// 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 or the MIT license // , 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 = "32838")] use core::cmp; use core::fmt; 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() -> (usize, usize) { (mem::size_of::(), mem::align_of::()) } /// 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 /// requests 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`, /// or returns `None` if any of the following conditions /// are not met: /// /// * `align` must be a power of two, /// /// * `align` must not exceed 2^31 (i.e. `1 << 31`), /// /// * `size`, when rounded up to the nearest multiple of `align`, /// must not overflow (i.e. the rounded value must be less than /// `usize::MAX`). #[inline] pub fn from_size_align(size: usize, align: usize) -> Option { if !align.is_power_of_two() { return None; } if align > (1 << 31) { return None; } // (power-of-two 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. if size > usize::MAX - (align - 1) { return None; } unsafe { Some(Layout::from_size_align_unchecked(size, align)) } } /// Creates a layout, bypassing all checks. /// /// # Unsafety /// /// This function is unsafe as it does not verify that `align` is /// a power-of-two that is also less than or equal to 2^31, nor /// that `size` aligned to `align` fits within the address space /// (i.e. the `Layout::from_size_align` preconditions). #[inline] pub unsafe fn from_size_align_unchecked(size: usize, align: usize) -> Layout { Layout { size: size, align: align } } /// The minimum size in bytes for a memory block of this layout. #[inline] pub fn size(&self) -> usize { self.size } /// The minimum byte alignment for a memory block of this layout. #[inline] pub fn align(&self) -> usize { self.align } /// Constructs a `Layout` suitable for holding a value of type `T`. pub fn new() -> Self { let (size, align) = size_align::(); Layout::from_size_align(size, align).unwrap() } /// 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: &T) -> Self { let (size, align) = (mem::size_of_val(t), mem::align_of_val(t)); Layout::from_size_align(size, align).unwrap() } /// 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 the combination of `self.size` and the given `align` /// violates the conditions listed in `from_size_align`. #[inline] pub fn align_to(&self, align: usize) -> Self { Layout::from_size_align(self.size, cmp::max(self.align, align)).unwrap() } /// 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`. #[inline] 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`. #[inline] 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, }; // We can assume that `self.align` is a power-of-two that does // not exceed 2^31. Furthermore, `alloc_size` has already been // rounded up to a multiple of `self.align`; therefore, the // call to `Layout::from_size_align` below should never panic. Some((Layout::from_size_align(alloc_size, self.align).unwrap(), 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 within 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 = match Layout::from_size_align(self.size, new_align) { None => return None, Some(l) => l, }; 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, }; let layout = match Layout::from_size_align(new_size, new_align) { None => return None, Some(l) => l, }; Some((layout, 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 { let size = match self.size().checked_mul(n) { None => return None, Some(scaled) => scaled, }; 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 incorporated *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 within 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, }; let layout = match Layout::from_size_align(new_size, self.align) { None => return None, Some(l) => l, }; Some((layout, self.size())) } /// Creates a layout describing the record for a `[T; n]`. /// /// On arithmetic overflow, returns `None`. pub fn array(n: usize) -> Option { Layout::new::() .repeat(n) .map(|(k, offs)| { debug_assert!(offs == mem::size_of::()); 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 { #[inline] pub fn invalid_input(details: &'static str) -> Self { AllocErr::Unsupported { details: details } } #[inline] pub fn is_memory_exhausted(&self) -> bool { if let AllocErr::Exhausted { .. } = *self { true } else { false } } #[inline] pub fn is_request_unsupported(&self) -> bool { if let AllocErr::Unsupported { .. } = *self { true } else { false } } #[inline] pub fn description(&self) -> &str { match *self { AllocErr::Exhausted { .. } => "allocator memory exhausted", AllocErr::Unsupported { .. } => "unsupported allocator request", } } } // (we need this for downstream impl of trait Error) impl fmt::Display for AllocErr { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { write!(f, "{}", self.description()) } } /// 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; impl CannotReallocInPlace { pub fn description(&self) -> &str { "cannot reallocate allocator's memory in place" } } // (we need this for downstream impl of trait Error) impl fmt::Display for CannotReallocInPlace { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { write!(f, "{}", self.description()) } } /// 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 signaling 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 /// signaling 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). /// /// Implementations 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. #[inline] 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 { 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 { 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(&mut self) -> Result, AllocErr> where Self: Sized { let k = Layout::new::(); if k.size() > 0 { unsafe { self.alloc(k).map(|p| Unique::new_unchecked(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(&mut self, ptr: Unique) where Self: Sized { let raw_ptr = ptr.as_ptr() as *mut u8; let k = Layout::new::(); 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(&mut self, n: usize) -> Result, AllocErr> where Self: Sized { match Layout::array::(n) { Some(ref layout) if layout.size() > 0 => { unsafe { self.alloc(layout.clone()) .map(|p| { Unique::new_unchecked(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(&mut self, ptr: Unique, n_old: usize, n_new: usize) -> Result, AllocErr> where Self: Sized { match (Layout::array::(n_old), Layout::array::(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_unchecked(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(&mut self, ptr: Unique, n: usize) -> Result<(), AllocErr> where Self: Sized { let raw_ptr = ptr.as_ptr() as *mut u8; match Layout::array::(n) { Some(ref k) if k.size() > 0 => { Ok(self.dealloc(raw_ptr, k.clone())) } _ => { Err(AllocErr::invalid_input("invalid layout for dealloc_array")) } } } }