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 #[stable(feature = "arc_weak", since = "1.4.0")]
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 /// use std::sync::Arc;
206 /// let x = Arc::new(3);
207 /// assert_eq!(Arc::try_unwrap(x), Ok(3));
209 /// let x = Arc::new(4);
210 /// let _y = x.clone();
211 /// assert_eq!(Arc::try_unwrap(x), Err(Arc::new(4)));
214 #[stable(feature = "arc_unique", since = "1.4.0")]
215 pub fn try_unwrap(this: Self) -> Result<T, Self> {
216 // See `drop` for why all these atomics are like this
217 if this.inner().strong.compare_and_swap(1, 0, Release) != 1 {
221 atomic::fence(Acquire);
224 let ptr = *this._ptr;
225 let elem = ptr::read(&(*ptr).data);
227 // Make a weak pointer to clean up the implicit strong-weak reference
228 let _weak = Weak { _ptr: this._ptr };
236 impl<T: ?Sized> Arc<T> {
237 /// Downgrades the `Arc<T>` to a `Weak<T>` reference.
242 /// use std::sync::Arc;
244 /// let five = Arc::new(5);
246 /// let weak_five = Arc::downgrade(&five);
248 #[stable(feature = "arc_weak", since = "1.4.0")]
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 {
260 // NOTE: this code currently ignores the possibility of overflow
261 // into usize::MAX; in general both Rc and Arc need to be adjusted
262 // to deal with overflow.
264 // Unlike with Clone(), we need this to be an Acquire read to
265 // synchronize with the write coming from `is_unique`, so that the
266 // events prior to that write happen before this read.
267 if this.inner().weak.compare_and_swap(cur, cur + 1, Acquire) == cur {
268 return Weak { _ptr: this._ptr }
273 /// Get the number of weak references to this value.
275 #[unstable(feature = "arc_counts", reason = "not clearly useful, and racy",
277 pub fn weak_count(this: &Self) -> usize {
278 this.inner().weak.load(SeqCst) - 1
281 /// Get the number of strong references to this value.
283 #[unstable(feature = "arc_counts", reason = "not clearly useful, and racy",
285 pub fn strong_count(this: &Self) -> usize {
286 this.inner().strong.load(SeqCst)
290 fn inner(&self) -> &ArcInner<T> {
291 // This unsafety is ok because while this arc is alive we're guaranteed
292 // that the inner pointer is valid. Furthermore, we know that the
293 // `ArcInner` structure itself is `Sync` because the inner data is
294 // `Sync` as well, so we're ok loaning out an immutable pointer to these
296 unsafe { &**self._ptr }
299 // Non-inlined part of `drop`.
301 unsafe fn drop_slow(&mut self) {
302 let ptr = *self._ptr;
304 // Destroy the data at this time, even though we may not free the box
305 // allocation itself (there may still be weak pointers lying around).
306 drop_in_place(&mut (*ptr).data);
308 if self.inner().weak.fetch_sub(1, Release) == 1 {
309 atomic::fence(Acquire);
310 deallocate(ptr as *mut u8,
317 #[stable(feature = "rust1", since = "1.0.0")]
318 impl<T: ?Sized> Clone for Arc<T> {
319 /// Makes a clone of the `Arc<T>`.
321 /// This increases the strong reference count.
326 /// use std::sync::Arc;
328 /// let five = Arc::new(5);
333 fn clone(&self) -> Arc<T> {
334 // Using a relaxed ordering is alright here, as knowledge of the
335 // original reference prevents other threads from erroneously deleting
338 // As explained in the [Boost documentation][1], Increasing the
339 // reference counter can always be done with memory_order_relaxed: New
340 // references to an object can only be formed from an existing
341 // reference, and passing an existing reference from one thread to
342 // another must already provide any required synchronization.
344 // [1]: (www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html)
345 let old_size = self.inner().strong.fetch_add(1, Relaxed);
347 // However we need to guard against massive refcounts in case someone
348 // is `mem::forget`ing Arcs. If we don't do this the count can overflow
349 // and users will use-after free. We racily saturate to `isize::MAX` on
350 // the assumption that there aren't ~2 billion threads incrementing
351 // the reference count at once. This branch will never be taken in
352 // any realistic program.
354 // We abort because such a program is incredibly degenerate, and we
355 // don't care to support it.
356 if old_size > MAX_REFCOUNT {
362 Arc { _ptr: self._ptr }
366 #[stable(feature = "rust1", since = "1.0.0")]
367 impl<T: ?Sized> Deref for Arc<T> {
371 fn deref(&self) -> &T {
376 impl<T: Clone> Arc<T> {
377 #[unstable(feature = "arc_make_unique", reason = "renamed to Arc::make_mut",
379 #[deprecated(since = "1.4.0", reason = "renamed to Arc::make_mut")]
380 pub fn make_unique(this: &mut Self) -> &mut T {
384 /// Make a mutable reference into the given `Arc<T>` by cloning the inner
385 /// data if the `Arc<T>` doesn't have one strong reference and no weak
388 /// This is also referred to as a copy-on-write.
393 /// use std::sync::Arc;
395 /// let mut data = Arc::new(5);
397 /// *Arc::make_mut(&mut data) += 1; // Won't clone anything
398 /// let mut other_data = data.clone(); // Won't clone inner data
399 /// *Arc::make_mut(&mut data) += 1; // Clones inner data
400 /// *Arc::make_mut(&mut data) += 1; // Won't clone anything
401 /// *Arc::make_mut(&mut other_data) *= 2; // Won't clone anything
403 /// // Note: data and other_data now point to different numbers
404 /// assert_eq!(*data, 8);
405 /// assert_eq!(*other_data, 12);
409 #[stable(feature = "arc_unique", since = "1.4.0")]
410 pub fn make_mut(this: &mut Self) -> &mut T {
411 // Note that we hold both a strong reference and a weak reference.
412 // Thus, releasing our strong reference only will not, by itself, cause
413 // the memory to be deallocated.
415 // Use Acquire to ensure that we see any writes to `weak` that happen
416 // before release writes (i.e., decrements) to `strong`. Since we hold a
417 // weak count, there's no chance the ArcInner itself could be
419 if this.inner().strong.compare_and_swap(1, 0, Acquire) != 1 {
420 // Another srong pointer exists; clone
421 *this = Arc::new((**this).clone());
422 } else if this.inner().weak.load(Relaxed) != 1 {
423 // Relaxed suffices in the above because this is fundamentally an
424 // optimization: we are always racing with weak pointers being
425 // dropped. Worst case, we end up allocated a new Arc unnecessarily.
427 // We removed the last strong ref, but there are additional weak
428 // refs remaining. We'll move the contents to a new Arc, and
429 // invalidate the other weak refs.
431 // Note that it is not possible for the read of `weak` to yield
432 // usize::MAX (i.e., locked), since the weak count can only be
433 // locked by a thread with a strong reference.
435 // Materialize our own implicit weak pointer, so that it can clean
436 // up the ArcInner as needed.
437 let weak = Weak { _ptr: this._ptr };
439 // mark the data itself as already deallocated
441 // there is no data race in the implicit write caused by `read`
442 // here (due to zeroing) because data is no longer accessed by
443 // other threads (due to there being no more strong refs at this
445 let mut swap = Arc::new(ptr::read(&(**weak._ptr).data));
446 mem::swap(this, &mut swap);
450 // We were the sole reference of either kind; bump back up the
452 this.inner().strong.store(1, Release);
455 // As with `get_mut()`, the unsafety is ok because our reference was
456 // either unique to begin with, or became one upon cloning the contents.
458 let inner = &mut **this._ptr;
464 impl<T: ?Sized> Arc<T> {
465 /// Returns a mutable reference to the contained value if the `Arc<T>` has
466 /// one strong reference and no weak references.
471 /// use std::sync::Arc;
473 /// let mut x = Arc::new(3);
474 /// *Arc::get_mut(&mut x).unwrap() = 4;
475 /// assert_eq!(*x, 4);
477 /// let _y = x.clone();
478 /// assert!(Arc::get_mut(&mut x).is_none());
481 #[stable(feature = "arc_unique", since = "1.4.0")]
482 pub fn get_mut(this: &mut Self) -> Option<&mut T> {
483 if this.is_unique() {
484 // This unsafety is ok because we're guaranteed that the pointer
485 // returned is the *only* pointer that will ever be returned to T. Our
486 // reference count is guaranteed to be 1 at this point, and we required
487 // the Arc itself to be `mut`, so we're returning the only possible
488 // reference to the inner data.
490 let inner = &mut **this._ptr;
491 Some(&mut inner.data)
498 /// Determine whether this is the unique reference (including weak refs) to
499 /// the underlying data.
501 /// Note that this requires locking the weak ref count.
502 fn is_unique(&mut self) -> bool {
503 // lock the weak pointer count if we appear to be the sole weak pointer
506 // The acquire label here ensures a happens-before relationship with any
507 // writes to `strong` prior to decrements of the `weak` count (via drop,
508 // which uses Release).
509 if self.inner().weak.compare_and_swap(1, usize::MAX, Acquire) == 1 {
510 // Due to the previous acquire read, this will observe any writes to
511 // `strong` that were due to upgrading weak pointers; only strong
512 // clones remain, which require that the strong count is > 1 anyway.
513 let unique = self.inner().strong.load(Relaxed) == 1;
515 // The release write here synchronizes with a read in `downgrade`,
516 // effectively preventing the above read of `strong` from happening
518 self.inner().weak.store(1, Release); // release the lock
526 #[stable(feature = "rust1", since = "1.0.0")]
527 impl<T: ?Sized> Drop for Arc<T> {
528 /// Drops the `Arc<T>`.
530 /// This will decrement the strong reference count. If the strong reference
531 /// count becomes zero and the only other references are `Weak<T>` ones,
532 /// `drop`s the inner value.
537 /// use std::sync::Arc;
540 /// let five = Arc::new(5);
544 /// drop(five); // explicit drop
547 /// let five = Arc::new(5);
551 /// } // implicit drop
555 // This structure has #[unsafe_no_drop_flag], so this drop glue may run
556 // more than once (but it is guaranteed to be zeroed after the first if
557 // it's run more than once)
558 let ptr = *self._ptr;
559 // if ptr.is_null() { return }
560 if ptr as *mut u8 as usize == 0 || ptr as *mut u8 as usize == mem::POST_DROP_USIZE {
564 // Because `fetch_sub` is already atomic, we do not need to synchronize
565 // with other threads unless we are going to delete the object. This
566 // same logic applies to the below `fetch_sub` to the `weak` count.
567 if self.inner().strong.fetch_sub(1, Release) != 1 {
571 // This fence is needed to prevent reordering of use of the data and
572 // deletion of the data. Because it is marked `Release`, the decreasing
573 // of the reference count synchronizes with this `Acquire` fence. This
574 // means that use of the data happens before decreasing the reference
575 // count, which happens before this fence, which happens before the
576 // deletion of the data.
578 // As explained in the [Boost documentation][1],
580 // > It is important to enforce any possible access to the object in one
581 // > thread (through an existing reference) to *happen before* deleting
582 // > the object in a different thread. This is achieved by a "release"
583 // > operation after dropping a reference (any access to the object
584 // > through this reference must obviously happened before), and an
585 // > "acquire" operation before deleting the object.
587 // [1]: (www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html)
588 atomic::fence(Acquire);
596 impl<T: ?Sized> Weak<T> {
597 /// Upgrades a weak reference to a strong reference.
599 /// Upgrades the `Weak<T>` reference to an `Arc<T>`, if possible.
601 /// Returns `None` if there were no strong references and the data was
607 /// use std::sync::Arc;
609 /// let five = Arc::new(5);
611 /// let weak_five = Arc::downgrade(&five);
613 /// let strong_five: Option<Arc<_>> = weak_five.upgrade();
615 #[stable(feature = "arc_weak", since = "1.4.0")]
616 pub fn upgrade(&self) -> Option<Arc<T>> {
617 // We use a CAS loop to increment the strong count instead of a
618 // fetch_add because once the count hits 0 it must never be above 0.
619 let inner = self.inner();
621 // Relaxed load because any write of 0 that we can observe
622 // leaves the field in a permanently zero state (so a
623 // "stale" read of 0 is fine), and any other value is
624 // confirmed via the CAS below.
625 let n = inner.strong.load(Relaxed);
630 // Relaxed is valid for the same reason it is on Arc's Clone impl
631 let old = inner.strong.compare_and_swap(n, n + 1, Relaxed);
633 return Some(Arc { _ptr: self._ptr })
639 fn inner(&self) -> &ArcInner<T> {
640 // See comments above for why this is "safe"
641 unsafe { &**self._ptr }
645 #[stable(feature = "arc_weak", since = "1.4.0")]
646 impl<T: ?Sized> Clone for Weak<T> {
647 /// Makes a clone of the `Weak<T>`.
649 /// This increases the weak reference count.
654 /// use std::sync::Arc;
656 /// let weak_five = Arc::downgrade(&Arc::new(5));
658 /// weak_five.clone();
661 fn clone(&self) -> Weak<T> {
662 // See comments in Arc::clone() for why this is relaxed. This can use a
663 // fetch_add (ignoring the lock) because the weak count is only locked
664 // where are *no other* weak pointers in existence. (So we can't be
665 // running this code in that case).
666 let old_size = self.inner().weak.fetch_add(1, Relaxed);
668 // See comments in Arc::clone() for why we do this (for mem::forget).
669 if old_size > MAX_REFCOUNT {
675 return Weak { _ptr: self._ptr }
679 #[stable(feature = "rust1", since = "1.0.0")]
680 impl<T: ?Sized> Drop for Weak<T> {
681 /// Drops the `Weak<T>`.
683 /// This will decrement the weak reference count.
688 /// use std::sync::Arc;
691 /// let five = Arc::new(5);
692 /// let weak_five = Arc::downgrade(&five);
696 /// drop(weak_five); // explicit drop
699 /// let five = Arc::new(5);
700 /// let weak_five = Arc::downgrade(&five);
704 /// } // implicit drop
707 let ptr = *self._ptr;
709 // see comments above for why this check is here
710 if ptr as *mut u8 as usize == 0 || ptr as *mut u8 as usize == mem::POST_DROP_USIZE {
714 // If we find out that we were the last weak pointer, then its time to
715 // deallocate the data entirely. See the discussion in Arc::drop() about
716 // the memory orderings
718 // It's not necessary to check for the locked state here, because the
719 // weak count can only be locked if there was precisely one weak ref,
720 // meaning that drop could only subsequently run ON that remaining weak
721 // ref, which can only happen after the lock is released.
722 if self.inner().weak.fetch_sub(1, Release) == 1 {
723 atomic::fence(Acquire);
725 deallocate(ptr as *mut u8,
733 #[stable(feature = "rust1", since = "1.0.0")]
734 impl<T: ?Sized + PartialEq> PartialEq for Arc<T> {
735 /// Equality for two `Arc<T>`s.
737 /// Two `Arc<T>`s are equal if their inner value are equal.
742 /// use std::sync::Arc;
744 /// let five = Arc::new(5);
746 /// five == Arc::new(5);
748 fn eq(&self, other: &Arc<T>) -> bool {
749 *(*self) == *(*other)
752 /// Inequality for two `Arc<T>`s.
754 /// Two `Arc<T>`s are unequal if their inner value are unequal.
759 /// use std::sync::Arc;
761 /// let five = Arc::new(5);
763 /// five != Arc::new(5);
765 fn ne(&self, other: &Arc<T>) -> bool {
766 *(*self) != *(*other)
769 #[stable(feature = "rust1", since = "1.0.0")]
770 impl<T: ?Sized + PartialOrd> PartialOrd for Arc<T> {
771 /// Partial comparison for two `Arc<T>`s.
773 /// The two are compared by calling `partial_cmp()` on their inner values.
778 /// use std::sync::Arc;
780 /// let five = Arc::new(5);
782 /// five.partial_cmp(&Arc::new(5));
784 fn partial_cmp(&self, other: &Arc<T>) -> Option<Ordering> {
785 (**self).partial_cmp(&**other)
788 /// Less-than comparison for two `Arc<T>`s.
790 /// The two are compared by calling `<` on their inner values.
795 /// use std::sync::Arc;
797 /// let five = Arc::new(5);
799 /// five < Arc::new(5);
801 fn lt(&self, other: &Arc<T>) -> bool {
805 /// 'Less-than or equal to' comparison for two `Arc<T>`s.
807 /// The two are compared by calling `<=` on their inner values.
812 /// use std::sync::Arc;
814 /// let five = Arc::new(5);
816 /// five <= Arc::new(5);
818 fn le(&self, other: &Arc<T>) -> bool {
819 *(*self) <= *(*other)
822 /// Greater-than comparison for two `Arc<T>`s.
824 /// The two are compared by calling `>` on their inner values.
829 /// use std::sync::Arc;
831 /// let five = Arc::new(5);
833 /// five > Arc::new(5);
835 fn gt(&self, other: &Arc<T>) -> bool {
839 /// 'Greater-than or equal to' comparison for two `Arc<T>`s.
841 /// The two are compared by calling `>=` on their inner values.
846 /// use std::sync::Arc;
848 /// let five = Arc::new(5);
850 /// five >= Arc::new(5);
852 fn ge(&self, other: &Arc<T>) -> bool {
853 *(*self) >= *(*other)
856 #[stable(feature = "rust1", since = "1.0.0")]
857 impl<T: ?Sized + Ord> Ord for Arc<T> {
858 fn cmp(&self, other: &Arc<T>) -> Ordering {
859 (**self).cmp(&**other)
862 #[stable(feature = "rust1", since = "1.0.0")]
863 impl<T: ?Sized + Eq> Eq for Arc<T> {}
865 #[stable(feature = "rust1", since = "1.0.0")]
866 impl<T: ?Sized + fmt::Display> fmt::Display for Arc<T> {
867 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
868 fmt::Display::fmt(&**self, f)
872 #[stable(feature = "rust1", since = "1.0.0")]
873 impl<T: ?Sized + fmt::Debug> fmt::Debug for Arc<T> {
874 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
875 fmt::Debug::fmt(&**self, f)
879 #[stable(feature = "rust1", since = "1.0.0")]
880 impl<T> fmt::Pointer for Arc<T> {
881 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
882 fmt::Pointer::fmt(&*self._ptr, f)
886 #[stable(feature = "rust1", since = "1.0.0")]
887 impl<T: Default> Default for Arc<T> {
888 #[stable(feature = "rust1", since = "1.0.0")]
889 fn default() -> Arc<T> {
890 Arc::new(Default::default())
894 #[stable(feature = "rust1", since = "1.0.0")]
895 impl<T: ?Sized + Hash> Hash for Arc<T> {
896 fn hash<H: Hasher>(&self, state: &mut H) {
903 use std::clone::Clone;
904 use std::sync::mpsc::channel;
907 use std::option::Option;
908 use std::option::Option::{Some, None};
909 use std::sync::atomic;
910 use std::sync::atomic::Ordering::{Acquire, SeqCst};
913 use super::{Arc, Weak};
914 use std::sync::Mutex;
916 struct Canary(*mut atomic::AtomicUsize);
924 (*c).fetch_add(1, SeqCst);
932 fn manually_share_arc() {
933 let v = vec!(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
934 let arc_v = Arc::new(v);
936 let (tx, rx) = channel();
938 let _t = thread::spawn(move || {
939 let arc_v: Arc<Vec<i32>> = rx.recv().unwrap();
940 assert_eq!((*arc_v)[3], 4);
943 tx.send(arc_v.clone()).unwrap();
945 assert_eq!((*arc_v)[2], 3);
946 assert_eq!((*arc_v)[4], 5);
950 fn test_arc_get_mut() {
951 let mut x = Arc::new(3);
952 *Arc::get_mut(&mut x).unwrap() = 4;
955 assert!(Arc::get_mut(&mut x).is_none());
957 assert!(Arc::get_mut(&mut x).is_some());
958 let _w = Arc::downgrade(&x);
959 assert!(Arc::get_mut(&mut x).is_none());
965 assert_eq!(Arc::try_unwrap(x), Ok(3));
968 assert_eq!(Arc::try_unwrap(x), Err(Arc::new(4)));
970 let _w = Arc::downgrade(&x);
971 assert_eq!(Arc::try_unwrap(x), Ok(5));
975 fn test_cowarc_clone_make_mut() {
976 let mut cow0 = Arc::new(75);
977 let mut cow1 = cow0.clone();
978 let mut cow2 = cow1.clone();
980 assert!(75 == *Arc::make_mut(&mut cow0));
981 assert!(75 == *Arc::make_mut(&mut cow1));
982 assert!(75 == *Arc::make_mut(&mut cow2));
984 *Arc::make_mut(&mut cow0) += 1;
985 *Arc::make_mut(&mut cow1) += 2;
986 *Arc::make_mut(&mut cow2) += 3;
988 assert!(76 == *cow0);
989 assert!(77 == *cow1);
990 assert!(78 == *cow2);
992 // none should point to the same backing memory
993 assert!(*cow0 != *cow1);
994 assert!(*cow0 != *cow2);
995 assert!(*cow1 != *cow2);
999 fn test_cowarc_clone_unique2() {
1000 let mut cow0 = Arc::new(75);
1001 let cow1 = cow0.clone();
1002 let cow2 = cow1.clone();
1004 assert!(75 == *cow0);
1005 assert!(75 == *cow1);
1006 assert!(75 == *cow2);
1008 *Arc::make_mut(&mut cow0) += 1;
1009 assert!(76 == *cow0);
1010 assert!(75 == *cow1);
1011 assert!(75 == *cow2);
1013 // cow1 and cow2 should share the same contents
1014 // cow0 should have a unique reference
1015 assert!(*cow0 != *cow1);
1016 assert!(*cow0 != *cow2);
1017 assert!(*cow1 == *cow2);
1021 fn test_cowarc_clone_weak() {
1022 let mut cow0 = Arc::new(75);
1023 let cow1_weak = Arc::downgrade(&cow0);
1025 assert!(75 == *cow0);
1026 assert!(75 == *cow1_weak.upgrade().unwrap());
1028 *Arc::make_mut(&mut cow0) += 1;
1030 assert!(76 == *cow0);
1031 assert!(cow1_weak.upgrade().is_none());
1036 let x = Arc::new(5);
1037 let y = Arc::downgrade(&x);
1038 assert!(y.upgrade().is_some());
1043 let x = Arc::new(5);
1044 let y = Arc::downgrade(&x);
1046 assert!(y.upgrade().is_none());
1050 fn weak_self_cyclic() {
1052 x: Mutex<Option<Weak<Cycle>>>,
1055 let a = Arc::new(Cycle { x: Mutex::new(None) });
1056 let b = Arc::downgrade(&a.clone());
1057 *a.x.lock().unwrap() = Some(b);
1059 // hopefully we don't double-free (or leak)...
1064 let mut canary = atomic::AtomicUsize::new(0);
1065 let x = Arc::new(Canary(&mut canary as *mut atomic::AtomicUsize));
1067 assert!(canary.load(Acquire) == 1);
1071 fn drop_arc_weak() {
1072 let mut canary = atomic::AtomicUsize::new(0);
1073 let arc = Arc::new(Canary(&mut canary as *mut atomic::AtomicUsize));
1074 let arc_weak = Arc::downgrade(&arc);
1075 assert!(canary.load(Acquire) == 0);
1077 assert!(canary.load(Acquire) == 1);
1082 fn test_strong_count() {
1083 let a = Arc::new(0u32);
1084 assert!(Arc::strong_count(&a) == 1);
1085 let w = Arc::downgrade(&a);
1086 assert!(Arc::strong_count(&a) == 1);
1087 let b = w.upgrade().expect("");
1088 assert!(Arc::strong_count(&b) == 2);
1089 assert!(Arc::strong_count(&a) == 2);
1092 assert!(Arc::strong_count(&b) == 1);
1094 assert!(Arc::strong_count(&b) == 2);
1095 assert!(Arc::strong_count(&c) == 2);
1099 fn test_weak_count() {
1100 let a = Arc::new(0u32);
1101 assert!(Arc::strong_count(&a) == 1);
1102 assert!(Arc::weak_count(&a) == 0);
1103 let w = Arc::downgrade(&a);
1104 assert!(Arc::strong_count(&a) == 1);
1105 assert!(Arc::weak_count(&a) == 1);
1107 assert!(Arc::weak_count(&a) == 2);
1110 assert!(Arc::strong_count(&a) == 1);
1111 assert!(Arc::weak_count(&a) == 0);
1113 assert!(Arc::strong_count(&a) == 2);
1114 assert!(Arc::weak_count(&a) == 0);
1115 let d = Arc::downgrade(&c);
1116 assert!(Arc::weak_count(&c) == 1);
1117 assert!(Arc::strong_count(&c) == 2);
1126 let a = Arc::new(5u32);
1127 assert_eq!(format!("{:?}", a), "5");
1130 // Make sure deriving works with Arc<T>
1131 #[derive(Eq, Ord, PartialEq, PartialOrd, Clone, Debug, Default)]
1138 let x: Arc<[i32]> = Arc::new([1, 2, 3]);
1139 assert_eq!(format!("{:?}", x), "[1, 2, 3]");
1140 let y = Arc::downgrade(&x.clone());
1142 assert!(y.upgrade().is_none());
1146 impl<T: ?Sized> borrow::Borrow<T> for Arc<T> {
1147 fn borrow(&self) -> &T {
1152 #[stable(since = "1.5.0", feature = "smart_ptr_as_ref")]
1153 impl<T: ?Sized> AsRef<T> for Arc<T> {
1154 fn as_ref(&self) -> &T { &**self }