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|
use super::super::plumbing::*;
use std::marker::PhantomData;
use std::mem::MaybeUninit;
use std::ptr;
use std::slice;
pub(super) struct CollectConsumer<'c, T: Send> {
/// A slice covering the target memory, not yet initialized!
target: &'c mut [MaybeUninit<T>],
}
impl<'c, T: Send + 'c> CollectConsumer<'c, T> {
/// The target memory is considered uninitialized, and will be
/// overwritten without reading or dropping existing values.
pub(super) fn new(target: &'c mut [MaybeUninit<T>]) -> Self {
CollectConsumer { target }
}
}
/// CollectResult represents an initialized part of the target slice.
///
/// This is a proxy owner of the elements in the slice; when it drops,
/// the elements will be dropped, unless its ownership is released before then.
#[must_use]
pub(super) struct CollectResult<'c, T> {
/// A slice covering the target memory, initialized up to our separate `len`.
target: &'c mut [MaybeUninit<T>],
/// The current initialized length in `target`
len: usize,
/// Lifetime invariance guarantees that the data flows from consumer to result,
/// especially for the `scope_fn` callback in `Collect::with_consumer`.
invariant_lifetime: PhantomData<&'c mut &'c mut [T]>,
}
unsafe impl<'c, T> Send for CollectResult<'c, T> where T: Send {}
impl<'c, T> CollectResult<'c, T> {
/// The current length of the collect result
pub(super) fn len(&self) -> usize {
self.len
}
/// Release ownership of the slice of elements, and return the length
pub(super) fn release_ownership(mut self) -> usize {
let ret = self.len;
self.len = 0;
ret
}
}
impl<'c, T> Drop for CollectResult<'c, T> {
fn drop(&mut self) {
// Drop the first `self.len` elements, which have been recorded
// to be initialized by the folder.
unsafe {
// TODO: use `MaybeUninit::slice_as_mut_ptr`
let start = self.target.as_mut_ptr() as *mut T;
ptr::drop_in_place(slice::from_raw_parts_mut(start, self.len));
}
}
}
impl<'c, T: Send + 'c> Consumer<T> for CollectConsumer<'c, T> {
type Folder = CollectResult<'c, T>;
type Reducer = CollectReducer;
type Result = CollectResult<'c, T>;
fn split_at(self, index: usize) -> (Self, Self, CollectReducer) {
let CollectConsumer { target } = self;
// Produce new consumers. Normal slicing ensures that the
// memory range given to each consumer is disjoint.
let (left, right) = target.split_at_mut(index);
(
CollectConsumer::new(left),
CollectConsumer::new(right),
CollectReducer,
)
}
fn into_folder(self) -> Self::Folder {
// Create a result/folder that consumes values and writes them
// into target. The initial result has length 0.
CollectResult {
target: self.target,
len: 0,
invariant_lifetime: PhantomData,
}
}
fn full(&self) -> bool {
false
}
}
impl<'c, T: Send + 'c> Folder<T> for CollectResult<'c, T> {
type Result = Self;
fn consume(mut self, item: T) -> Self {
let dest = self
.target
.get_mut(self.len)
.expect("too many values pushed to consumer");
// Write item and increase the initialized length
unsafe {
dest.as_mut_ptr().write(item);
self.len += 1;
}
self
}
fn complete(self) -> Self::Result {
// NB: We don't explicitly check that the local writes were complete,
// but Collect will assert the total result length in the end.
self
}
fn full(&self) -> bool {
false
}
}
/// Pretend to be unindexed for `special_collect_into_vec`,
/// but we should never actually get used that way...
impl<'c, T: Send + 'c> UnindexedConsumer<T> for CollectConsumer<'c, T> {
fn split_off_left(&self) -> Self {
unreachable!("CollectConsumer must be indexed!")
}
fn to_reducer(&self) -> Self::Reducer {
CollectReducer
}
}
/// CollectReducer combines adjacent chunks; the result must always
/// be contiguous so that it is one combined slice.
pub(super) struct CollectReducer;
impl<'c, T> Reducer<CollectResult<'c, T>> for CollectReducer {
fn reduce(
self,
mut left: CollectResult<'c, T>,
right: CollectResult<'c, T>,
) -> CollectResult<'c, T> {
// Merge if the CollectResults are adjacent and in left to right order
// else: drop the right piece now and total length will end up short in the end,
// when the correctness of the collected result is asserted.
let left_end = left.target[left.len..].as_ptr();
if left_end == right.target.as_ptr() {
let len = left.len + right.release_ownership();
unsafe {
left.target = slice::from_raw_parts_mut(left.target.as_mut_ptr(), len);
}
left.len = len;
}
left
}
}
|
