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Auto merge of #53227 - nivkner:pin_move, r=RalfJung
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move the Pin API into its own module for centralized documentation

This implements the change proposed by @withoutboats in #49150, as suggested by @RalfJung in the review of #53104,
along with the documentation that was originally in it, that was deemed more appropriate in module-level documentation.

r? @RalfJung
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@bors
bors committed Aug 27, 2018
2 parents f7202e4 + 83ca347 commit 8c2b371
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Showing 18 changed files with 496 additions and 365 deletions.
211 changes: 9 additions & 202 deletions src/liballoc/boxed.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -64,12 +64,14 @@ use core::future::{Future, FutureObj, LocalFutureObj, UnsafeFutureObj};
use core::hash::{Hash, Hasher};
use core::iter::FusedIterator;
use core::marker::{Unpin, Unsize};
use core::mem::{self, PinMut};
use core::mem;
use core::pin::PinMut;
use core::ops::{CoerceUnsized, Deref, DerefMut, Generator, GeneratorState};
use core::ptr::{self, NonNull, Unique};
use core::task::{Context, Poll, Spawn, SpawnErrorKind, SpawnObjError};

use raw_vec::RawVec;
use pin::PinBox;
use str::from_boxed_utf8_unchecked;

/// A pointer type for heap allocation.
Expand Down Expand Up @@ -758,166 +760,6 @@ impl<T> Generator for Box<T>
}
}

/// A pinned, heap allocated reference.
#[unstable(feature = "pin", issue = "49150")]
#[fundamental]
#[repr(transparent)]
pub struct PinBox<T: ?Sized> {
inner: Box<T>,
}

#[unstable(feature = "pin", issue = "49150")]
impl<T> PinBox<T> {
/// Allocate memory on the heap, move the data into it and pin it.
#[unstable(feature = "pin", issue = "49150")]
pub fn new(data: T) -> PinBox<T> {
PinBox { inner: Box::new(data) }
}
}

#[unstable(feature = "pin", issue = "49150")]
impl<T: ?Sized> PinBox<T> {
/// Get a pinned reference to the data in this PinBox.
#[inline]
pub fn as_pin_mut<'a>(&'a mut self) -> PinMut<'a, T> {
unsafe { PinMut::new_unchecked(&mut *self.inner) }
}

/// Constructs a `PinBox` from a raw pointer.
///
/// After calling this function, the raw pointer is owned by the
/// resulting `PinBox`. Specifically, the `PinBox` destructor will call
/// the destructor of `T` and free the allocated memory. Since the
/// way `PinBox` allocates and releases memory is unspecified, the
/// only valid pointer to pass to this function is the one taken
/// from another `PinBox` via the [`PinBox::into_raw`] function.
///
/// 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.
///
/// [`PinBox::into_raw`]: struct.PinBox.html#method.into_raw
///
/// # Examples
///
/// ```
/// #![feature(pin)]
/// use std::boxed::PinBox;
/// let x = PinBox::new(5);
/// let ptr = PinBox::into_raw(x);
/// let x = unsafe { PinBox::from_raw(ptr) };
/// ```
#[inline]
pub unsafe fn from_raw(raw: *mut T) -> Self {
PinBox { inner: Box::from_raw(raw) }
}

/// Consumes the `PinBox`, returning the wrapped raw pointer.
///
/// After calling this function, the caller is responsible for the
/// memory previously managed by the `PinBox`. In particular, the
/// caller should properly destroy `T` and release the memory. The
/// proper way to do so is to convert the raw pointer back into a
/// `PinBox` with the [`PinBox::from_raw`] function.
///
/// Note: this is an associated function, which means that you have
/// to call it as `PinBox::into_raw(b)` instead of `b.into_raw()`. This
/// is so that there is no conflict with a method on the inner type.
///
/// [`PinBox::from_raw`]: struct.PinBox.html#method.from_raw
///
/// # Examples
///
/// ```
/// #![feature(pin)]
/// use std::boxed::PinBox;
/// let x = PinBox::new(5);
/// let ptr = PinBox::into_raw(x);
/// ```
#[inline]
pub fn into_raw(b: PinBox<T>) -> *mut T {
Box::into_raw(b.inner)
}

/// Get a mutable reference to the data inside this PinBox.
///
/// This function is unsafe. Users must guarantee that the data is never
/// moved out of this reference.
#[inline]
pub unsafe fn get_mut<'a>(this: &'a mut PinBox<T>) -> &'a mut T {
&mut *this.inner
}

/// Convert this PinBox into an unpinned Box.
///
/// This function is unsafe. Users must guarantee that the data is never
/// moved out of the box.
#[inline]
pub unsafe fn unpin(this: PinBox<T>) -> Box<T> {
this.inner
}
}

#[unstable(feature = "pin", issue = "49150")]
impl<T: ?Sized> From<Box<T>> for PinBox<T> {
fn from(boxed: Box<T>) -> PinBox<T> {
PinBox { inner: boxed }
}
}

#[unstable(feature = "pin", issue = "49150")]
impl<T: Unpin + ?Sized> From<PinBox<T>> for Box<T> {
fn from(pinned: PinBox<T>) -> Box<T> {
pinned.inner
}
}

#[unstable(feature = "pin", issue = "49150")]
impl<T: ?Sized> Deref for PinBox<T> {
type Target = T;

fn deref(&self) -> &T {
&*self.inner
}
}

#[unstable(feature = "pin", issue = "49150")]
impl<T: Unpin + ?Sized> DerefMut for PinBox<T> {
fn deref_mut(&mut self) -> &mut T {
&mut *self.inner
}
}

#[unstable(feature = "pin", issue = "49150")]
impl<T: fmt::Display + ?Sized> fmt::Display for PinBox<T> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
fmt::Display::fmt(&*self.inner, f)
}
}

#[unstable(feature = "pin", issue = "49150")]
impl<T: fmt::Debug + ?Sized> fmt::Debug for PinBox<T> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
fmt::Debug::fmt(&*self.inner, f)
}
}

#[unstable(feature = "pin", issue = "49150")]
impl<T: ?Sized> fmt::Pointer for PinBox<T> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
// It's not possible to extract the inner Uniq directly from the Box,
// instead we cast it to a *const which aliases the Unique
let ptr: *const T = &*self.inner;
fmt::Pointer::fmt(&ptr, f)
}
}

#[unstable(feature = "pin", issue = "49150")]
impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<PinBox<U>> for PinBox<T> {}

#[unstable(feature = "pin", issue = "49150")]
impl<T: ?Sized> Unpin for PinBox<T> {}

#[unstable(feature = "futures_api", issue = "50547")]
impl<F: ?Sized + Future + Unpin> Future for Box<F> {
type Output = F::Output;
Expand All @@ -927,15 +769,6 @@ impl<F: ?Sized + Future + Unpin> Future for Box<F> {
}
}

#[unstable(feature = "futures_api", issue = "50547")]
impl<F: ?Sized + Future> Future for PinBox<F> {
type Output = F::Output;

fn poll(mut self: PinMut<Self>, cx: &mut Context) -> Poll<Self::Output> {
self.as_pin_mut().poll(cx)
}
}

#[unstable(feature = "futures_api", issue = "50547")]
unsafe impl<'a, T, F> UnsafeFutureObj<'a, T> for Box<F>
where F: Future<Output = T> + 'a
Expand All @@ -955,25 +788,6 @@ unsafe impl<'a, T, F> UnsafeFutureObj<'a, T> for Box<F>
}
}

#[unstable(feature = "futures_api", issue = "50547")]
unsafe impl<'a, T, F> UnsafeFutureObj<'a, T> for PinBox<F>
where F: Future<Output = T> + 'a
{
fn into_raw(self) -> *mut () {
PinBox::into_raw(self) as *mut ()
}

unsafe fn poll(ptr: *mut (), cx: &mut Context) -> Poll<T> {
let ptr = ptr as *mut F;
let pin: PinMut<F> = PinMut::new_unchecked(&mut *ptr);
pin.poll(cx)
}

unsafe fn drop(ptr: *mut ()) {
drop(PinBox::from_raw(ptr as *mut F))
}
}

#[unstable(feature = "futures_api", issue = "50547")]
impl<Sp> Spawn for Box<Sp>
where Sp: Spawn + ?Sized
Expand All @@ -990,13 +804,6 @@ impl<Sp> Spawn for Box<Sp>
}
}

#[unstable(feature = "futures_api", issue = "50547")]
impl<'a, F: Future<Output = ()> + Send + 'a> From<PinBox<F>> for FutureObj<'a, ()> {
fn from(boxed: PinBox<F>) -> Self {
FutureObj::new(boxed)
}
}

#[unstable(feature = "futures_api", issue = "50547")]
impl<'a, F: Future<Output = ()> + Send + 'a> From<Box<F>> for FutureObj<'a, ()> {
fn from(boxed: Box<F>) -> Self {
Expand All @@ -1005,15 +812,15 @@ impl<'a, F: Future<Output = ()> + Send + 'a> From<Box<F>> for FutureObj<'a, ()>
}

#[unstable(feature = "futures_api", issue = "50547")]
impl<'a, F: Future<Output = ()> + 'a> From<PinBox<F>> for LocalFutureObj<'a, ()> {
fn from(boxed: PinBox<F>) -> Self {
impl<'a, F: Future<Output = ()> + 'a> From<Box<F>> for LocalFutureObj<'a, ()> {
fn from(boxed: Box<F>) -> Self {
LocalFutureObj::new(boxed)
}
}

#[unstable(feature = "futures_api", issue = "50547")]
impl<'a, F: Future<Output = ()> + 'a> From<Box<F>> for LocalFutureObj<'a, ()> {
fn from(boxed: Box<F>) -> Self {
LocalFutureObj::new(boxed)
#[unstable(feature = "pin", issue = "49150")]
impl<T: Unpin + ?Sized> From<PinBox<T>> for Box<T> {
fn from(pinned: PinBox<T>) -> Box<T> {
unsafe { PinBox::unpin(pinned) }
}
}
1 change: 1 addition & 0 deletions src/liballoc/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -160,6 +160,7 @@ pub mod collections;
pub mod sync;
pub mod rc;
pub mod raw_vec;
pub mod pin;
pub mod prelude;
pub mod borrow;
pub mod fmt;
Expand Down
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