Expand description
A pointer to an object protected by the epoch GC.
The pointer is valid for use only during the lifetime 'g
.
The pointer must be properly aligned. Since it is aligned, a tag can be stored into the unused least significant bits of the address.
Implementations
pub fn as_raw(&self) -> *const T
pub fn as_raw(&self) -> *const T
Converts the pointer to a raw pointer (without the tag).
Examples
use crossbeam_epoch::{self as epoch, Atomic, Owned};
use std::sync::atomic::Ordering::SeqCst;
let o = Owned::new(1234);
let raw = &*o as *const _;
let a = Atomic::from(o);
let guard = &epoch::pin();
let p = a.load(SeqCst, guard);
assert_eq!(p.as_raw(), raw);
pub fn null() -> Shared<'g, T>
pub fn null() -> Shared<'g, T>
Returns a new null pointer.
Examples
use crossbeam_epoch::Shared;
let p = Shared::<i32>::null();
assert!(p.is_null());
pub fn is_null(&self) -> bool
pub fn is_null(&self) -> bool
Returns true
if the pointer is null.
Examples
use crossbeam_epoch::{self as epoch, Atomic, Owned};
use std::sync::atomic::Ordering::SeqCst;
let a = Atomic::null();
let guard = &epoch::pin();
assert!(a.load(SeqCst, guard).is_null());
a.store(Owned::new(1234), SeqCst);
assert!(!a.load(SeqCst, guard).is_null());
pub unsafe fn deref(&self) -> &'g T
pub unsafe fn deref(&self) -> &'g T
Dereferences the pointer.
Returns a reference to the pointee that is valid during the lifetime 'g
.
Safety
Dereferencing a pointer is unsafe because it could be pointing to invalid memory.
Another concern is the possibility of data races due to lack of proper synchronization. For example, consider the following scenario:
- A thread creates a new object:
a.store(Owned::new(10), Relaxed)
- Another thread reads it:
*a.load(Relaxed, guard).as_ref().unwrap()
The problem is that relaxed orderings don’t synchronize initialization of the object with
the read from the second thread. This is a data race. A possible solution would be to use
Release
and Acquire
orderings.
Examples
use crossbeam_epoch::{self as epoch, Atomic};
use std::sync::atomic::Ordering::SeqCst;
let a = Atomic::new(1234);
let guard = &epoch::pin();
let p = a.load(SeqCst, guard);
unsafe {
assert_eq!(p.deref(), &1234);
}
pub unsafe fn deref_mut(&mut self) -> &'g mut T
pub unsafe fn deref_mut(&mut self) -> &'g mut T
Dereferences the pointer.
Returns a mutable reference to the pointee that is valid during the lifetime 'g
.
Safety
-
There is no guarantee that there are no more threads attempting to read/write from/to the actual object at the same time.
The user must know that there are no concurrent accesses towards the object itself.
-
Other than the above, all safety concerns of
deref()
applies here.
Examples
use crossbeam_epoch::{self as epoch, Atomic};
use std::sync::atomic::Ordering::SeqCst;
let a = Atomic::new(vec![1, 2, 3, 4]);
let guard = &epoch::pin();
let mut p = a.load(SeqCst, guard);
unsafe {
assert!(!p.is_null());
let b = p.deref_mut();
assert_eq!(b, &vec![1, 2, 3, 4]);
b.push(5);
assert_eq!(b, &vec![1, 2, 3, 4, 5]);
}
let p = a.load(SeqCst, guard);
unsafe {
assert_eq!(p.deref(), &vec![1, 2, 3, 4, 5]);
}
pub unsafe fn as_ref(&self) -> Option<&'g T>
pub unsafe fn as_ref(&self) -> Option<&'g T>
Converts the pointer to a reference.
Returns None
if the pointer is null, or else a reference to the object wrapped in Some
.
Safety
Dereferencing a pointer is unsafe because it could be pointing to invalid memory.
Another concern is the possibility of data races due to lack of proper synchronization. For example, consider the following scenario:
- A thread creates a new object:
a.store(Owned::new(10), Relaxed)
- Another thread reads it:
*a.load(Relaxed, guard).as_ref().unwrap()
The problem is that relaxed orderings don’t synchronize initialization of the object with
the read from the second thread. This is a data race. A possible solution would be to use
Release
and Acquire
orderings.
Examples
use crossbeam_epoch::{self as epoch, Atomic};
use std::sync::atomic::Ordering::SeqCst;
let a = Atomic::new(1234);
let guard = &epoch::pin();
let p = a.load(SeqCst, guard);
unsafe {
assert_eq!(p.as_ref(), Some(&1234));
}
pub unsafe fn into_owned(self) -> Owned<T>
pub unsafe fn into_owned(self) -> Owned<T>
Takes ownership of the pointee.
Panics
Panics if this pointer is null, but only in debug mode.
Safety
This method may be called only if the pointer is valid and nobody else is holding a reference to the same object.
Examples
use crossbeam_epoch::{self as epoch, Atomic};
use std::sync::atomic::Ordering::SeqCst;
let a = Atomic::new(1234);
unsafe {
let guard = &epoch::unprotected();
let p = a.load(SeqCst, guard);
drop(p.into_owned());
}
pub unsafe fn try_into_owned(self) -> Option<Owned<T>>
pub unsafe fn try_into_owned(self) -> Option<Owned<T>>
Takes ownership of the pointee if it is not null.
Safety
This method may be called only if the pointer is valid and nobody else is holding a reference to the same object, or if the pointer is null.
Examples
use crossbeam_epoch::{self as epoch, Atomic};
use std::sync::atomic::Ordering::SeqCst;
let a = Atomic::new(1234);
unsafe {
let guard = &epoch::unprotected();
let p = a.load(SeqCst, guard);
if let Some(x) = p.try_into_owned() {
drop(x);
}
}
pub fn tag(&self) -> usize
pub fn tag(&self) -> usize
Returns the tag stored within the pointer.
Examples
use crossbeam_epoch::{self as epoch, Atomic, Owned};
use std::sync::atomic::Ordering::SeqCst;
let a = Atomic::<u64>::from(Owned::new(0u64).with_tag(2));
let guard = &epoch::pin();
let p = a.load(SeqCst, guard);
assert_eq!(p.tag(), 2);
pub fn with_tag(&self, tag: usize) -> Shared<'g, T>
pub fn with_tag(&self, tag: usize) -> Shared<'g, T>
Returns the same pointer, but tagged with tag
. tag
is truncated to be fit into the
unused bits of the pointer to T
.
Examples
use crossbeam_epoch::{self as epoch, Atomic};
use std::sync::atomic::Ordering::SeqCst;
let a = Atomic::new(0u64);
let guard = &epoch::pin();
let p1 = a.load(SeqCst, guard);
let p2 = p1.with_tag(2);
assert_eq!(p1.tag(), 0);
assert_eq!(p2.tag(), 2);
assert_eq!(p1.as_raw(), p2.as_raw());
Trait Implementations
1.21.0 · sourcefn max(self, other: Self) -> Selfwhere
Self: Sized,
fn max(self, other: Self) -> Selfwhere
Self: Sized,
1.21.0 · sourcefn min(self, other: Self) -> Selfwhere
Self: Sized,
fn min(self, other: Self) -> Selfwhere
Self: Sized,
1.50.0 · sourcefn clamp(self, min: Self, max: Self) -> Selfwhere
Self: Sized + PartialOrd<Self>,
fn clamp(self, min: Self, max: Self) -> Selfwhere
Self: Sized + PartialOrd<Self>,
fn partial_cmp(&self, other: &Shared<'g, T>) -> Option<Ordering>
fn partial_cmp(&self, other: &Shared<'g, T>) -> Option<Ordering>
1.0.0 · sourcefn le(&self, other: &Rhs) -> bool
fn le(&self, other: &Rhs) -> bool
self
and other
) and is used by the <=
operator. Read morefn into_usize(self) -> usize
fn into_usize(self) -> usize
unsafe fn from_usize(data: usize) -> Shared<'_, T>
unsafe fn from_usize(data: usize) -> Shared<'_, T>
data
. Read moreAuto Trait Implementations
Blanket Implementations
fn as_bind_group_shader_type(
&self,
_images: &HashMap<Handle<Image>, <Image as RenderAsset>::PreparedAsset, RandomState, Global>
) -> U
fn as_bind_group_shader_type(
&self,
_images: &HashMap<Handle<Image>, <Image as RenderAsset>::PreparedAsset, RandomState, Global>
) -> U
T
[ShaderType
] for self
. When used in [AsBindGroup
]
derives, it is safe to assume that all images in self
exist. Read moreconst: unstable · sourcefn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
fn into_any(self: Box<T, Global>) -> Box<dyn Any + 'static, Global>
fn into_any(self: Box<T, Global>) -> Box<dyn Any + 'static, Global>
Box<dyn Trait>
(where Trait: Downcast
) to Box<dyn Any>
. Box<dyn Any>
can
then be further downcast
into Box<ConcreteType>
where ConcreteType
implements Trait
. Read morefn into_any_rc(self: Rc<T>) -> Rc<dyn Any + 'static>
fn into_any_rc(self: Rc<T>) -> Rc<dyn Any + 'static>
Rc<Trait>
(where Trait: Downcast
) to Rc<Any>
. Rc<Any>
can then be
further downcast
into Rc<ConcreteType>
where ConcreteType
implements Trait
. Read morefn as_any(&self) -> &(dyn Any + 'static)
fn as_any(&self) -> &(dyn Any + 'static)
&Trait
(where Trait: Downcast
) to &Any
. This is needed since Rust cannot
generate &Any
’s vtable from &Trait
’s. Read morefn as_any_mut(&mut self) -> &mut (dyn Any + 'static)
fn as_any_mut(&mut self) -> &mut (dyn Any + 'static)
&mut Trait
(where Trait: Downcast
) to &Any
. This is needed since Rust cannot
generate &mut Any
’s vtable from &mut Trait
’s. Read moresourcefn equivalent(&self, key: &K) -> bool
fn equivalent(&self, key: &K) -> bool
key
and return true
if they are equal.fn from_world(_world: &mut World) -> T
fn from_world(_world: &mut World) -> T
Self
using data from the given [World]sourcefn instrument(self, span: Span) -> Instrumented<Self>
fn instrument(self, span: Span) -> Instrumented<Self>
sourcefn in_current_span(self) -> Instrumented<Self>
fn in_current_span(self) -> Instrumented<Self>
type Output = T
type Output = T
Self
fn to_subset(&self) -> Option<SS>
fn to_subset(&self) -> Option<SS>
self
from the equivalent element of its
superset. Read morefn is_in_subset(&self) -> bool
fn is_in_subset(&self) -> bool
self
is actually part of its subset T
(and can be converted to it).fn to_subset_unchecked(&self) -> SS
fn to_subset_unchecked(&self) -> SS
self.to_subset
but without any property checks. Always succeeds.fn from_subset(element: &SS) -> SP
fn from_subset(element: &SS) -> SP
self
to the equivalent element of its superset.