Struct crossbeam_epoch::Shared [] [src]

pub struct Shared<'g, T: 'g> { /* fields omitted */ }

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.

Methods

impl<'g, T> Shared<'g, T>
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Returns a new null pointer.

Examples

use crossbeam_epoch::Shared;

let p = Shared::<i32>::null();
assert!(p.is_null());

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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());

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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);

Important traits for &'a mut I
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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 possiblity of data races due to lack of proper synchronization. For example, consider the following scenario:

  1. A thread creates a new object: a.store(Owned::new(10), Relaxed)
  2. 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);
}

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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 possiblity of data races due to lack of proper synchronization. For example, consider the following scenario:

  1. A thread creates a new object: a.store(Owned::new(10), Relaxed)
  2. 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));
}

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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());
}

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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);

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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

impl<'g, T> From<Shared<'g, T>> for Atomic<T>
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Returns a new atomic pointer pointing to ptr.

Examples

use crossbeam_epoch::{Atomic, Shared};

let a = Atomic::<i32>::from(Shared::<i32>::null());

impl<'g, T> Clone for Shared<'g, T>
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Returns a copy of the value. Read more

1.0.0
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Performs copy-assignment from source. Read more

impl<'g, T> Copy for Shared<'g, T>
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impl<'g, T> Pointer<T> for Shared<'g, T>
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Returns the machine representation of the pointer.

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Returns a new pointer pointing to the tagged pointer data.

impl<'g, T> From<*const T> for Shared<'g, T>
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Returns a new pointer pointing to raw.

Panics

Panics if raw is not properly aligned.

Examples

use crossbeam_epoch::Shared;

let p = unsafe { Shared::from(Box::into_raw(Box::new(1234)) as *const _) };
assert!(!p.is_null());

impl<'g, T> PartialEq<Shared<'g, T>> for Shared<'g, T>
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This method tests for self and other values to be equal, and is used by ==. Read more

1.0.0
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This method tests for !=.

impl<'g, T> Eq for Shared<'g, T>
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impl<'g, T> PartialOrd<Shared<'g, T>> for Shared<'g, T>
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This method returns an ordering between self and other values if one exists. Read more

1.0.0
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This method tests less than (for self and other) and is used by the < operator. Read more

1.0.0
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This method tests less than or equal to (for self and other) and is used by the <= operator. Read more

1.0.0
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This method tests greater than (for self and other) and is used by the > operator. Read more

1.0.0
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This method tests greater than or equal to (for self and other) and is used by the >= operator. Read more

impl<'g, T> Ord for Shared<'g, T>
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This method returns an Ordering between self and other. Read more

1.21.0
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Compares and returns the maximum of two values. Read more

1.21.0
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Compares and returns the minimum of two values. Read more

impl<'g, T> Debug for Shared<'g, T>
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Formats the value using the given formatter. Read more

impl<'g, T> Pointer for Shared<'g, T>
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Formats the value using the given formatter.

impl<'g, T> Default for Shared<'g, T>
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Returns the "default value" for a type. Read more