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fuchsia / third_party / rust / c949d8ee69268c5c176c89834782b2654e0766ad / . / src / liballoc / sync.rs
blob: 390a079165054abfc049644d5bbcca4948483f80 [file] [log] [blame]
#![stable(feature = "rust1", since = "1.0.0")]
//! Thread-safe reference-counting pointers.
//!
//! See the [`Arc<T>`][arc] documentation for more details.
//!
//! [arc]: struct.Arc.html
use core::any::Any;
use core::sync::atomic;
use core::sync::atomic::Ordering::{Acquire, Relaxed, Release, SeqCst};
use core::borrow;
use core::fmt;
use core::cmp::Ordering;
use core::intrinsics::abort;
use core::mem::{self, align_of_val, size_of_val};
use core::ops::{Deref, Receiver};
use core::ops::{CoerceUnsized, DispatchFromDyn};
use core::pin::Pin;
use core::ptr::{self, NonNull};
use core::marker::{Unpin, Unsize, PhantomData};
use core::hash::{Hash, Hasher};
use core::{isize, usize};
use core::convert::From;
use alloc::{Global, Alloc, Layout, box_free, handle_alloc_error};
use boxed::Box;
use rc::is_dangling;
use string::String;
use vec::Vec;
/// A soft limit on the amount of references that may be made to an `Arc`.
///
/// Going above this limit will abort your program (although not
/// necessarily) at _exactly_ `MAX_REFCOUNT + 1` references.
const MAX_REFCOUNT: usize = (isize::MAX) as usize;
/// A thread-safe reference-counting pointer. 'Arc' stands for 'Atomically
/// Reference Counted'.
///
/// The type `Arc<T>` provides shared ownership of a value of type `T`,
/// allocated in the heap. Invoking [`clone`][clone] on `Arc` produces
/// a new `Arc` instance, which points to the same value on the heap as the
/// source `Arc`, while increasing a reference count. When the last `Arc`
/// pointer to a given value is destroyed, the pointed-to value is also
/// destroyed.
///
/// Shared references in Rust disallow mutation by default, and `Arc` is no
/// exception: you cannot generally obtain a mutable reference to something
/// inside an `Arc`. If you need to mutate through an `Arc`, use
/// [`Mutex`][mutex], [`RwLock`][rwlock], or one of the [`Atomic`][atomic]
/// types.
///
/// ## Thread Safety
///
/// Unlike [`Rc<T>`], `Arc<T>` uses atomic operations for its reference
/// counting. This means that it is thread-safe. The disadvantage is that
/// atomic operations are more expensive than ordinary memory accesses. If you
/// are not sharing reference-counted values between threads, consider using
/// [`Rc<T>`] for lower overhead. [`Rc<T>`] is a safe default, because the
/// compiler will catch any attempt to send an [`Rc<T>`] between threads.
/// However, a library might choose `Arc<T>` in order to give library consumers
/// more flexibility.
///
/// `Arc<T>` will implement [`Send`] and [`Sync`] as long as the `T` implements
/// [`Send`] and [`Sync`]. Why can't you put a non-thread-safe type `T` in an
/// `Arc<T>` to make it thread-safe? This may be a bit counter-intuitive at
/// first: after all, isn't the point of `Arc<T>` thread safety? The key is
/// this: `Arc<T>` makes it thread safe to have multiple ownership of the same
/// data, but it doesn't add thread safety to its data. Consider
/// `Arc<`[`RefCell<T>`]`>`. [`RefCell<T>`] isn't [`Sync`], and if `Arc<T>` was always
/// [`Send`], `Arc<`[`RefCell<T>`]`>` would be as well. But then we'd have a problem:
/// [`RefCell<T>`] is not thread safe; it keeps track of the borrowing count using
/// non-atomic operations.
///
/// In the end, this means that you may need to pair `Arc<T>` with some sort of
/// [`std::sync`] type, usually [`Mutex<T>`][mutex].
///
/// ## Breaking cycles with `Weak`
///
/// The [`downgrade`][downgrade] method can be used to create a non-owning
/// [`Weak`][weak] pointer. A [`Weak`][weak] pointer can be [`upgrade`][upgrade]d
/// to an `Arc`, but this will return [`None`] if the value has already been
/// dropped.
///
/// A cycle between `Arc` pointers will never be deallocated. For this reason,
/// [`Weak`][weak] is used to break cycles. For example, a tree could have
/// strong `Arc` pointers from parent nodes to children, and [`Weak`][weak]
/// pointers from children back to their parents.
///
/// # Cloning references
///
/// Creating a new reference from an existing reference counted pointer is done using the
/// `Clone` trait implemented for [`Arc<T>`][arc] and [`Weak<T>`][weak].
///
/// ```
/// use std::sync::Arc;
/// let foo = Arc::new(vec![1.0, 2.0, 3.0]);
/// // The two syntaxes below are equivalent.
/// let a = foo.clone();
/// let b = Arc::clone(&foo);
/// // a, b, and foo are all Arcs that point to the same memory location
/// ```
///
/// The [`Arc::clone(&from)`] syntax is the most idiomatic because it conveys more explicitly
/// the meaning of the code. In the example above, this syntax makes it easier to see that
/// this code is creating a new reference rather than copying the whole content of foo.
///
/// ## `Deref` behavior
///
/// `Arc<T>` automatically dereferences to `T` (via the [`Deref`][deref] trait),
/// so you can call `T`'s methods on a value of type `Arc<T>`. To avoid name
/// clashes with `T`'s methods, the methods of `Arc<T>` itself are associated
/// functions, called using function-like syntax:
///
/// ```
/// use std::sync::Arc;
/// let my_arc = Arc::new(());
///
/// Arc::downgrade(&my_arc);
/// ```
///
/// [`Weak<T>`][weak] does not auto-dereference to `T`, because the value may have
/// already been destroyed.
///
/// [arc]: struct.Arc.html
/// [weak]: struct.Weak.html
/// [`Rc<T>`]: ../../std/rc/struct.Rc.html
/// [clone]: ../../std/clone/trait.Clone.html#tymethod.clone
/// [mutex]: ../../std/sync/struct.Mutex.html
/// [rwlock]: ../../std/sync/struct.RwLock.html
/// [atomic]: ../../std/sync/atomic/index.html
/// [`Send`]: ../../std/marker/trait.Send.html
/// [`Sync`]: ../../std/marker/trait.Sync.html
/// [deref]: ../../std/ops/trait.Deref.html
/// [downgrade]: struct.Arc.html#method.downgrade
/// [upgrade]: struct.Weak.html#method.upgrade
/// [`None`]: ../../std/option/enum.Option.html#variant.None
/// [`RefCell<T>`]: ../../std/cell/struct.RefCell.html
/// [`std::sync`]: ../../std/sync/index.html
/// [`Arc::clone(&from)`]: #method.clone
///
/// # Examples
///
/// Sharing some immutable data between threads:
///
// Note that we **do not** run these tests here. The windows builders get super
// unhappy if a thread outlives the main thread and then exits at the same time
// (something deadlocks) so we just avoid this entirely by not running these
// tests.
/// ```no_run
/// use std::sync::Arc;
/// use std::thread;
///
/// let five = Arc::new(5);
///
/// for _ in 0..10 {
/// let five = Arc::clone(&five);
///
/// thread::spawn(move || {
/// println!("{:?}", five);
/// });
/// }
/// ```
///
/// Sharing a mutable [`AtomicUsize`]:
///
/// [`AtomicUsize`]: ../../std/sync/atomic/struct.AtomicUsize.html
///
/// ```no_run
/// use std::sync::Arc;
/// use std::sync::atomic::{AtomicUsize, Ordering};
/// use std::thread;
///
/// let val = Arc::new(AtomicUsize::new(5));
///
/// for _ in 0..10 {
/// let val = Arc::clone(&val);
///
/// thread::spawn(move || {
/// let v = val.fetch_add(1, Ordering::SeqCst);
/// println!("{:?}", v);
/// });
/// }
/// ```
///
/// See the [`rc` documentation][rc_examples] for more examples of reference
/// counting in general.
///
/// [rc_examples]: ../../std/rc/index.html#examples
#[cfg_attr(not(test), lang = "arc")]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Arc<T: ?Sized> {
ptr: NonNull<ArcInner<T>>,
phantom: PhantomData<T>,
}
#[stable(feature = "rust1", since = "1.0.0")]
unsafe impl<T: ?Sized + Sync + Send> Send for Arc<T> {}
#[stable(feature = "rust1", since = "1.0.0")]
unsafe impl<T: ?Sized + Sync + Send> Sync for Arc<T> {}
#[unstable(feature = "coerce_unsized", issue = "27732")]
impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Arc<U>> for Arc<T> {}
#[unstable(feature = "dispatch_from_dyn", issue = "0")]
impl<T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<Arc<U>> for Arc<T> {}
/// `Weak` is a version of [`Arc`] that holds a non-owning reference to the
/// managed value. The value is accessed by calling [`upgrade`] on the `Weak`
/// pointer, which returns an [`Option`]`<`[`Arc`]`<T>>`.
///
/// Since a `Weak` reference does not count towards ownership, it will not
/// prevent the inner value from being dropped, and `Weak` itself makes no
/// guarantees about the value still being present and may return [`None`]
/// when [`upgrade`]d.
///
/// A `Weak` pointer is useful for keeping a temporary reference to the value
/// within [`Arc`] without extending its lifetime. It is also used to prevent
/// circular references between [`Arc`] pointers, since mutual owning references
/// would never allow either [`Arc`] to be dropped. For example, a tree could
/// have strong [`Arc`] pointers from parent nodes to children, and `Weak`
/// pointers from children back to their parents.
///
/// The typical way to obtain a `Weak` pointer is to call [`Arc::downgrade`].
///
/// [`Arc`]: struct.Arc.html
/// [`Arc::downgrade`]: struct.Arc.html#method.downgrade
/// [`upgrade`]: struct.Weak.html#method.upgrade
/// [`Option`]: ../../std/option/enum.Option.html
/// [`None`]: ../../std/option/enum.Option.html#variant.None
#[stable(feature = "arc_weak", since = "1.4.0")]
pub struct Weak<T: ?Sized> {
// This is a `NonNull` to allow optimizing the size of this type in enums,
// but it is not necessarily a valid pointer.
// `Weak::new` sets this to `usize::MAX` so that it doesn’t need
// to allocate space on the heap. That's not a value a real pointer
// will ever have because RcBox has alignment at least 2.
ptr: NonNull<ArcInner<T>>,
}
#[stable(feature = "arc_weak", since = "1.4.0")]
unsafe impl<T: ?Sized + Sync + Send> Send for Weak<T> {}
#[stable(feature = "arc_weak", since = "1.4.0")]
unsafe impl<T: ?Sized + Sync + Send> Sync for Weak<T> {}
#[unstable(feature = "coerce_unsized", issue = "27732")]
impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Weak<U>> for Weak<T> {}
#[unstable(feature = "dispatch_from_dyn", issue = "0")]
impl<T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<Weak<U>> for Weak<T> {}
#[stable(feature = "arc_weak", since = "1.4.0")]
impl<T: ?Sized + fmt::Debug> fmt::Debug for Weak<T> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
write!(f, "(Weak)")
}
}
struct ArcInner<T: ?Sized> {
strong: atomic::AtomicUsize,
// the value usize::MAX acts as a sentinel for temporarily "locking" the
// ability to upgrade weak pointers or downgrade strong ones; this is used
// to avoid races in `make_mut` and `get_mut`.
weak: atomic::AtomicUsize,
data: T,
}
unsafe impl<T: ?Sized + Sync + Send> Send for ArcInner<T> {}
unsafe impl<T: ?Sized + Sync + Send> Sync for ArcInner<T> {}
impl<T> Arc<T> {
/// Constructs a new `Arc<T>`.
///
/// # Examples
///
/// ```
/// use std::sync::Arc;
///
/// let five = Arc::new(5);
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn new(data: T) -> Arc<T> {
// Start the weak pointer count as 1 which is the weak pointer that's
// held by all the strong pointers (kinda), see std/rc.rs for more info
let x: Box<_> = box ArcInner {
strong: atomic::AtomicUsize::new(1),
weak: atomic::AtomicUsize::new(1),
data,
};
Arc { ptr: Box::into_raw_non_null(x), phantom: PhantomData }
}
/// Constructs a new `Pin<Arc<T>>`. If `T` does not implement `Unpin`, then
/// `data` will be pinned in memory and unable to be moved.
#[stable(feature = "pin", since = "1.33.0")]
pub fn pin(data: T) -> Pin<Arc<T>> {
unsafe { Pin::new_unchecked(Arc::new(data)) }
}
/// Returns the contained value, if the `Arc` has exactly one strong reference.
///
/// Otherwise, an [`Err`][result] is returned with the same `Arc` that was
/// passed in.
///
/// This will succeed even if there are outstanding weak references.
///
/// [result]: ../../std/result/enum.Result.html
///
/// # Examples
///
/// ```
/// use std::sync::Arc;
///
/// let x = Arc::new(3);
/// assert_eq!(Arc::try_unwrap(x), Ok(3));
///
/// let x = Arc::new(4);
/// let _y = Arc::clone(&x);
/// assert_eq!(*Arc::try_unwrap(x).unwrap_err(), 4);
/// ```
#[inline]
#[stable(feature = "arc_unique", since = "1.4.0")]
pub fn try_unwrap(this: Self) -> Result<T, Self> {
// See `drop` for why all these atomics are like this
if this.inner().strong.compare_exchange(1, 0, Release, Relaxed).is_err() {
return Err(this);
}
atomic::fence(Acquire);
unsafe {
let elem = ptr::read(&this.ptr.as_ref().data);
// Make a weak pointer to clean up the implicit strong-weak reference
let _weak = Weak { ptr: this.ptr };
mem::forget(this);
Ok(elem)
}
}
}
impl<T: ?Sized> Arc<T> {
/// Consumes the `Arc`, returning the wrapped pointer.
///
/// To avoid a memory leak the pointer must be converted back to an `Arc` using
/// [`Arc::from_raw`][from_raw].
///
/// [from_raw]: struct.Arc.html#method.from_raw
///
/// # Examples
///
/// ```
/// use std::sync::Arc;
///
/// let x = Arc::new(10);
/// let x_ptr = Arc::into_raw(x);
/// assert_eq!(unsafe { *x_ptr }, 10);
/// ```
#[stable(feature = "rc_raw", since = "1.17.0")]
pub fn into_raw(this: Self) -> *const T {
let ptr: *const T = &*this;
mem::forget(this);
ptr
}
/// Constructs an `Arc` from a raw pointer.
///
/// The raw pointer must have been previously returned by a call to a
/// [`Arc::into_raw`][into_raw].
///
/// This function is unsafe because improper use may lead to memory problems. For example, a
/// double-free may occur if the function is called twice on the same raw pointer.
///
/// [into_raw]: struct.Arc.html#method.into_raw
///
/// # Examples
///
/// ```
/// use std::sync::Arc;
///
/// let x = Arc::new(10);
/// let x_ptr = Arc::into_raw(x);
///
/// unsafe {
/// // Convert back to an `Arc` to prevent leak.
/// let x = Arc::from_raw(x_ptr);
/// assert_eq!(*x, 10);
///
/// // Further calls to `Arc::from_raw(x_ptr)` would be memory unsafe.
/// }
///
/// // The memory was freed when `x` went out of scope above, so `x_ptr` is now dangling!
/// ```
#[stable(feature = "rc_raw", since = "1.17.0")]
pub unsafe fn from_raw(ptr: *const T) -> Self {
// Align the unsized value to the end of the ArcInner.
// Because it is ?Sized, it will always be the last field in memory.
let align = align_of_val(&*ptr);
let layout = Layout::new::<ArcInner<()>>();
let offset = (layout.size() + layout.padding_needed_for(align)) as isize;
// Reverse the offset to find the original ArcInner.
let fake_ptr = ptr as *mut ArcInner<T>;
let arc_ptr = set_data_ptr(fake_ptr, (ptr as *mut u8).offset(-offset));
Arc {
ptr: NonNull::new_unchecked(arc_ptr),
phantom: PhantomData,
}
}
/// Creates a new [`Weak`][weak] pointer to this value.
///
/// [weak]: struct.Weak.html
///
/// # Examples
///
/// ```
/// use std::sync::Arc;
///
/// let five = Arc::new(5);
///
/// let weak_five = Arc::downgrade(&five);
/// ```
#[stable(feature = "arc_weak", since = "1.4.0")]
pub fn downgrade(this: &Self) -> Weak<T> {
// This Relaxed is OK because we're checking the value in the CAS
// below.
let mut cur = this.inner().weak.load(Relaxed);
loop {
// check if the weak counter is currently "locked"; if so, spin.
if cur == usize::MAX {
cur = this.inner().weak.load(Relaxed);
continue;
}
// NOTE: this code currently ignores the possibility of overflow
// into usize::MAX; in general both Rc and Arc need to be adjusted
// to deal with overflow.
// Unlike with Clone(), we need this to be an Acquire read to
// synchronize with the write coming from `is_unique`, so that the
// events prior to that write happen before this read.
match this.inner().weak.compare_exchange_weak(cur, cur + 1, Acquire, Relaxed) {
Ok(_) => {
// Make sure we do not create a dangling Weak
debug_assert!(!is_dangling(this.ptr));
return Weak { ptr: this.ptr };
}
Err(old) => cur = old,
}
}
}
/// Gets the number of [`Weak`][weak] pointers to this value.
///
/// [weak]: struct.Weak.html
///
/// # Safety
///
/// This method by itself is safe, but using it correctly requires extra care.
/// Another thread can change the weak count at any time,
/// including potentially between calling this method and acting on the result.
///
/// # Examples
///
/// ```
/// use std::sync::Arc;
///
/// let five = Arc::new(5);
/// let _weak_five = Arc::downgrade(&five);
///
/// // This assertion is deterministic because we haven't shared
/// // the `Arc` or `Weak` between threads.
/// assert_eq!(1, Arc::weak_count(&five));
/// ```
#[inline]
#[stable(feature = "arc_counts", since = "1.15.0")]
pub fn weak_count(this: &Self) -> usize {
let cnt = this.inner().weak.load(SeqCst);
// If the weak count is currently locked, the value of the
// count was 0 just before taking the lock.
if cnt == usize::MAX { 0 } else { cnt - 1 }
}
/// Gets the number of strong (`Arc`) pointers to this value.
///
/// # Safety
///
/// This method by itself is safe, but using it correctly requires extra care.
/// Another thread can change the strong count at any time,
/// including potentially between calling this method and acting on the result.
///
/// # Examples
///
/// ```
/// use std::sync::Arc;
///
/// let five = Arc::new(5);
/// let _also_five = Arc::clone(&five);
///
/// // This assertion is deterministic because we haven't shared
/// // the `Arc` between threads.
/// assert_eq!(2, Arc::strong_count(&five));
/// ```
#[inline]
#[stable(feature = "arc_counts", since = "1.15.0")]
pub fn strong_count(this: &Self) -> usize {
this.inner().strong.load(SeqCst)
}
#[inline]
fn inner(&self) -> &ArcInner<T> {
// This unsafety is ok because while this arc is alive we're guaranteed
// that the inner pointer is valid. Furthermore, we know that the
// `ArcInner` structure itself is `Sync` because the inner data is
// `Sync` as well, so we're ok loaning out an immutable pointer to these
// contents.
unsafe { self.ptr.as_ref() }
}
// Non-inlined part of `drop`.
#[inline(never)]
unsafe fn drop_slow(&mut self) {
// Destroy the data at this time, even though we may not free the box
// allocation itself (there may still be weak pointers lying around).
ptr::drop_in_place(&mut self.ptr.as_mut().data);
if self.inner().weak.fetch_sub(1, Release) == 1 {
atomic::fence(Acquire);
Global.dealloc(self.ptr.cast(), Layout::for_value(self.ptr.as_ref()))
}
}
#[inline]
#[stable(feature = "ptr_eq", since = "1.17.0")]
/// Returns true if the two `Arc`s point to the same value (not
/// just values that compare as equal).
///
/// # Examples
///
/// ```
/// use std::sync::Arc;
///
/// let five = Arc::new(5);
/// let same_five = Arc::clone(&five);
/// let other_five = Arc::new(5);
///
/// assert!(Arc::ptr_eq(&five, &same_five));
/// assert!(!Arc::ptr_eq(&five, &other_five));
/// ```
pub fn ptr_eq(this: &Self, other: &Self) -> bool {
this.ptr.as_ptr() == other.ptr.as_ptr()
}
}
impl<T: ?Sized> Arc<T> {
// Allocates an `ArcInner<T>` with sufficient space for an unsized value
unsafe fn allocate_for_ptr(ptr: *const T) -> *mut ArcInner<T> {
// Calculate layout using the given value.
// Previously, layout was calculated on the expression
// `&*(ptr as *const ArcInner<T>)`, but this created a misaligned
// reference (see #54908).
let layout = Layout::new::<ArcInner<()>>()
.extend(Layout::for_value(&*ptr)).unwrap().0
.pad_to_align().unwrap();
let mem = Global.alloc(layout)
.unwrap_or_else(|_| handle_alloc_error(layout));
// Initialize the ArcInner
let inner = set_data_ptr(ptr as *mut T, mem.as_ptr() as *mut u8) as *mut ArcInner<T>;
debug_assert_eq!(Layout::for_value(&*inner), layout);
ptr::write(&mut (*inner).strong, atomic::AtomicUsize::new(1));
ptr::write(&mut (*inner).weak, atomic::AtomicUsize::new(1));
inner
}
fn from_box(v: Box<T>) -> Arc<T> {
unsafe {
let box_unique = Box::into_unique(v);
let bptr = box_unique.as_ptr();
let value_size = size_of_val(&*bptr);
let ptr = Self::allocate_for_ptr(bptr);
// Copy value as bytes
ptr::copy_nonoverlapping(
bptr as *const T as *const u8,
&mut (*ptr).data as *mut _ as *mut u8,
value_size);
// Free the allocation without dropping its contents
box_free(box_unique);
Arc { ptr: NonNull::new_unchecked(ptr), phantom: PhantomData }
}
}
}
// Sets the data pointer of a `?Sized` raw pointer.
//
// For a slice/trait object, this sets the `data` field and leaves the rest
// unchanged. For a sized raw pointer, this simply sets the pointer.
unsafe fn set_data_ptr<T: ?Sized, U>(mut ptr: *mut T, data: *mut U) -> *mut T {
ptr::write(&mut ptr as *mut _ as *mut *mut u8, data as *mut u8);
ptr
}
impl<T> Arc<[T]> {
// Copy elements from slice into newly allocated Arc<[T]>
//
// Unsafe because the caller must either take ownership or bind `T: Copy`
unsafe fn copy_from_slice(v: &[T]) -> Arc<[T]> {
let v_ptr = v as *const [T];
let ptr = Self::allocate_for_ptr(v_ptr);
ptr::copy_nonoverlapping(
v.as_ptr(),
&mut (*ptr).data as *mut [T] as *mut T,
v.len());
Arc { ptr: NonNull::new_unchecked(ptr), phantom: PhantomData }
}
}
// Specialization trait used for From<&[T]>
trait ArcFromSlice<T> {
fn from_slice(slice: &[T]) -> Self;
}
impl<T: Clone> ArcFromSlice<T> for Arc<[T]> {
#[inline]
default fn from_slice(v: &[T]) -> Self {
// Panic guard while cloning T elements.
// In the event of a panic, elements that have been written
// into the new ArcInner will be dropped, then the memory freed.
struct Guard<T> {
mem: NonNull<u8>,
elems: *mut T,
layout: Layout,
n_elems: usize,
}
impl<T> Drop for Guard<T> {
fn drop(&mut self) {
use core::slice::from_raw_parts_mut;
unsafe {
let slice = from_raw_parts_mut(self.elems, self.n_elems);
ptr::drop_in_place(slice);
Global.dealloc(self.mem.cast(), self.layout.clone());
}
}
}
unsafe {
let v_ptr = v as *const [T];
let ptr = Self::allocate_for_ptr(v_ptr);
let mem = ptr as *mut _ as *mut u8;
let layout = Layout::for_value(&*ptr);
// Pointer to first element
let elems = &mut (*ptr).data as *mut [T] as *mut T;
let mut guard = Guard{
mem: NonNull::new_unchecked(mem),
elems: elems,
layout: layout,
n_elems: 0,
};
for (i, item) in v.iter().enumerate() {
ptr::write(elems.add(i), item.clone());
guard.n_elems += 1;
}
// All clear. Forget the guard so it doesn't free the new ArcInner.
mem::forget(guard);
Arc { ptr: NonNull::new_unchecked(ptr), phantom: PhantomData }
}
}
}
impl<T: Copy> ArcFromSlice<T> for Arc<[T]> {
#[inline]
fn from_slice(v: &[T]) -> Self {
unsafe { Arc::copy_from_slice(v) }
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> Clone for Arc<T> {
/// Makes a clone of the `Arc` pointer.
///
/// This creates another pointer to the same inner value, increasing the
/// strong reference count.
///
/// # Examples
///
/// ```
/// use std::sync::Arc;
///
/// let five = Arc::new(5);
///
/// let _ = Arc::clone(&five);
/// ```
#[inline]
fn clone(&self) -> Arc<T> {
// Using a relaxed ordering is alright here, as knowledge of the
// original reference prevents other threads from erroneously deleting
// the object.
//
// As explained in the [Boost documentation][1], Increasing the
// reference counter can always be done with memory_order_relaxed: New
// references to an object can only be formed from an existing
// reference, and passing an existing reference from one thread to
// another must already provide any required synchronization.
//
// [1]: (www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html)
let old_size = self.inner().strong.fetch_add(1, Relaxed);
// However we need to guard against massive refcounts in case someone
// is `mem::forget`ing Arcs. If we don't do this the count can overflow
// and users will use-after free. We racily saturate to `isize::MAX` on
// the assumption that there aren't ~2 billion threads incrementing
// the reference count at once. This branch will never be taken in
// any realistic program.
//
// We abort because such a program is incredibly degenerate, and we
// don't care to support it.
if old_size > MAX_REFCOUNT {
unsafe {
abort();
}
}
Arc { ptr: self.ptr, phantom: PhantomData }
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> Deref for Arc<T> {
type Target = T;
#[inline]
fn deref(&self) -> &T {
&self.inner().data
}
}
#[unstable(feature = "receiver_trait", issue = "0")]
impl<T: ?Sized> Receiver for Arc<T> {}
impl<T: Clone> Arc<T> {
/// Makes a mutable reference into the given `Arc`.
///
/// If there are other `Arc` or [`Weak`][weak] pointers to the same value,
/// then `make_mut` will invoke [`clone`][clone] on the inner value to
/// ensure unique ownership. This is also referred to as clone-on-write.
///
/// See also [`get_mut`][get_mut], which will fail rather than cloning.
///
/// [weak]: struct.Weak.html
/// [clone]: ../../std/clone/trait.Clone.html#tymethod.clone
/// [get_mut]: struct.Arc.html#method.get_mut
///
/// # Examples
///
/// ```
/// use std::sync::Arc;
///
/// let mut data = Arc::new(5);
///
/// *Arc::make_mut(&mut data) += 1; // Won't clone anything
/// let mut other_data = Arc::clone(&data); // Won't clone inner data
/// *Arc::make_mut(&mut data) += 1; // Clones inner data
/// *Arc::make_mut(&mut data) += 1; // Won't clone anything
/// *Arc::make_mut(&mut other_data) *= 2; // Won't clone anything
///
/// // Now `data` and `other_data` point to different values.
/// assert_eq!(*data, 8);
/// assert_eq!(*other_data, 12);
/// ```
#[inline]
#[stable(feature = "arc_unique", since = "1.4.0")]
pub fn make_mut(this: &mut Self) -> &mut T {
// Note that we hold both a strong reference and a weak reference.
// Thus, releasing our strong reference only will not, by itself, cause
// the memory to be deallocated.
//
// Use Acquire to ensure that we see any writes to `weak` that happen
// before release writes (i.e., decrements) to `strong`. Since we hold a
// weak count, there's no chance the ArcInner itself could be
// deallocated.
if this.inner().strong.compare_exchange(1, 0, Acquire, Relaxed).is_err() {
// Another strong pointer exists; clone
*this = Arc::new((**this).clone());
} else if this.inner().weak.load(Relaxed) != 1 {
// Relaxed suffices in the above because this is fundamentally an
// optimization: we are always racing with weak pointers being
// dropped. Worst case, we end up allocated a new Arc unnecessarily.
// We removed the last strong ref, but there are additional weak
// refs remaining. We'll move the contents to a new Arc, and
// invalidate the other weak refs.
// Note that it is not possible for the read of `weak` to yield
// usize::MAX (i.e., locked), since the weak count can only be
// locked by a thread with a strong reference.
// Materialize our own implicit weak pointer, so that it can clean
// up the ArcInner as needed.
let weak = Weak { ptr: this.ptr };
// mark the data itself as already deallocated
unsafe {
// there is no data race in the implicit write caused by `read`
// here (due to zeroing) because data is no longer accessed by
// other threads (due to there being no more strong refs at this
// point).
let mut swap = Arc::new(ptr::read(&weak.ptr.as_ref().data));
mem::swap(this, &mut swap);
mem::forget(swap);
}
} else {
// We were the sole reference of either kind; bump back up the
// strong ref count.
this.inner().strong.store(1, Release);
}
// As with `get_mut()`, the unsafety is ok because our reference was
// either unique to begin with, or became one upon cloning the contents.
unsafe {
&mut this.ptr.as_mut().data
}
}
}
impl<T: ?Sized> Arc<T> {
/// Returns a mutable reference to the inner value, if there are
/// no other `Arc` or [`Weak`][weak] pointers to the same value.
///
/// Returns [`None`][option] otherwise, because it is not safe to
/// mutate a shared value.
///
/// See also [`make_mut`][make_mut], which will [`clone`][clone]
/// the inner value when it's shared.
///
/// [weak]: struct.Weak.html
/// [option]: ../../std/option/enum.Option.html
/// [make_mut]: struct.Arc.html#method.make_mut
/// [clone]: ../../std/clone/trait.Clone.html#tymethod.clone
///
/// # Examples
///
/// ```
/// use std::sync::Arc;
///
/// let mut x = Arc::new(3);
/// *Arc::get_mut(&mut x).unwrap() = 4;
/// assert_eq!(*x, 4);
///
/// let _y = Arc::clone(&x);
/// assert!(Arc::get_mut(&mut x).is_none());
/// ```
#[inline]
#[stable(feature = "arc_unique", since = "1.4.0")]
pub fn get_mut(this: &mut Self) -> Option<&mut T> {
if this.is_unique() {
// This unsafety is ok because we're guaranteed that the pointer
// returned is the *only* pointer that will ever be returned to T. Our
// reference count is guaranteed to be 1 at this point, and we required
// the Arc itself to be `mut`, so we're returning the only possible
// reference to the inner data.
unsafe {
Some(&mut this.ptr.as_mut().data)
}
} else {
None
}
}
/// Determine whether this is the unique reference (including weak refs) to
/// the underlying data.
///
/// Note that this requires locking the weak ref count.
fn is_unique(&mut self) -> bool {
// lock the weak pointer count if we appear to be the sole weak pointer
// holder.
//
// The acquire label here ensures a happens-before relationship with any
// writes to `strong` (in particular in `Weak::upgrade`) prior to decrements
// of the `weak` count (via `Weak::drop`, which uses release). If the upgraded
// weak ref was never dropped, the CAS here will fail so we do not care to synchronize.
if self.inner().weak.compare_exchange(1, usize::MAX, Acquire, Relaxed).is_ok() {
// This needs to be an `Acquire` to synchronize with the decrement of the `strong`
// counter in `drop` -- the only access that happens when any but the last reference
// is being dropped.
let unique = self.inner().strong.load(Acquire) == 1;
// The release write here synchronizes with a read in `downgrade`,
// effectively preventing the above read of `strong` from happening
// after the write.
self.inner().weak.store(1, Release); // release the lock
unique
} else {
false
}
}
}
#[stable(feature = "rust1", since = "1.0.0")]
unsafe impl<#[may_dangle] T: ?Sized> Drop for Arc<T> {
/// Drops the `Arc`.
///
/// This will decrement the strong reference count. If the strong reference
/// count reaches zero then the only other references (if any) are
/// [`Weak`], so we `drop` the inner value.
///
/// # Examples
///
/// ```
/// use std::sync::Arc;
///
/// struct Foo;
///
/// impl Drop for Foo {
/// fn drop(&mut self) {
/// println!("dropped!");
/// }
/// }
///
/// let foo = Arc::new(Foo);
/// let foo2 = Arc::clone(&foo);
///
/// drop(foo); // Doesn't print anything
/// drop(foo2); // Prints "dropped!"
/// ```
///
/// [`Weak`]: ../../std/sync/struct.Weak.html
#[inline]
fn drop(&mut self) {
// Because `fetch_sub` is already atomic, we do not need to synchronize
// with other threads unless we are going to delete the object. This
// same logic applies to the below `fetch_sub` to the `weak` count.
if self.inner().strong.fetch_sub(1, Release) != 1 {
return;
}
// This fence is needed to prevent reordering of use of the data and
// deletion of the data. Because it is marked `Release`, the decreasing
// of the reference count synchronizes with this `Acquire` fence. This
// means that use of the data happens before decreasing the reference
// count, which happens before this fence, which happens before the
// deletion of the data.
//
// As explained in the [Boost documentation][1],
//
// > It is important to enforce any possible access to the object in one
// > thread (through an existing reference) to *happen before* deleting
// > the object in a different thread. This is achieved by a "release"
// > operation after dropping a reference (any access to the object
// > through this reference must obviously happened before), and an
// > "acquire" operation before deleting the object.
//
// In particular, while the contents of an Arc are usually immutable, it's
// possible to have interior writes to something like a Mutex<T>. Since a
// Mutex is not acquired when it is deleted, we can't rely on its
// synchronization logic to make writes in thread A visible to a destructor
// running in thread B.
//
// Also note that the Acquire fence here could probably be replaced with an
// Acquire load, which could improve performance in highly-contended
// situations. See [2].
//
// [1]: (www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html)
// [2]: (https://github.com/rust-lang/rust/pull/41714)
atomic::fence(Acquire);
unsafe {
self.drop_slow();
}
}
}
impl Arc<dyn Any + Send + Sync> {
#[inline]
#[stable(feature = "rc_downcast", since = "1.29.0")]
/// Attempt to downcast the `Arc<dyn Any + Send + Sync>` to a concrete type.
///
/// # Examples
///
/// ```
/// use std::any::Any;
/// use std::sync::Arc;
///
/// fn print_if_string(value: Arc<dyn Any + Send + Sync>) {
/// if let Ok(string) = value.downcast::<String>() {
/// println!("String ({}): {}", string.len(), string);
/// }
/// }
///
/// fn main() {
/// let my_string = "Hello World".to_string();
/// print_if_string(Arc::new(my_string));
/// print_if_string(Arc::new(0i8));
/// }
/// ```
pub fn downcast<T>(self) -> Result<Arc<T>, Self>
where
T: Any + Send + Sync + 'static,
{
if (*self).is::<T>() {
let ptr = self.ptr.cast::<ArcInner<T>>();
mem::forget(self);
Ok(Arc { ptr, phantom: PhantomData })
} else {
Err(self)
}
}
}
impl<T> Weak<T> {
/// Constructs a new `Weak<T>`, without allocating any memory.
/// Calling [`upgrade`] on the return value always gives [`None`].
///
/// [`upgrade`]: struct.Weak.html#method.upgrade
/// [`None`]: ../../std/option/enum.Option.html#variant.None
///
/// # Examples
///
/// ```
/// use std::sync::Weak;
///
/// let empty: Weak<i64> = Weak::new();
/// assert!(empty.upgrade().is_none());
/// ```
#[stable(feature = "downgraded_weak", since = "1.10.0")]
pub fn new() -> Weak<T> {
Weak {
ptr: NonNull::new(usize::MAX as *mut ArcInner<T>).expect("MAX is not 0"),
}
}
}
impl<T: ?Sized> Weak<T> {
/// Attempts to upgrade the `Weak` pointer to an [`Arc`], extending
/// the lifetime of the value if successful.
///
/// Returns [`None`] if the value has since been dropped.
///
/// [`Arc`]: struct.Arc.html
/// [`None`]: ../../std/option/enum.Option.html#variant.None
///
/// # Examples
///
/// ```
/// use std::sync::Arc;
///
/// let five = Arc::new(5);
///
/// let weak_five = Arc::downgrade(&five);
///
/// let strong_five: Option<Arc<_>> = weak_five.upgrade();
/// assert!(strong_five.is_some());
///
/// // Destroy all strong pointers.
/// drop(strong_five);
/// drop(five);
///
/// assert!(weak_five.upgrade().is_none());
/// ```
#[stable(feature = "arc_weak", since = "1.4.0")]
pub fn upgrade(&self) -> Option<Arc<T>> {
// We use a CAS loop to increment the strong count instead of a
// fetch_add because once the count hits 0 it must never be above 0.
let inner = self.inner()?;
// Relaxed load because any write of 0 that we can observe
// leaves the field in a permanently zero state (so a
// "stale" read of 0 is fine), and any other value is
// confirmed via the CAS below.
let mut n = inner.strong.load(Relaxed);
loop {
if n == 0 {
return None;
}
// See comments in `Arc::clone` for why we do this (for `mem::forget`).
if n > MAX_REFCOUNT {
unsafe {
abort();
}
}
// Relaxed is valid for the same reason it is on Arc's Clone impl
match inner.strong.compare_exchange_weak(n, n + 1, Relaxed, Relaxed) {
Ok(_) => return Some(Arc {
// null checked above
ptr: self.ptr,
phantom: PhantomData,
}),
Err(old) => n = old,
}
}
}
/// Return `None` when the pointer is dangling and there is no allocated `ArcInner`,
/// i.e., this `Weak` was created by `Weak::new`
#[inline]
fn inner(&self) -> Option<&ArcInner<T>> {
if is_dangling(self.ptr) {
None
} else {
Some(unsafe { self.ptr.as_ref() })
}
}
/// Returns true if the two `Weak`s point to the same value (not just values
/// that compare as equal).
///
/// # Notes
///
/// Since this compares pointers it means that `Weak::new()` will equal each
/// other, even though they don't point to any value.
///
///
/// # Examples
///
/// ```
/// #![feature(weak_ptr_eq)]
/// use std::sync::{Arc, Weak};
///
/// let first_rc = Arc::new(5);
/// let first = Arc::downgrade(&first_rc);
/// let second = Arc::downgrade(&first_rc);
///
/// assert!(Weak::ptr_eq(&first, &second));
///
/// let third_rc = Arc::new(5);
/// let third = Arc::downgrade(&third_rc);
///
/// assert!(!Weak::ptr_eq(&first, &third));
/// ```
///
/// Comparing `Weak::new`.
///
/// ```
/// #![feature(weak_ptr_eq)]
/// use std::sync::{Arc, Weak};
///
/// let first = Weak::new();
/// let second = Weak::new();
/// assert!(Weak::ptr_eq(&first, &second));
///
/// let third_rc = Arc::new(());
/// let third = Arc::downgrade(&third_rc);
/// assert!(!Weak::ptr_eq(&first, &third));
/// ```
#[inline]
#[unstable(feature = "weak_ptr_eq", issue = "55981")]
pub fn ptr_eq(this: &Self, other: &Self) -> bool {
this.ptr.as_ptr() == other.ptr.as_ptr()
}
}
#[stable(feature = "arc_weak", since = "1.4.0")]
impl<T: ?Sized> Clone for Weak<T> {
/// Makes a clone of the `Weak` pointer that points to the same value.
///
/// # Examples
///
/// ```
/// use std::sync::{Arc, Weak};
///
/// let weak_five = Arc::downgrade(&Arc::new(5));
///
/// let _ = Weak::clone(&weak_five);
/// ```
#[inline]
fn clone(&self) -> Weak<T> {
let inner = if let Some(inner) = self.inner() {
inner
} else {
return Weak { ptr: self.ptr };
};
// See comments in Arc::clone() for why this is relaxed. This can use a
// fetch_add (ignoring the lock) because the weak count is only locked
// where are *no other* weak pointers in existence. (So we can't be
// running this code in that case).
let old_size = inner.weak.fetch_add(1, Relaxed);
// See comments in Arc::clone() for why we do this (for mem::forget).
if old_size > MAX_REFCOUNT {
unsafe {
abort();
}
}
return Weak { ptr: self.ptr };
}
}
#[stable(feature = "downgraded_weak", since = "1.10.0")]
impl<T> Default for Weak<T> {
/// Constructs a new `Weak<T>`, without allocating memory.
/// Calling [`upgrade`] on the return value always
/// gives [`None`].
///
/// [`None`]: ../../std/option/enum.Option.html#variant.None
/// [`upgrade`]: ../../std/sync/struct.Weak.html#method.upgrade
///
/// # Examples
///
/// ```
/// use std::sync::Weak;
///
/// let empty: Weak<i64> = Default::default();
/// assert!(empty.upgrade().is_none());
/// ```
fn default() -> Weak<T> {
Weak::new()
}
}
#[stable(feature = "arc_weak", since = "1.4.0")]
impl<T: ?Sized> Drop for Weak<T> {
/// Drops the `Weak` pointer.
///
/// # Examples
///
/// ```
/// use std::sync::{Arc, Weak};
///
/// struct Foo;
///
/// impl Drop for Foo {
/// fn drop(&mut self) {
/// println!("dropped!");
/// }
/// }
///
/// let foo = Arc::new(Foo);
/// let weak_foo = Arc::downgrade(&foo);
/// let other_weak_foo = Weak::clone(&weak_foo);
///
/// drop(weak_foo); // Doesn't print anything
/// drop(foo); // Prints "dropped!"
///
/// assert!(other_weak_foo.upgrade().is_none());
/// ```
fn drop(&mut self) {
// If we find out that we were the last weak pointer, then its time to
// deallocate the data entirely. See the discussion in Arc::drop() about
// the memory orderings
//
// It's not necessary to check for the locked state here, because the
// weak count can only be locked if there was precisely one weak ref,
// meaning that drop could only subsequently run ON that remaining weak
// ref, which can only happen after the lock is released.
let inner = if let Some(inner) = self.inner() {
inner
} else {
return
};
if inner.weak.fetch_sub(1, Release) == 1 {
atomic::fence(Acquire);
unsafe {
Global.dealloc(self.ptr.cast(), Layout::for_value(self.ptr.as_ref()))
}
}
}
}
#[stable(feature = "rust1", since = "1.0.0")]
trait ArcEqIdent<T: ?Sized + PartialEq> {
fn eq(&self, other: &Arc<T>) -> bool;
fn ne(&self, other: &Arc<T>) -> bool;
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized + PartialEq> ArcEqIdent<T> for Arc<T> {
#[inline]
default fn eq(&self, other: &Arc<T>) -> bool {
**self == **other
}
#[inline]
default fn ne(&self, other: &Arc<T>) -> bool {
**self != **other
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized + Eq> ArcEqIdent<T> for Arc<T> {
#[inline]
fn eq(&self, other: &Arc<T>) -> bool {
Arc::ptr_eq(self, other) || **self == **other
}
#[inline]
fn ne(&self, other: &Arc<T>) -> bool {
!Arc::ptr_eq(self, other) && **self != **other
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized + PartialEq> PartialEq for Arc<T> {
/// Equality for two `Arc`s.
///
/// Two `Arc`s are equal if their inner values are equal.
///
/// If `T` also implements `Eq`, two `Arc`s that point to the same value are
/// always equal.
///
/// # Examples
///
/// ```
/// use std::sync::Arc;
///
/// let five = Arc::new(5);
///
/// assert!(five == Arc::new(5));
/// ```
#[inline]
fn eq(&self, other: &Arc<T>) -> bool {
ArcEqIdent::eq(self, other)
}
/// Inequality for two `Arc`s.
///
/// Two `Arc`s are unequal if their inner values are unequal.
///
/// If `T` also implements `Eq`, two `Arc`s that point to the same value are
/// never unequal.
///
/// # Examples
///
/// ```
/// use std::sync::Arc;
///
/// let five = Arc::new(5);
///
/// assert!(five != Arc::new(6));
/// ```
#[inline]
fn ne(&self, other: &Arc<T>) -> bool {
ArcEqIdent::ne(self, other)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized + PartialOrd> PartialOrd for Arc<T> {
/// Partial comparison for two `Arc`s.
///
/// The two are compared by calling `partial_cmp()` on their inner values.
///
/// # Examples
///
/// ```
/// use std::sync::Arc;
/// use std::cmp::Ordering;
///
/// let five = Arc::new(5);
///
/// assert_eq!(Some(Ordering::Less), five.partial_cmp(&Arc::new(6)));
/// ```
fn partial_cmp(&self, other: &Arc<T>) -> Option<Ordering> {
(**self).partial_cmp(&**other)
}
/// Less-than comparison for two `Arc`s.
///
/// The two are compared by calling `<` on their inner values.
///
/// # Examples
///
/// ```
/// use std::sync::Arc;
///
/// let five = Arc::new(5);
///
/// assert!(five < Arc::new(6));
/// ```
fn lt(&self, other: &Arc<T>) -> bool {
*(*self) < *(*other)
}
/// 'Less than or equal to' comparison for two `Arc`s.
///
/// The two are compared by calling `<=` on their inner values.
///
/// # Examples
///
/// ```
/// use std::sync::Arc;
///
/// let five = Arc::new(5);
///
/// assert!(five <= Arc::new(5));
/// ```
fn le(&self, other: &Arc<T>) -> bool {
*(*self) <= *(*other)
}
/// Greater-than comparison for two `Arc`s.
///
/// The two are compared by calling `>` on their inner values.
///
/// # Examples
///
/// ```
/// use std::sync::Arc;
///
/// let five = Arc::new(5);
///
/// assert!(five > Arc::new(4));
/// ```
fn gt(&self, other: &Arc<T>) -> bool {
*(*self) > *(*other)
}
/// 'Greater than or equal to' comparison for two `Arc`s.
///
/// The two are compared by calling `>=` on their inner values.
///
/// # Examples
///
/// ```
/// use std::sync::Arc;
///
/// let five = Arc::new(5);
///
/// assert!(five >= Arc::new(5));
/// ```
fn ge(&self, other: &Arc<T>) -> bool {
*(*self) >= *(*other)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized + Ord> Ord for Arc<T> {
/// Comparison for two `Arc`s.
///
/// The two are compared by calling `cmp()` on their inner values.
///
/// # Examples
///
/// ```
/// use std::sync::Arc;
/// use std::cmp::Ordering;
///
/// let five = Arc::new(5);
///
/// assert_eq!(Ordering::Less, five.cmp(&Arc::new(6)));
/// ```
fn cmp(&self, other: &Arc<T>) -> Ordering {
(**self).cmp(&**other)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized + Eq> Eq for Arc<T> {}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized + fmt::Display> fmt::Display for Arc<T> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
fmt::Display::fmt(&**self, f)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized + fmt::Debug> fmt::Debug for Arc<T> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
fmt::Debug::fmt(&**self, f)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> fmt::Pointer for Arc<T> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
fmt::Pointer::fmt(&(&**self as *const T), f)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: Default> Default for Arc<T> {
/// Creates a new `Arc<T>`, with the `Default` value for `T`.
///
/// # Examples
///
/// ```
/// use std::sync::Arc;
///
/// let x: Arc<i32> = Default::default();
/// assert_eq!(*x, 0);
/// ```
fn default() -> Arc<T> {
Arc::new(Default::default())
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized + Hash> Hash for Arc<T> {
fn hash<H: Hasher>(&self, state: &mut H) {
(**self).hash(state)
}
}
#[stable(feature = "from_for_ptrs", since = "1.6.0")]
impl<T> From<T> for Arc<T> {
fn from(t: T) -> Self {
Arc::new(t)
}
}
#[stable(feature = "shared_from_slice", since = "1.21.0")]
impl<'a, T: Clone> From<&'a [T]> for Arc<[T]> {
#[inline]
fn from(v: &[T]) -> Arc<[T]> {
<Self as ArcFromSlice<T>>::from_slice(v)
}
}
#[stable(feature = "shared_from_slice", since = "1.21.0")]
impl<'a> From<&'a str> for Arc<str> {
#[inline]
fn from(v: &str) -> Arc<str> {
let arc = Arc::<[u8]>::from(v.as_bytes());
unsafe { Arc::from_raw(Arc::into_raw(arc) as *const str) }
}
}
#[stable(feature = "shared_from_slice", since = "1.21.0")]
impl From<String> for Arc<str> {
#[inline]
fn from(v: String) -> Arc<str> {
Arc::from(&v[..])
}
}
#[stable(feature = "shared_from_slice", since = "1.21.0")]
impl<T: ?Sized> From<Box<T>> for Arc<T> {
#[inline]
fn from(v: Box<T>) -> Arc<T> {
Arc::from_box(v)
}
}
#[stable(feature = "shared_from_slice", since = "1.21.0")]
impl<T> From<Vec<T>> for Arc<[T]> {
#[inline]
fn from(mut v: Vec<T>) -> Arc<[T]> {
unsafe {
let arc = Arc::copy_from_slice(&v);
// Allow the Vec to free its memory, but not destroy its contents
v.set_len(0);
arc
}
}
}
#[cfg(test)]
mod tests {
use std::boxed::Box;
use std::clone::Clone;
use std::sync::mpsc::channel;
use std::mem::drop;
use std::ops::Drop;
use std::option::Option;
use std::option::Option::{None, Some};
use std::sync::atomic;
use std::sync::atomic::Ordering::{Acquire, SeqCst};
use std::thread;
use std::sync::Mutex;
use std::convert::From;
use super::{Arc, Weak};
use vec::Vec;
struct Canary(*mut atomic::AtomicUsize);
impl Drop for Canary {
fn drop(&mut self) {
unsafe {
match *self {
Canary(c) => {
(*c).fetch_add(1, SeqCst);
}
}
}
}
}
#[test]
#[cfg_attr(target_os = "emscripten", ignore)]
fn manually_share_arc() {
let v = vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
let arc_v = Arc::new(v);
let (tx, rx) = channel();
let _t = thread::spawn(move || {
let arc_v: Arc<Vec<i32>> = rx.recv().unwrap();
assert_eq!((*arc_v)[3], 4);
});
tx.send(arc_v.clone()).unwrap();
assert_eq!((*arc_v)[2], 3);
assert_eq!((*arc_v)[4], 5);
}
#[test]
fn test_arc_get_mut() {
let mut x = Arc::new(3);
*Arc::get_mut(&mut x).unwrap() = 4;
assert_eq!(*x, 4);
let y = x.clone();
assert!(Arc::get_mut(&mut x).is_none());
drop(y);
assert!(Arc::get_mut(&mut x).is_some());
let _w = Arc::downgrade(&x);
assert!(Arc::get_mut(&mut x).is_none());
}
#[test]
fn try_unwrap() {
let x = Arc::new(3);
assert_eq!(Arc::try_unwrap(x), Ok(3));
let x = Arc::new(4);
let _y = x.clone();
assert_eq!(Arc::try_unwrap(x), Err(Arc::new(4)));
let x = Arc::new(5);
let _w = Arc::downgrade(&x);
assert_eq!(Arc::try_unwrap(x), Ok(5));
}
#[test]
fn into_from_raw() {
let x = Arc::new(box "hello");
let y = x.clone();
let x_ptr = Arc::into_raw(x);
drop(y);
unsafe {
assert_eq!(**x_ptr, "hello");
let x = Arc::from_raw(x_ptr);
assert_eq!(**x, "hello");
assert_eq!(Arc::try_unwrap(x).map(|x| *x), Ok("hello"));
}
}
#[test]
fn test_into_from_raw_unsized() {
use std::fmt::Display;
use std::string::ToString;
let arc: Arc<str> = Arc::from("foo");
let ptr = Arc::into_raw(arc.clone());
let arc2 = unsafe { Arc::from_raw(ptr) };
assert_eq!(unsafe { &*ptr }, "foo");
assert_eq!(arc, arc2);
let arc: Arc<dyn Display> = Arc::new(123);
let ptr = Arc::into_raw(arc.clone());
let arc2 = unsafe { Arc::from_raw(ptr) };
assert_eq!(unsafe { &*ptr }.to_string(), "123");
assert_eq!(arc2.to_string(), "123");
}
#[test]
fn test_cowarc_clone_make_mut() {
let mut cow0 = Arc::new(75);
let mut cow1 = cow0.clone();
let mut cow2 = cow1.clone();
assert!(75 == *Arc::make_mut(&mut cow0));
assert!(75 == *Arc::make_mut(&mut cow1));
assert!(75 == *Arc::make_mut(&mut cow2));
*Arc::make_mut(&mut cow0) += 1;
*Arc::make_mut(&mut cow1) += 2;
*Arc::make_mut(&mut cow2) += 3;
assert!(76 == *cow0);
assert!(77 == *cow1);
assert!(78 == *cow2);
// none should point to the same backing memory
assert!(*cow0 != *cow1);
assert!(*cow0 != *cow2);
assert!(*cow1 != *cow2);
}
#[test]
fn test_cowarc_clone_unique2() {
let mut cow0 = Arc::new(75);
let cow1 = cow0.clone();
let cow2 = cow1.clone();
assert!(75 == *cow0);
assert!(75 == *cow1);
assert!(75 == *cow2);
*Arc::make_mut(&mut cow0) += 1;
assert!(76 == *cow0);
assert!(75 == *cow1);
assert!(75 == *cow2);
// cow1 and cow2 should share the same contents
// cow0 should have a unique reference
assert!(*cow0 != *cow1);
assert!(*cow0 != *cow2);
assert!(*cow1 == *cow2);
}
#[test]
fn test_cowarc_clone_weak() {
let mut cow0 = Arc::new(75);
let cow1_weak = Arc::downgrade(&cow0);
assert!(75 == *cow0);
assert!(75 == *cow1_weak.upgrade().unwrap());
*Arc::make_mut(&mut cow0) += 1;
assert!(76 == *cow0);
assert!(cow1_weak.upgrade().is_none());
}
#[test]
fn test_live() {
let x = Arc::new(5);
let y = Arc::downgrade(&x);
assert!(y.upgrade().is_some());
}
#[test]
fn test_dead() {
let x = Arc::new(5);
let y = Arc::downgrade(&x);
drop(x);
assert!(y.upgrade().is_none());
}
#[test]
fn weak_self_cyclic() {
struct Cycle {
x: Mutex<Option<Weak<Cycle>>>,
}
let a = Arc::new(Cycle { x: Mutex::new(None) });
let b = Arc::downgrade(&a.clone());
*a.x.lock().unwrap() = Some(b);
// hopefully we don't double-free (or leak)...
}
#[test]
fn drop_arc() {
let mut canary = atomic::AtomicUsize::new(0);
let x = Arc::new(Canary(&mut canary as *mut atomic::AtomicUsize));
drop(x);
assert!(canary.load(Acquire) == 1);
}
#[test]
fn drop_arc_weak() {
let mut canary = atomic::AtomicUsize::new(0);
let arc = Arc::new(Canary(&mut canary as *mut atomic::AtomicUsize));
let arc_weak = Arc::downgrade(&arc);
assert!(canary.load(Acquire) == 0);
drop(arc);
assert!(canary.load(Acquire) == 1);
drop(arc_weak);
}
#[test]
fn test_strong_count() {
let a = Arc::new(0);
assert!(Arc::strong_count(&a) == 1);
let w = Arc::downgrade(&a);
assert!(Arc::strong_count(&a) == 1);
let b = w.upgrade().expect("");
assert!(Arc::strong_count(&b) == 2);
assert!(Arc::strong_count(&a) == 2);
drop(w);
drop(a);
assert!(Arc::strong_count(&b) == 1);
let c = b.clone();
assert!(Arc::strong_count(&b) == 2);
assert!(Arc::strong_count(&c) == 2);
}
#[test]
fn test_weak_count() {
let a = Arc::new(0);
assert!(Arc::strong_count(&a) == 1);
assert!(Arc::weak_count(&a) == 0);
let w = Arc::downgrade(&a);
assert!(Arc::strong_count(&a) == 1);
assert!(Arc::weak_count(&a) == 1);
let x = w.clone();
assert!(Arc::weak_count(&a) == 2);
drop(w);
drop(x);
assert!(Arc::strong_count(&a) == 1);
assert!(Arc::weak_count(&a) == 0);
let c = a.clone();
assert!(Arc::strong_count(&a) == 2);
assert!(Arc::weak_count(&a) == 0);
let d = Arc::downgrade(&c);
assert!(Arc::weak_count(&c) == 1);
assert!(Arc::strong_count(&c) == 2);
drop(a);
drop(c);
drop(d);
}
#[test]
fn show_arc() {
let a = Arc::new(5);
assert_eq!(format!("{:?}", a), "5");
}
// Make sure deriving works with Arc<T>
#[derive(Eq, Ord, PartialEq, PartialOrd, Clone, Debug, Default)]
struct Foo {
inner: Arc<i32>,
}
#[test]
fn test_unsized() {
let x: Arc<[i32]> = Arc::new([1, 2, 3]);
assert_eq!(format!("{:?}", x), "[1, 2, 3]");
let y = Arc::downgrade(&x.clone());
drop(x);
assert!(y.upgrade().is_none());
}
#[test]
fn test_from_owned() {
let foo = 123;
let foo_arc = Arc::from(foo);
assert!(123 == *foo_arc);
}
#[test]
fn test_new_weak() {
let foo: Weak<usize> = Weak::new();
assert!(foo.upgrade().is_none());
}
#[test]
fn test_ptr_eq() {
let five = Arc::new(5);
let same_five = five.clone();
let other_five = Arc::new(5);
assert!(Arc::ptr_eq(&five, &same_five));
assert!(!Arc::ptr_eq(&five, &other_five));
}
#[test]
#[cfg_attr(target_os = "emscripten", ignore)]
fn test_weak_count_locked() {
let mut a = Arc::new(atomic::AtomicBool::new(false));
let a2 = a.clone();
let t = thread::spawn(move || {
for _i in 0..1000000 {
Arc::get_mut(&mut a);
}
a.store(true, SeqCst);
});
while !a2.load(SeqCst) {
let n = Arc::weak_count(&a2);
assert!(n < 2, "bad weak count: {}", n);
}
t.join().unwrap();
}
#[test]
fn test_from_str() {
let r: Arc<str> = Arc::from("foo");
assert_eq!(&r[..], "foo");
}
#[test]
fn test_copy_from_slice() {
let s: &[u32] = &[1, 2, 3];
let r: Arc<[u32]> = Arc::from(s);
assert_eq!(&r[..], [1, 2, 3]);
}
#[test]
fn test_clone_from_slice() {
#[derive(Clone, Debug, Eq, PartialEq)]
struct X(u32);
let s: &[X] = &[X(1), X(2), X(3)];
let r: Arc<[X]> = Arc::from(s);
assert_eq!(&r[..], s);
}
#[test]
#[should_panic]
fn test_clone_from_slice_panic() {
use std::string::{String, ToString};
struct Fail(u32, String);
impl Clone for Fail {
fn clone(&self) -> Fail {
if self.0 == 2 {
panic!();
}
Fail(self.0, self.1.clone())
}
}
let s: &[Fail] = &[
Fail(0, "foo".to_string()),
Fail(1, "bar".to_string()),
Fail(2, "baz".to_string()),
];
// Should panic, but not cause memory corruption
let _r: Arc<[Fail]> = Arc::from(s);
}
#[test]
fn test_from_box() {
let b: Box<u32> = box 123;
let r: Arc<u32> = Arc::from(b);
assert_eq!(*r, 123);
}
#[test]
fn test_from_box_str() {
use std::string::String;
let s = String::from("foo").into_boxed_str();
let r: Arc<str> = Arc::from(s);
assert_eq!(&r[..], "foo");
}
#[test]
fn test_from_box_slice() {
let s = vec![1, 2, 3].into_boxed_slice();
let r: Arc<[u32]> = Arc::from(s);
assert_eq!(&r[..], [1, 2, 3]);
}
#[test]
fn test_from_box_trait() {
use std::fmt::Display;
use std::string::ToString;
let b: Box<dyn Display> = box 123;
let r: Arc<dyn Display> = Arc::from(b);
assert_eq!(r.to_string(), "123");
}
#[test]
fn test_from_box_trait_zero_sized() {
use std::fmt::Debug;
let b: Box<dyn Debug> = box ();
let r: Arc<dyn Debug> = Arc::from(b);
assert_eq!(format!("{:?}", r), "()");
}
#[test]
fn test_from_vec() {
let v = vec![1, 2, 3];
let r: Arc<[u32]> = Arc::from(v);
assert_eq!(&r[..], [1, 2, 3]);
}
#[test]
fn test_downcast() {
use std::any::Any;
let r1: Arc<dyn Any + Send + Sync> = Arc::new(i32::max_value());
let r2: Arc<dyn Any + Send + Sync> = Arc::new("abc");
assert!(r1.clone().downcast::<u32>().is_err());
let r1i32 = r1.downcast::<i32>();
assert!(r1i32.is_ok());
assert_eq!(r1i32.unwrap(), Arc::new(i32::max_value()));
assert!(r2.clone().downcast::<i32>().is_err());
let r2str = r2.downcast::<&'static str>();
assert!(r2str.is_ok());
assert_eq!(r2str.unwrap(), Arc::new("abc"));
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> borrow::Borrow<T> for Arc<T> {
fn borrow(&self) -> &T {
&**self
}
}
#[stable(since = "1.5.0", feature = "smart_ptr_as_ref")]
impl<T: ?Sized> AsRef<T> for Arc<T> {
fn as_ref(&self) -> &T {
&**self
}
}
#[stable(feature = "pin", since = "1.33.0")]
impl<T: ?Sized> Unpin for Arc<T> { }