; |
810 | /// | |
811 | /// let five = Arc::new(5); | |
7cac9316 | 812 | /// let same_five = Arc::clone(&five); |
9e0c209e SL |
813 | /// let other_five = Arc::new(5); |
814 | /// | |
815 | /// assert!(Arc::ptr_eq(&five, &same_five)); | |
816 | /// assert!(!Arc::ptr_eq(&five, &other_five)); | |
817 | /// ``` | |
e74abb32 XL |
818 | /// |
819 | /// [`ptr::eq`]: ../../std/ptr/fn.eq.html | |
9e0c209e | 820 | pub fn ptr_eq(this: &Self, other: &Self) -> bool { |
7cac9316 | 821 | this.ptr.as_ptr() == other.ptr.as_ptr() |
9e0c209e | 822 | } |
1a4d82fc JJ |
823 | } |
824 | ||
3b2f2976 | 825 | impl<T: ?Sized> Arc<T> { |
416331ca | 826 | /// Allocates an `ArcInner<T>` with sufficient space for |
e74abb32 | 827 | /// a possibly-unsized inner value where the value has the layout provided. |
416331ca XL |
828 | /// |
829 | /// The function `mem_to_arcinner` is called with the data pointer | |
830 | /// and must return back a (potentially fat)-pointer for the `ArcInner<T>`. | |
e1599b0c | 831 | unsafe fn allocate_for_layout( |
416331ca | 832 | value_layout: Layout, |
dfeec247 | 833 | mem_to_arcinner: impl FnOnce(*mut u8) -> *mut ArcInner<T>, |
416331ca XL |
834 | ) -> *mut ArcInner<T> { |
835 | // Calculate layout using the given value layout. | |
a1dfa0c6 XL |
836 | // Previously, layout was calculated on the expression |
837 | // `&*(ptr as *const ArcInner<T>)`, but this created a misaligned | |
838 | // reference (see #54908). | |
dfeec247 | 839 | let layout = Layout::new::<ArcInner<()>>().extend(value_layout).unwrap().0.pad_to_align(); |
3b2f2976 | 840 | |
ba9703b0 XL |
841 | let mem = Global |
842 | .alloc(layout, AllocInit::Uninitialized) | |
843 | .unwrap_or_else(|_| handle_alloc_error(layout)); | |
3b2f2976 | 844 | |
a1dfa0c6 | 845 | // Initialize the ArcInner |
ba9703b0 | 846 | let inner = mem_to_arcinner(mem.ptr.as_ptr()); |
a1dfa0c6 | 847 | debug_assert_eq!(Layout::for_value(&*inner), layout); |
3b2f2976 XL |
848 | |
849 | ptr::write(&mut (*inner).strong, atomic::AtomicUsize::new(1)); | |
850 | ptr::write(&mut (*inner).weak, atomic::AtomicUsize::new(1)); | |
851 | ||
852 | inner | |
853 | } | |
854 | ||
e74abb32 | 855 | /// Allocates an `ArcInner<T>` with sufficient space for an unsized inner value. |
416331ca XL |
856 | unsafe fn allocate_for_ptr(ptr: *const T) -> *mut ArcInner<T> { |
857 | // Allocate for the `ArcInner<T>` using the given value. | |
dfeec247 XL |
858 | Self::allocate_for_layout(Layout::for_value(&*ptr), |mem| { |
859 | set_data_ptr(ptr as *mut T, mem) as *mut ArcInner<T> | |
860 | }) | |
416331ca XL |
861 | } |
862 | ||
3b2f2976 XL |
863 | fn from_box(v: Box<T>) -> Arc<T> { |
864 | unsafe { | |
83c7162d XL |
865 | let box_unique = Box::into_unique(v); |
866 | let bptr = box_unique.as_ptr(); | |
3b2f2976 XL |
867 | |
868 | let value_size = size_of_val(&*bptr); | |
869 | let ptr = Self::allocate_for_ptr(bptr); | |
870 | ||
871 | // Copy value as bytes | |
872 | ptr::copy_nonoverlapping( | |
873 | bptr as *const T as *const u8, | |
874 | &mut (*ptr).data as *mut _ as *mut u8, | |
dfeec247 XL |
875 | value_size, |
876 | ); | |
3b2f2976 XL |
877 | |
878 | // Free the allocation without dropping its contents | |
83c7162d | 879 | box_free(box_unique); |
3b2f2976 | 880 | |
416331ca | 881 | Self::from_ptr(ptr) |
3b2f2976 XL |
882 | } |
883 | } | |
884 | } | |
885 | ||
416331ca XL |
886 | impl<T> Arc<[T]> { |
887 | /// Allocates an `ArcInner<[T]>` with the given length. | |
888 | unsafe fn allocate_for_slice(len: usize) -> *mut ArcInner<[T]> { | |
dfeec247 XL |
889 | Self::allocate_for_layout(Layout::array::<T>(len).unwrap(), |mem| { |
890 | ptr::slice_from_raw_parts_mut(mem as *mut T, len) as *mut ArcInner<[T]> | |
891 | }) | |
416331ca XL |
892 | } |
893 | } | |
894 | ||
895 | /// Sets the data pointer of a `?Sized` raw pointer. | |
896 | /// | |
897 | /// For a slice/trait object, this sets the `data` field and leaves the rest | |
898 | /// unchanged. For a sized raw pointer, this simply sets the pointer. | |
3b2f2976 XL |
899 | unsafe fn set_data_ptr<T: ?Sized, U>(mut ptr: *mut T, data: *mut U) -> *mut T { |
900 | ptr::write(&mut ptr as *mut _ as *mut *mut u8, data as *mut u8); | |
901 | ptr | |
902 | } | |
903 | ||
904 | impl<T> Arc<[T]> { | |
416331ca XL |
905 | /// Copy elements from slice into newly allocated Arc<[T]> |
906 | /// | |
907 | /// Unsafe because the caller must either take ownership or bind `T: Copy`. | |
3b2f2976 | 908 | unsafe fn copy_from_slice(v: &[T]) -> Arc<[T]> { |
416331ca | 909 | let ptr = Self::allocate_for_slice(v.len()); |
3b2f2976 | 910 | |
dfeec247 | 911 | ptr::copy_nonoverlapping(v.as_ptr(), &mut (*ptr).data as *mut [T] as *mut T, v.len()); |
3b2f2976 | 912 | |
416331ca | 913 | Self::from_ptr(ptr) |
3b2f2976 | 914 | } |
3b2f2976 | 915 | |
416331ca XL |
916 | /// Constructs an `Arc<[T]>` from an iterator known to be of a certain size. |
917 | /// | |
918 | /// Behavior is undefined should the size be wrong. | |
919 | unsafe fn from_iter_exact(iter: impl iter::Iterator<Item = T>, len: usize) -> Arc<[T]> { | |
3b2f2976 XL |
920 | // Panic guard while cloning T elements. |
921 | // In the event of a panic, elements that have been written | |
922 | // into the new ArcInner will be dropped, then the memory freed. | |
923 | struct Guard<T> { | |
83c7162d | 924 | mem: NonNull<u8>, |
3b2f2976 XL |
925 | elems: *mut T, |
926 | layout: Layout, | |
927 | n_elems: usize, | |
928 | } | |
929 | ||
930 | impl<T> Drop for Guard<T> { | |
931 | fn drop(&mut self) { | |
3b2f2976 XL |
932 | unsafe { |
933 | let slice = from_raw_parts_mut(self.elems, self.n_elems); | |
934 | ptr::drop_in_place(slice); | |
935 | ||
416331ca | 936 | Global.dealloc(self.mem.cast(), self.layout); |
3b2f2976 XL |
937 | } |
938 | } | |
939 | } | |
940 | ||
416331ca | 941 | let ptr = Self::allocate_for_slice(len); |
3b2f2976 | 942 | |
416331ca XL |
943 | let mem = ptr as *mut _ as *mut u8; |
944 | let layout = Layout::for_value(&*ptr); | |
3b2f2976 | 945 | |
416331ca XL |
946 | // Pointer to first element |
947 | let elems = &mut (*ptr).data as *mut [T] as *mut T; | |
3b2f2976 | 948 | |
dfeec247 | 949 | let mut guard = Guard { mem: NonNull::new_unchecked(mem), elems, layout, n_elems: 0 }; |
3b2f2976 | 950 | |
416331ca XL |
951 | for (i, item) in iter.enumerate() { |
952 | ptr::write(elems.add(i), item); | |
953 | guard.n_elems += 1; | |
954 | } | |
955 | ||
956 | // All clear. Forget the guard so it doesn't free the new ArcInner. | |
957 | mem::forget(guard); | |
958 | ||
959 | Self::from_ptr(ptr) | |
960 | } | |
961 | } | |
3b2f2976 | 962 | |
416331ca XL |
963 | /// Specialization trait used for `From<&[T]>`. |
964 | trait ArcFromSlice<T> { | |
965 | fn from_slice(slice: &[T]) -> Self; | |
966 | } | |
3b2f2976 | 967 | |
416331ca XL |
968 | impl<T: Clone> ArcFromSlice<T> for Arc<[T]> { |
969 | #[inline] | |
970 | default fn from_slice(v: &[T]) -> Self { | |
dfeec247 | 971 | unsafe { Self::from_iter_exact(v.iter().cloned(), v.len()) } |
3b2f2976 XL |
972 | } |
973 | } | |
974 | ||
975 | impl<T: Copy> ArcFromSlice<T> for Arc<[T]> { | |
976 | #[inline] | |
977 | fn from_slice(v: &[T]) -> Self { | |
978 | unsafe { Arc::copy_from_slice(v) } | |
979 | } | |
980 | } | |
981 | ||
85aaf69f | 982 | #[stable(feature = "rust1", since = "1.0.0")] |
62682a34 | 983 | impl<T: ?Sized> Clone for Arc<T> { |
c30ab7b3 | 984 | /// Makes a clone of the `Arc` pointer. |
1a4d82fc | 985 | /// |
e74abb32 | 986 | /// This creates another pointer to the same allocation, increasing the |
c30ab7b3 | 987 | /// strong reference count. |
1a4d82fc JJ |
988 | /// |
989 | /// # Examples | |
990 | /// | |
991 | /// ``` | |
992 | /// use std::sync::Arc; | |
993 | /// | |
85aaf69f | 994 | /// let five = Arc::new(5); |
1a4d82fc | 995 | /// |
0bf4aa26 | 996 | /// let _ = Arc::clone(&five); |
1a4d82fc JJ |
997 | /// ``` |
998 | #[inline] | |
999 | fn clone(&self) -> Arc<T> { | |
c34b1796 AL |
1000 | // Using a relaxed ordering is alright here, as knowledge of the |
1001 | // original reference prevents other threads from erroneously deleting | |
1002 | // the object. | |
1a4d82fc | 1003 | // |
c34b1796 AL |
1004 | // As explained in the [Boost documentation][1], Increasing the |
1005 | // reference counter can always be done with memory_order_relaxed: New | |
1006 | // references to an object can only be formed from an existing | |
1007 | // reference, and passing an existing reference from one thread to | |
1008 | // another must already provide any required synchronization. | |
1a4d82fc JJ |
1009 | // |
1010 | // [1]: (www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html) | |
c1a9b12d SL |
1011 | let old_size = self.inner().strong.fetch_add(1, Relaxed); |
1012 | ||
1013 | // However we need to guard against massive refcounts in case someone | |
1014 | // is `mem::forget`ing Arcs. If we don't do this the count can overflow | |
1015 | // and users will use-after free. We racily saturate to `isize::MAX` on | |
1016 | // the assumption that there aren't ~2 billion threads incrementing | |
1017 | // the reference count at once. This branch will never be taken in | |
1018 | // any realistic program. | |
1019 | // | |
1020 | // We abort because such a program is incredibly degenerate, and we | |
1021 | // don't care to support it. | |
1022 | if old_size > MAX_REFCOUNT { | |
b039eaaf SL |
1023 | unsafe { |
1024 | abort(); | |
1025 | } | |
c1a9b12d SL |
1026 | } |
1027 | ||
416331ca | 1028 | Self::from_inner(self.ptr) |
1a4d82fc JJ |
1029 | } |
1030 | } | |
1031 | ||
85aaf69f | 1032 | #[stable(feature = "rust1", since = "1.0.0")] |
62682a34 | 1033 | impl<T: ?Sized> Deref for Arc<T> { |
1a4d82fc JJ |
1034 | type Target = T; |
1035 | ||
1036 | #[inline] | |
1037 | fn deref(&self) -> &T { | |
1038 | &self.inner().data | |
1039 | } | |
1040 | } | |
1041 | ||
dfeec247 | 1042 | #[unstable(feature = "receiver_trait", issue = "none")] |
0731742a XL |
1043 | impl<T: ?Sized> Receiver for Arc<T> {} |
1044 | ||
c34b1796 | 1045 | impl<T: Clone> Arc<T> { |
c30ab7b3 SL |
1046 | /// Makes a mutable reference into the given `Arc`. |
1047 | /// | |
e74abb32 XL |
1048 | /// If there are other `Arc` or [`Weak`][weak] pointers to the same allocation, |
1049 | /// then `make_mut` will create a new allocation and invoke [`clone`][clone] on the inner value | |
1050 | /// to ensure unique ownership. This is also referred to as clone-on-write. | |
1051 | /// | |
1052 | /// Note that this differs from the behavior of [`Rc::make_mut`] which disassociates | |
1053 | /// any remaining `Weak` pointers. | |
1a4d82fc | 1054 | /// |
c30ab7b3 SL |
1055 | /// See also [`get_mut`][get_mut], which will fail rather than cloning. |
1056 | /// | |
1057 | /// [weak]: struct.Weak.html | |
1058 | /// [clone]: ../../std/clone/trait.Clone.html#tymethod.clone | |
1059 | /// [get_mut]: struct.Arc.html#method.get_mut | |
e74abb32 | 1060 | /// [`Rc::make_mut`]: ../rc/struct.Rc.html#method.make_mut |
62682a34 | 1061 | /// |
1a4d82fc JJ |
1062 | /// # Examples |
1063 | /// | |
1064 | /// ``` | |
1065 | /// use std::sync::Arc; | |
1066 | /// | |
e9174d1e SL |
1067 | /// let mut data = Arc::new(5); |
1068 | /// | |
1069 | /// *Arc::make_mut(&mut data) += 1; // Won't clone anything | |
7cac9316 | 1070 | /// let mut other_data = Arc::clone(&data); // Won't clone inner data |
e9174d1e SL |
1071 | /// *Arc::make_mut(&mut data) += 1; // Clones inner data |
1072 | /// *Arc::make_mut(&mut data) += 1; // Won't clone anything | |
1073 | /// *Arc::make_mut(&mut other_data) *= 2; // Won't clone anything | |
1074 | /// | |
e74abb32 | 1075 | /// // Now `data` and `other_data` point to different allocations. |
e9174d1e SL |
1076 | /// assert_eq!(*data, 8); |
1077 | /// assert_eq!(*other_data, 12); | |
1a4d82fc JJ |
1078 | /// ``` |
1079 | #[inline] | |
e9174d1e SL |
1080 | #[stable(feature = "arc_unique", since = "1.4.0")] |
1081 | pub fn make_mut(this: &mut Self) -> &mut T { | |
c1a9b12d SL |
1082 | // Note that we hold both a strong reference and a weak reference. |
1083 | // Thus, releasing our strong reference only will not, by itself, cause | |
1084 | // the memory to be deallocated. | |
62682a34 | 1085 | // |
c1a9b12d SL |
1086 | // Use Acquire to ensure that we see any writes to `weak` that happen |
1087 | // before release writes (i.e., decrements) to `strong`. Since we hold a | |
1088 | // weak count, there's no chance the ArcInner itself could be | |
1089 | // deallocated. | |
54a0048b | 1090 | if this.inner().strong.compare_exchange(1, 0, Acquire, Relaxed).is_err() { |
9cc50fc6 | 1091 | // Another strong pointer exists; clone |
c1a9b12d SL |
1092 | *this = Arc::new((**this).clone()); |
1093 | } else if this.inner().weak.load(Relaxed) != 1 { | |
1094 | // Relaxed suffices in the above because this is fundamentally an | |
1095 | // optimization: we are always racing with weak pointers being | |
1096 | // dropped. Worst case, we end up allocated a new Arc unnecessarily. | |
1097 | ||
1098 | // We removed the last strong ref, but there are additional weak | |
1099 | // refs remaining. We'll move the contents to a new Arc, and | |
1100 | // invalidate the other weak refs. | |
1101 | ||
1102 | // Note that it is not possible for the read of `weak` to yield | |
1103 | // usize::MAX (i.e., locked), since the weak count can only be | |
1104 | // locked by a thread with a strong reference. | |
1105 | ||
1106 | // Materialize our own implicit weak pointer, so that it can clean | |
1107 | // up the ArcInner as needed. | |
54a0048b | 1108 | let weak = Weak { ptr: this.ptr }; |
c1a9b12d SL |
1109 | |
1110 | // mark the data itself as already deallocated | |
1111 | unsafe { | |
1112 | // there is no data race in the implicit write caused by `read` | |
1113 | // here (due to zeroing) because data is no longer accessed by | |
1114 | // other threads (due to there being no more strong refs at this | |
1115 | // point). | |
7cac9316 | 1116 | let mut swap = Arc::new(ptr::read(&weak.ptr.as_ref().data)); |
c1a9b12d SL |
1117 | mem::swap(this, &mut swap); |
1118 | mem::forget(swap); | |
1119 | } | |
1120 | } else { | |
1121 | // We were the sole reference of either kind; bump back up the | |
1122 | // strong ref count. | |
1123 | this.inner().strong.store(1, Release); | |
1a4d82fc | 1124 | } |
c1a9b12d | 1125 | |
9346a6ac | 1126 | // As with `get_mut()`, the unsafety is ok because our reference was |
c34b1796 | 1127 | // either unique to begin with, or became one upon cloning the contents. |
dfeec247 | 1128 | unsafe { &mut this.ptr.as_mut().data } |
1a4d82fc JJ |
1129 | } |
1130 | } | |
1131 | ||
c1a9b12d | 1132 | impl<T: ?Sized> Arc<T> { |
e74abb32 XL |
1133 | /// Returns a mutable reference into the given `Arc`, if there are |
1134 | /// no other `Arc` or [`Weak`][weak] pointers to the same allocation. | |
c30ab7b3 SL |
1135 | /// |
1136 | /// Returns [`None`][option] otherwise, because it is not safe to | |
1137 | /// mutate a shared value. | |
1138 | /// | |
1139 | /// See also [`make_mut`][make_mut], which will [`clone`][clone] | |
e74abb32 | 1140 | /// the inner value when there are other pointers. |
c30ab7b3 SL |
1141 | /// |
1142 | /// [weak]: struct.Weak.html | |
1143 | /// [option]: ../../std/option/enum.Option.html | |
1144 | /// [make_mut]: struct.Arc.html#method.make_mut | |
1145 | /// [clone]: ../../std/clone/trait.Clone.html#tymethod.clone | |
c1a9b12d SL |
1146 | /// |
1147 | /// # Examples | |
1148 | /// | |
1149 | /// ``` | |
e9174d1e | 1150 | /// use std::sync::Arc; |
c1a9b12d SL |
1151 | /// |
1152 | /// let mut x = Arc::new(3); | |
1153 | /// *Arc::get_mut(&mut x).unwrap() = 4; | |
1154 | /// assert_eq!(*x, 4); | |
1155 | /// | |
7cac9316 | 1156 | /// let _y = Arc::clone(&x); |
c1a9b12d | 1157 | /// assert!(Arc::get_mut(&mut x).is_none()); |
c1a9b12d SL |
1158 | /// ``` |
1159 | #[inline] | |
e9174d1e SL |
1160 | #[stable(feature = "arc_unique", since = "1.4.0")] |
1161 | pub fn get_mut(this: &mut Self) -> Option<&mut T> { | |
c1a9b12d SL |
1162 | if this.is_unique() { |
1163 | // This unsafety is ok because we're guaranteed that the pointer | |
1164 | // returned is the *only* pointer that will ever be returned to T. Our | |
1165 | // reference count is guaranteed to be 1 at this point, and we required | |
1166 | // the Arc itself to be `mut`, so we're returning the only possible | |
1167 | // reference to the inner data. | |
dfeec247 | 1168 | unsafe { Some(Arc::get_mut_unchecked(this)) } |
c1a9b12d SL |
1169 | } else { |
1170 | None | |
1171 | } | |
1172 | } | |
1173 | ||
e74abb32 | 1174 | /// Returns a mutable reference into the given `Arc`, |
e1599b0c XL |
1175 | /// without any check. |
1176 | /// | |
1177 | /// See also [`get_mut`], which is safe and does appropriate checks. | |
1178 | /// | |
1179 | /// [`get_mut`]: struct.Arc.html#method.get_mut | |
1180 | /// | |
1181 | /// # Safety | |
1182 | /// | |
e74abb32 | 1183 | /// Any other `Arc` or [`Weak`] pointers to the same allocation must not be dereferenced |
e1599b0c XL |
1184 | /// for the duration of the returned borrow. |
1185 | /// This is trivially the case if no such pointers exist, | |
1186 | /// for example immediately after `Arc::new`. | |
1187 | /// | |
1188 | /// # Examples | |
1189 | /// | |
1190 | /// ``` | |
1191 | /// #![feature(get_mut_unchecked)] | |
1192 | /// | |
1193 | /// use std::sync::Arc; | |
1194 | /// | |
1195 | /// let mut x = Arc::new(String::new()); | |
1196 | /// unsafe { | |
1197 | /// Arc::get_mut_unchecked(&mut x).push_str("foo") | |
1198 | /// } | |
1199 | /// assert_eq!(*x, "foo"); | |
1200 | /// ``` | |
1201 | #[inline] | |
1202 | #[unstable(feature = "get_mut_unchecked", issue = "63292")] | |
1203 | pub unsafe fn get_mut_unchecked(this: &mut Self) -> &mut T { | |
1204 | &mut this.ptr.as_mut().data | |
1205 | } | |
1206 | ||
c1a9b12d SL |
1207 | /// Determine whether this is the unique reference (including weak refs) to |
1208 | /// the underlying data. | |
1209 | /// | |
1210 | /// Note that this requires locking the weak ref count. | |
1211 | fn is_unique(&mut self) -> bool { | |
1212 | // lock the weak pointer count if we appear to be the sole weak pointer | |
1213 | // holder. | |
1214 | // | |
1215 | // The acquire label here ensures a happens-before relationship with any | |
8faf50e0 XL |
1216 | // writes to `strong` (in particular in `Weak::upgrade`) prior to decrements |
1217 | // of the `weak` count (via `Weak::drop`, which uses release). If the upgraded | |
1218 | // weak ref was never dropped, the CAS here will fail so we do not care to synchronize. | |
54a0048b | 1219 | if self.inner().weak.compare_exchange(1, usize::MAX, Acquire, Relaxed).is_ok() { |
8faf50e0 XL |
1220 | // This needs to be an `Acquire` to synchronize with the decrement of the `strong` |
1221 | // counter in `drop` -- the only access that happens when any but the last reference | |
1222 | // is being dropped. | |
1223 | let unique = self.inner().strong.load(Acquire) == 1; | |
c1a9b12d SL |
1224 | |
1225 | // The release write here synchronizes with a read in `downgrade`, | |
1226 | // effectively preventing the above read of `strong` from happening | |
1227 | // after the write. | |
1228 | self.inner().weak.store(1, Release); // release the lock | |
1229 | unique | |
1230 | } else { | |
1231 | false | |
1232 | } | |
1233 | } | |
1234 | } | |
1235 | ||
85aaf69f | 1236 | #[stable(feature = "rust1", since = "1.0.0")] |
32a655c1 | 1237 | unsafe impl<#[may_dangle] T: ?Sized> Drop for Arc<T> { |
c30ab7b3 | 1238 | /// Drops the `Arc`. |
1a4d82fc | 1239 | /// |
c34b1796 | 1240 | /// This will decrement the strong reference count. If the strong reference |
c30ab7b3 | 1241 | /// count reaches zero then the only other references (if any) are |
b7449926 | 1242 | /// [`Weak`], so we `drop` the inner value. |
1a4d82fc JJ |
1243 | /// |
1244 | /// # Examples | |
1245 | /// | |
1246 | /// ``` | |
1247 | /// use std::sync::Arc; | |
1248 | /// | |
c30ab7b3 | 1249 | /// struct Foo; |
1a4d82fc | 1250 | /// |
c30ab7b3 SL |
1251 | /// impl Drop for Foo { |
1252 | /// fn drop(&mut self) { | |
1253 | /// println!("dropped!"); | |
1254 | /// } | |
1a4d82fc | 1255 | /// } |
1a4d82fc | 1256 | /// |
c30ab7b3 | 1257 | /// let foo = Arc::new(Foo); |
7cac9316 | 1258 | /// let foo2 = Arc::clone(&foo); |
1a4d82fc | 1259 | /// |
c30ab7b3 SL |
1260 | /// drop(foo); // Doesn't print anything |
1261 | /// drop(foo2); // Prints "dropped!" | |
1a4d82fc | 1262 | /// ``` |
0731742a XL |
1263 | /// |
1264 | /// [`Weak`]: ../../std/sync/struct.Weak.html | |
c34b1796 | 1265 | #[inline] |
1a4d82fc | 1266 | fn drop(&mut self) { |
c34b1796 AL |
1267 | // Because `fetch_sub` is already atomic, we do not need to synchronize |
1268 | // with other threads unless we are going to delete the object. This | |
1269 | // same logic applies to the below `fetch_sub` to the `weak` count. | |
b039eaaf | 1270 | if self.inner().strong.fetch_sub(1, Release) != 1 { |
92a42be0 | 1271 | return; |
b039eaaf | 1272 | } |
1a4d82fc | 1273 | |
c34b1796 AL |
1274 | // This fence is needed to prevent reordering of use of the data and |
1275 | // deletion of the data. Because it is marked `Release`, the decreasing | |
1276 | // of the reference count synchronizes with this `Acquire` fence. This | |
1277 | // means that use of the data happens before decreasing the reference | |
1278 | // count, which happens before this fence, which happens before the | |
1279 | // deletion of the data. | |
1a4d82fc JJ |
1280 | // |
1281 | // As explained in the [Boost documentation][1], | |
1282 | // | |
c34b1796 AL |
1283 | // > It is important to enforce any possible access to the object in one |
1284 | // > thread (through an existing reference) to *happen before* deleting | |
1285 | // > the object in a different thread. This is achieved by a "release" | |
1286 | // > operation after dropping a reference (any access to the object | |
1287 | // > through this reference must obviously happened before), and an | |
1288 | // > "acquire" operation before deleting the object. | |
1a4d82fc | 1289 | // |
7cac9316 XL |
1290 | // In particular, while the contents of an Arc are usually immutable, it's |
1291 | // possible to have interior writes to something like a Mutex<T>. Since a | |
1292 | // Mutex is not acquired when it is deleted, we can't rely on its | |
1293 | // synchronization logic to make writes in thread A visible to a destructor | |
1294 | // running in thread B. | |
1295 | // | |
1296 | // Also note that the Acquire fence here could probably be replaced with an | |
1297 | // Acquire load, which could improve performance in highly-contended | |
1298 | // situations. See [2]. | |
1299 | // | |
1a4d82fc | 1300 | // [1]: (www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html) |
7cac9316 | 1301 | // [2]: (https://github.com/rust-lang/rust/pull/41714) |
ba9703b0 | 1302 | acquire!(self.inner().strong); |
1a4d82fc | 1303 | |
c34b1796 | 1304 | unsafe { |
b039eaaf | 1305 | self.drop_slow(); |
1a4d82fc JJ |
1306 | } |
1307 | } | |
1308 | } | |
1309 | ||
8faf50e0 | 1310 | impl Arc<dyn Any + Send + Sync> { |
94b46f34 | 1311 | #[inline] |
8faf50e0 XL |
1312 | #[stable(feature = "rc_downcast", since = "1.29.0")] |
1313 | /// Attempt to downcast the `Arc<dyn Any + Send + Sync>` to a concrete type. | |
94b46f34 XL |
1314 | /// |
1315 | /// # Examples | |
1316 | /// | |
1317 | /// ``` | |
94b46f34 XL |
1318 | /// use std::any::Any; |
1319 | /// use std::sync::Arc; | |
1320 | /// | |
8faf50e0 | 1321 | /// fn print_if_string(value: Arc<dyn Any + Send + Sync>) { |
94b46f34 XL |
1322 | /// if let Ok(string) = value.downcast::<String>() { |
1323 | /// println!("String ({}): {}", string.len(), string); | |
1324 | /// } | |
1325 | /// } | |
1326 | /// | |
e74abb32 XL |
1327 | /// let my_string = "Hello World".to_string(); |
1328 | /// print_if_string(Arc::new(my_string)); | |
1329 | /// print_if_string(Arc::new(0i8)); | |
94b46f34 XL |
1330 | /// ``` |
1331 | pub fn downcast<T>(self) -> Result<Arc<T>, Self> | |
1332 | where | |
1333 | T: Any + Send + Sync + 'static, | |
1334 | { | |
1335 | if (*self).is::<T>() { | |
1336 | let ptr = self.ptr.cast::<ArcInner<T>>(); | |
1337 | mem::forget(self); | |
416331ca | 1338 | Ok(Arc::from_inner(ptr)) |
94b46f34 XL |
1339 | } else { |
1340 | Err(self) | |
1341 | } | |
1342 | } | |
1343 | } | |
1344 | ||
a7813a04 | 1345 | impl<T> Weak<T> { |
8faf50e0 XL |
1346 | /// Constructs a new `Weak<T>`, without allocating any memory. |
1347 | /// Calling [`upgrade`] on the return value always gives [`None`]. | |
c30ab7b3 | 1348 | /// |
cc61c64b XL |
1349 | /// [`upgrade`]: struct.Weak.html#method.upgrade |
1350 | /// [`None`]: ../../std/option/enum.Option.html#variant.None | |
a7813a04 XL |
1351 | /// |
1352 | /// # Examples | |
1353 | /// | |
1354 | /// ``` | |
1355 | /// use std::sync::Weak; | |
1356 | /// | |
1357 | /// let empty: Weak<i64> = Weak::new(); | |
c30ab7b3 | 1358 | /// assert!(empty.upgrade().is_none()); |
a7813a04 XL |
1359 | /// ``` |
1360 | #[stable(feature = "downgraded_weak", since = "1.10.0")] | |
1361 | pub fn new() -> Weak<T> { | |
dfeec247 | 1362 | Weak { ptr: NonNull::new(usize::MAX as *mut ArcInner<T>).expect("MAX is not 0") } |
a7813a04 | 1363 | } |
dc9dc135 XL |
1364 | |
1365 | /// Returns a raw pointer to the object `T` pointed to by this `Weak<T>`. | |
1366 | /// | |
ba9703b0 XL |
1367 | /// The pointer is valid only if there are some strong references. The pointer may be dangling, |
1368 | /// unaligned or even [`null`] otherwise. | |
dc9dc135 XL |
1369 | /// |
1370 | /// # Examples | |
1371 | /// | |
1372 | /// ``` | |
1373 | /// #![feature(weak_into_raw)] | |
1374 | /// | |
416331ca | 1375 | /// use std::sync::Arc; |
dc9dc135 XL |
1376 | /// use std::ptr; |
1377 | /// | |
1378 | /// let strong = Arc::new("hello".to_owned()); | |
1379 | /// let weak = Arc::downgrade(&strong); | |
1380 | /// // Both point to the same object | |
ba9703b0 | 1381 | /// assert!(ptr::eq(&*strong, weak.as_ptr())); |
dc9dc135 | 1382 | /// // The strong here keeps it alive, so we can still access the object. |
ba9703b0 | 1383 | /// assert_eq!("hello", unsafe { &*weak.as_ptr() }); |
dc9dc135 XL |
1384 | /// |
1385 | /// drop(strong); | |
ba9703b0 | 1386 | /// // But not any more. We can do weak.as_ptr(), but accessing the pointer would lead to |
dc9dc135 | 1387 | /// // undefined behaviour. |
ba9703b0 | 1388 | /// // assert_eq!("hello", unsafe { &*weak.as_ptr() }); |
dc9dc135 XL |
1389 | /// ``` |
1390 | /// | |
1391 | /// [`null`]: ../../std/ptr/fn.null.html | |
1392 | #[unstable(feature = "weak_into_raw", issue = "60728")] | |
ba9703b0 XL |
1393 | pub fn as_ptr(&self) -> *const T { |
1394 | let offset = data_offset_sized::<T>(); | |
1395 | let ptr = self.ptr.cast::<u8>().as_ptr().wrapping_offset(offset); | |
1396 | ptr as *const T | |
dc9dc135 XL |
1397 | } |
1398 | ||
1399 | /// Consumes the `Weak<T>` and turns it into a raw pointer. | |
1400 | /// | |
1401 | /// This converts the weak pointer into a raw pointer, preserving the original weak count. It | |
1402 | /// can be turned back into the `Weak<T>` with [`from_raw`]. | |
1403 | /// | |
1404 | /// The same restrictions of accessing the target of the pointer as with | |
ba9703b0 | 1405 | /// [`as_ptr`] apply. |
dc9dc135 XL |
1406 | /// |
1407 | /// # Examples | |
1408 | /// | |
1409 | /// ``` | |
1410 | /// #![feature(weak_into_raw)] | |
1411 | /// | |
1412 | /// use std::sync::{Arc, Weak}; | |
1413 | /// | |
1414 | /// let strong = Arc::new("hello".to_owned()); | |
1415 | /// let weak = Arc::downgrade(&strong); | |
416331ca | 1416 | /// let raw = weak.into_raw(); |
dc9dc135 XL |
1417 | /// |
1418 | /// assert_eq!(1, Arc::weak_count(&strong)); | |
1419 | /// assert_eq!("hello", unsafe { &*raw }); | |
1420 | /// | |
1421 | /// drop(unsafe { Weak::from_raw(raw) }); | |
1422 | /// assert_eq!(0, Arc::weak_count(&strong)); | |
1423 | /// ``` | |
1424 | /// | |
1425 | /// [`from_raw`]: struct.Weak.html#method.from_raw | |
ba9703b0 | 1426 | /// [`as_ptr`]: struct.Weak.html#method.as_ptr |
dc9dc135 | 1427 | #[unstable(feature = "weak_into_raw", issue = "60728")] |
416331ca | 1428 | pub fn into_raw(self) -> *const T { |
ba9703b0 | 1429 | let result = self.as_ptr(); |
416331ca | 1430 | mem::forget(self); |
dc9dc135 XL |
1431 | result |
1432 | } | |
1433 | ||
1434 | /// Converts a raw pointer previously created by [`into_raw`] back into | |
1435 | /// `Weak<T>`. | |
1436 | /// | |
1437 | /// This can be used to safely get a strong reference (by calling [`upgrade`] | |
1438 | /// later) or to deallocate the weak count by dropping the `Weak<T>`. | |
1439 | /// | |
60c5eb7d XL |
1440 | /// It takes ownership of one weak count (with the exception of pointers created by [`new`], |
1441 | /// as these don't have any corresponding weak count). | |
dc9dc135 XL |
1442 | /// |
1443 | /// # Safety | |
1444 | /// | |
ba9703b0 XL |
1445 | /// The pointer must have originated from the [`into_raw`] and must still own its potential |
1446 | /// weak reference count. | |
60c5eb7d XL |
1447 | /// |
1448 | /// It is allowed for the strong count to be 0 at the time of calling this, but the weak count | |
1449 | /// must be non-zero or the pointer must have originated from a dangling `Weak<T>` (one created | |
1450 | /// by [`new`]). | |
dc9dc135 XL |
1451 | /// |
1452 | /// # Examples | |
1453 | /// | |
1454 | /// ``` | |
1455 | /// #![feature(weak_into_raw)] | |
1456 | /// | |
1457 | /// use std::sync::{Arc, Weak}; | |
1458 | /// | |
1459 | /// let strong = Arc::new("hello".to_owned()); | |
1460 | /// | |
416331ca XL |
1461 | /// let raw_1 = Arc::downgrade(&strong).into_raw(); |
1462 | /// let raw_2 = Arc::downgrade(&strong).into_raw(); | |
dc9dc135 XL |
1463 | /// |
1464 | /// assert_eq!(2, Arc::weak_count(&strong)); | |
1465 | /// | |
416331ca | 1466 | /// assert_eq!("hello", &*unsafe { Weak::from_raw(raw_1) }.upgrade().unwrap()); |
dc9dc135 XL |
1467 | /// assert_eq!(1, Arc::weak_count(&strong)); |
1468 | /// | |
1469 | /// drop(strong); | |
1470 | /// | |
1471 | /// // Decrement the last weak count. | |
416331ca | 1472 | /// assert!(unsafe { Weak::from_raw(raw_2) }.upgrade().is_none()); |
dc9dc135 XL |
1473 | /// ``` |
1474 | /// | |
60c5eb7d | 1475 | /// [`new`]: struct.Weak.html#method.new |
dc9dc135 XL |
1476 | /// [`into_raw`]: struct.Weak.html#method.into_raw |
1477 | /// [`upgrade`]: struct.Weak.html#method.upgrade | |
1478 | /// [`Weak`]: struct.Weak.html | |
1479 | /// [`Arc`]: struct.Arc.html | |
60c5eb7d | 1480 | /// [`forget`]: ../../std/mem/fn.forget.html |
dc9dc135 XL |
1481 | #[unstable(feature = "weak_into_raw", issue = "60728")] |
1482 | pub unsafe fn from_raw(ptr: *const T) -> Self { | |
1483 | if ptr.is_null() { | |
1484 | Self::new() | |
1485 | } else { | |
1486 | // See Arc::from_raw for details | |
1487 | let offset = data_offset(ptr); | |
1488 | let fake_ptr = ptr as *mut ArcInner<T>; | |
1489 | let ptr = set_data_ptr(fake_ptr, (ptr as *mut u8).offset(-offset)); | |
dfeec247 | 1490 | Weak { ptr: NonNull::new(ptr).expect("Invalid pointer passed to from_raw") } |
dc9dc135 XL |
1491 | } |
1492 | } | |
a7813a04 XL |
1493 | } |
1494 | ||
62682a34 | 1495 | impl<T: ?Sized> Weak<T> { |
e74abb32 XL |
1496 | /// Attempts to upgrade the `Weak` pointer to an [`Arc`], delaying |
1497 | /// dropping of the inner value if successful. | |
1a4d82fc | 1498 | /// |
e74abb32 | 1499 | /// Returns [`None`] if the inner value has since been dropped. |
1a4d82fc | 1500 | /// |
cc61c64b XL |
1501 | /// [`Arc`]: struct.Arc.html |
1502 | /// [`None`]: ../../std/option/enum.Option.html#variant.None | |
1a4d82fc JJ |
1503 | /// |
1504 | /// # Examples | |
1505 | /// | |
1506 | /// ``` | |
1507 | /// use std::sync::Arc; | |
1508 | /// | |
85aaf69f | 1509 | /// let five = Arc::new(5); |
1a4d82fc | 1510 | /// |
e9174d1e | 1511 | /// let weak_five = Arc::downgrade(&five); |
1a4d82fc JJ |
1512 | /// |
1513 | /// let strong_five: Option<Arc<_>> = weak_five.upgrade(); | |
c30ab7b3 SL |
1514 | /// assert!(strong_five.is_some()); |
1515 | /// | |
1516 | /// // Destroy all strong pointers. | |
1517 | /// drop(strong_five); | |
1518 | /// drop(five); | |
1519 | /// | |
1520 | /// assert!(weak_five.upgrade().is_none()); | |
1a4d82fc | 1521 | /// ``` |
e9174d1e | 1522 | #[stable(feature = "arc_weak", since = "1.4.0")] |
1a4d82fc | 1523 | pub fn upgrade(&self) -> Option<Arc<T>> { |
c34b1796 | 1524 | // We use a CAS loop to increment the strong count instead of a |
9346a6ac | 1525 | // fetch_add because once the count hits 0 it must never be above 0. |
8faf50e0 | 1526 | let inner = self.inner()?; |
54a0048b SL |
1527 | |
1528 | // Relaxed load because any write of 0 that we can observe | |
1529 | // leaves the field in a permanently zero state (so a | |
1530 | // "stale" read of 0 is fine), and any other value is | |
1531 | // confirmed via the CAS below. | |
1532 | let mut n = inner.strong.load(Relaxed); | |
1533 | ||
1a4d82fc | 1534 | loop { |
b039eaaf | 1535 | if n == 0 { |
92a42be0 SL |
1536 | return None; |
1537 | } | |
1538 | ||
1539 | // See comments in `Arc::clone` for why we do this (for `mem::forget`). | |
1540 | if n > MAX_REFCOUNT { | |
3157f602 XL |
1541 | unsafe { |
1542 | abort(); | |
1543 | } | |
b039eaaf | 1544 | } |
c1a9b12d SL |
1545 | |
1546 | // Relaxed is valid for the same reason it is on Arc's Clone impl | |
54a0048b | 1547 | match inner.strong.compare_exchange_weak(n, n + 1, Relaxed, Relaxed) { |
416331ca | 1548 | Ok(_) => return Some(Arc::from_inner(self.ptr)), // null checked above |
54a0048b | 1549 | Err(old) => n = old, |
b039eaaf | 1550 | } |
1a4d82fc JJ |
1551 | } |
1552 | } | |
1553 | ||
e74abb32 | 1554 | /// Gets the number of strong (`Arc`) pointers pointing to this allocation. |
9fa01778 XL |
1555 | /// |
1556 | /// If `self` was created using [`Weak::new`], this will return 0. | |
1557 | /// | |
1558 | /// [`Weak::new`]: #method.new | |
60c5eb7d | 1559 | #[stable(feature = "weak_counts", since = "1.41.0")] |
9fa01778 | 1560 | pub fn strong_count(&self) -> usize { |
dfeec247 | 1561 | if let Some(inner) = self.inner() { inner.strong.load(SeqCst) } else { 0 } |
9fa01778 XL |
1562 | } |
1563 | ||
1564 | /// Gets an approximation of the number of `Weak` pointers pointing to this | |
e74abb32 | 1565 | /// allocation. |
9fa01778 | 1566 | /// |
60c5eb7d XL |
1567 | /// If `self` was created using [`Weak::new`], or if there are no remaining |
1568 | /// strong pointers, this will return 0. | |
9fa01778 XL |
1569 | /// |
1570 | /// # Accuracy | |
1571 | /// | |
1572 | /// Due to implementation details, the returned value can be off by 1 in | |
1573 | /// either direction when other threads are manipulating any `Arc`s or | |
e74abb32 | 1574 | /// `Weak`s pointing to the same allocation. |
9fa01778 XL |
1575 | /// |
1576 | /// [`Weak::new`]: #method.new | |
60c5eb7d XL |
1577 | #[stable(feature = "weak_counts", since = "1.41.0")] |
1578 | pub fn weak_count(&self) -> usize { | |
dfeec247 XL |
1579 | self.inner() |
1580 | .map(|inner| { | |
1581 | let weak = inner.weak.load(SeqCst); | |
1582 | let strong = inner.strong.load(SeqCst); | |
1583 | if strong == 0 { | |
1584 | 0 | |
1585 | } else { | |
1586 | // Since we observed that there was at least one strong pointer | |
1587 | // after reading the weak count, we know that the implicit weak | |
1588 | // reference (present whenever any strong references are alive) | |
1589 | // was still around when we observed the weak count, and can | |
1590 | // therefore safely subtract it. | |
1591 | weak - 1 | |
1592 | } | |
1593 | }) | |
1594 | .unwrap_or(0) | |
9fa01778 XL |
1595 | } |
1596 | ||
1597 | /// Returns `None` when the pointer is dangling and there is no allocated `ArcInner`, | |
1598 | /// (i.e., when this `Weak` was created by `Weak::new`). | |
1a4d82fc | 1599 | #[inline] |
8faf50e0 | 1600 | fn inner(&self) -> Option<&ArcInner<T>> { |
dfeec247 | 1601 | if is_dangling(self.ptr) { None } else { Some(unsafe { self.ptr.as_ref() }) } |
1a4d82fc | 1602 | } |
0731742a | 1603 | |
e74abb32 XL |
1604 | /// Returns `true` if the two `Weak`s point to the same allocation (similar to |
1605 | /// [`ptr::eq`]), or if both don't point to any allocation | |
e1599b0c | 1606 | /// (because they were created with `Weak::new()`). |
0731742a XL |
1607 | /// |
1608 | /// # Notes | |
1609 | /// | |
1610 | /// Since this compares pointers it means that `Weak::new()` will equal each | |
e74abb32 | 1611 | /// other, even though they don't point to any allocation. |
0731742a | 1612 | /// |
0731742a XL |
1613 | /// # Examples |
1614 | /// | |
1615 | /// ``` | |
dc9dc135 | 1616 | /// use std::sync::Arc; |
0731742a XL |
1617 | /// |
1618 | /// let first_rc = Arc::new(5); | |
1619 | /// let first = Arc::downgrade(&first_rc); | |
1620 | /// let second = Arc::downgrade(&first_rc); | |
1621 | /// | |
dc9dc135 | 1622 | /// assert!(first.ptr_eq(&second)); |
0731742a XL |
1623 | /// |
1624 | /// let third_rc = Arc::new(5); | |
1625 | /// let third = Arc::downgrade(&third_rc); | |
1626 | /// | |
dc9dc135 | 1627 | /// assert!(!first.ptr_eq(&third)); |
0731742a XL |
1628 | /// ``` |
1629 | /// | |
1630 | /// Comparing `Weak::new`. | |
1631 | /// | |
1632 | /// ``` | |
0731742a XL |
1633 | /// use std::sync::{Arc, Weak}; |
1634 | /// | |
1635 | /// let first = Weak::new(); | |
1636 | /// let second = Weak::new(); | |
dc9dc135 | 1637 | /// assert!(first.ptr_eq(&second)); |
0731742a XL |
1638 | /// |
1639 | /// let third_rc = Arc::new(()); | |
1640 | /// let third = Arc::downgrade(&third_rc); | |
dc9dc135 | 1641 | /// assert!(!first.ptr_eq(&third)); |
0731742a | 1642 | /// ``` |
e74abb32 XL |
1643 | /// |
1644 | /// [`ptr::eq`]: ../../std/ptr/fn.eq.html | |
0731742a | 1645 | #[inline] |
e1599b0c | 1646 | #[stable(feature = "weak_ptr_eq", since = "1.39.0")] |
dc9dc135 XL |
1647 | pub fn ptr_eq(&self, other: &Self) -> bool { |
1648 | self.ptr.as_ptr() == other.ptr.as_ptr() | |
0731742a | 1649 | } |
1a4d82fc JJ |
1650 | } |
1651 | ||
e9174d1e | 1652 | #[stable(feature = "arc_weak", since = "1.4.0")] |
62682a34 | 1653 | impl<T: ?Sized> Clone for Weak<T> { |
e74abb32 | 1654 | /// Makes a clone of the `Weak` pointer that points to the same allocation. |
1a4d82fc JJ |
1655 | /// |
1656 | /// # Examples | |
1657 | /// | |
1658 | /// ``` | |
7cac9316 | 1659 | /// use std::sync::{Arc, Weak}; |
1a4d82fc | 1660 | /// |
e9174d1e | 1661 | /// let weak_five = Arc::downgrade(&Arc::new(5)); |
1a4d82fc | 1662 | /// |
0bf4aa26 | 1663 | /// let _ = Weak::clone(&weak_five); |
1a4d82fc JJ |
1664 | /// ``` |
1665 | #[inline] | |
1666 | fn clone(&self) -> Weak<T> { | |
8faf50e0 XL |
1667 | let inner = if let Some(inner) = self.inner() { |
1668 | inner | |
1669 | } else { | |
1670 | return Weak { ptr: self.ptr }; | |
1671 | }; | |
c1a9b12d SL |
1672 | // See comments in Arc::clone() for why this is relaxed. This can use a |
1673 | // fetch_add (ignoring the lock) because the weak count is only locked | |
1674 | // where are *no other* weak pointers in existence. (So we can't be | |
1675 | // running this code in that case). | |
8faf50e0 | 1676 | let old_size = inner.weak.fetch_add(1, Relaxed); |
c1a9b12d SL |
1677 | |
1678 | // See comments in Arc::clone() for why we do this (for mem::forget). | |
1679 | if old_size > MAX_REFCOUNT { | |
b039eaaf SL |
1680 | unsafe { |
1681 | abort(); | |
1682 | } | |
c1a9b12d SL |
1683 | } |
1684 | ||
e74abb32 | 1685 | Weak { ptr: self.ptr } |
1a4d82fc JJ |
1686 | } |
1687 | } | |
1688 | ||
a7813a04 XL |
1689 | #[stable(feature = "downgraded_weak", since = "1.10.0")] |
1690 | impl<T> Default for Weak<T> { | |
8faf50e0 | 1691 | /// Constructs a new `Weak<T>`, without allocating memory. |
0731742a | 1692 | /// Calling [`upgrade`] on the return value always |
b7449926 | 1693 | /// gives [`None`]. |
c30ab7b3 | 1694 | /// |
cc61c64b | 1695 | /// [`None`]: ../../std/option/enum.Option.html#variant.None |
0731742a | 1696 | /// [`upgrade`]: ../../std/sync/struct.Weak.html#method.upgrade |
c30ab7b3 SL |
1697 | /// |
1698 | /// # Examples | |
1699 | /// | |
1700 | /// ``` | |
1701 | /// use std::sync::Weak; | |
1702 | /// | |
1703 | /// let empty: Weak<i64> = Default::default(); | |
1704 | /// assert!(empty.upgrade().is_none()); | |
1705 | /// ``` | |
a7813a04 XL |
1706 | fn default() -> Weak<T> { |
1707 | Weak::new() | |
1708 | } | |
1709 | } | |
1710 | ||
7453a54e | 1711 | #[stable(feature = "arc_weak", since = "1.4.0")] |
62682a34 | 1712 | impl<T: ?Sized> Drop for Weak<T> { |
c30ab7b3 | 1713 | /// Drops the `Weak` pointer. |
1a4d82fc | 1714 | /// |
1a4d82fc JJ |
1715 | /// # Examples |
1716 | /// | |
1717 | /// ``` | |
7cac9316 | 1718 | /// use std::sync::{Arc, Weak}; |
1a4d82fc | 1719 | /// |
c30ab7b3 | 1720 | /// struct Foo; |
1a4d82fc | 1721 | /// |
c30ab7b3 SL |
1722 | /// impl Drop for Foo { |
1723 | /// fn drop(&mut self) { | |
1724 | /// println!("dropped!"); | |
1725 | /// } | |
1a4d82fc | 1726 | /// } |
1a4d82fc | 1727 | /// |
c30ab7b3 SL |
1728 | /// let foo = Arc::new(Foo); |
1729 | /// let weak_foo = Arc::downgrade(&foo); | |
7cac9316 | 1730 | /// let other_weak_foo = Weak::clone(&weak_foo); |
1a4d82fc | 1731 | /// |
c30ab7b3 SL |
1732 | /// drop(weak_foo); // Doesn't print anything |
1733 | /// drop(foo); // Prints "dropped!" | |
1734 | /// | |
1735 | /// assert!(other_weak_foo.upgrade().is_none()); | |
1a4d82fc JJ |
1736 | /// ``` |
1737 | fn drop(&mut self) { | |
c34b1796 AL |
1738 | // If we find out that we were the last weak pointer, then its time to |
1739 | // deallocate the data entirely. See the discussion in Arc::drop() about | |
1740 | // the memory orderings | |
c1a9b12d SL |
1741 | // |
1742 | // It's not necessary to check for the locked state here, because the | |
1743 | // weak count can only be locked if there was precisely one weak ref, | |
1744 | // meaning that drop could only subsequently run ON that remaining weak | |
1745 | // ref, which can only happen after the lock is released. | |
dfeec247 | 1746 | let inner = if let Some(inner) = self.inner() { inner } else { return }; |
8faf50e0 XL |
1747 | |
1748 | if inner.weak.fetch_sub(1, Release) == 1 { | |
ba9703b0 | 1749 | acquire!(inner.weak); |
dfeec247 | 1750 | unsafe { Global.dealloc(self.ptr.cast(), Layout::for_value(self.ptr.as_ref())) } |
1a4d82fc JJ |
1751 | } |
1752 | } | |
1753 | } | |
1754 | ||
0731742a XL |
1755 | #[stable(feature = "rust1", since = "1.0.0")] |
1756 | trait ArcEqIdent<T: ?Sized + PartialEq> { | |
1757 | fn eq(&self, other: &Arc<T>) -> bool; | |
1758 | fn ne(&self, other: &Arc<T>) -> bool; | |
1759 | } | |
1760 | ||
1761 | #[stable(feature = "rust1", since = "1.0.0")] | |
1762 | impl<T: ?Sized + PartialEq> ArcEqIdent<T> for Arc<T> { | |
1763 | #[inline] | |
1764 | default fn eq(&self, other: &Arc<T>) -> bool { | |
1765 | **self == **other | |
1766 | } | |
1767 | #[inline] | |
1768 | default fn ne(&self, other: &Arc<T>) -> bool { | |
1769 | **self != **other | |
1770 | } | |
1771 | } | |
1772 | ||
48663c56 XL |
1773 | /// We're doing this specialization here, and not as a more general optimization on `&T`, because it |
1774 | /// would otherwise add a cost to all equality checks on refs. We assume that `Arc`s are used to | |
1775 | /// store large values, that are slow to clone, but also heavy to check for equality, causing this | |
1776 | /// cost to pay off more easily. It's also more likely to have two `Arc` clones, that point to | |
1777 | /// the same value, than two `&T`s. | |
e74abb32 XL |
1778 | /// |
1779 | /// We can only do this when `T: Eq` as a `PartialEq` might be deliberately irreflexive. | |
0731742a XL |
1780 | #[stable(feature = "rust1", since = "1.0.0")] |
1781 | impl<T: ?Sized + Eq> ArcEqIdent<T> for Arc<T> { | |
1782 | #[inline] | |
1783 | fn eq(&self, other: &Arc<T>) -> bool { | |
1784 | Arc::ptr_eq(self, other) || **self == **other | |
1785 | } | |
1786 | ||
1787 | #[inline] | |
1788 | fn ne(&self, other: &Arc<T>) -> bool { | |
1789 | !Arc::ptr_eq(self, other) && **self != **other | |
1790 | } | |
1791 | } | |
1792 | ||
85aaf69f | 1793 | #[stable(feature = "rust1", since = "1.0.0")] |
62682a34 | 1794 | impl<T: ?Sized + PartialEq> PartialEq for Arc<T> { |
c30ab7b3 | 1795 | /// Equality for two `Arc`s. |
1a4d82fc | 1796 | /// |
e74abb32 XL |
1797 | /// Two `Arc`s are equal if their inner values are equal, even if they are |
1798 | /// stored in different allocation. | |
1a4d82fc | 1799 | /// |
e74abb32 XL |
1800 | /// If `T` also implements `Eq` (implying reflexivity of equality), |
1801 | /// two `Arc`s that point to the same allocation are always equal. | |
0731742a | 1802 | /// |
1a4d82fc JJ |
1803 | /// # Examples |
1804 | /// | |
1805 | /// ``` | |
1806 | /// use std::sync::Arc; | |
1807 | /// | |
85aaf69f | 1808 | /// let five = Arc::new(5); |
1a4d82fc | 1809 | /// |
c30ab7b3 | 1810 | /// assert!(five == Arc::new(5)); |
1a4d82fc | 1811 | /// ``` |
0731742a | 1812 | #[inline] |
b039eaaf | 1813 | fn eq(&self, other: &Arc<T>) -> bool { |
0731742a | 1814 | ArcEqIdent::eq(self, other) |
b039eaaf | 1815 | } |
1a4d82fc | 1816 | |
c30ab7b3 | 1817 | /// Inequality for two `Arc`s. |
1a4d82fc | 1818 | /// |
c30ab7b3 | 1819 | /// Two `Arc`s are unequal if their inner values are unequal. |
1a4d82fc | 1820 | /// |
e74abb32 XL |
1821 | /// If `T` also implements `Eq` (implying reflexivity of equality), |
1822 | /// two `Arc`s that point to the same value are never unequal. | |
0731742a | 1823 | /// |
1a4d82fc JJ |
1824 | /// # Examples |
1825 | /// | |
1826 | /// ``` | |
1827 | /// use std::sync::Arc; | |
1828 | /// | |
85aaf69f | 1829 | /// let five = Arc::new(5); |
1a4d82fc | 1830 | /// |
c30ab7b3 | 1831 | /// assert!(five != Arc::new(6)); |
1a4d82fc | 1832 | /// ``` |
0731742a | 1833 | #[inline] |
b039eaaf | 1834 | fn ne(&self, other: &Arc<T>) -> bool { |
0731742a | 1835 | ArcEqIdent::ne(self, other) |
b039eaaf | 1836 | } |
1a4d82fc | 1837 | } |
0731742a | 1838 | |
85aaf69f | 1839 | #[stable(feature = "rust1", since = "1.0.0")] |
62682a34 | 1840 | impl<T: ?Sized + PartialOrd> PartialOrd for Arc<T> { |
c30ab7b3 | 1841 | /// Partial comparison for two `Arc`s. |
1a4d82fc JJ |
1842 | /// |
1843 | /// The two are compared by calling `partial_cmp()` on their inner values. | |
1844 | /// | |
1845 | /// # Examples | |
1846 | /// | |
1847 | /// ``` | |
1848 | /// use std::sync::Arc; | |
c30ab7b3 | 1849 | /// use std::cmp::Ordering; |
1a4d82fc | 1850 | /// |
85aaf69f | 1851 | /// let five = Arc::new(5); |
1a4d82fc | 1852 | /// |
c30ab7b3 | 1853 | /// assert_eq!(Some(Ordering::Less), five.partial_cmp(&Arc::new(6))); |
1a4d82fc JJ |
1854 | /// ``` |
1855 | fn partial_cmp(&self, other: &Arc<T>) -> Option<Ordering> { | |
1856 | (**self).partial_cmp(&**other) | |
1857 | } | |
1858 | ||
c30ab7b3 | 1859 | /// Less-than comparison for two `Arc`s. |
1a4d82fc JJ |
1860 | /// |
1861 | /// The two are compared by calling `<` on their inner values. | |
1862 | /// | |
1863 | /// # Examples | |
1864 | /// | |
1865 | /// ``` | |
1866 | /// use std::sync::Arc; | |
1867 | /// | |
85aaf69f | 1868 | /// let five = Arc::new(5); |
1a4d82fc | 1869 | /// |
c30ab7b3 | 1870 | /// assert!(five < Arc::new(6)); |
1a4d82fc | 1871 | /// ``` |
b039eaaf SL |
1872 | fn lt(&self, other: &Arc<T>) -> bool { |
1873 | *(*self) < *(*other) | |
1874 | } | |
1a4d82fc | 1875 | |
c30ab7b3 | 1876 | /// 'Less than or equal to' comparison for two `Arc`s. |
1a4d82fc JJ |
1877 | /// |
1878 | /// The two are compared by calling `<=` on their inner values. | |
1879 | /// | |
1880 | /// # Examples | |
1881 | /// | |
1882 | /// ``` | |
1883 | /// use std::sync::Arc; | |
1884 | /// | |
85aaf69f | 1885 | /// let five = Arc::new(5); |
1a4d82fc | 1886 | /// |
c30ab7b3 | 1887 | /// assert!(five <= Arc::new(5)); |
1a4d82fc | 1888 | /// ``` |
b039eaaf SL |
1889 | fn le(&self, other: &Arc<T>) -> bool { |
1890 | *(*self) <= *(*other) | |
1891 | } | |
1a4d82fc | 1892 | |
c30ab7b3 | 1893 | /// Greater-than comparison for two `Arc`s. |
1a4d82fc JJ |
1894 | /// |
1895 | /// The two are compared by calling `>` on their inner values. | |
1896 | /// | |
1897 | /// # Examples | |
1898 | /// | |
1899 | /// ``` | |
1900 | /// use std::sync::Arc; | |
1901 | /// | |
85aaf69f | 1902 | /// let five = Arc::new(5); |
1a4d82fc | 1903 | /// |
c30ab7b3 | 1904 | /// assert!(five > Arc::new(4)); |
1a4d82fc | 1905 | /// ``` |
b039eaaf SL |
1906 | fn gt(&self, other: &Arc<T>) -> bool { |
1907 | *(*self) > *(*other) | |
1908 | } | |
1a4d82fc | 1909 | |
c30ab7b3 | 1910 | /// 'Greater than or equal to' comparison for two `Arc`s. |
1a4d82fc JJ |
1911 | /// |
1912 | /// The two are compared by calling `>=` on their inner values. | |
1913 | /// | |
1914 | /// # Examples | |
1915 | /// | |
1916 | /// ``` | |
1917 | /// use std::sync::Arc; | |
1918 | /// | |
85aaf69f | 1919 | /// let five = Arc::new(5); |
1a4d82fc | 1920 | /// |
c30ab7b3 | 1921 | /// assert!(five >= Arc::new(5)); |
1a4d82fc | 1922 | /// ``` |
b039eaaf SL |
1923 | fn ge(&self, other: &Arc<T>) -> bool { |
1924 | *(*self) >= *(*other) | |
1925 | } | |
1a4d82fc | 1926 | } |
85aaf69f | 1927 | #[stable(feature = "rust1", since = "1.0.0")] |
62682a34 | 1928 | impl<T: ?Sized + Ord> Ord for Arc<T> { |
c30ab7b3 SL |
1929 | /// Comparison for two `Arc`s. |
1930 | /// | |
1931 | /// The two are compared by calling `cmp()` on their inner values. | |
1932 | /// | |
1933 | /// # Examples | |
1934 | /// | |
1935 | /// ``` | |
1936 | /// use std::sync::Arc; | |
1937 | /// use std::cmp::Ordering; | |
1938 | /// | |
1939 | /// let five = Arc::new(5); | |
1940 | /// | |
1941 | /// assert_eq!(Ordering::Less, five.cmp(&Arc::new(6))); | |
1942 | /// ``` | |
b039eaaf SL |
1943 | fn cmp(&self, other: &Arc<T>) -> Ordering { |
1944 | (**self).cmp(&**other) | |
1945 | } | |
1a4d82fc | 1946 | } |
85aaf69f | 1947 | #[stable(feature = "rust1", since = "1.0.0")] |
62682a34 | 1948 | impl<T: ?Sized + Eq> Eq for Arc<T> {} |
1a4d82fc | 1949 | |
85aaf69f | 1950 | #[stable(feature = "rust1", since = "1.0.0")] |
62682a34 | 1951 | impl<T: ?Sized + fmt::Display> fmt::Display for Arc<T> { |
9fa01778 | 1952 | fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
85aaf69f | 1953 | fmt::Display::fmt(&**self, f) |
1a4d82fc JJ |
1954 | } |
1955 | } | |
1956 | ||
85aaf69f | 1957 | #[stable(feature = "rust1", since = "1.0.0")] |
62682a34 | 1958 | impl<T: ?Sized + fmt::Debug> fmt::Debug for Arc<T> { |
9fa01778 | 1959 | fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
85aaf69f | 1960 | fmt::Debug::fmt(&**self, f) |
1a4d82fc JJ |
1961 | } |
1962 | } | |
1963 | ||
9346a6ac | 1964 | #[stable(feature = "rust1", since = "1.0.0")] |
7453a54e | 1965 | impl<T: ?Sized> fmt::Pointer for Arc<T> { |
9fa01778 | 1966 | fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
ff7c6d11 | 1967 | fmt::Pointer::fmt(&(&**self as *const T), f) |
9346a6ac AL |
1968 | } |
1969 | } | |
1970 | ||
85aaf69f | 1971 | #[stable(feature = "rust1", since = "1.0.0")] |
d9579d0f | 1972 | impl<T: Default> Default for Arc<T> { |
c30ab7b3 SL |
1973 | /// Creates a new `Arc<T>`, with the `Default` value for `T`. |
1974 | /// | |
1975 | /// # Examples | |
1976 | /// | |
1977 | /// ``` | |
1978 | /// use std::sync::Arc; | |
1979 | /// | |
1980 | /// let x: Arc<i32> = Default::default(); | |
1981 | /// assert_eq!(*x, 0); | |
1982 | /// ``` | |
b039eaaf SL |
1983 | fn default() -> Arc<T> { |
1984 | Arc::new(Default::default()) | |
1985 | } | |
1a4d82fc JJ |
1986 | } |
1987 | ||
85aaf69f | 1988 | #[stable(feature = "rust1", since = "1.0.0")] |
62682a34 | 1989 | impl<T: ?Sized + Hash> Hash for Arc<T> { |
85aaf69f SL |
1990 | fn hash<H: Hasher>(&self, state: &mut H) { |
1991 | (**self).hash(state) | |
1992 | } | |
1993 | } | |
1a4d82fc | 1994 | |
92a42be0 SL |
1995 | #[stable(feature = "from_for_ptrs", since = "1.6.0")] |
1996 | impl<T> From<T> for Arc<T> { | |
1997 | fn from(t: T) -> Self { | |
1998 | Arc::new(t) | |
1999 | } | |
2000 | } | |
2001 | ||
3b2f2976 | 2002 | #[stable(feature = "shared_from_slice", since = "1.21.0")] |
9fa01778 | 2003 | impl<T: Clone> From<&[T]> for Arc<[T]> { |
3b2f2976 XL |
2004 | #[inline] |
2005 | fn from(v: &[T]) -> Arc<[T]> { | |
2006 | <Self as ArcFromSlice<T>>::from_slice(v) | |
2007 | } | |
2008 | } | |
2009 | ||
2010 | #[stable(feature = "shared_from_slice", since = "1.21.0")] | |
9fa01778 | 2011 | impl From<&str> for Arc<str> { |
3b2f2976 XL |
2012 | #[inline] |
2013 | fn from(v: &str) -> Arc<str> { | |
ff7c6d11 XL |
2014 | let arc = Arc::<[u8]>::from(v.as_bytes()); |
2015 | unsafe { Arc::from_raw(Arc::into_raw(arc) as *const str) } | |
3b2f2976 XL |
2016 | } |
2017 | } | |
2018 | ||
2019 | #[stable(feature = "shared_from_slice", since = "1.21.0")] | |
2020 | impl From<String> for Arc<str> { | |
2021 | #[inline] | |
2022 | fn from(v: String) -> Arc<str> { | |
2023 | Arc::from(&v[..]) | |
2024 | } | |
2025 | } | |
2026 | ||
2027 | #[stable(feature = "shared_from_slice", since = "1.21.0")] | |
2028 | impl<T: ?Sized> From<Box<T>> for Arc<T> { | |
2029 | #[inline] | |
2030 | fn from(v: Box<T>) -> Arc<T> { | |
2031 | Arc::from_box(v) | |
2032 | } | |
2033 | } | |
2034 | ||
2035 | #[stable(feature = "shared_from_slice", since = "1.21.0")] | |
2036 | impl<T> From<Vec<T>> for Arc<[T]> { | |
2037 | #[inline] | |
2038 | fn from(mut v: Vec<T>) -> Arc<[T]> { | |
2039 | unsafe { | |
2040 | let arc = Arc::copy_from_slice(&v); | |
2041 | ||
2042 | // Allow the Vec to free its memory, but not destroy its contents | |
2043 | v.set_len(0); | |
2044 | ||
2045 | arc | |
2046 | } | |
2047 | } | |
2048 | } | |
2049 | ||
74b04a01 | 2050 | #[stable(feature = "boxed_slice_try_from", since = "1.43.0")] |
416331ca XL |
2051 | impl<T, const N: usize> TryFrom<Arc<[T]>> for Arc<[T; N]> |
2052 | where | |
2053 | [T; N]: LengthAtMost32, | |
2054 | { | |
2055 | type Error = Arc<[T]>; | |
1a4d82fc | 2056 | |
416331ca XL |
2057 | fn try_from(boxed_slice: Arc<[T]>) -> Result<Self, Self::Error> { |
2058 | if boxed_slice.len() == N { | |
2059 | Ok(unsafe { Arc::from_raw(Arc::into_raw(boxed_slice) as *mut [T; N]) }) | |
2060 | } else { | |
2061 | Err(boxed_slice) | |
3b2f2976 | 2062 | } |
3b2f2976 | 2063 | } |
416331ca | 2064 | } |
3b2f2976 | 2065 | |
416331ca XL |
2066 | #[stable(feature = "shared_from_iter", since = "1.37.0")] |
2067 | impl<T> iter::FromIterator<T> for Arc<[T]> { | |
2068 | /// Takes each element in the `Iterator` and collects it into an `Arc<[T]>`. | |
2069 | /// | |
2070 | /// # Performance characteristics | |
2071 | /// | |
2072 | /// ## The general case | |
2073 | /// | |
2074 | /// In the general case, collecting into `Arc<[T]>` is done by first | |
2075 | /// collecting into a `Vec<T>`. That is, when writing the following: | |
2076 | /// | |
2077 | /// ```rust | |
2078 | /// # use std::sync::Arc; | |
2079 | /// let evens: Arc<[u8]> = (0..10).filter(|&x| x % 2 == 0).collect(); | |
2080 | /// # assert_eq!(&*evens, &[0, 2, 4, 6, 8]); | |
2081 | /// ``` | |
2082 | /// | |
2083 | /// this behaves as if we wrote: | |
2084 | /// | |
2085 | /// ```rust | |
2086 | /// # use std::sync::Arc; | |
2087 | /// let evens: Arc<[u8]> = (0..10).filter(|&x| x % 2 == 0) | |
2088 | /// .collect::<Vec<_>>() // The first set of allocations happens here. | |
2089 | /// .into(); // A second allocation for `Arc<[T]>` happens here. | |
2090 | /// # assert_eq!(&*evens, &[0, 2, 4, 6, 8]); | |
2091 | /// ``` | |
2092 | /// | |
2093 | /// This will allocate as many times as needed for constructing the `Vec<T>` | |
2094 | /// and then it will allocate once for turning the `Vec<T>` into the `Arc<[T]>`. | |
2095 | /// | |
2096 | /// ## Iterators of known length | |
2097 | /// | |
2098 | /// When your `Iterator` implements `TrustedLen` and is of an exact size, | |
2099 | /// a single allocation will be made for the `Arc<[T]>`. For example: | |
2100 | /// | |
2101 | /// ```rust | |
2102 | /// # use std::sync::Arc; | |
2103 | /// let evens: Arc<[u8]> = (0..10).collect(); // Just a single allocation happens here. | |
2104 | /// # assert_eq!(&*evens, &*(0..10).collect::<Vec<_>>()); | |
2105 | /// ``` | |
2106 | fn from_iter<I: iter::IntoIterator<Item = T>>(iter: I) -> Self { | |
2107 | ArcFromIter::from_iter(iter.into_iter()) | |
3b2f2976 | 2108 | } |
416331ca | 2109 | } |
3b2f2976 | 2110 | |
416331ca XL |
2111 | /// Specialization trait used for collecting into `Arc<[T]>`. |
2112 | trait ArcFromIter<T, I> { | |
2113 | fn from_iter(iter: I) -> Self; | |
2114 | } | |
3b2f2976 | 2115 | |
416331ca XL |
2116 | impl<T, I: Iterator<Item = T>> ArcFromIter<T, I> for Arc<[T]> { |
2117 | default fn from_iter(iter: I) -> Self { | |
2118 | iter.collect::<Vec<T>>().into() | |
3b2f2976 | 2119 | } |
416331ca | 2120 | } |
3b2f2976 | 2121 | |
416331ca XL |
2122 | impl<T, I: iter::TrustedLen<Item = T>> ArcFromIter<T, I> for Arc<[T]> { |
2123 | default fn from_iter(iter: I) -> Self { | |
2124 | // This is the case for a `TrustedLen` iterator. | |
2125 | let (low, high) = iter.size_hint(); | |
2126 | if let Some(high) = high { | |
2127 | debug_assert_eq!( | |
dfeec247 XL |
2128 | low, |
2129 | high, | |
416331ca XL |
2130 | "TrustedLen iterator's size hint is not exact: {:?}", |
2131 | (low, high) | |
2132 | ); | |
3b2f2976 | 2133 | |
416331ca XL |
2134 | unsafe { |
2135 | // SAFETY: We need to ensure that the iterator has an exact length and we have. | |
2136 | Arc::from_iter_exact(iter, low) | |
3b2f2976 | 2137 | } |
416331ca XL |
2138 | } else { |
2139 | // Fall back to normal implementation. | |
2140 | iter.collect::<Vec<T>>().into() | |
3b2f2976 | 2141 | } |
3b2f2976 | 2142 | } |
416331ca | 2143 | } |
3b2f2976 | 2144 | |
416331ca XL |
2145 | impl<'a, T: 'a + Clone> ArcFromIter<&'a T, slice::Iter<'a, T>> for Arc<[T]> { |
2146 | fn from_iter(iter: slice::Iter<'a, T>) -> Self { | |
2147 | // Delegate to `impl<T: Clone> From<&[T]> for Arc<[T]>`. | |
2148 | // | |
2149 | // In the case that `T: Copy`, we get to use `ptr::copy_nonoverlapping` | |
2150 | // which is even more performant. | |
2151 | // | |
2152 | // In the fall-back case we have `T: Clone`. This is still better | |
2153 | // than the `TrustedLen` implementation as slices have a known length | |
2154 | // and so we get to avoid calling `size_hint` and avoid the branching. | |
2155 | iter.as_slice().into() | |
94b46f34 | 2156 | } |
1a4d82fc | 2157 | } |
e9174d1e | 2158 | |
92a42be0 | 2159 | #[stable(feature = "rust1", since = "1.0.0")] |
e9174d1e | 2160 | impl<T: ?Sized> borrow::Borrow<T> for Arc<T> { |
b039eaaf SL |
2161 | fn borrow(&self) -> &T { |
2162 | &**self | |
2163 | } | |
2164 | } | |
2165 | ||
2166 | #[stable(since = "1.5.0", feature = "smart_ptr_as_ref")] | |
2167 | impl<T: ?Sized> AsRef<T> for Arc<T> { | |
2168 | fn as_ref(&self) -> &T { | |
2169 | &**self | |
2170 | } | |
e9174d1e | 2171 | } |
b7449926 | 2172 | |
0731742a | 2173 | #[stable(feature = "pin", since = "1.33.0")] |
dfeec247 | 2174 | impl<T: ?Sized> Unpin for Arc<T> {} |
dc9dc135 | 2175 | |
416331ca | 2176 | /// Computes the offset of the data field within `ArcInner`. |
dc9dc135 | 2177 | unsafe fn data_offset<T: ?Sized>(ptr: *const T) -> isize { |
416331ca XL |
2178 | // Align the unsized value to the end of the `ArcInner`. |
2179 | // Because it is `?Sized`, it will always be the last field in memory. | |
dfeec247 XL |
2180 | // Note: This is a detail of the current implementation of the compiler, |
2181 | // and is not a guaranteed language detail. Do not rely on it outside of std. | |
416331ca | 2182 | data_offset_align(align_of_val(&*ptr)) |
dc9dc135 XL |
2183 | } |
2184 | ||
416331ca | 2185 | /// Computes the offset of the data field within `ArcInner`. |
dc9dc135 XL |
2186 | /// |
2187 | /// Unlike [`data_offset`], this doesn't need the pointer, but it works only on `T: Sized`. | |
2188 | fn data_offset_sized<T>() -> isize { | |
416331ca XL |
2189 | data_offset_align(align_of::<T>()) |
2190 | } | |
2191 | ||
2192 | #[inline] | |
2193 | fn data_offset_align(align: usize) -> isize { | |
dc9dc135 XL |
2194 | let layout = Layout::new::<ArcInner<()>>(); |
2195 | (layout.size() + layout.padding_needed_for(align)) as isize | |
2196 | } |