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use std::marker::PhantomData;
use std::mem;
use std::ptr;
use std::sync::atomic::{self, Ordering};
use super::{Owned, Shared, Guard};
/// Like `std::sync::atomic::AtomicPtr`.
///
/// Provides atomic access to a (nullable) pointer of type `T`, interfacing with
/// the `Owned` and `Shared` types.
#[derive(Debug)]
pub struct Atomic<T> {
ptr: atomic::AtomicPtr<T>,
_marker: PhantomData<*const ()>,
}
unsafe impl<T: Sync> Send for Atomic<T> {}
unsafe impl<T: Sync> Sync for Atomic<T> {}
fn opt_shared_into_raw<T>(val: Option<Shared<T>>) -> *mut T {
val.map(|p| p.as_raw()).unwrap_or(ptr::null_mut())
}
fn opt_owned_as_raw<T>(val: &Option<Owned<T>>) -> *mut T {
val.as_ref().map(Owned::as_raw).unwrap_or(ptr::null_mut())
}
fn opt_owned_into_raw<T>(val: Option<Owned<T>>) -> *mut T {
let ptr = val.as_ref().map(Owned::as_raw).unwrap_or(ptr::null_mut());
mem::forget(val);
ptr
}
impl<T> Atomic<T> {
/// Create a new, null atomic pointer.
#[cfg(feature = "nightly")]
pub const fn null() -> Atomic<T> {
Atomic {
ptr: atomic::AtomicPtr::new(0 as *mut _),
_marker: PhantomData
}
}
#[cfg(not(feature = "nightly"))]
pub fn null() -> Atomic<T> {
Atomic {
ptr: atomic::AtomicPtr::new(0 as *mut _),
_marker: PhantomData
}
}
/// Create a new atomic pointer
pub fn new(data: T) -> Atomic<T> {
Atomic {
ptr: atomic::AtomicPtr::new(Box::into_raw(Box::new(data))),
_marker: PhantomData
}
}
/// Do an atomic load with the given memory ordering.
///
/// In order to perform the load, we must pass in a borrow of a
/// `Guard`. This is a way of guaranteeing that the thread has pinned the
/// epoch for the entire lifetime `'a`. In return, you get an optional
/// `Shared` pointer back (`None` if the `Atomic` is currently null), with
/// lifetime tied to the guard.
///
/// # Panics
///
/// Panics if `ord` is `Release` or `AcqRel`.
pub fn load<'a>(&self, ord: Ordering, _: &'a Guard) -> Option<Shared<'a, T>> {
unsafe { Shared::from_raw(self.ptr.load(ord)) }
}
/// Do an atomic store with the given memory ordering.
///
/// Transfers ownership of the given `Owned` pointer, if any. Since no
/// lifetime information is acquired, no `Guard` value is needed.
///
/// # Panics
///
/// Panics if `ord` is `Acquire` or `AcqRel`.
pub fn store(&self, val: Option<Owned<T>>, ord: Ordering) {
self.ptr.store(opt_owned_into_raw(val), ord)
}
/// Do an atomic store with the given memory ordering, immediately yielding
/// a shared reference to the pointer that was stored.
///
/// Transfers ownership of the given `Owned` pointer, yielding a `Shared`
/// reference to it. Since the reference is valid only for the curent epoch,
/// it's lifetime is tied to a `Guard` value.
///
/// # Panics
///
/// Panics if `ord` is `Acquire` or `AcqRel`.
pub fn store_and_ref<'a>(&self, val: Owned<T>, ord: Ordering, _: &'a Guard)
-> Shared<'a, T>
{
unsafe {
let shared = Shared::from_owned(val);
self.store_shared(Some(shared), ord);
shared
}
}
/// Do an atomic store of a `Shared` pointer with the given memory ordering.
///
/// This operation does not require a guard, because it does not yield any
/// new information about the lifetime of a pointer.
///
/// # Panics
///
/// Panics if `ord` is `Acquire` or `AcqRel`.
pub fn store_shared(&self, val: Option<Shared<T>>, ord: Ordering) {
self.ptr.store(opt_shared_into_raw(val), ord)
}
/// Do a compare-and-set from a `Shared` to an `Owned` pointer with the
/// given memory ordering.
///
/// As with `store`, this operation does not require a guard; it produces no new
/// lifetime information. The `Result` indicates whether the CAS succeeded; if
/// not, ownership of the `new` pointer is returned to the caller.
pub fn cas(&self, old: Option<Shared<T>>, new: Option<Owned<T>>, ord: Ordering)
-> Result<(), Option<Owned<T>>>
{
if self.ptr.compare_and_swap(opt_shared_into_raw(old),
opt_owned_as_raw(&new),
ord) == opt_shared_into_raw(old)
{
mem::forget(new);
Ok(())
} else {
Err(new)
}
}
/// Do a compare-and-set from a `Shared` to an `Owned` pointer with the
/// given memory ordering, immediatley acquiring a new `Shared` reference to
/// the previously-owned pointer if successful.
///
/// This operation is analogous to `store_and_ref`.
pub fn cas_and_ref<'a>(&self, old: Option<Shared<T>>, new: Owned<T>,
ord: Ordering, _: &'a Guard)
-> Result<Shared<'a, T>, Owned<T>>
{
if self.ptr.compare_and_swap(opt_shared_into_raw(old), new.as_raw(), ord)
== opt_shared_into_raw(old)
{
Ok(unsafe { Shared::from_owned(new) })
} else {
Err(new)
}
}
/// Do a compare-and-set from a `Shared` to another `Shared` pointer with
/// the given memory ordering.
///
/// The boolean return value is `true` when the CAS is successful.
pub fn cas_shared(&self, old: Option<Shared<T>>, new: Option<Shared<T>>, ord: Ordering)
-> bool
{
self.ptr.compare_and_swap(opt_shared_into_raw(old),
opt_shared_into_raw(new),
ord) == opt_shared_into_raw(old)
}
/// Do an atomic swap with an `Owned` pointer with the given memory ordering.
pub fn swap<'a>(&self, new: Option<Owned<T>>, ord: Ordering, _: &'a Guard)
-> Option<Shared<'a, T>> {
unsafe { Shared::from_raw(self.ptr.swap(opt_owned_into_raw(new), ord)) }
}
/// Do an atomic swap with a `Shared` pointer with the given memory ordering.
pub fn swap_shared<'a>(&self, new: Option<Shared<T>>, ord: Ordering, _: &'a Guard)
-> Option<Shared<'a, T>> {
unsafe { Shared::from_raw(self.ptr.swap(opt_shared_into_raw(new), ord)) }
}
}