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integrate Lazy into std layout

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This commit refactors the initial implementation to fit into std and
makes some other changes:

- use MaybeUninit internally in SyncOnceCell
- correctly impl Drop for lazy::Once
- port Lazy::take from once_cell from: https://github.com/matklad/once_cell/pull/100

Co-Authored-By: Paul Dicker <pitdicker@users.noreply.github.com>
This commit is contained in:
Ashley Mannix 2020-01-14 13:34:23 +10:00
parent cac1768b03
commit 237a97760a
7 changed files with 1004 additions and 548 deletions
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2
Cargo.lock
View file

@ -1372,8 +1372,8 @@ checksum = "7e81a7c05f79578dbc15793d8b619db9ba32b4577003ef3af1a91c416798c58d"
name = "installer"
version = "0.0.0"
dependencies = [
"anyhow",
"clap",
"failure",
"flate2",
"lazy_static",
"num_cpus",

379
src/libcore/lazy.rs Normal file
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@ -0,0 +1,379 @@
//! Lazy values and one-time initialization of static data.
use crate::cell::{Cell, UnsafeCell};
use crate::fmt;
use crate::mem;
use crate::ops::Deref;
/// A cell which can be written to only once.
///
/// Unlike `RefCell`, a `OnceCell` only provides shared `&T` references to its value.
/// Unlike `Cell`, a `OnceCell` doesn't require copying or replacing the value to access it.
///
/// # Examples
///
/// ```
/// #![feature(once_cell)]
///
/// use std::lazy::OnceCell;
///
/// let cell = OnceCell::new();
/// assert!(cell.get().is_none());
///
/// let value: &String = cell.get_or_init(|| {
/// "Hello, World!".to_string()
/// });
/// assert_eq!(value, "Hello, World!");
/// assert!(cell.get().is_some());
/// ```
#[unstable(feature = "once_cell", issue = "68198")]
pub struct OnceCell<T> {
// Invariant: written to at most once.
inner: UnsafeCell<Option<T>>,
}
#[unstable(feature = "once_cell", issue = "68198")]
impl<T> Default for OnceCell<T> {
fn default() -> Self {
Self::new()
}
}
#[unstable(feature = "once_cell", issue = "68198")]
impl<T: fmt::Debug> fmt::Debug for OnceCell<T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self.get() {
Some(v) => f.debug_tuple("OnceCell").field(v).finish(),
None => f.write_str("OnceCell(Uninit)"),
}
}
}
#[unstable(feature = "once_cell", issue = "68198")]
impl<T: Clone> Clone for OnceCell<T> {
fn clone(&self) -> OnceCell<T> {
let res = OnceCell::new();
if let Some(value) = self.get() {
match res.set(value.clone()) {
Ok(()) => (),
Err(_) => unreachable!(),
}
}
res
}
}
#[unstable(feature = "once_cell", issue = "68198")]
impl<T: PartialEq> PartialEq for OnceCell<T> {
fn eq(&self, other: &Self) -> bool {
self.get() == other.get()
}
}
#[unstable(feature = "once_cell", issue = "68198")]
impl<T: Eq> Eq for OnceCell<T> {}
#[unstable(feature = "once_cell", issue = "68198")]
impl<T> From<T> for OnceCell<T> {
fn from(value: T) -> Self {
OnceCell { inner: UnsafeCell::new(Some(value)) }
}
}
impl<T> OnceCell<T> {
/// Creates a new empty cell.
#[unstable(feature = "once_cell", issue = "68198")]
pub const fn new() -> OnceCell<T> {
OnceCell { inner: UnsafeCell::new(None) }
}
/// Gets the reference to the underlying value.
///
/// Returns `None` if the cell is empty.
#[unstable(feature = "once_cell", issue = "68198")]
pub fn get(&self) -> Option<&T> {
// Safety: Safe due to `inner`'s invariant
unsafe { &*self.inner.get() }.as_ref()
}
/// Gets the mutable reference to the underlying value.
///
/// Returns `None` if the cell is empty.
#[unstable(feature = "once_cell", issue = "68198")]
pub fn get_mut(&mut self) -> Option<&mut T> {
// Safety: Safe because we have unique access
unsafe { &mut *self.inner.get() }.as_mut()
}
/// Sets the contents of the cell to `value`.
///
/// # Errors
///
/// This method returns `Ok(())` if the cell was empty and `Err(value)` if
/// it was full.
///
/// # Examples
///
/// ```
/// #![feature(once_cell)]
///
/// use std::lazy::OnceCell;
///
/// let cell = OnceCell::new();
/// assert!(cell.get().is_none());
///
/// assert_eq!(cell.set(92), Ok(()));
/// assert_eq!(cell.set(62), Err(62));
///
/// assert!(cell.get().is_some());
/// ```
#[unstable(feature = "once_cell", issue = "68198")]
pub fn set(&self, value: T) -> Result<(), T> {
// Safety: Safe because we cannot have overlapping mutable borrows
let slot = unsafe { &*self.inner.get() };
if slot.is_some() {
return Err(value);
}
// Safety: This is the only place where we set the slot, no races
// due to reentrancy/concurrency are possible, and we've
// checked that slot is currently `None`, so this write
// maintains the `inner`'s invariant.
let slot = unsafe { &mut *self.inner.get() };
*slot = Some(value);
Ok(())
}
/// Gets the contents of the cell, initializing it with `f`
/// if the cell was empty.
///
/// # Panics
///
/// If `f` panics, the panic is propagated to the caller, and the cell
/// remains uninitialized.
///
/// It is an error to reentrantly initialize the cell from `f`. Doing
/// so results in a panic.
///
/// # Examples
///
/// ```
/// #![feature(once_cell)]
///
/// use std::lazy::OnceCell;
///
/// let cell = OnceCell::new();
/// let value = cell.get_or_init(|| 92);
/// assert_eq!(value, &92);
/// let value = cell.get_or_init(|| unreachable!());
/// assert_eq!(value, &92);
/// ```
#[unstable(feature = "once_cell", issue = "68198")]
pub fn get_or_init<F>(&self, f: F) -> &T
where
F: FnOnce() -> T,
{
match self.get_or_try_init(|| Ok::<T, !>(f())) {
Ok(val) => val,
}
}
/// Gets the contents of the cell, initializing it with `f` if
/// the cell was empty. If the cell was empty and `f` failed, an
/// error is returned.
///
/// # Panics
///
/// If `f` panics, the panic is propagated to the caller, and the cell
/// remains uninitialized.
///
/// It is an error to reentrantly initialize the cell from `f`. Doing
/// so results in a panic.
///
/// # Examples
///
/// ```
/// #![feature(once_cell)]
///
/// use std::lazy::OnceCell;
///
/// let cell = OnceCell::new();
/// assert_eq!(cell.get_or_try_init(|| Err(())), Err(()));
/// assert!(cell.get().is_none());
/// let value = cell.get_or_try_init(|| -> Result<i32, ()> {
/// Ok(92)
/// });
/// assert_eq!(value, Ok(&92));
/// assert_eq!(cell.get(), Some(&92))
/// ```
#[unstable(feature = "once_cell", issue = "68198")]
pub fn get_or_try_init<F, E>(&self, f: F) -> Result<&T, E>
where
F: FnOnce() -> Result<T, E>,
{
if let Some(val) = self.get() {
return Ok(val);
}
let val = f()?;
// Note that *some* forms of reentrant initialization might lead to
// UB (see `reentrant_init` test). I believe that just removing this
// `assert`, while keeping `set/get` would be sound, but it seems
// better to panic, rather than to silently use an old value.
assert!(self.set(val).is_ok(), "reentrant init");
Ok(self.get().unwrap())
}
/// Consumes the cell, returning the wrapped value.
///
/// Returns `None` if the cell was empty.
///
/// # Examples
///
/// ```
/// #![feature(once_cell)]
///
/// use std::lazy::OnceCell;
///
/// let cell: OnceCell<String> = OnceCell::new();
/// assert_eq!(cell.into_inner(), None);
///
/// let cell = OnceCell::new();
/// cell.set("hello".to_string()).unwrap();
/// assert_eq!(cell.into_inner(), Some("hello".to_string()));
/// ```
#[unstable(feature = "once_cell", issue = "68198")]
pub fn into_inner(self) -> Option<T> {
// Because `into_inner` takes `self` by value, the compiler statically verifies
// that it is not currently borrowed. So it is safe to move out `Option<T>`.
self.inner.into_inner()
}
/// Takes the value out of this `OnceCell`, moving it back to an uninitialized state.
///
/// Has no effect and returns `None` if the `OnceCell` hasn't been initialized.
///
/// Safety is guaranteed by requiring a mutable reference.
///
/// # Examples
///
/// ```
/// #![feature(once_cell)]
///
/// use std::lazy::OnceCell;
///
/// let mut cell: OnceCell<String> = OnceCell::new();
/// assert_eq!(cell.take(), None);
///
/// let mut cell = OnceCell::new();
/// cell.set("hello".to_string()).unwrap();
/// assert_eq!(cell.take(), Some("hello".to_string()));
/// assert_eq!(cell.get(), None);
/// ```
#[unstable(feature = "once_cell", issue = "68198")]
pub fn take(&mut self) -> Option<T> {
mem::take(self).into_inner()
}
}
/// A value which is initialized on the first access.
///
/// # Examples
///
/// ```
/// #![feature(once_cell)]
///
/// use std::lazy::Lazy;
///
/// let lazy: Lazy<i32> = Lazy::new(|| {
/// println!("initializing");
/// 92
/// });
/// println!("ready");
/// println!("{}", *lazy);
/// println!("{}", *lazy);
///
/// // Prints:
/// // ready
/// // initializing
/// // 92
/// // 92
/// ```
#[unstable(feature = "once_cell", issue = "68198")]
pub struct Lazy<T, F = fn() -> T> {
cell: OnceCell<T>,
init: Cell<Option<F>>,
}
#[unstable(feature = "once_cell", issue = "68198")]
impl<T: fmt::Debug, F> fmt::Debug for Lazy<T, F> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("Lazy").field("cell", &self.cell).field("init", &"..").finish()
}
}
impl<T, F> Lazy<T, F> {
/// Creates a new lazy value with the given initializing function.
///
/// # Examples
///
/// ```
/// #![feature(once_cell)]
///
/// # fn main() {
/// use std::lazy::Lazy;
///
/// let hello = "Hello, World!".to_string();
///
/// let lazy = Lazy::new(|| hello.to_uppercase());
///
/// assert_eq!(&*lazy, "HELLO, WORLD!");
/// # }
/// ```
#[unstable(feature = "once_cell", issue = "68198")]
pub const fn new(init: F) -> Lazy<T, F> {
Lazy { cell: OnceCell::new(), init: Cell::new(Some(init)) }
}
}
impl<T, F: FnOnce() -> T> Lazy<T, F> {
/// Forces the evaluation of this lazy value and returns a reference to
/// the result.
///
/// This is equivalent to the `Deref` impl, but is explicit.
///
/// # Examples
///
/// ```
/// #![feature(once_cell)]
///
/// use std::lazy::Lazy;
///
/// let lazy = Lazy::new(|| 92);
///
/// assert_eq!(Lazy::force(&lazy), &92);
/// assert_eq!(&*lazy, &92);
/// ```
#[unstable(feature = "once_cell", issue = "68198")]
pub fn force(this: &Lazy<T, F>) -> &T {
this.cell.get_or_init(|| match this.init.take() {
Some(f) => f(),
None => panic!("`Lazy` instance has previously been poisoned"),
})
}
}
#[unstable(feature = "once_cell", issue = "68198")]
impl<T, F: FnOnce() -> T> Deref for Lazy<T, F> {
type Target = T;
fn deref(&self) -> &T {
Lazy::force(self)
}
}
#[unstable(feature = "once_cell", issue = "68198")]
impl<T: Default> Default for Lazy<T> {
/// Creates a new lazy value using `Default` as the initializing function.
fn default() -> Lazy<T> {
Lazy::new(T::default)
}
}

2
src/libcore/lib.rs
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@ -239,6 +239,8 @@ pub mod char;
pub mod ffi;
#[cfg(not(test))] // See #65860
pub mod iter;
#[unstable(feature = "once_cell", issue = "68198")]
pub mod lazy;
pub mod option;
pub mod panic;
pub mod panicking;

124
src/libcore/tests/lazy.rs Normal file
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@ -0,0 +1,124 @@
use core::{
cell::Cell,
lazy::{Lazy, OnceCell},
sync::atomic::{AtomicUsize, Ordering::SeqCst},
};
#[test]
fn once_cell() {
let c = OnceCell::new();
assert!(c.get().is_none());
c.get_or_init(|| 92);
assert_eq!(c.get(), Some(&92));
c.get_or_init(|| panic!("Kabom!"));
assert_eq!(c.get(), Some(&92));
}
#[test]
fn once_cell_get_mut() {
let mut c = OnceCell::new();
assert!(c.get_mut().is_none());
c.set(90).unwrap();
*c.get_mut().unwrap() += 2;
assert_eq!(c.get_mut(), Some(&mut 92));
}
#[test]
fn once_cell_drop() {
static DROP_CNT: AtomicUsize = AtomicUsize::new(0);
struct Dropper;
impl Drop for Dropper {
fn drop(&mut self) {
DROP_CNT.fetch_add(1, SeqCst);
}
}
let x = OnceCell::new();
x.get_or_init(|| Dropper);
assert_eq!(DROP_CNT.load(SeqCst), 0);
drop(x);
assert_eq!(DROP_CNT.load(SeqCst), 1);
}
#[test]
fn unsync_once_cell_drop_empty() {
let x = OnceCell::<&'static str>::new();
drop(x);
}
#[test]
fn clone() {
let s = OnceCell::new();
let c = s.clone();
assert!(c.get().is_none());
s.set("hello").unwrap();
let c = s.clone();
assert_eq!(c.get().map(|c| *c), Some("hello"));
}
#[test]
fn from_impl() {
assert_eq!(OnceCell::from("value").get(), Some(&"value"));
assert_ne!(OnceCell::from("foo").get(), Some(&"bar"));
}
#[test]
fn partialeq_impl() {
assert!(OnceCell::from("value") == OnceCell::from("value"));
assert!(OnceCell::from("foo") != OnceCell::from("bar"));
assert!(OnceCell::<&'static str>::new() == OnceCell::new());
assert!(OnceCell::<&'static str>::new() != OnceCell::from("value"));
}
#[test]
fn into_inner() {
let cell: OnceCell<&'static str> = OnceCell::new();
assert_eq!(cell.into_inner(), None);
let cell = OnceCell::new();
cell.set("hello").unwrap();
assert_eq!(cell.into_inner(), Some("hello"));
}
#[test]
fn lazy_new() {
let called = Cell::new(0);
let x = Lazy::new(|| {
called.set(called.get() + 1);
92
});
assert_eq!(called.get(), 0);
let y = *x - 30;
assert_eq!(y, 62);
assert_eq!(called.get(), 1);
let y = *x - 30;
assert_eq!(y, 62);
assert_eq!(called.get(), 1);
}
#[test]
fn aliasing_in_get() {
let x = OnceCell::new();
x.set(42).unwrap();
let at_x = x.get().unwrap(); // --- (shared) borrow of inner `Option<T>` --+
let _ = x.set(27); // <-- temporary (unique) borrow of inner `Option<T>` |
println!("{}", at_x); // <------- up until here ---------------------------+
}
#[test]
#[should_panic(expected = "reentrant init")]
fn reentrant_init() {
let x: OnceCell<Box<i32>> = OnceCell::new();
let dangling_ref: Cell<Option<&i32>> = Cell::new(None);
x.get_or_init(|| {
let r = x.get_or_init(|| Box::new(92));
dangling_ref.set(Some(r));
Box::new(62)
});
eprintln!("use after free: {:?}", dangling_ref.get().unwrap());
}

2
src/libcore/tests/lib.rs
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@ -43,6 +43,7 @@
#![feature(option_unwrap_none)]
#![feature(peekable_next_if)]
#![feature(partition_point)]
#![feature(once_cell)]
#![feature(unsafe_block_in_unsafe_fn)]
#![deny(unsafe_op_in_unsafe_fn)]
@ -62,6 +63,7 @@ mod fmt;
mod hash;
mod intrinsics;
mod iter;
mod lazy;
mod manually_drop;
mod mem;
mod nonzero;

1030
src/libstd/lazy.rs
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File diff suppressed because it is too large Load diff

7
src/libstd/lib.rs
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@ -285,6 +285,7 @@
#![feature(linkage)]
#![feature(llvm_asm)]
#![feature(log_syntax)]
#![feature(maybe_uninit_extra)]
#![feature(maybe_uninit_ref)]
#![feature(maybe_uninit_slice)]
#![feature(min_specialization)]
@ -292,6 +293,7 @@
#![feature(negative_impls)]
#![feature(never_type)]
#![feature(nll)]
#![feature(once_cell)]
#![feature(optin_builtin_traits)]
#![feature(or_patterns)]
#![feature(panic_info_message)]
@ -476,10 +478,7 @@ pub mod process;
pub mod sync;
pub mod time;
#[unstable(
feature = "std_lazy",
issue = "99",
)]
#[unstable(feature = "once_cell", issue = "68198")]
pub mod lazy;
#[stable(feature = "futures_api", since = "1.36.0")]