1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 #![stable(feature = "rust1", since = "1.0.0")]
13 //! Threadsafe reference-counted boxes (the `Arc<T>` type).
15 //! The `Arc<T>` type provides shared ownership of an immutable value.
16 //! Destruction is deterministic, and will occur as soon as the last owner is
17 //! gone. It is marked as `Send` because it uses atomic reference counting.
19 //! If you do not need thread-safety, and just need shared ownership, consider
20 //! the [`Rc<T>` type](../rc/struct.Rc.html). It is the same as `Arc<T>`, but
21 //! does not use atomics, making it both thread-unsafe as well as significantly
22 //! faster when updating the reference count.
24 //! The `downgrade` method can be used to create a non-owning `Weak<T>` pointer
25 //! to the box. A `Weak<T>` pointer can be upgraded to an `Arc<T>` pointer, but
26 //! will return `None` if the value has already been dropped.
28 //! For example, a tree with parent pointers can be represented by putting the
29 //! nodes behind strong `Arc<T>` pointers, and then storing the parent pointers
30 //! as `Weak<T>` pointers.
34 //! Sharing some immutable data between threads:
37 //! use std::sync::Arc;
40 //! let five = Arc::new(5);
43 //! let five = five.clone();
45 //! thread::spawn(move || {
46 //! println!("{:?}", five);
51 //! Sharing mutable data safely between threads with a `Mutex`:
54 //! use std::sync::{Arc, Mutex};
57 //! let five = Arc::new(Mutex::new(5));
60 //! let five = five.clone();
62 //! thread::spawn(move || {
63 //! let mut number = five.lock().unwrap();
67 //! println!("{}", *number); // prints 6
74 use core::sync::atomic;
75 use core::sync::atomic::Ordering::{Relaxed, Release, Acquire, SeqCst};
78 use core::cmp::Ordering;
79 use core::mem::{align_of_val, size_of_val};
80 use core::intrinsics::{drop_in_place, abort};
82 use core::nonzero::NonZero;
83 use core::ops::{Deref, CoerceUnsized};
85 use core::marker::Unsize;
86 use core::hash::{Hash, Hasher};
87 use core::{usize, isize};
90 const MAX_REFCOUNT: usize = (isize::MAX) as usize;
92 /// An atomically reference counted wrapper for shared state.
96 /// In this example, a large vector of floats is shared between several threads.
97 /// With simple pipes, without `Arc`, a copy would have to be made for each
100 /// When you clone an `Arc<T>`, it will create another pointer to the data and
101 /// increase the reference counter.
104 /// use std::sync::Arc;
108 /// let numbers: Vec<_> = (0..100u32).collect();
109 /// let shared_numbers = Arc::new(numbers);
112 /// let child_numbers = shared_numbers.clone();
114 /// thread::spawn(move || {
115 /// let local_numbers = &child_numbers[..];
117 /// // Work with the local numbers
122 #[unsafe_no_drop_flag]
123 #[stable(feature = "rust1", since = "1.0.0")]
124 pub struct Arc<T: ?Sized> {
125 // FIXME #12808: strange name to try to avoid interfering with
126 // field accesses of the contained type via Deref
127 _ptr: NonZero<*mut ArcInner<T>>,
130 unsafe impl<T: ?Sized + Sync + Send> Send for Arc<T> { }
131 unsafe impl<T: ?Sized + Sync + Send> Sync for Arc<T> { }
133 impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Arc<U>> for Arc<T> {}
135 /// A weak pointer to an `Arc`.
137 /// Weak pointers will not keep the data inside of the `Arc` alive, and can be
138 /// used to break cycles between `Arc` pointers.
139 #[unsafe_no_drop_flag]
140 #[unstable(feature = "arc_weak", reason = "needs FCP", issue = "27718")]
141 pub struct Weak<T: ?Sized> {
142 // FIXME #12808: strange name to try to avoid interfering with
143 // field accesses of the contained type via Deref
144 _ptr: NonZero<*mut ArcInner<T>>,
147 unsafe impl<T: ?Sized + Sync + Send> Send for Weak<T> { }
148 unsafe impl<T: ?Sized + Sync + Send> Sync for Weak<T> { }
150 impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Weak<U>> for Weak<T> {}
152 #[stable(feature = "rust1", since = "1.0.0")]
153 impl<T: ?Sized + fmt::Debug> fmt::Debug for Weak<T> {
154 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
159 struct ArcInner<T: ?Sized> {
160 strong: atomic::AtomicUsize,
162 // the value usize::MAX acts as a sentinel for temporarily "locking" the
163 // ability to upgrade weak pointers or downgrade strong ones; this is used
164 // to avoid races in `make_mut` and `get_mut`.
165 weak: atomic::AtomicUsize,
170 unsafe impl<T: ?Sized + Sync + Send> Send for ArcInner<T> {}
171 unsafe impl<T: ?Sized + Sync + Send> Sync for ArcInner<T> {}
174 /// Constructs a new `Arc<T>`.
179 /// use std::sync::Arc;
181 /// let five = Arc::new(5);
184 #[stable(feature = "rust1", since = "1.0.0")]
185 pub fn new(data: T) -> Arc<T> {
186 // Start the weak pointer count as 1 which is the weak pointer that's
187 // held by all the strong pointers (kinda), see std/rc.rs for more info
188 let x: Box<_> = box ArcInner {
189 strong: atomic::AtomicUsize::new(1),
190 weak: atomic::AtomicUsize::new(1),
193 Arc { _ptr: unsafe { NonZero::new(Box::into_raw(x)) } }
196 /// Unwraps the contained value if the `Arc<T>` has only one strong reference.
197 /// This will succeed even if there are outstanding weak references.
199 /// Otherwise, an `Err` is returned with the same `Arc<T>`.
204 /// #![feature(arc_unique)]
205 /// use std::sync::Arc;
207 /// let x = Arc::new(3);
208 /// assert_eq!(Arc::try_unwrap(x), Ok(3));
210 /// let x = Arc::new(4);
211 /// let _y = x.clone();
212 /// assert_eq!(Arc::try_unwrap(x), Err(Arc::new(4)));
215 #[unstable(feature = "arc_unique", reason = "needs FCP", issue = "27718")]
216 pub fn try_unwrap(this: Self) -> Result<T, Self> {
217 // See `drop` for why all these atomics are like this
218 if this.inner().strong.compare_and_swap(1, 0, Release) != 1 { return Err(this) }
220 atomic::fence(Acquire);
223 let ptr = *this._ptr;
224 let elem = ptr::read(&(*ptr).data);
226 // Make a weak pointer to clean up the implicit strong-weak reference
227 let _weak = Weak { _ptr: this._ptr };
235 impl<T: ?Sized> Arc<T> {
236 /// Downgrades the `Arc<T>` to a `Weak<T>` reference.
241 /// #![feature(arc_weak)]
242 /// use std::sync::Arc;
244 /// let five = Arc::new(5);
246 /// let weak_five = Arc::downgrade(&five);
248 #[unstable(feature = "arc_weak", reason = "needs FCP", issue = "27718")]
249 pub fn downgrade(this: &Self) -> Weak<T> {
251 // This Relaxed is OK because we're checking the value in the CAS
253 let cur = this.inner().weak.load(Relaxed);
255 // check if the weak counter is currently "locked"; if so, spin.
256 if cur == usize::MAX { continue }
258 // NOTE: this code currently ignores the possibility of overflow
259 // into usize::MAX; in general both Rc and Arc need to be adjusted
260 // to deal with overflow.
262 // Unlike with Clone(), we need this to be an Acquire read to
263 // synchronize with the write coming from `is_unique`, so that the
264 // events prior to that write happen before this read.
265 if this.inner().weak.compare_and_swap(cur, cur + 1, Acquire) == cur {
266 return Weak { _ptr: this._ptr }
271 /// Get the number of weak references to this value.
273 #[unstable(feature = "arc_counts", reason = "not clearly useful, and racy", issue = "27718")]
274 pub fn weak_count(this: &Self) -> usize {
275 this.inner().weak.load(SeqCst) - 1
278 /// Get the number of strong references to this value.
280 #[unstable(feature = "arc_counts", reason = "not clearly useful, and racy", issue = "27718")]
281 pub fn strong_count(this: &Self) -> usize {
282 this.inner().strong.load(SeqCst)
286 fn inner(&self) -> &ArcInner<T> {
287 // This unsafety is ok because while this arc is alive we're guaranteed
288 // that the inner pointer is valid. Furthermore, we know that the
289 // `ArcInner` structure itself is `Sync` because the inner data is
290 // `Sync` as well, so we're ok loaning out an immutable pointer to these
292 unsafe { &**self._ptr }
295 // Non-inlined part of `drop`.
297 unsafe fn drop_slow(&mut self) {
298 let ptr = *self._ptr;
300 // Destroy the data at this time, even though we may not free the box
301 // allocation itself (there may still be weak pointers lying around).
302 drop_in_place(&mut (*ptr).data);
304 if self.inner().weak.fetch_sub(1, Release) == 1 {
305 atomic::fence(Acquire);
306 deallocate(ptr as *mut u8, size_of_val(&*ptr), align_of_val(&*ptr))
311 #[stable(feature = "rust1", since = "1.0.0")]
312 impl<T: ?Sized> Clone for Arc<T> {
313 /// Makes a clone of the `Arc<T>`.
315 /// This increases the strong reference count.
320 /// use std::sync::Arc;
322 /// let five = Arc::new(5);
327 fn clone(&self) -> Arc<T> {
328 // Using a relaxed ordering is alright here, as knowledge of the
329 // original reference prevents other threads from erroneously deleting
332 // As explained in the [Boost documentation][1], Increasing the
333 // reference counter can always be done with memory_order_relaxed: New
334 // references to an object can only be formed from an existing
335 // reference, and passing an existing reference from one thread to
336 // another must already provide any required synchronization.
338 // [1]: (www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html)
339 let old_size = self.inner().strong.fetch_add(1, Relaxed);
341 // However we need to guard against massive refcounts in case someone
342 // is `mem::forget`ing Arcs. If we don't do this the count can overflow
343 // and users will use-after free. We racily saturate to `isize::MAX` on
344 // the assumption that there aren't ~2 billion threads incrementing
345 // the reference count at once. This branch will never be taken in
346 // any realistic program.
348 // We abort because such a program is incredibly degenerate, and we
349 // don't care to support it.
350 if old_size > MAX_REFCOUNT {
354 Arc { _ptr: self._ptr }
358 #[stable(feature = "rust1", since = "1.0.0")]
359 impl<T: ?Sized> Deref for Arc<T> {
363 fn deref(&self) -> &T {
368 impl<T: Clone> Arc<T> {
369 #[unstable(feature = "arc_unique", reason = "renamed to Arc::make_mut", issue = "27718")]
370 #[deprecated(since = "1.4.0", reason = "renamed to Arc::make_mut")]
371 pub fn make_unique(this: &mut Self) -> &mut T {
375 /// Make a mutable reference into the given `Arc<T>` by cloning the inner
376 /// data if the `Arc<T>` doesn't have one strong reference and no weak
379 /// This is also referred to as a copy-on-write.
384 /// #![feature(arc_unique)]
385 /// use std::sync::Arc;
387 /// let mut data = Arc::new(5);
389 /// *Arc::make_mut(&mut data) += 1; // Won't clone anything
390 /// let mut other_data = data.clone(); // Won't clone inner data
391 /// *Arc::make_mut(&mut data) += 1; // Clones inner data
392 /// *Arc::make_mut(&mut data) += 1; // Won't clone anything
393 /// *Arc::make_mut(&mut other_data) *= 2; // Won't clone anything
395 /// // Note: data and other_data now point to different numbers
396 /// assert_eq!(*data, 8);
397 /// assert_eq!(*other_data, 12);
401 #[unstable(feature = "arc_unique", reason = "needs FCP", issue = "27718")]
402 pub fn make_mut(this: &mut Self) -> &mut T {
403 // Note that we hold both a strong reference and a weak reference.
404 // Thus, releasing our strong reference only will not, by itself, cause
405 // the memory to be deallocated.
407 // Use Acquire to ensure that we see any writes to `weak` that happen
408 // before release writes (i.e., decrements) to `strong`. Since we hold a
409 // weak count, there's no chance the ArcInner itself could be
411 if this.inner().strong.compare_and_swap(1, 0, Acquire) != 1 {
412 // Another srong pointer exists; clone
413 *this = Arc::new((**this).clone());
414 } else if this.inner().weak.load(Relaxed) != 1 {
415 // Relaxed suffices in the above because this is fundamentally an
416 // optimization: we are always racing with weak pointers being
417 // dropped. Worst case, we end up allocated a new Arc unnecessarily.
419 // We removed the last strong ref, but there are additional weak
420 // refs remaining. We'll move the contents to a new Arc, and
421 // invalidate the other weak refs.
423 // Note that it is not possible for the read of `weak` to yield
424 // usize::MAX (i.e., locked), since the weak count can only be
425 // locked by a thread with a strong reference.
427 // Materialize our own implicit weak pointer, so that it can clean
428 // up the ArcInner as needed.
429 let weak = Weak { _ptr: this._ptr };
431 // mark the data itself as already deallocated
433 // there is no data race in the implicit write caused by `read`
434 // here (due to zeroing) because data is no longer accessed by
435 // other threads (due to there being no more strong refs at this
437 let mut swap = Arc::new(ptr::read(&(**weak._ptr).data));
438 mem::swap(this, &mut swap);
442 // We were the sole reference of either kind; bump back up the
444 this.inner().strong.store(1, Release);
447 // As with `get_mut()`, the unsafety is ok because our reference was
448 // either unique to begin with, or became one upon cloning the contents.
450 let inner = &mut **this._ptr;
456 impl<T: ?Sized> Arc<T> {
457 /// Returns a mutable reference to the contained value if the `Arc<T>` has
458 /// one strong reference and no weak references.
463 /// #![feature(arc_unique)]
464 /// use std::sync::Arc;
466 /// let mut x = Arc::new(3);
467 /// *Arc::get_mut(&mut x).unwrap() = 4;
468 /// assert_eq!(*x, 4);
470 /// let _y = x.clone();
471 /// assert!(Arc::get_mut(&mut x).is_none());
474 #[unstable(feature = "arc_unique", reason = "needs FCP", issue = "27718")]
475 pub fn get_mut(this: &mut Self) -> Option<&mut T> {
476 if this.is_unique() {
477 // This unsafety is ok because we're guaranteed that the pointer
478 // returned is the *only* pointer that will ever be returned to T. Our
479 // reference count is guaranteed to be 1 at this point, and we required
480 // the Arc itself to be `mut`, so we're returning the only possible
481 // reference to the inner data.
483 let inner = &mut **this._ptr;
484 Some(&mut inner.data)
491 /// Determine whether this is the unique reference (including weak refs) to
492 /// the underlying data.
494 /// Note that this requires locking the weak ref count.
495 fn is_unique(&mut self) -> bool {
496 // lock the weak pointer count if we appear to be the sole weak pointer
499 // The acquire label here ensures a happens-before relationship with any
500 // writes to `strong` prior to decrements of the `weak` count (via drop,
501 // which uses Release).
502 if self.inner().weak.compare_and_swap(1, usize::MAX, Acquire) == 1 {
503 // Due to the previous acquire read, this will observe any writes to
504 // `strong` that were due to upgrading weak pointers; only strong
505 // clones remain, which require that the strong count is > 1 anyway.
506 let unique = self.inner().strong.load(Relaxed) == 1;
508 // The release write here synchronizes with a read in `downgrade`,
509 // effectively preventing the above read of `strong` from happening
511 self.inner().weak.store(1, Release); // release the lock
519 #[stable(feature = "rust1", since = "1.0.0")]
520 impl<T: ?Sized> Drop for Arc<T> {
521 /// Drops the `Arc<T>`.
523 /// This will decrement the strong reference count. If the strong reference
524 /// count becomes zero and the only other references are `Weak<T>` ones,
525 /// `drop`s the inner value.
530 /// use std::sync::Arc;
533 /// let five = Arc::new(5);
537 /// drop(five); // explicit drop
540 /// let five = Arc::new(5);
544 /// } // implicit drop
548 // This structure has #[unsafe_no_drop_flag], so this drop glue may run
549 // more than once (but it is guaranteed to be zeroed after the first if
550 // it's run more than once)
551 let ptr = *self._ptr;
552 // if ptr.is_null() { return }
553 if ptr as *mut u8 as usize == 0 || ptr as *mut u8 as usize == mem::POST_DROP_USIZE {
557 // Because `fetch_sub` is already atomic, we do not need to synchronize
558 // with other threads unless we are going to delete the object. This
559 // same logic applies to the below `fetch_sub` to the `weak` count.
560 if self.inner().strong.fetch_sub(1, Release) != 1 { return }
562 // This fence is needed to prevent reordering of use of the data and
563 // deletion of the data. Because it is marked `Release`, the decreasing
564 // of the reference count synchronizes with this `Acquire` fence. This
565 // means that use of the data happens before decreasing the reference
566 // count, which happens before this fence, which happens before the
567 // deletion of the data.
569 // As explained in the [Boost documentation][1],
571 // > It is important to enforce any possible access to the object in one
572 // > thread (through an existing reference) to *happen before* deleting
573 // > the object in a different thread. This is achieved by a "release"
574 // > operation after dropping a reference (any access to the object
575 // > through this reference must obviously happened before), and an
576 // > "acquire" operation before deleting the object.
578 // [1]: (www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html)
579 atomic::fence(Acquire);
587 impl<T: ?Sized> Weak<T> {
588 /// Upgrades a weak reference to a strong reference.
590 /// Upgrades the `Weak<T>` reference to an `Arc<T>`, if possible.
592 /// Returns `None` if there were no strong references and the data was
598 /// #![feature(arc_weak)]
599 /// use std::sync::Arc;
601 /// let five = Arc::new(5);
603 /// let weak_five = Arc::downgrade(&five);
605 /// let strong_five: Option<Arc<_>> = weak_five.upgrade();
607 #[unstable(feature = "arc_weak", reason = "needs FCP", issue = "27718")]
608 pub fn upgrade(&self) -> Option<Arc<T>> {
609 // We use a CAS loop to increment the strong count instead of a
610 // fetch_add because once the count hits 0 it must never be above 0.
611 let inner = self.inner();
613 // Relaxed load because any write of 0 that we can observe
614 // leaves the field in a permanently zero state (so a
615 // "stale" read of 0 is fine), and any other value is
616 // confirmed via the CAS below.
617 let n = inner.strong.load(Relaxed);
618 if n == 0 { return None }
620 // Relaxed is valid for the same reason it is on Arc's Clone impl
621 let old = inner.strong.compare_and_swap(n, n + 1, Relaxed);
622 if old == n { return Some(Arc { _ptr: self._ptr }) }
627 fn inner(&self) -> &ArcInner<T> {
628 // See comments above for why this is "safe"
629 unsafe { &**self._ptr }
633 #[unstable(feature = "arc_weak", reason = "needs FCP", issue = "27718")]
634 impl<T: ?Sized> Clone for Weak<T> {
635 /// Makes a clone of the `Weak<T>`.
637 /// This increases the weak reference count.
642 /// #![feature(arc_weak)]
643 /// use std::sync::Arc;
645 /// let weak_five = Arc::downgrade(&Arc::new(5));
647 /// weak_five.clone();
650 fn clone(&self) -> Weak<T> {
651 // See comments in Arc::clone() for why this is relaxed. This can use a
652 // fetch_add (ignoring the lock) because the weak count is only locked
653 // where are *no other* weak pointers in existence. (So we can't be
654 // running this code in that case).
655 let old_size = self.inner().weak.fetch_add(1, Relaxed);
657 // See comments in Arc::clone() for why we do this (for mem::forget).
658 if old_size > MAX_REFCOUNT {
662 return Weak { _ptr: self._ptr }
666 #[stable(feature = "rust1", since = "1.0.0")]
667 impl<T: ?Sized> Drop for Weak<T> {
668 /// Drops the `Weak<T>`.
670 /// This will decrement the weak reference count.
675 /// #![feature(arc_weak)]
676 /// use std::sync::Arc;
679 /// let five = Arc::new(5);
680 /// let weak_five = Arc::downgrade(&five);
684 /// drop(weak_five); // explicit drop
687 /// let five = Arc::new(5);
688 /// let weak_five = Arc::downgrade(&five);
692 /// } // implicit drop
695 let ptr = *self._ptr;
697 // see comments above for why this check is here
698 if ptr as *mut u8 as usize == 0 || ptr as *mut u8 as usize == mem::POST_DROP_USIZE {
702 // If we find out that we were the last weak pointer, then its time to
703 // deallocate the data entirely. See the discussion in Arc::drop() about
704 // the memory orderings
706 // It's not necessary to check for the locked state here, because the
707 // weak count can only be locked if there was precisely one weak ref,
708 // meaning that drop could only subsequently run ON that remaining weak
709 // ref, which can only happen after the lock is released.
710 if self.inner().weak.fetch_sub(1, Release) == 1 {
711 atomic::fence(Acquire);
712 unsafe { deallocate(ptr as *mut u8,
714 align_of_val(&*ptr)) }
719 #[stable(feature = "rust1", since = "1.0.0")]
720 impl<T: ?Sized + PartialEq> PartialEq for Arc<T> {
721 /// Equality for two `Arc<T>`s.
723 /// Two `Arc<T>`s are equal if their inner value are equal.
728 /// use std::sync::Arc;
730 /// let five = Arc::new(5);
732 /// five == Arc::new(5);
734 fn eq(&self, other: &Arc<T>) -> bool { *(*self) == *(*other) }
736 /// Inequality for two `Arc<T>`s.
738 /// Two `Arc<T>`s are unequal if their inner value are unequal.
743 /// use std::sync::Arc;
745 /// let five = Arc::new(5);
747 /// five != Arc::new(5);
749 fn ne(&self, other: &Arc<T>) -> bool { *(*self) != *(*other) }
751 #[stable(feature = "rust1", since = "1.0.0")]
752 impl<T: ?Sized + PartialOrd> PartialOrd for Arc<T> {
753 /// Partial comparison for two `Arc<T>`s.
755 /// The two are compared by calling `partial_cmp()` on their inner values.
760 /// use std::sync::Arc;
762 /// let five = Arc::new(5);
764 /// five.partial_cmp(&Arc::new(5));
766 fn partial_cmp(&self, other: &Arc<T>) -> Option<Ordering> {
767 (**self).partial_cmp(&**other)
770 /// Less-than comparison for two `Arc<T>`s.
772 /// The two are compared by calling `<` on their inner values.
777 /// use std::sync::Arc;
779 /// let five = Arc::new(5);
781 /// five < Arc::new(5);
783 fn lt(&self, other: &Arc<T>) -> bool { *(*self) < *(*other) }
785 /// 'Less-than or equal to' comparison for two `Arc<T>`s.
787 /// The two are compared by calling `<=` on their inner values.
792 /// use std::sync::Arc;
794 /// let five = Arc::new(5);
796 /// five <= Arc::new(5);
798 fn le(&self, other: &Arc<T>) -> bool { *(*self) <= *(*other) }
800 /// Greater-than comparison for two `Arc<T>`s.
802 /// The two are compared by calling `>` on their inner values.
807 /// use std::sync::Arc;
809 /// let five = Arc::new(5);
811 /// five > Arc::new(5);
813 fn gt(&self, other: &Arc<T>) -> bool { *(*self) > *(*other) }
815 /// 'Greater-than or equal to' comparison for two `Arc<T>`s.
817 /// The two are compared by calling `>=` on their inner values.
822 /// use std::sync::Arc;
824 /// let five = Arc::new(5);
826 /// five >= Arc::new(5);
828 fn ge(&self, other: &Arc<T>) -> bool { *(*self) >= *(*other) }
830 #[stable(feature = "rust1", since = "1.0.0")]
831 impl<T: ?Sized + Ord> Ord for Arc<T> {
832 fn cmp(&self, other: &Arc<T>) -> Ordering { (**self).cmp(&**other) }
834 #[stable(feature = "rust1", since = "1.0.0")]
835 impl<T: ?Sized + Eq> Eq for Arc<T> {}
837 #[stable(feature = "rust1", since = "1.0.0")]
838 impl<T: ?Sized + fmt::Display> fmt::Display for Arc<T> {
839 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
840 fmt::Display::fmt(&**self, f)
844 #[stable(feature = "rust1", since = "1.0.0")]
845 impl<T: ?Sized + fmt::Debug> fmt::Debug for Arc<T> {
846 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
847 fmt::Debug::fmt(&**self, f)
851 #[stable(feature = "rust1", since = "1.0.0")]
852 impl<T> fmt::Pointer for Arc<T> {
853 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
854 fmt::Pointer::fmt(&*self._ptr, f)
858 #[stable(feature = "rust1", since = "1.0.0")]
859 impl<T: Default> Default for Arc<T> {
860 #[stable(feature = "rust1", since = "1.0.0")]
861 fn default() -> Arc<T> { Arc::new(Default::default()) }
864 #[stable(feature = "rust1", since = "1.0.0")]
865 impl<T: ?Sized + Hash> Hash for Arc<T> {
866 fn hash<H: Hasher>(&self, state: &mut H) {
873 use std::clone::Clone;
874 use std::sync::mpsc::channel;
877 use std::option::Option;
878 use std::option::Option::{Some, None};
879 use std::sync::atomic;
880 use std::sync::atomic::Ordering::{Acquire, SeqCst};
883 use super::{Arc, Weak};
884 use std::sync::Mutex;
886 struct Canary(*mut atomic::AtomicUsize);
894 (*c).fetch_add(1, SeqCst);
902 fn manually_share_arc() {
903 let v = vec!(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
904 let arc_v = Arc::new(v);
906 let (tx, rx) = channel();
908 let _t = thread::spawn(move || {
909 let arc_v: Arc<Vec<i32>> = rx.recv().unwrap();
910 assert_eq!((*arc_v)[3], 4);
913 tx.send(arc_v.clone()).unwrap();
915 assert_eq!((*arc_v)[2], 3);
916 assert_eq!((*arc_v)[4], 5);
920 fn test_arc_get_mut() {
921 let mut x = Arc::new(3);
922 *Arc::get_mut(&mut x).unwrap() = 4;
925 assert!(Arc::get_mut(&mut x).is_none());
927 assert!(Arc::get_mut(&mut x).is_some());
928 let _w = Arc::downgrade(&x);
929 assert!(Arc::get_mut(&mut x).is_none());
935 assert_eq!(Arc::try_unwrap(x), Ok(3));
938 assert_eq!(Arc::try_unwrap(x), Err(Arc::new(4)));
940 let _w = Arc::downgrade(&x);
941 assert_eq!(Arc::try_unwrap(x), Ok(5));
945 fn test_cowarc_clone_make_mut() {
946 let mut cow0 = Arc::new(75);
947 let mut cow1 = cow0.clone();
948 let mut cow2 = cow1.clone();
950 assert!(75 == *Arc::make_mut(&mut cow0));
951 assert!(75 == *Arc::make_mut(&mut cow1));
952 assert!(75 == *Arc::make_mut(&mut cow2));
954 *Arc::make_mut(&mut cow0) += 1;
955 *Arc::make_mut(&mut cow1) += 2;
956 *Arc::make_mut(&mut cow2) += 3;
958 assert!(76 == *cow0);
959 assert!(77 == *cow1);
960 assert!(78 == *cow2);
962 // none should point to the same backing memory
963 assert!(*cow0 != *cow1);
964 assert!(*cow0 != *cow2);
965 assert!(*cow1 != *cow2);
969 fn test_cowarc_clone_unique2() {
970 let mut cow0 = Arc::new(75);
971 let cow1 = cow0.clone();
972 let cow2 = cow1.clone();
974 assert!(75 == *cow0);
975 assert!(75 == *cow1);
976 assert!(75 == *cow2);
978 *Arc::make_mut(&mut cow0) += 1;
979 assert!(76 == *cow0);
980 assert!(75 == *cow1);
981 assert!(75 == *cow2);
983 // cow1 and cow2 should share the same contents
984 // cow0 should have a unique reference
985 assert!(*cow0 != *cow1);
986 assert!(*cow0 != *cow2);
987 assert!(*cow1 == *cow2);
991 fn test_cowarc_clone_weak() {
992 let mut cow0 = Arc::new(75);
993 let cow1_weak = Arc::downgrade(&cow0);
995 assert!(75 == *cow0);
996 assert!(75 == *cow1_weak.upgrade().unwrap());
998 *Arc::make_mut(&mut cow0) += 1;
1000 assert!(76 == *cow0);
1001 assert!(cow1_weak.upgrade().is_none());
1006 let x = Arc::new(5);
1007 let y = Arc::downgrade(&x);
1008 assert!(y.upgrade().is_some());
1013 let x = Arc::new(5);
1014 let y = Arc::downgrade(&x);
1016 assert!(y.upgrade().is_none());
1020 fn weak_self_cyclic() {
1022 x: Mutex<Option<Weak<Cycle>>>
1025 let a = Arc::new(Cycle { x: Mutex::new(None) });
1026 let b = Arc::downgrade(&a.clone());
1027 *a.x.lock().unwrap() = Some(b);
1029 // hopefully we don't double-free (or leak)...
1034 let mut canary = atomic::AtomicUsize::new(0);
1035 let x = Arc::new(Canary(&mut canary as *mut atomic::AtomicUsize));
1037 assert!(canary.load(Acquire) == 1);
1041 fn drop_arc_weak() {
1042 let mut canary = atomic::AtomicUsize::new(0);
1043 let arc = Arc::new(Canary(&mut canary as *mut atomic::AtomicUsize));
1044 let arc_weak = Arc::downgrade(&arc);
1045 assert!(canary.load(Acquire) == 0);
1047 assert!(canary.load(Acquire) == 1);
1052 fn test_strong_count() {
1053 let a = Arc::new(0u32);
1054 assert!(Arc::strong_count(&a) == 1);
1055 let w = Arc::downgrade(&a);
1056 assert!(Arc::strong_count(&a) == 1);
1057 let b = w.upgrade().expect("");
1058 assert!(Arc::strong_count(&b) == 2);
1059 assert!(Arc::strong_count(&a) == 2);
1062 assert!(Arc::strong_count(&b) == 1);
1064 assert!(Arc::strong_count(&b) == 2);
1065 assert!(Arc::strong_count(&c) == 2);
1069 fn test_weak_count() {
1070 let a = Arc::new(0u32);
1071 assert!(Arc::strong_count(&a) == 1);
1072 assert!(Arc::weak_count(&a) == 0);
1073 let w = Arc::downgrade(&a);
1074 assert!(Arc::strong_count(&a) == 1);
1075 assert!(Arc::weak_count(&a) == 1);
1077 assert!(Arc::weak_count(&a) == 2);
1080 assert!(Arc::strong_count(&a) == 1);
1081 assert!(Arc::weak_count(&a) == 0);
1083 assert!(Arc::strong_count(&a) == 2);
1084 assert!(Arc::weak_count(&a) == 0);
1085 let d = Arc::downgrade(&c);
1086 assert!(Arc::weak_count(&c) == 1);
1087 assert!(Arc::strong_count(&c) == 2);
1096 let a = Arc::new(5u32);
1097 assert_eq!(format!("{:?}", a), "5");
1100 // Make sure deriving works with Arc<T>
1101 #[derive(Eq, Ord, PartialEq, PartialOrd, Clone, Debug, Default)]
1102 struct Foo { inner: Arc<i32> }
1106 let x: Arc<[i32]> = Arc::new([1, 2, 3]);
1107 assert_eq!(format!("{:?}", x), "[1, 2, 3]");
1108 let y = Arc::downgrade(&x.clone());
1110 assert!(y.upgrade().is_none());
1114 impl<T: ?Sized> borrow::Borrow<T> for Arc<T> {
1115 fn borrow(&self) -> &T { &**self }