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
::abort
;
82 use core
::mem
::uninitialized
;
84 use core
::ops
::CoerceUnsized
;
85 use core
::ptr
::{self, Shared}
;
86 use core
::marker
::Unsize
;
87 use core
::hash
::{Hash, Hasher}
;
88 use core
::{usize, isize}
;
89 use core
::convert
::From
;
92 const MAX_REFCOUNT
: usize = (isize::MAX
) as usize;
94 /// An atomically reference counted wrapper for shared state.
98 /// In this example, a large vector is shared between several threads.
99 /// With simple pipes, without `Arc`, a copy would have to be made for each
102 /// When you clone an `Arc<T>`, it will create another pointer to the data and
103 /// increase the reference counter.
106 /// use std::sync::Arc;
110 /// let numbers: Vec<_> = (0..100).collect();
111 /// let shared_numbers = Arc::new(numbers);
114 /// let child_numbers = shared_numbers.clone();
116 /// thread::spawn(move || {
117 /// let local_numbers = &child_numbers[..];
119 /// // Work with the local numbers
124 #[unsafe_no_drop_flag]
125 #[stable(feature = "rust1", since = "1.0.0")]
126 pub struct Arc
<T
: ?Sized
> {
127 ptr
: Shared
<ArcInner
<T
>>,
130 #[stable(feature = "rust1", since = "1.0.0")]
131 unsafe impl<T
: ?Sized
+ Sync
+ Send
> Send
for Arc
<T
> {}
132 #[stable(feature = "rust1", since = "1.0.0")]
133 unsafe impl<T
: ?Sized
+ Sync
+ Send
> Sync
for Arc
<T
> {}
135 #[unstable(feature = "coerce_unsized", issue = "27732")]
136 impl<T
: ?Sized
+ Unsize
<U
>, U
: ?Sized
> CoerceUnsized
<Arc
<U
>> for Arc
<T
> {}
138 /// A weak pointer to an `Arc`.
140 /// Weak pointers will not keep the data inside of the `Arc` alive, and can be
141 /// used to break cycles between `Arc` pointers.
142 #[unsafe_no_drop_flag]
143 #[stable(feature = "arc_weak", since = "1.4.0")]
144 pub struct Weak
<T
: ?Sized
> {
145 ptr
: Shared
<ArcInner
<T
>>,
148 #[stable(feature = "arc_weak", since = "1.4.0")]
149 unsafe impl<T
: ?Sized
+ Sync
+ Send
> Send
for Weak
<T
> {}
150 #[stable(feature = "arc_weak", since = "1.4.0")]
151 unsafe impl<T
: ?Sized
+ Sync
+ Send
> Sync
for Weak
<T
> {}
153 #[unstable(feature = "coerce_unsized", issue = "27732")]
154 impl<T
: ?Sized
+ Unsize
<U
>, U
: ?Sized
> CoerceUnsized
<Weak
<U
>> for Weak
<T
> {}
156 #[stable(feature = "arc_weak", since = "1.4.0")]
157 impl<T
: ?Sized
+ fmt
::Debug
> fmt
::Debug
for Weak
<T
> {
158 fn fmt(&self, f
: &mut fmt
::Formatter
) -> fmt
::Result
{
163 struct ArcInner
<T
: ?Sized
> {
164 strong
: atomic
::AtomicUsize
,
166 // the value usize::MAX acts as a sentinel for temporarily "locking" the
167 // ability to upgrade weak pointers or downgrade strong ones; this is used
168 // to avoid races in `make_mut` and `get_mut`.
169 weak
: atomic
::AtomicUsize
,
174 unsafe impl<T
: ?Sized
+ Sync
+ Send
> Send
for ArcInner
<T
> {}
175 unsafe impl<T
: ?Sized
+ Sync
+ Send
> Sync
for ArcInner
<T
> {}
178 /// Constructs a new `Arc<T>`.
183 /// use std::sync::Arc;
185 /// let five = Arc::new(5);
188 #[stable(feature = "rust1", since = "1.0.0")]
189 pub fn new(data
: T
) -> Arc
<T
> {
190 // Start the weak pointer count as 1 which is the weak pointer that's
191 // held by all the strong pointers (kinda), see std/rc.rs for more info
192 let x
: Box
<_
> = box ArcInner
{
193 strong
: atomic
::AtomicUsize
::new(1),
194 weak
: atomic
::AtomicUsize
::new(1),
197 Arc { ptr: unsafe { Shared::new(Box::into_raw(x)) }
}
200 /// Unwraps the contained value if the `Arc<T>` has exactly one strong reference.
202 /// Otherwise, an `Err` is returned with the same `Arc<T>`.
204 /// This will succeed even if there are outstanding weak references.
209 /// use std::sync::Arc;
211 /// let x = Arc::new(3);
212 /// assert_eq!(Arc::try_unwrap(x), Ok(3));
214 /// let x = Arc::new(4);
215 /// let _y = x.clone();
216 /// assert_eq!(Arc::try_unwrap(x), Err(Arc::new(4)));
219 #[stable(feature = "arc_unique", since = "1.4.0")]
220 pub fn try_unwrap(this
: Self) -> Result
<T
, Self> {
221 // See `drop` for why all these atomics are like this
222 if this
.inner().strong
.compare_exchange(1, 0, Release
, Relaxed
).is_err() {
226 atomic
::fence(Acquire
);
230 let elem
= ptr
::read(&(*ptr
).data
);
232 // Make a weak pointer to clean up the implicit strong-weak reference
233 let _weak
= Weak { ptr: this.ptr }
;
241 impl<T
: ?Sized
> Arc
<T
> {
242 /// Downgrades the `Arc<T>` to a `Weak<T>` reference.
247 /// use std::sync::Arc;
249 /// let five = Arc::new(5);
251 /// let weak_five = Arc::downgrade(&five);
253 #[stable(feature = "arc_weak", since = "1.4.0")]
254 pub fn downgrade(this
: &Self) -> Weak
<T
> {
255 // This Relaxed is OK because we're checking the value in the CAS
257 let mut cur
= this
.inner().weak
.load(Relaxed
);
260 // check if the weak counter is currently "locked"; if so, spin.
261 if cur
== usize::MAX
{
262 cur
= this
.inner().weak
.load(Relaxed
);
266 // NOTE: this code currently ignores the possibility of overflow
267 // into usize::MAX; in general both Rc and Arc need to be adjusted
268 // to deal with overflow.
270 // Unlike with Clone(), we need this to be an Acquire read to
271 // synchronize with the write coming from `is_unique`, so that the
272 // events prior to that write happen before this read.
273 match this
.inner().weak
.compare_exchange_weak(cur
, cur
+ 1, Acquire
, Relaxed
) {
274 Ok(_
) => return Weak { ptr: this.ptr }
,
275 Err(old
) => cur
= old
,
280 /// Get the number of weak references to this value.
282 #[unstable(feature = "arc_counts", reason = "not clearly useful, and racy",
284 pub fn weak_count(this
: &Self) -> usize {
285 this
.inner().weak
.load(SeqCst
) - 1
288 /// Get the number of strong references to this value.
290 #[unstable(feature = "arc_counts", reason = "not clearly useful, and racy",
292 pub fn strong_count(this
: &Self) -> usize {
293 this
.inner().strong
.load(SeqCst
)
297 fn inner(&self) -> &ArcInner
<T
> {
298 // This unsafety is ok because while this arc is alive we're guaranteed
299 // that the inner pointer is valid. Furthermore, we know that the
300 // `ArcInner` structure itself is `Sync` because the inner data is
301 // `Sync` as well, so we're ok loaning out an immutable pointer to these
303 unsafe { &**self.ptr }
306 // Non-inlined part of `drop`.
308 unsafe fn drop_slow(&mut self) {
311 // Destroy the data at this time, even though we may not free the box
312 // allocation itself (there may still be weak pointers lying around).
313 ptr
::drop_in_place(&mut (*ptr
).data
);
315 if self.inner().weak
.fetch_sub(1, Release
) == 1 {
316 atomic
::fence(Acquire
);
317 deallocate(ptr
as *mut u8, size_of_val(&*ptr
), align_of_val(&*ptr
))
322 #[stable(feature = "rust1", since = "1.0.0")]
323 impl<T
: ?Sized
> Clone
for Arc
<T
> {
324 /// Makes a clone of the `Arc<T>`.
326 /// This increases the strong reference count.
331 /// use std::sync::Arc;
333 /// let five = Arc::new(5);
338 fn clone(&self) -> Arc
<T
> {
339 // Using a relaxed ordering is alright here, as knowledge of the
340 // original reference prevents other threads from erroneously deleting
343 // As explained in the [Boost documentation][1], Increasing the
344 // reference counter can always be done with memory_order_relaxed: New
345 // references to an object can only be formed from an existing
346 // reference, and passing an existing reference from one thread to
347 // another must already provide any required synchronization.
349 // [1]: (www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html)
350 let old_size
= self.inner().strong
.fetch_add(1, Relaxed
);
352 // However we need to guard against massive refcounts in case someone
353 // is `mem::forget`ing Arcs. If we don't do this the count can overflow
354 // and users will use-after free. We racily saturate to `isize::MAX` on
355 // the assumption that there aren't ~2 billion threads incrementing
356 // the reference count at once. This branch will never be taken in
357 // any realistic program.
359 // We abort because such a program is incredibly degenerate, and we
360 // don't care to support it.
361 if old_size
> MAX_REFCOUNT
{
367 Arc { ptr: self.ptr }
371 #[stable(feature = "rust1", since = "1.0.0")]
372 impl<T
: ?Sized
> Deref
for Arc
<T
> {
376 fn deref(&self) -> &T
{
381 impl<T
: Clone
> Arc
<T
> {
382 /// Make a mutable reference into the given `Arc<T>`.
383 /// If the `Arc<T>` has more than one strong reference, or any weak
384 /// references, the inner data is cloned.
386 /// This is also referred to as a copy-on-write.
391 /// use std::sync::Arc;
393 /// let mut data = Arc::new(5);
395 /// *Arc::make_mut(&mut data) += 1; // Won't clone anything
396 /// let mut other_data = data.clone(); // Won't clone inner data
397 /// *Arc::make_mut(&mut data) += 1; // Clones inner data
398 /// *Arc::make_mut(&mut data) += 1; // Won't clone anything
399 /// *Arc::make_mut(&mut other_data) *= 2; // Won't clone anything
401 /// // Note: data and other_data now point to different numbers
402 /// assert_eq!(*data, 8);
403 /// assert_eq!(*other_data, 12);
407 #[stable(feature = "arc_unique", since = "1.4.0")]
408 pub fn make_mut(this
: &mut Self) -> &mut T
{
409 // Note that we hold both a strong reference and a weak reference.
410 // Thus, releasing our strong reference only will not, by itself, cause
411 // the memory to be deallocated.
413 // Use Acquire to ensure that we see any writes to `weak` that happen
414 // before release writes (i.e., decrements) to `strong`. Since we hold a
415 // weak count, there's no chance the ArcInner itself could be
417 if this
.inner().strong
.compare_exchange(1, 0, Acquire
, Relaxed
).is_err() {
418 // Another strong pointer exists; clone
419 *this
= Arc
::new((**this
).clone());
420 } else if this
.inner().weak
.load(Relaxed
) != 1 {
421 // Relaxed suffices in the above because this is fundamentally an
422 // optimization: we are always racing with weak pointers being
423 // dropped. Worst case, we end up allocated a new Arc unnecessarily.
425 // We removed the last strong ref, but there are additional weak
426 // refs remaining. We'll move the contents to a new Arc, and
427 // invalidate the other weak refs.
429 // Note that it is not possible for the read of `weak` to yield
430 // usize::MAX (i.e., locked), since the weak count can only be
431 // locked by a thread with a strong reference.
433 // Materialize our own implicit weak pointer, so that it can clean
434 // up the ArcInner as needed.
435 let weak
= Weak { ptr: this.ptr }
;
437 // mark the data itself as already deallocated
439 // there is no data race in the implicit write caused by `read`
440 // here (due to zeroing) because data is no longer accessed by
441 // other threads (due to there being no more strong refs at this
443 let mut swap
= Arc
::new(ptr
::read(&(**weak
.ptr
).data
));
444 mem
::swap(this
, &mut swap
);
448 // We were the sole reference of either kind; bump back up the
450 this
.inner().strong
.store(1, Release
);
453 // As with `get_mut()`, the unsafety is ok because our reference was
454 // either unique to begin with, or became one upon cloning the contents.
456 let inner
= &mut **this
.ptr
;
462 impl<T
: ?Sized
> Arc
<T
> {
463 /// Returns a mutable reference to the contained value if the `Arc<T>` has
464 /// one strong reference and no weak references.
469 /// use std::sync::Arc;
471 /// let mut x = Arc::new(3);
472 /// *Arc::get_mut(&mut x).unwrap() = 4;
473 /// assert_eq!(*x, 4);
475 /// let _y = x.clone();
476 /// assert!(Arc::get_mut(&mut x).is_none());
479 #[stable(feature = "arc_unique", since = "1.4.0")]
480 pub fn get_mut(this
: &mut Self) -> Option
<&mut T
> {
481 if this
.is_unique() {
482 // This unsafety is ok because we're guaranteed that the pointer
483 // returned is the *only* pointer that will ever be returned to T. Our
484 // reference count is guaranteed to be 1 at this point, and we required
485 // the Arc itself to be `mut`, so we're returning the only possible
486 // reference to the inner data.
488 let inner
= &mut **this
.ptr
;
489 Some(&mut inner
.data
)
496 /// Determine whether this is the unique reference (including weak refs) to
497 /// the underlying data.
499 /// Note that this requires locking the weak ref count.
500 fn is_unique(&mut self) -> bool
{
501 // lock the weak pointer count if we appear to be the sole weak pointer
504 // The acquire label here ensures a happens-before relationship with any
505 // writes to `strong` prior to decrements of the `weak` count (via drop,
506 // which uses Release).
507 if self.inner().weak
.compare_exchange(1, usize::MAX
, Acquire
, Relaxed
).is_ok() {
508 // Due to the previous acquire read, this will observe any writes to
509 // `strong` that were due to upgrading weak pointers; only strong
510 // clones remain, which require that the strong count is > 1 anyway.
511 let unique
= self.inner().strong
.load(Relaxed
) == 1;
513 // The release write here synchronizes with a read in `downgrade`,
514 // effectively preventing the above read of `strong` from happening
516 self.inner().weak
.store(1, Release
); // release the lock
524 #[stable(feature = "rust1", since = "1.0.0")]
525 impl<T
: ?Sized
> Drop
for Arc
<T
> {
526 /// Drops the `Arc<T>`.
528 /// This will decrement the strong reference count. If the strong reference
529 /// count becomes zero and the only other references are `Weak<T>` ones,
530 /// `drop`s the inner value.
535 /// use std::sync::Arc;
538 /// let five = Arc::new(5);
542 /// drop(five); // explicit drop
545 /// let five = Arc::new(5);
549 /// } // implicit drop
551 #[unsafe_destructor_blind_to_params]
554 // This structure has #[unsafe_no_drop_flag], so this drop glue may run
555 // more than once (but it is guaranteed to be zeroed after the first if
556 // it's run more than once)
557 let thin
= *self.ptr
as *const ();
559 if thin
as usize == mem
::POST_DROP_USIZE
{
563 // Because `fetch_sub` is already atomic, we do not need to synchronize
564 // with other threads unless we are going to delete the object. This
565 // same logic applies to the below `fetch_sub` to the `weak` count.
566 if self.inner().strong
.fetch_sub(1, Release
) != 1 {
570 // This fence is needed to prevent reordering of use of the data and
571 // deletion of the data. Because it is marked `Release`, the decreasing
572 // of the reference count synchronizes with this `Acquire` fence. This
573 // means that use of the data happens before decreasing the reference
574 // count, which happens before this fence, which happens before the
575 // deletion of the data.
577 // As explained in the [Boost documentation][1],
579 // > It is important to enforce any possible access to the object in one
580 // > thread (through an existing reference) to *happen before* deleting
581 // > the object in a different thread. This is achieved by a "release"
582 // > operation after dropping a reference (any access to the object
583 // > through this reference must obviously happened before), and an
584 // > "acquire" operation before deleting the object.
586 // [1]: (www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html)
587 atomic
::fence(Acquire
);
595 impl<T
: ?Sized
> Weak
<T
> {
596 /// Upgrades a weak reference to a strong reference.
598 /// Upgrades the `Weak<T>` reference to an `Arc<T>`, if possible.
600 /// Returns `None` if there were no strong references and the data was
606 /// use std::sync::Arc;
608 /// let five = Arc::new(5);
610 /// let weak_five = Arc::downgrade(&five);
612 /// let strong_five: Option<Arc<_>> = weak_five.upgrade();
614 #[stable(feature = "arc_weak", since = "1.4.0")]
615 pub fn upgrade(&self) -> Option
<Arc
<T
>> {
616 // We use a CAS loop to increment the strong count instead of a
617 // fetch_add because once the count hits 0 it must never be above 0.
618 let inner
= self.inner();
620 // Relaxed load because any write of 0 that we can observe
621 // leaves the field in a permanently zero state (so a
622 // "stale" read of 0 is fine), and any other value is
623 // confirmed via the CAS below.
624 let mut n
= inner
.strong
.load(Relaxed
);
631 // See comments in `Arc::clone` for why we do this (for `mem::forget`).
632 if n
> MAX_REFCOUNT
{
636 // Relaxed is valid for the same reason it is on Arc's Clone impl
637 match inner
.strong
.compare_exchange_weak(n
, n
+ 1, Relaxed
, Relaxed
) {
638 Ok(_
) => return Some(Arc { ptr: self.ptr }
),
645 fn inner(&self) -> &ArcInner
<T
> {
646 // See comments above for why this is "safe"
647 unsafe { &**self.ptr }
651 #[stable(feature = "arc_weak", since = "1.4.0")]
652 impl<T
: ?Sized
> Clone
for Weak
<T
> {
653 /// Makes a clone of the `Weak<T>`.
655 /// This increases the weak reference count.
660 /// use std::sync::Arc;
662 /// let weak_five = Arc::downgrade(&Arc::new(5));
664 /// weak_five.clone();
667 fn clone(&self) -> Weak
<T
> {
668 // See comments in Arc::clone() for why this is relaxed. This can use a
669 // fetch_add (ignoring the lock) because the weak count is only locked
670 // where are *no other* weak pointers in existence. (So we can't be
671 // running this code in that case).
672 let old_size
= self.inner().weak
.fetch_add(1, Relaxed
);
674 // See comments in Arc::clone() for why we do this (for mem::forget).
675 if old_size
> MAX_REFCOUNT
{
681 return Weak { ptr: self.ptr }
;
685 #[stable(feature = "arc_weak", since = "1.4.0")]
686 impl<T
: ?Sized
> Drop
for Weak
<T
> {
687 /// Drops the `Weak<T>`.
689 /// This will decrement the weak reference count.
694 /// use std::sync::Arc;
697 /// let five = Arc::new(5);
698 /// let weak_five = Arc::downgrade(&five);
702 /// drop(weak_five); // explicit drop
705 /// let five = Arc::new(5);
706 /// let weak_five = Arc::downgrade(&five);
710 /// } // implicit drop
714 let thin
= ptr
as *const ();
716 // see comments above for why this check is here
717 if thin
as usize == mem
::POST_DROP_USIZE
{
721 // If we find out that we were the last weak pointer, then its time to
722 // deallocate the data entirely. See the discussion in Arc::drop() about
723 // the memory orderings
725 // It's not necessary to check for the locked state here, because the
726 // weak count can only be locked if there was precisely one weak ref,
727 // meaning that drop could only subsequently run ON that remaining weak
728 // ref, which can only happen after the lock is released.
729 if self.inner().weak
.fetch_sub(1, Release
) == 1 {
730 atomic
::fence(Acquire
);
731 unsafe { deallocate(ptr as *mut u8, size_of_val(&*ptr), align_of_val(&*ptr)) }
736 #[stable(feature = "rust1", since = "1.0.0")]
737 impl<T
: ?Sized
+ PartialEq
> PartialEq
for Arc
<T
> {
738 /// Equality for two `Arc<T>`s.
740 /// Two `Arc<T>`s are equal if their inner value are equal.
745 /// use std::sync::Arc;
747 /// let five = Arc::new(5);
749 /// five == Arc::new(5);
751 fn eq(&self, other
: &Arc
<T
>) -> bool
{
752 *(*self) == *(*other
)
755 /// Inequality for two `Arc<T>`s.
757 /// Two `Arc<T>`s are unequal if their inner value are unequal.
762 /// use std::sync::Arc;
764 /// let five = Arc::new(5);
766 /// five != Arc::new(5);
768 fn ne(&self, other
: &Arc
<T
>) -> bool
{
769 *(*self) != *(*other
)
772 #[stable(feature = "rust1", since = "1.0.0")]
773 impl<T
: ?Sized
+ PartialOrd
> PartialOrd
for Arc
<T
> {
774 /// Partial comparison for two `Arc<T>`s.
776 /// The two are compared by calling `partial_cmp()` on their inner values.
781 /// use std::sync::Arc;
783 /// let five = Arc::new(5);
785 /// five.partial_cmp(&Arc::new(5));
787 fn partial_cmp(&self, other
: &Arc
<T
>) -> Option
<Ordering
> {
788 (**self).partial_cmp(&**other
)
791 /// Less-than comparison for two `Arc<T>`s.
793 /// The two are compared by calling `<` on their inner values.
798 /// use std::sync::Arc;
800 /// let five = Arc::new(5);
802 /// five < Arc::new(5);
804 fn lt(&self, other
: &Arc
<T
>) -> bool
{
808 /// 'Less-than or equal to' comparison for two `Arc<T>`s.
810 /// The two are compared by calling `<=` on their inner values.
815 /// use std::sync::Arc;
817 /// let five = Arc::new(5);
819 /// five <= Arc::new(5);
821 fn le(&self, other
: &Arc
<T
>) -> bool
{
822 *(*self) <= *(*other
)
825 /// Greater-than comparison for two `Arc<T>`s.
827 /// The two are compared by calling `>` on their inner values.
832 /// use std::sync::Arc;
834 /// let five = Arc::new(5);
836 /// five > Arc::new(5);
838 fn gt(&self, other
: &Arc
<T
>) -> bool
{
842 /// 'Greater-than or equal to' comparison for two `Arc<T>`s.
844 /// The two are compared by calling `>=` on their inner values.
849 /// use std::sync::Arc;
851 /// let five = Arc::new(5);
853 /// five >= Arc::new(5);
855 fn ge(&self, other
: &Arc
<T
>) -> bool
{
856 *(*self) >= *(*other
)
859 #[stable(feature = "rust1", since = "1.0.0")]
860 impl<T
: ?Sized
+ Ord
> Ord
for Arc
<T
> {
861 fn cmp(&self, other
: &Arc
<T
>) -> Ordering
{
862 (**self).cmp(&**other
)
865 #[stable(feature = "rust1", since = "1.0.0")]
866 impl<T
: ?Sized
+ Eq
> Eq
for Arc
<T
> {}
868 #[stable(feature = "rust1", since = "1.0.0")]
869 impl<T
: ?Sized
+ fmt
::Display
> fmt
::Display
for Arc
<T
> {
870 fn fmt(&self, f
: &mut fmt
::Formatter
) -> fmt
::Result
{
871 fmt
::Display
::fmt(&**self, f
)
875 #[stable(feature = "rust1", since = "1.0.0")]
876 impl<T
: ?Sized
+ fmt
::Debug
> fmt
::Debug
for Arc
<T
> {
877 fn fmt(&self, f
: &mut fmt
::Formatter
) -> fmt
::Result
{
878 fmt
::Debug
::fmt(&**self, f
)
882 #[stable(feature = "rust1", since = "1.0.0")]
883 impl<T
: ?Sized
> fmt
::Pointer
for Arc
<T
> {
884 fn fmt(&self, f
: &mut fmt
::Formatter
) -> fmt
::Result
{
885 fmt
::Pointer
::fmt(&*self.ptr
, f
)
889 #[stable(feature = "rust1", since = "1.0.0")]
890 impl<T
: Default
> Default
for Arc
<T
> {
891 fn default() -> Arc
<T
> {
892 Arc
::new(Default
::default())
896 #[stable(feature = "rust1", since = "1.0.0")]
897 impl<T
: ?Sized
+ Hash
> Hash
for Arc
<T
> {
898 fn hash
<H
: Hasher
>(&self, state
: &mut H
) {
903 #[stable(feature = "from_for_ptrs", since = "1.6.0")]
904 impl<T
> From
<T
> for Arc
<T
> {
905 fn from(t
: T
) -> Self {
911 /// Constructs a new `Weak<T>` without an accompanying instance of T.
913 /// This allocates memory for T, but does not initialize it. Calling
914 /// Weak<T>::upgrade() on the return value always gives None.
919 /// #![feature(downgraded_weak)]
921 /// use std::sync::Weak;
923 /// let empty: Weak<i64> = Weak::new();
925 #[unstable(feature = "downgraded_weak",
926 reason
= "recently added",
928 pub fn new() -> Weak
<T
> {
930 Weak
{ ptr
: Shared
::new(Box
::into_raw(box ArcInner
{
931 strong
: atomic
::AtomicUsize
::new(0),
932 weak
: atomic
::AtomicUsize
::new(1),
933 data
: uninitialized(),
941 use std
::clone
::Clone
;
942 use std
::sync
::mpsc
::channel
;
945 use std
::option
::Option
;
946 use std
::option
::Option
::{Some, None}
;
947 use std
::sync
::atomic
;
948 use std
::sync
::atomic
::Ordering
::{Acquire, SeqCst}
;
951 use super::{Arc, Weak}
;
952 use std
::sync
::Mutex
;
953 use std
::convert
::From
;
955 struct Canary(*mut atomic
::AtomicUsize
);
957 impl Drop
for Canary
{
962 (*c
).fetch_add(1, SeqCst
);
970 fn manually_share_arc() {
971 let v
= vec
![1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
972 let arc_v
= Arc
::new(v
);
974 let (tx
, rx
) = channel();
976 let _t
= thread
::spawn(move || {
977 let arc_v
: Arc
<Vec
<i32>> = rx
.recv().unwrap();
978 assert_eq
!((*arc_v
)[3], 4);
981 tx
.send(arc_v
.clone()).unwrap();
983 assert_eq
!((*arc_v
)[2], 3);
984 assert_eq
!((*arc_v
)[4], 5);
988 fn test_arc_get_mut() {
989 let mut x
= Arc
::new(3);
990 *Arc
::get_mut(&mut x
).unwrap() = 4;
993 assert
!(Arc
::get_mut(&mut x
).is_none());
995 assert
!(Arc
::get_mut(&mut x
).is_some());
996 let _w
= Arc
::downgrade(&x
);
997 assert
!(Arc
::get_mut(&mut x
).is_none());
1002 let x
= Arc
::new(3);
1003 assert_eq
!(Arc
::try_unwrap(x
), Ok(3));
1004 let x
= Arc
::new(4);
1006 assert_eq
!(Arc
::try_unwrap(x
), Err(Arc
::new(4)));
1007 let x
= Arc
::new(5);
1008 let _w
= Arc
::downgrade(&x
);
1009 assert_eq
!(Arc
::try_unwrap(x
), Ok(5));
1013 fn test_cowarc_clone_make_mut() {
1014 let mut cow0
= Arc
::new(75);
1015 let mut cow1
= cow0
.clone();
1016 let mut cow2
= cow1
.clone();
1018 assert
!(75 == *Arc
::make_mut(&mut cow0
));
1019 assert
!(75 == *Arc
::make_mut(&mut cow1
));
1020 assert
!(75 == *Arc
::make_mut(&mut cow2
));
1022 *Arc
::make_mut(&mut cow0
) += 1;
1023 *Arc
::make_mut(&mut cow1
) += 2;
1024 *Arc
::make_mut(&mut cow2
) += 3;
1026 assert
!(76 == *cow0
);
1027 assert
!(77 == *cow1
);
1028 assert
!(78 == *cow2
);
1030 // none should point to the same backing memory
1031 assert
!(*cow0
!= *cow1
);
1032 assert
!(*cow0
!= *cow2
);
1033 assert
!(*cow1
!= *cow2
);
1037 fn test_cowarc_clone_unique2() {
1038 let mut cow0
= Arc
::new(75);
1039 let cow1
= cow0
.clone();
1040 let cow2
= cow1
.clone();
1042 assert
!(75 == *cow0
);
1043 assert
!(75 == *cow1
);
1044 assert
!(75 == *cow2
);
1046 *Arc
::make_mut(&mut cow0
) += 1;
1047 assert
!(76 == *cow0
);
1048 assert
!(75 == *cow1
);
1049 assert
!(75 == *cow2
);
1051 // cow1 and cow2 should share the same contents
1052 // cow0 should have a unique reference
1053 assert
!(*cow0
!= *cow1
);
1054 assert
!(*cow0
!= *cow2
);
1055 assert
!(*cow1
== *cow2
);
1059 fn test_cowarc_clone_weak() {
1060 let mut cow0
= Arc
::new(75);
1061 let cow1_weak
= Arc
::downgrade(&cow0
);
1063 assert
!(75 == *cow0
);
1064 assert
!(75 == *cow1_weak
.upgrade().unwrap());
1066 *Arc
::make_mut(&mut cow0
) += 1;
1068 assert
!(76 == *cow0
);
1069 assert
!(cow1_weak
.upgrade().is_none());
1074 let x
= Arc
::new(5);
1075 let y
= Arc
::downgrade(&x
);
1076 assert
!(y
.upgrade().is_some());
1081 let x
= Arc
::new(5);
1082 let y
= Arc
::downgrade(&x
);
1084 assert
!(y
.upgrade().is_none());
1088 fn weak_self_cyclic() {
1090 x
: Mutex
<Option
<Weak
<Cycle
>>>,
1093 let a
= Arc
::new(Cycle { x: Mutex::new(None) }
);
1094 let b
= Arc
::downgrade(&a
.clone());
1095 *a
.x
.lock().unwrap() = Some(b
);
1097 // hopefully we don't double-free (or leak)...
1102 let mut canary
= atomic
::AtomicUsize
::new(0);
1103 let x
= Arc
::new(Canary(&mut canary
as *mut atomic
::AtomicUsize
));
1105 assert
!(canary
.load(Acquire
) == 1);
1109 fn drop_arc_weak() {
1110 let mut canary
= atomic
::AtomicUsize
::new(0);
1111 let arc
= Arc
::new(Canary(&mut canary
as *mut atomic
::AtomicUsize
));
1112 let arc_weak
= Arc
::downgrade(&arc
);
1113 assert
!(canary
.load(Acquire
) == 0);
1115 assert
!(canary
.load(Acquire
) == 1);
1120 fn test_strong_count() {
1121 let a
= Arc
::new(0);
1122 assert
!(Arc
::strong_count(&a
) == 1);
1123 let w
= Arc
::downgrade(&a
);
1124 assert
!(Arc
::strong_count(&a
) == 1);
1125 let b
= w
.upgrade().expect("");
1126 assert
!(Arc
::strong_count(&b
) == 2);
1127 assert
!(Arc
::strong_count(&a
) == 2);
1130 assert
!(Arc
::strong_count(&b
) == 1);
1132 assert
!(Arc
::strong_count(&b
) == 2);
1133 assert
!(Arc
::strong_count(&c
) == 2);
1137 fn test_weak_count() {
1138 let a
= Arc
::new(0);
1139 assert
!(Arc
::strong_count(&a
) == 1);
1140 assert
!(Arc
::weak_count(&a
) == 0);
1141 let w
= Arc
::downgrade(&a
);
1142 assert
!(Arc
::strong_count(&a
) == 1);
1143 assert
!(Arc
::weak_count(&a
) == 1);
1145 assert
!(Arc
::weak_count(&a
) == 2);
1148 assert
!(Arc
::strong_count(&a
) == 1);
1149 assert
!(Arc
::weak_count(&a
) == 0);
1151 assert
!(Arc
::strong_count(&a
) == 2);
1152 assert
!(Arc
::weak_count(&a
) == 0);
1153 let d
= Arc
::downgrade(&c
);
1154 assert
!(Arc
::weak_count(&c
) == 1);
1155 assert
!(Arc
::strong_count(&c
) == 2);
1164 let a
= Arc
::new(5);
1165 assert_eq
!(format
!("{:?}", a
), "5");
1168 // Make sure deriving works with Arc<T>
1169 #[derive(Eq, Ord, PartialEq, PartialOrd, Clone, Debug, Default)]
1176 let x
: Arc
<[i32]> = Arc
::new([1, 2, 3]);
1177 assert_eq
!(format
!("{:?}", x
), "[1, 2, 3]");
1178 let y
= Arc
::downgrade(&x
.clone());
1180 assert
!(y
.upgrade().is_none());
1184 fn test_from_owned() {
1186 let foo_arc
= Arc
::from(foo
);
1187 assert
!(123 == *foo_arc
);
1191 fn test_new_weak() {
1192 let foo
: Weak
<usize> = Weak
::new();
1193 assert
!(foo
.upgrade().is_none());
1197 #[stable(feature = "rust1", since = "1.0.0")]
1198 impl<T
: ?Sized
> borrow
::Borrow
<T
> for Arc
<T
> {
1199 fn borrow(&self) -> &T
{
1204 #[stable(since = "1.5.0", feature = "smart_ptr_as_ref")]
1205 impl<T
: ?Sized
> AsRef
<T
> for Arc
<T
> {
1206 fn as_ref(&self) -> &T
{