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Rollup merge of #69799 - TimDiekmann:zst, r=Amanieu

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Allow ZSTs in `AllocRef`

Allows ZSTs in all `AllocRef` methods. The implementation of `AllocRef` for `Global` and `System` were adjusted to reflect those changes.

This is the second item on the roadmap to support ZSTs in `AllocRef`: https://github.com/rust-lang/wg-allocators/issues/38#issuecomment-595861542
After this has landed, I will adapt `RawVec`, but since this will be a pretty big overhaul, it makes sense to do a different PR for it.

~~Requires #69794 to land first~~

r? @Amanieu
This commit is contained in:
Mazdak Farrokhzad 2020-03-10 06:47:52 +01:00 committed by GitHub
commit 6ad5e69b5a
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5 changed files with 96 additions and 81 deletions
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30
src/liballoc/alloc.rs
View File

@ -165,14 +165,20 @@ pub unsafe fn alloc_zeroed(layout: Layout) -> *mut u8 {
#[unstable(feature = "allocator_api", issue = "32838")]
unsafe impl AllocRef for Global {
#[inline]
unsafe fn alloc(&mut self, layout: Layout) -> Result<(NonNull<u8>, usize), AllocErr> {
NonNull::new(alloc(layout)).ok_or(AllocErr).map(|p| (p, layout.size()))
fn alloc(&mut self, layout: Layout) -> Result<(NonNull<u8>, usize), AllocErr> {
if layout.size() == 0 {
Ok((layout.dangling(), 0))
} else {
unsafe { NonNull::new(alloc(layout)).ok_or(AllocErr).map(|p| (p, layout.size())) }
}
}
#[inline]
unsafe fn dealloc(&mut self, ptr: NonNull<u8>, layout: Layout) {
if layout.size() != 0 {
dealloc(ptr.as_ptr(), layout)
}
}
#[inline]
unsafe fn realloc(
@ -181,13 +187,29 @@ unsafe impl AllocRef for Global {
layout: Layout,
new_size: usize,
) -> Result<(NonNull<u8>, usize), AllocErr> {
NonNull::new(realloc(ptr.as_ptr(), layout, new_size)).ok_or(AllocErr).map(|p| (p, new_size))
match (layout.size(), new_size) {
(0, 0) => Ok((layout.dangling(), 0)),
(0, _) => self.alloc(Layout::from_size_align_unchecked(new_size, layout.align())),
(_, 0) => {
self.dealloc(ptr, layout);
Ok((layout.dangling(), 0))
}
(_, _) => NonNull::new(realloc(ptr.as_ptr(), layout, new_size))
.ok_or(AllocErr)
.map(|p| (p, new_size)),
}
}
#[inline]
unsafe fn alloc_zeroed(&mut self, layout: Layout) -> Result<(NonNull<u8>, usize), AllocErr> {
fn alloc_zeroed(&mut self, layout: Layout) -> Result<(NonNull<u8>, usize), AllocErr> {
if layout.size() == 0 {
Ok((layout.dangling(), 0))
} else {
unsafe {
NonNull::new(alloc_zeroed(layout)).ok_or(AllocErr).map(|p| (p, layout.size()))
}
}
}
}
/// The allocator for unique pointers.

2
src/liballoc/raw_vec.rs
View File

@ -73,7 +73,6 @@ impl<T, A: AllocRef> RawVec<T, A> {
}
fn allocate_in(mut capacity: usize, zeroed: bool, mut a: A) -> Self {
unsafe {
let elem_size = mem::size_of::<T>();
let alloc_size = capacity.checked_mul(elem_size).unwrap_or_else(|| capacity_overflow());
@ -97,7 +96,6 @@ impl<T, A: AllocRef> RawVec<T, A> {
RawVec { ptr: ptr.into(), cap: capacity, a }
}
}
}
impl<T> RawVec<T, Global> {

2
src/liballoc/raw_vec/tests.rs
View File

@ -20,7 +20,7 @@ fn allocator_param() {
fuel: usize,
}
unsafe impl AllocRef for BoundedAlloc {
unsafe fn alloc(&mut self, layout: Layout) -> Result<(NonNull<u8>, usize), AllocErr> {
fn alloc(&mut self, layout: Layout) -> Result<(NonNull<u8>, usize), AllocErr> {
let size = layout.size();
if size > self.fuel {
return Err(AllocErr);

56
src/libcore/alloc.rs
View File

@ -606,20 +606,11 @@ pub unsafe trait GlobalAlloc {
/// method (`dealloc`) or by being passed to a reallocation method
/// (see above) that returns `Ok`.
///
/// A note regarding zero-sized types and zero-sized layouts: many
/// methods in the `AllocRef` trait state that allocation requests
/// must be non-zero size, or else undefined behavior can result.
///
/// * If an `AllocRef` implementation chooses to return `Ok` in this
/// case (i.e., the pointer denotes a zero-sized inaccessible block)
/// then that returned pointer must be considered "currently
/// allocated". On such an allocator, *all* methods that take
/// currently-allocated pointers as inputs must accept these
/// zero-sized pointers, *without* causing undefined behavior.
///
/// * In other words, if a zero-sized pointer can flow out of an
/// allocator, then that allocator must likewise accept that pointer
/// flowing back into its deallocation and reallocation methods.
/// Unlike [`GlobalAlloc`], zero-sized allocations are allowed in
/// `AllocRef`. If an underlying allocator does not support this (like
/// jemalloc) or return a null pointer (such as `libc::malloc`), this case
/// must be caught. In this case [`Layout::dangling()`] can be used to
/// create a dangling, but aligned `NonNull<u8>`.
///
/// Some of the methods require that a layout *fit* a memory block.
/// What it means for a layout to "fit" a memory block means (or
@ -649,6 +640,9 @@ pub unsafe trait GlobalAlloc {
/// * if an allocator does not support overallocating, it is fine to
/// simply return `layout.size()` as the allocated size.
///
/// [`GlobalAlloc`]: self::GlobalAlloc
/// [`Layout::dangling()`]: self::Layout::dangling
///
/// # Safety
///
/// The `AllocRef` trait is an `unsafe` trait for a number of reasons, and
@ -669,14 +663,6 @@ pub unsafe trait GlobalAlloc {
/// the future.
#[unstable(feature = "allocator_api", issue = "32838")]
pub unsafe trait AllocRef {
// (Note: some existing allocators have unspecified but well-defined
// behavior in response to a zero size allocation request ;
// e.g., in C, `malloc` of 0 will either return a null pointer or a
// unique pointer, but will not have arbitrary undefined
// behavior.
// However in jemalloc for example,
// `mallocx(0)` is documented as undefined behavior.)
/// On success, returns a pointer meeting the size and alignment
/// guarantees of `layout` and the actual size of the allocated block,
/// which must be greater than or equal to `layout.size()`.
@ -690,15 +676,6 @@ pub unsafe trait AllocRef {
/// behavior, e.g., to ensure initialization to particular sets of
/// bit patterns.)
///
/// # Safety
///
/// This function is unsafe because undefined behavior can result
/// if the caller does not ensure that `layout` has non-zero size.
///
/// (Extension subtraits might provide more specific bounds on
/// behavior, e.g., guarantee a sentinel address or a null pointer
/// in response to a zero-size allocation request.)
///
/// # Errors
///
/// Returning `Err` indicates that either memory is exhausted or
@ -716,7 +693,7 @@ pub unsafe trait AllocRef {
/// rather than directly invoking `panic!` or similar.
///
/// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
unsafe fn alloc(&mut self, layout: Layout) -> Result<(NonNull<u8>, usize), AllocErr>;
fn alloc(&mut self, layout: Layout) -> Result<(NonNull<u8>, usize), AllocErr>;
/// Deallocate the memory referenced by `ptr`.
///
@ -738,10 +715,6 @@ pub unsafe trait AllocRef {
/// Behaves like `alloc`, but also ensures that the contents
/// are set to zero before being returned.
///
/// # Safety
///
/// This function is unsafe for the same reasons that `alloc` is.
///
/// # Errors
///
/// Returning `Err` indicates that either memory is exhausted or
@ -753,17 +726,17 @@ pub unsafe trait AllocRef {
/// rather than directly invoking `panic!` or similar.
///
/// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
unsafe fn alloc_zeroed(&mut self, layout: Layout) -> Result<(NonNull<u8>, usize), AllocErr> {
fn alloc_zeroed(&mut self, layout: Layout) -> Result<(NonNull<u8>, usize), AllocErr> {
let size = layout.size();
let result = self.alloc(layout);
if let Ok((p, _)) = result {
ptr::write_bytes(p.as_ptr(), 0, size);
unsafe { ptr::write_bytes(p.as_ptr(), 0, size) }
}
result
}
// == METHODS FOR MEMORY REUSE ==
// realloc. alloc_excess, realloc_excess
// realloc, realloc_zeroed, grow_in_place, grow_in_place_zeroed, shrink_in_place
/// Returns a pointer suitable for holding data described by
/// a new layout with `layout`’s alignment and a size given
@ -793,8 +766,6 @@ pub unsafe trait AllocRef {
/// * `layout` must *fit* the `ptr` (see above). (The `new_size`
/// argument need not fit it.)
///
/// * `new_size` must be greater than zero.
///
/// * `new_size`, when rounded up to the nearest multiple of `layout.align()`,
/// must not overflow (i.e., the rounded value must be less than `usize::MAX`).
///
@ -1009,8 +980,7 @@ pub unsafe trait AllocRef {
/// * `layout` must *fit* the `ptr` (see above); note the
/// `new_size` argument need not fit it,
///
/// * `new_size` must not be greater than `layout.size()`
/// (and must be greater than zero),
/// * `new_size` must not be greater than `layout.size()`,
///
/// # Errors
///

37
src/libstd/alloc.rs
View File

@ -133,25 +133,42 @@ pub use alloc_crate::alloc::*;
#[derive(Debug, Default, Copy, Clone)]
pub struct System;
// The AllocRef impl just forwards to the GlobalAlloc impl, which is in `std::sys::*::alloc`.
// The AllocRef impl checks the layout size to be non-zero and forwards to the GlobalAlloc impl,
// which is in `std::sys::*::alloc`.
#[unstable(feature = "allocator_api", issue = "32838")]
unsafe impl AllocRef for System {
#[inline]
unsafe fn alloc(&mut self, layout: Layout) -> Result<(NonNull<u8>, usize), AllocErr> {
NonNull::new(GlobalAlloc::alloc(self, layout)).ok_or(AllocErr).map(|p| (p, layout.size()))
fn alloc(&mut self, layout: Layout) -> Result<(NonNull<u8>, usize), AllocErr> {
if layout.size() == 0 {
Ok((layout.dangling(), 0))
} else {
unsafe {
NonNull::new(GlobalAlloc::alloc(self, layout))
.ok_or(AllocErr)
.map(|p| (p, layout.size()))
}
}
}
#[inline]
unsafe fn alloc_zeroed(&mut self, layout: Layout) -> Result<(NonNull<u8>, usize), AllocErr> {
fn alloc_zeroed(&mut self, layout: Layout) -> Result<(NonNull<u8>, usize), AllocErr> {
if layout.size() == 0 {
Ok((layout.dangling(), 0))
} else {
unsafe {
NonNull::new(GlobalAlloc::alloc_zeroed(self, layout))
.ok_or(AllocErr)
.map(|p| (p, layout.size()))
}
}
}
#[inline]
unsafe fn dealloc(&mut self, ptr: NonNull<u8>, layout: Layout) {
if layout.size() != 0 {
GlobalAlloc::dealloc(self, ptr.as_ptr(), layout)
}
}
#[inline]
unsafe fn realloc(
@ -160,9 +177,17 @@ unsafe impl AllocRef for System {
layout: Layout,
new_size: usize,
) -> Result<(NonNull<u8>, usize), AllocErr> {
NonNull::new(GlobalAlloc::realloc(self, ptr.as_ptr(), layout, new_size))
match (layout.size(), new_size) {
(0, 0) => Ok((layout.dangling(), 0)),
(0, _) => self.alloc(Layout::from_size_align_unchecked(new_size, layout.align())),
(_, 0) => {
self.dealloc(ptr, layout);
Ok((layout.dangling(), 0))
}
(_, _) => NonNull::new(GlobalAlloc::realloc(self, ptr.as_ptr(), layout, new_size))
.ok_or(AllocErr)
.map(|p| (p, new_size))
.map(|p| (p, new_size)),
}
}
}