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Add API for Alloc trait.

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Includes `alloc_zeroed` method that `RawVec` has come to depend on.

Exposed private `Layout::from_size_align` ctor to be `pub`, and added
explicit conditions for when it will panic (namely, when `align` is
not power-of-two, or if rounding up `size` to a multiple of `align`
overflows). Normalized all `Layout` construction to go through
`Layout::from_size_align`.

Addressed review feedback regarding `struct Layout` and zero-sized
layouts.

Restrict specification for `dealloc`, adding additional constraint
that the given alignment has to match that used to allocate the block.
(This is a maximally conservative constraint on the alignment. An open
question to resolve (before stabilization) is whether we can return to
a looser constraint such as the one previously specified.)

Split `fn realloc_in_place` into separate `fn grow_in_place` and `fn
shrink_in_place` methods, which have default impls that check against
usable_size for reuse. Make `realloc` default impl try `grow_in_place`
or `shrink_in_place` as appropriate before fallback on
alloc+copy+dealloc.

Drive-by: When reviewing calls to `padding_needed_for`, discovered
what I think was an over-conservative choice for its argument
alignment.  Namely, in `fn extend`, we automatically realign the whole
resulting layout to satisfy both old (self) and new alignments. When
the old alignment exceeds the new, this means we would insert
unnecessary padding. So I changed the code to pass in `next.align`
instead of `new_align` to `padding_needed_for`.

Replaced ref to `realloc_in_place` with `grow_in_place`/`shrink_in_place`.

Revised docs replacing my idiosyncratic style of `fn foo` with just
`foo` when referring to the function or method `foo`.

(Alpha-renamed `Allocator` to `Alloc`.)

Post-rebased, added `Debug` derive for `allocator::Excess` to satisfy
`missing_debug_implementations`.
This commit is contained in:
Felix S. Klock II 2017-05-23 14:47:09 +02:00
parent 258ae6dd9b
commit 066fafe206
2 changed files with 990 additions and 0 deletions
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// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
#![unstable(feature = "allocator_api",
reason = "the precise API and guarantees it provides may be tweaked \
slightly, especially to possibly take into account the \
types being stored to make room for a future \
tracing garbage collector",
issue = "27700")]
use core::cmp;
use core::mem;
use core::usize;
use core::ptr::{self, Unique};
/// Represents the combination of a starting address and
/// a total capacity of the returned block.
#[derive(Debug)]
pub struct Excess(pub *mut u8, pub usize);
fn size_align<T>() -> (usize, usize) {
(mem::size_of::<T>(), mem::align_of::<T>())
}
/// Layout of a block of memory.
///
/// An instance of `Layout` describes a particular layout of memory.
/// You build a `Layout` up as an input to give to an allocator.
///
/// All layouts have an associated non-negative size and a
/// power-of-two alignment.
///
/// (Note however that layouts are *not* required to have positive
/// size, even though many allocators require that all memory
/// requeusts have positive size. A caller to the `Alloc::alloc`
/// method must either ensure that conditions like this are met, or
/// use specific allocators with looser requirements.)
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct Layout {
// size of the requested block of memory, measured in bytes.
size: usize,
// alignment of the requested block of memory, measured in bytes.
// we ensure that this is always a power-of-two, because API's
// like `posix_memalign` require it and it is a reasonable
// constraint to impose on Layout constructors.
//
// (However, we do not analogously require `align >= sizeof(void*)`,
// even though that is *also* a requirement of `posix_memalign`.)
align: usize,
}
// FIXME: audit default implementations for overflow errors,
// (potentially switching to overflowing_add and
// overflowing_mul as necessary).
impl Layout {
/// Constructs a `Layout` from a given `size` and `align`.
///
/// # Panics
///
/// Panics if any of the following conditions are not met:
///
/// * `align` must be a power of two,
///
/// * `size`, when rounded up to the nearest multiple of `align`,
/// must not overflow (i.e. the rounded value must be less than
/// `usize::MAX`).
pub fn from_size_align(size: usize, align: usize) -> Layout {
assert!(align.is_power_of_two()); // (this implies align != 0.)
// Rounded up size is:
// size_rounded_up = (size + align - 1) & !(align - 1);
//
// We know from above that align != 0. If adding (align - 1)
// does not overflow, then rounding up will be fine.
//
// Conversely, &-masking with !(align - 1) will subtract off
// only low-order-bits. Thus if overflow occurs with the sum,
// the &-mask cannot subtract enough to undo that overflow.
//
// Above implies that checking for summation overflow is both
// necessary and sufficient.
assert!(size <= usize::MAX - (align - 1));
Layout { size: size, align: align }
}
/// The minimum size in bytes for a memory block of this layout.
pub fn size(&self) -> usize { self.size }
/// The minimum byte alignment for a memory block of this layout.
pub fn align(&self) -> usize { self.align }
/// Constructs a `Layout` suitable for holding a value of type `T`.
pub fn new<T>() -> Self {
let (size, align) = size_align::<T>();
Layout::from_size_align(size, align)
}
/// Produces layout describing a record that could be used to
/// allocate backing structure for `T` (which could be a trait
/// or other unsized type like a slice).
pub fn for_value<T: ?Sized>(t: &T) -> Self {
let (size, align) = (mem::size_of_val(t), mem::align_of_val(t));
Layout::from_size_align(size, align)
}
/// Creates a layout describing the record that can hold a value
/// of the same layout as `self`, but that also is aligned to
/// alignment `align` (measured in bytes).
///
/// If `self` already meets the prescribed alignment, then returns
/// `self`.
///
/// Note that this method does not add any padding to the overall
/// size, regardless of whether the returned layout has a different
/// alignment. In other words, if `K` has size 16, `K.align_to(32)`
/// will *still* have size 16.
///
/// # Panics
///
/// Panics if `align` is not a power of two.
pub fn align_to(&self, align: usize) -> Self {
assert!(align.is_power_of_two());
Layout::from_size_align(self.size, cmp::max(self.align, align))
}
/// Returns the amount of padding we must insert after `self`
/// to ensure that the following address will satisfy `align`
/// (measured in bytes).
///
/// E.g. if `self.size` is 9, then `self.padding_needed_for(4)`
/// returns 3, because that is the minimum number of bytes of
/// padding required to get a 4-aligned address (assuming that the
/// corresponding memory block starts at a 4-aligned address).
///
/// The return value of this function has no meaning if `align` is
/// not a power-of-two.
///
/// Note that the utility of the returned value requires `align`
/// to be less than or equal to the alignment of the starting
/// address for the whole allocated block of memory. One way to
/// satisfy this constraint is to ensure `align <= self.align`.
pub fn padding_needed_for(&self, align: usize) -> usize {
let len = self.size();
// Rounded up value is:
// len_rounded_up = (len + align - 1) & !(align - 1);
// and then we return the padding difference: `len_rounded_up - len`.
//
// We use modular arithmetic throughout:
//
// 1. align is guaranteed to be > 0, so align - 1 is always
// valid.
//
// 2. `len + align - 1` can overflow by at most `align - 1`,
// so the &-mask wth `!(align - 1)` will ensure that in the
// case of overflow, `len_rounded_up` will itself be 0.
// Thus the returned padding, when added to `len`, yields 0,
// which trivially satisfies the alignment `align`.
//
// (Of course, attempts to allocate blocks of memory whose
// size and padding overflow in the above manner should cause
// the allocator to yield an error anyway.)
let len_rounded_up = len.wrapping_add(align).wrapping_sub(1) & !align.wrapping_sub(1);
return len_rounded_up.wrapping_sub(len);
}
/// Creates a layout describing the record for `n` instances of
/// `self`, with a suitable amount of padding between each to
/// ensure that each instance is given its requested size and
/// alignment. On success, returns `(k, offs)` where `k` is the
/// layout of the array and `offs` is the distance between the start
/// of each element in the array.
///
/// On arithmetic overflow, returns `None`.
pub fn repeat(&self, n: usize) -> Option<(Self, usize)> {
let padded_size = match self.size.checked_add(self.padding_needed_for(self.align)) {
None => return None,
Some(padded_size) => padded_size,
};
let alloc_size = match padded_size.checked_mul(n) {
None => return None,
Some(alloc_size) => alloc_size,
};
Some((Layout::from_size_align(alloc_size, self.align), padded_size))
}
/// Creates a layout describing the record for `self` followed by
/// `next`, including any necessary padding to ensure that `next`
/// will be properly aligned. Note that the result layout will
/// satisfy the alignment properties of both `self` and `next`.
///
/// Returns `Some((k, offset))`, where `k` is layout of the concatenated
/// record and `offset` is the relative location, in bytes, of the
/// start of the `next` embedded witnin the concatenated record
/// (assuming that the record itself starts at offset 0).
///
/// On arithmetic overflow, returns `None`.
pub fn extend(&self, next: Self) -> Option<(Self, usize)> {
let new_align = cmp::max(self.align, next.align);
let realigned = Layout::from_size_align(self.size, new_align);
let pad = realigned.padding_needed_for(next.align);
let offset = match self.size.checked_add(pad) {
None => return None,
Some(offset) => offset,
};
let new_size = match offset.checked_add(next.size) {
None => return None,
Some(new_size) => new_size,
};
Some((Layout::from_size_align(new_size, new_align), offset))
}
/// Creates a layout describing the record for `n` instances of
/// `self`, with no padding between each instance.
///
/// Note that, unlike `repeat`, `repeat_packed` does not guarantee
/// that the repeated instances of `self` will be properly
/// aligned, even if a given instance of `self` is properly
/// aligned. In other words, if the layout returned by
/// `repeat_packed` is used to allocate an array, it is not
/// guaranteed that all elements in the array will be properly
/// aligned.
///
/// On arithmetic overflow, returns `None`.
pub fn repeat_packed(&self, n: usize) -> Option<Self> {
let size = match self.size().checked_mul(n) {
None => return None,
Some(scaled) => scaled,
};
Some(Layout::from_size_align(size, self.align))
}
/// Creates a layout describing the record for `self` followed by
/// `next` with no additional padding between the two. Since no
/// padding is inserted, the alignment of `next` is irrelevant,
/// and is not incoporated *at all* into the resulting layout.
///
/// Returns `(k, offset)`, where `k` is layout of the concatenated
/// record and `offset` is the relative location, in bytes, of the
/// start of the `next` embedded witnin the concatenated record
/// (assuming that the record itself starts at offset 0).
///
/// (The `offset` is always the same as `self.size()`; we use this
/// signature out of convenience in matching the signature of
/// `extend`.)
///
/// On arithmetic overflow, returns `None`.
pub fn extend_packed(&self, next: Self) -> Option<(Self, usize)> {
let new_size = match self.size().checked_add(next.size()) {
None => return None,
Some(new_size) => new_size,
};
Some((Layout::from_size_align(new_size, self.align), self.size()))
}
/// Creates a layout describing the record for a `[T; n]`.
///
/// On arithmetic overflow, returns `None`.
pub fn array<T>(n: usize) -> Option<Self> {
Layout::new::<T>()
.repeat(n)
.map(|(k, offs)| {
debug_assert!(offs == mem::size_of::<T>());
k
})
}
}
/// The `AllocErr` error specifies whether an allocation failure is
/// specifically due to resource exhaustion or if it is due to
/// something wrong when combining the given input arguments with this
/// allocator.
#[derive(Clone, PartialEq, Eq, Debug)]
pub enum AllocErr {
/// Error due to hitting some resource limit or otherwise running
/// out of memory. This condition strongly implies that *some*
/// series of deallocations would allow a subsequent reissuing of
/// the original allocation request to succeed.
Exhausted { request: Layout },
/// Error due to allocator being fundamentally incapable of
/// satisfying the original request. This condition implies that
/// such an allocation request will never succeed on the given
/// allocator, regardless of environment, memory pressure, or
/// other contextual conditions.
///
/// For example, an allocator that does not support requests for
/// large memory blocks might return this error variant.
Unsupported { details: &'static str },
}
impl AllocErr {
pub fn invalid_input(details: &'static str) -> Self {
AllocErr::Unsupported { details: details }
}
pub fn is_memory_exhausted(&self) -> bool {
if let AllocErr::Exhausted { .. } = *self { true } else { false }
}
pub fn is_request_unsupported(&self) -> bool {
if let AllocErr::Unsupported { .. } = *self { true } else { false }
}
}
/// The `CannotReallocInPlace` error is used when `grow_in_place` or
/// `shrink_in_place` were unable to reuse the given memory block for
/// a requested layout.
#[derive(Clone, PartialEq, Eq, Debug)]
pub struct CannotReallocInPlace;
/// An implementation of `Alloc` can allocate, reallocate, and
/// deallocate arbitrary blocks of data described via `Layout`.
///
/// Some of the methods require that a memory block be *currently
/// allocated* via an allocator. This means that:
///
/// * the starting address for that memory block was previously
/// returned by a previous call to an allocation method (`alloc`,
/// `alloc_zeroed`, `alloc_excess`, `alloc_one`, `alloc_array`) or
/// reallocation method (`realloc`, `realloc_excess`, or
/// `realloc_array`), and
///
/// * the memory block has not been subsequently deallocated, where
/// blocks are deallocated either by being passed to a deallocation
/// method (`dealloc`, `dealloc_one`, `dealloc_array`) 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 `Alloc` trait state that allocation requests
/// must be non-zero size, or else undefined behavior can result.
///
/// * However, some higher-level allocation methods (`alloc_one`,
/// `alloc_array`) are well-defined on zero-sized types and can
/// optionally support them: it is left up to the implementor
/// whether to return `Err`, or to return `Ok` with some pointer.
///
/// * If an `Alloc` 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.
///
/// 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
/// equivalently, for a memory block to "fit" a layout) is that the
/// following two conditions must hold:
///
/// 1. The block's starting address must be aligned to `layout.align()`.
///
/// 2. The block's size must fall in the range `[use_min, use_max]`, where:
///
/// * `use_min` is `self.usable_size(layout).0`, and
///
/// * `use_max` is the capacity that was (or would have been)
/// returned when (if) the block was allocated via a call to
/// `alloc_excess` or `realloc_excess`.
///
/// Note that:
///
/// * the size of the layout most recently used to allocate the block
/// is guaranteed to be in the range `[use_min, use_max]`, and
///
/// * a lower-bound on `use_max` can be safely approximated by a call to
/// `usable_size`.
///
/// * if a layout `k` fits a memory block (denoted by `ptr`)
/// currently allocated via an allocator `a`, then it is legal to
/// use that layout to deallocate it, i.e. `a.dealloc(ptr, k);`.
pub unsafe trait Alloc {
// (Note: 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. Rust should consider revising the alloc::heap crate
// to reflect this reality.)
/// Returns a pointer meeting the size and alignment guarantees of
/// `layout`.
///
/// If this method returns an `Ok(addr)`, then the `addr` returned
/// will be non-null address pointing to a block of storage
/// suitable for holding an instance of `layout`.
///
/// The returned block of storage may or may not have its contents
/// initialized. (Extension subtraits might restrict this
/// behavior, e.g. to ensure initialization to particular sets of
/// bit patterns.)
///
/// # Unsafety
///
/// 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
/// `layout` does not meet allocator's size or alignment
/// constraints.
///
/// Implementations are encouraged to return `Err` on memory
/// exhaustion rather than panicking or aborting, but this is not
/// a strict requirement. (Specifically: it is *legal* to
/// implement this trait atop an underlying native allocation
/// library that aborts on memory exhaustion.)
///
/// Clients wishing to abort computation in response to an
/// allocation error are encouraged to call the allocator's `oom`
/// method, rather than directly invoking `panic!` or similar.
unsafe fn alloc(&mut self, layout: Layout) -> Result<*mut u8, AllocErr>;
/// Deallocate the memory referenced by `ptr`.
///
/// # Unsafety
///
/// This function is unsafe because undefined behavior can result
/// if the caller does not ensure all of the following:
///
/// * `ptr` must denote a block of memory currently allocated via
/// this allocator,
///
/// * `layout` must *fit* that block of memory,
///
/// * In addition to fitting the block of memory `layout`, the
/// alignment of the `layout` must match the alignment used
/// to allocate that block of memory.
unsafe fn dealloc(&mut self, ptr: *mut u8, layout: Layout);
/// Allocator-specific method for signalling an out-of-memory
/// condition.
///
/// `oom` aborts the thread or process, optionally performing
/// cleanup or logging diagnostic information before panicking or
/// aborting.
///
/// `oom` is meant to be used by clients unable to cope with an
/// unsatisfied allocation request (signaled by an error such as
/// `AllocErr::Exhausted`), and wish to abandon computation rather
/// than attempt to recover locally. Such clients should pass the
/// signalling error value back into `oom`, where the allocator
/// may incorporate that error value into its diagnostic report
/// before aborting.
///
/// Implementations of the `oom` method are discouraged from
/// infinitely regressing in nested calls to `oom`. In
/// practice this means implementors should eschew allocating,
/// especially from `self` (directly or indirectly).
///
/// Implementions of the allocation and reallocation methods
/// (e.g. `alloc`, `alloc_one`, `realloc`) are discouraged from
/// panicking (or aborting) in the event of memory exhaustion;
/// instead they should return an appropriate error from the
/// invoked method, and let the client decide whether to invoke
/// this `oom` method in response.
fn oom(&mut self, _: AllocErr) -> ! {
unsafe { ::core::intrinsics::abort() }
}
// == ALLOCATOR-SPECIFIC QUANTITIES AND LIMITS ==
// usable_size
/// Returns bounds on the guaranteed usable size of a successful
/// allocation created with the specified `layout`.
///
/// In particular, if one has a memory block allocated via a given
/// allocator `a` and layout `k` where `a.usable_size(k)` returns
/// `(l, u)`, then one can pass that block to `a.dealloc()` with a
/// layout in the size range [l, u].
///
/// (All implementors of `usable_size` must ensure that
/// `l <= k.size() <= u`)
///
/// Both the lower- and upper-bounds (`l` and `u` respectively)
/// are provided, because an allocator based on size classes could
/// misbehave if one attempts to deallocate a block without
/// providing a correct value for its size (i.e., one within the
/// range `[l, u]`).
///
/// Clients who wish to make use of excess capacity are encouraged
/// to use the `alloc_excess` and `realloc_excess` instead, as
/// this method is constrained to report conservative values that
/// serve as valid bounds for *all possible* allocation method
/// calls.
///
/// However, for clients that do not wish to track the capacity
/// returned by `alloc_excess` locally, this method is likely to
/// produce useful results.
fn usable_size(&self, layout: &Layout) -> (usize, usize) {
(layout.size(), layout.size())
}
// == METHODS FOR MEMORY REUSE ==
// realloc. alloc_excess, realloc_excess
/// Returns a pointer suitable for holding data described by
/// `new_layout`, meeting its size and alignment guarantees. To
/// accomplish this, this may extend or shrink the allocation
/// referenced by `ptr` to fit `new_layout`.
///
/// If this returns `Ok`, then ownership of the memory block
/// referenced by `ptr` has been transferred to this
/// allocator. The memory may or may not have been freed, and
/// should be considered unusable (unless of course it was
/// transferred back to the caller again via the return value of
/// this method).
///
/// If this method returns `Err`, then ownership of the memory
/// block has not been transferred to this allocator, and the
/// contents of the memory block are unaltered.
///
/// For best results, `new_layout` should not impose a different
/// alignment constraint than `layout`. (In other words,
/// `new_layout.align()` should equal `layout.align()`.) However,
/// behavior is well-defined (though underspecified) when this
/// constraint is violated; further discussion below.
///
/// # Unsafety
///
/// This function is unsafe because undefined behavior can result
/// if the caller does not ensure all of the following:
///
/// * `ptr` must be currently allocated via this allocator,
///
/// * `layout` must *fit* the `ptr` (see above). (The `new_layout`
/// argument need not fit it.)
///
/// * `new_layout` must have size greater than zero.
///
/// * the alignment of `new_layout` is non-zero.
///
/// (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
///
/// Returns `Err` only if `new_layout` does not match the
/// alignment of `layout`, or does not meet the allocator's size
/// and alignment constraints of the allocator, or if reallocation
/// otherwise fails.
///
/// (Note the previous sentence did not say "if and only if" -- in
/// particular, an implementation of this method *can* return `Ok`
/// if `new_layout.align() != old_layout.align()`; or it can
/// return `Err` in that scenario, depending on whether this
/// allocator can dynamically adjust the alignment constraint for
/// the block.)
///
/// Implementations are encouraged to return `Err` on memory
/// exhaustion rather than panicking or aborting, but this is not
/// a strict requirement. (Specifically: it is *legal* to
/// implement this trait atop an underlying native allocation
/// library that aborts on memory exhaustion.)
///
/// Clients wishing to abort computation in response to an
/// reallocation error are encouraged to call the allocator's `oom`
/// method, rather than directly invoking `panic!` or similar.
unsafe fn realloc(&mut self,
ptr: *mut u8,
layout: Layout,
new_layout: Layout) -> Result<*mut u8, AllocErr> {
let new_size = new_layout.size();
let old_size = layout.size();
let aligns_match = layout.align == new_layout.align;
if new_size >= old_size && aligns_match {
if let Ok(()) = self.grow_in_place(ptr, layout.clone(), new_layout.clone()) {
return Ok(ptr);
}
} else if new_size < old_size && aligns_match {
if let Ok(()) = self.shrink_in_place(ptr, layout.clone(), new_layout.clone()) {
return Ok(ptr);
}
}
// otherwise, fall back on alloc + copy + dealloc.
let result = self.alloc(new_layout);
if let Ok(new_ptr) = result {
ptr::copy_nonoverlapping(ptr as *const u8, new_ptr, cmp::min(old_size, new_size));
self.dealloc(ptr, layout);
}
result
}
/// Behaves like `alloc`, but also ensures that the contents
/// are set to zero before being returned.
///
/// # Unsafety
///
/// This function is unsafe for the same reasons that `alloc` is.
///
/// # Errors
///
/// Returning `Err` indicates that either memory is exhausted or
/// `layout` does not meet allocator's size or alignment
/// constraints, just as in `alloc`.
///
/// Clients wishing to abort computation in response to an
/// allocation error are encouraged to call the allocator's `oom`
/// method, rather than directly invoking `panic!` or similar.
unsafe fn alloc_zeroed(&mut self, layout: Layout) -> Result<*mut u8, AllocErr> {
let size = layout.size();
let p = self.alloc(layout);
if let Ok(p) = p {
ptr::write_bytes(p, 0, size);
}
p
}
/// Behaves like `alloc`, but also returns the whole size of
/// the returned block. For some `layout` inputs, like arrays, this
/// may include extra storage usable for additional data.
///
/// # Unsafety
///
/// This function is unsafe for the same reasons that `alloc` is.
///
/// # Errors
///
/// Returning `Err` indicates that either memory is exhausted or
/// `layout` does not meet allocator's size or alignment
/// constraints, just as in `alloc`.
///
/// Clients wishing to abort computation in response to an
/// allocation error are encouraged to call the allocator's `oom`
/// method, rather than directly invoking `panic!` or similar.
unsafe fn alloc_excess(&mut self, layout: Layout) -> Result<Excess, AllocErr> {
let usable_size = self.usable_size(&layout);
self.alloc(layout).map(|p| Excess(p, usable_size.1))
}
/// Behaves like `realloc`, but also returns the whole size of
/// the returned block. For some `layout` inputs, like arrays, this
/// may include extra storage usable for additional data.
///
/// # Unsafety
///
/// This function is unsafe for the same reasons that `realloc` is.
///
/// # Errors
///
/// Returning `Err` indicates that either memory is exhausted or
/// `layout` does not meet allocator's size or alignment
/// constraints, just as in `realloc`.
///
/// Clients wishing to abort computation in response to an
/// reallocation error are encouraged to call the allocator's `oom`
/// method, rather than directly invoking `panic!` or similar.
unsafe fn realloc_excess(&mut self,
ptr: *mut u8,
layout: Layout,
new_layout: Layout) -> Result<Excess, AllocErr> {
let usable_size = self.usable_size(&new_layout);
self.realloc(ptr, layout, new_layout)
.map(|p| Excess(p, usable_size.1))
}
/// Attempts to extend the allocation referenced by `ptr` to fit `new_layout`.
///
/// If this returns `Ok`, then the allocator has asserted that the
/// memory block referenced by `ptr` now fits `new_layout`, and thus can
/// be used to carry data of that layout. (The allocator is allowed to
/// expend effort to accomplish this, such as extending the memory block to
/// include successor blocks, or virtual memory tricks.)
///
/// Regardless of what this method returns, ownership of the
/// memory block referenced by `ptr` has not been transferred, and
/// the contents of the memory block are unaltered.
///
/// # Unsafety
///
/// This function is unsafe because undefined behavior can result
/// if the caller does not ensure all of the following:
///
/// * `ptr` must be currently allocated via this allocator,
///
/// * `layout` must *fit* the `ptr` (see above); note the
/// `new_layout` argument need not fit it,
///
/// * `new_layout.size()` must not be less than `layout.size()`,
///
/// * `new_layout.align()` must equal `layout.align()`.
///
/// # Errors
///
/// Returns `Err(CannotReallocInPlace)` when the allocator is
/// unable to assert that the memory block referenced by `ptr`
/// could fit `layout`.
///
/// Note that one cannot pass `CannotReallocInPlace` to the `oom`
/// method; clients are expected either to be able to recover from
/// `grow_in_place` failures without aborting, or to fall back on
/// another reallocation method before resorting to an abort.
unsafe fn grow_in_place(&mut self,
ptr: *mut u8,
layout: Layout,
new_layout: Layout) -> Result<(), CannotReallocInPlace> {
let _ = ptr; // this default implementation doesn't care about the actual address.
debug_assert!(new_layout.size >= layout.size);
debug_assert!(new_layout.align == layout.align);
let (_l, u) = self.usable_size(&layout);
// _l <= layout.size() [guaranteed by usable_size()]
// layout.size() <= new_layout.size() [required by this method]
if new_layout.size <= u {
return Ok(());
} else {
return Err(CannotReallocInPlace);
}
}
/// Attempts to shrink the allocation referenced by `ptr` to fit `new_layout`.
///
/// If this returns `Ok`, then the allocator has asserted that the
/// memory block referenced by `ptr` now fits `new_layout`, and
/// thus can only be used to carry data of that smaller
/// layout. (The allocator is allowed to take advantage of this,
/// carving off portions of the block for reuse elsewhere.) The
/// truncated contents of the block within the smaller layout are
/// unaltered, and ownership of block has not been transferred.
///
/// If this returns `Err`, then the memory block is considered to
/// still represent the original (larger) `layout`. None of the
/// block has been carved off for reuse elsewhere, ownership of
/// the memory block has not been transferred, and the contents of
/// the memory block are unaltered.
///
/// # Unsafety
///
/// This function is unsafe because undefined behavior can result
/// if the caller does not ensure all of the following:
///
/// * `ptr` must be currently allocated via this allocator,
///
/// * `layout` must *fit* the `ptr` (see above); note the
/// `new_layout` argument need not fit it,
///
/// * `new_layout.size()` must not be greater than `layout.size()`
/// (and must be greater than zero),
///
/// * `new_layout.align()` must equal `layout.align()`.
///
/// # Errors
///
/// Returns `Err(CannotReallocInPlace)` when the allocator is
/// unable to assert that the memory block referenced by `ptr`
/// could fit `layout`.
///
/// Note that one cannot pass `CannotReallocInPlace` to the `oom`
/// method; clients are expected either to be able to recover from
/// `shrink_in_place` failures without aborting, or to fall back
/// on another reallocation method before resorting to an abort.
unsafe fn shrink_in_place(&mut self,
ptr: *mut u8,
layout: Layout,
new_layout: Layout) -> Result<(), CannotReallocInPlace> {
let _ = ptr; // this default implementation doesn't care about the actual address.
debug_assert!(new_layout.size <= layout.size);
debug_assert!(new_layout.align == layout.align);
let (l, _u) = self.usable_size(&layout);
// layout.size() <= _u [guaranteed by usable_size()]
// new_layout.size() <= layout.size() [required by this method]
if l <= new_layout.size {
return Ok(());
} else {
return Err(CannotReallocInPlace);
}
}
// == COMMON USAGE PATTERNS ==
// alloc_one, dealloc_one, alloc_array, realloc_array. dealloc_array
/// Allocates a block suitable for holding an instance of `T`.
///
/// Captures a common usage pattern for allocators.
///
/// The returned block is suitable for passing to the
/// `alloc`/`realloc` methods of this allocator.
///
/// Note to implementors: If this returns `Ok(ptr)`, then `ptr`
/// must be considered "currently allocated" and must be
/// acceptable input to methods such as `realloc` or `dealloc`,
/// *even if* `T` is a zero-sized type. In other words, if your
/// `Alloc` implementation overrides this method in a manner
/// that can return a zero-sized `ptr`, then all reallocation and
/// deallocation methods need to be similarly overridden to accept
/// such values as input.
///
/// # Errors
///
/// Returning `Err` indicates that either memory is exhausted or
/// `T` does not meet allocator's size or alignment constraints.
///
/// For zero-sized `T`, may return either of `Ok` or `Err`, but
/// will *not* yield undefined behavior.
///
/// Clients wishing to abort computation in response to an
/// allocation error are encouraged to call the allocator's `oom`
/// method, rather than directly invoking `panic!` or similar.
fn alloc_one<T>(&mut self) -> Result<Unique<T>, AllocErr>
where Self: Sized
{
let k = Layout::new::<T>();
if k.size() > 0 {
unsafe { self.alloc(k).map(|p|Unique::new(*p as *mut T)) }
} else {
Err(AllocErr::invalid_input("zero-sized type invalid for alloc_one"))
}
}
/// Deallocates a block suitable for holding an instance of `T`.
///
/// The given block must have been produced by this allocator,
/// and must be suitable for storing a `T` (in terms of alignment
/// as well as minimum and maximum size); otherwise yields
/// undefined behavior.
///
/// Captures a common usage pattern for allocators.
///
/// # Unsafety
///
/// This function is unsafe because undefined behavior can result
/// if the caller does not ensure both:
///
/// * `ptr` must denote a block of memory currently allocated via this allocator
///
/// * the layout of `T` must *fit* that block of memory.
unsafe fn dealloc_one<T>(&mut self, ptr: Unique<T>)
where Self: Sized
{
let raw_ptr = ptr.as_ptr() as *mut u8;
let k = Layout::new::<T>();
if k.size() > 0 {
self.dealloc(raw_ptr, k);
}
}
/// Allocates a block suitable for holding `n` instances of `T`.
///
/// Captures a common usage pattern for allocators.
///
/// The returned block is suitable for passing to the
/// `alloc`/`realloc` methods of this allocator.
///
/// Note to implementors: If this returns `Ok(ptr)`, then `ptr`
/// must be considered "currently allocated" and must be
/// acceptable input to methods such as `realloc` or `dealloc`,
/// *even if* `T` is a zero-sized type. In other words, if your
/// `Alloc` implementation overrides this method in a manner
/// that can return a zero-sized `ptr`, then all reallocation and
/// deallocation methods need to be similarly overridden to accept
/// such values as input.
///
/// # Errors
///
/// Returning `Err` indicates that either memory is exhausted or
/// `[T; n]` does not meet allocator's size or alignment
/// constraints.
///
/// For zero-sized `T` or `n == 0`, may return either of `Ok` or
/// `Err`, but will *not* yield undefined behavior.
///
/// Always returns `Err` on arithmetic overflow.
///
/// Clients wishing to abort computation in response to an
/// allocation error are encouraged to call the allocator's `oom`
/// method, rather than directly invoking `panic!` or similar.
fn alloc_array<T>(&mut self, n: usize) -> Result<Unique<T>, AllocErr>
where Self: Sized
{
match Layout::array::<T>(n) {
Some(ref layout) if layout.size() > 0 => {
unsafe {
self.alloc(layout.clone())
.map(|p| {
Unique::new(p as *mut T)
})
}
}
_ => Err(AllocErr::invalid_input("invalid layout for alloc_array")),
}
}
/// Reallocates a block previously suitable for holding `n_old`
/// instances of `T`, returning a block suitable for holding
/// `n_new` instances of `T`.
///
/// Captures a common usage pattern for allocators.
///
/// The returned block is suitable for passing to the
/// `alloc`/`realloc` methods of this allocator.
///
/// # Unsafety
///
/// This function is unsafe because undefined behavior can result
/// if the caller does not ensure all of the following:
///
/// * `ptr` must be currently allocated via this allocator,
///
/// * the layout of `[T; n_old]` must *fit* that block of memory.
///
/// # Errors
///
/// Returning `Err` indicates that either memory is exhausted or
/// `[T; n_new]` does not meet allocator's size or alignment
/// constraints.
///
/// For zero-sized `T` or `n_new == 0`, may return either of `Ok` or
/// `Err`, but will *not* yield undefined behavior.
///
/// Always returns `Err` on arithmetic overflow.
///
/// Clients wishing to abort computation in response to an
/// reallocation error are encouraged to call the allocator's `oom`
/// method, rather than directly invoking `panic!` or similar.
unsafe fn realloc_array<T>(&mut self,
ptr: Unique<T>,
n_old: usize,
n_new: usize) -> Result<Unique<T>, AllocErr>
where Self: Sized
{
match (Layout::array::<T>(n_old), Layout::array::<T>(n_new), ptr.as_ptr()) {
(Some(ref k_old), Some(ref k_new), ptr) if k_old.size() > 0 && k_new.size() > 0 => {
self.realloc(ptr as *mut u8, k_old.clone(), k_new.clone())
.map(|p|Unique::new(p as *mut T))
}
_ => {
Err(AllocErr::invalid_input("invalid layout for realloc_array"))
}
}
}
/// Deallocates a block suitable for holding `n` instances of `T`.
///
/// Captures a common usage pattern for allocators.
///
/// # Unsafety
///
/// This function is unsafe because undefined behavior can result
/// if the caller does not ensure both:
///
/// * `ptr` must denote a block of memory currently allocated via this allocator
///
/// * the layout of `[T; n]` must *fit* that block of memory.
///
/// # Errors
///
/// Returning `Err` indicates that either `[T; n]` or the given
/// memory block does not meet allocator's size or alignment
/// constraints.
///
/// Always returns `Err` on arithmetic overflow.
unsafe fn dealloc_array<T>(&mut self, ptr: Unique<T>, n: usize) -> Result<(), AllocErr>
where Self: Sized
{
let raw_ptr = ptr.as_ptr() as *mut u8;
match Layout::array::<T>(n) {
Some(ref k) if k.size() > 0 => {
Ok(self.dealloc(raw_ptr, k.clone()))
}
_ => {
Err(AllocErr::invalid_input("invalid layout for dealloc_array"))
}
}
}
}

4
src/liballoc/lib.rs
View File

@ -143,6 +143,10 @@ extern crate std_unicode;
#[macro_use]
mod macros;
// Allocator trait and helper struct definitions
pub mod allocator;
// Heaps provided for low-level allocation strategies
pub mod heap;