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//! Specifications for containers
#![forbid(missing_docs)]
use std::collections::VecDeque;
pub mod columnation;
pub mod flatcontainer;
/// A container transferring data through dataflow edges
///
/// A container stores a number of elements and thus is able to describe it length (`len()`) and
/// whether it is empty (`is_empty()`). It supports removing all elements (`clear`).
///
/// A container must implement default. The default implementation is not required to allocate
/// memory for variable-length components.
///
/// We require the container to be cloneable to enable efficient copies when providing references
/// of containers to operators. Care must be taken that the type's `clone_from` implementation
/// is efficient (which is not necessarily the case when deriving `Clone`.)
/// TODO: Don't require `Container: Clone`
pub trait Container: Default + Clone + 'static {
/// The type of elements when reading non-destructively from the container.
type ItemRef<'a> where Self: 'a;
/// The type of elements when draining the container.
type Item<'a> where Self: 'a;
/// Push `item` into self
#[inline]
fn push<T>(&mut self, item: T) where Self: PushInto<T> {
self.push_into(item)
}
/// The number of elements in this container
///
/// The length of a container must be consistent between sending and receiving it.
/// When exchanging a container and partitioning it into pieces, the sum of the length
/// of all pieces must be equal to the length of the original container. When combining
/// containers, the length of the result must be the sum of the individual parts.
fn len(&self) -> usize;
/// Determine if the container contains any elements, corresponding to `len() == 0`.
fn is_empty(&self) -> bool {
self.len() == 0
}
/// Remove all contents from `self` while retaining allocated memory.
/// After calling `clear`, `is_empty` must return `true` and `len` 0.
fn clear(&mut self);
/// Iterator type when reading from the container.
type Iter<'a>: Iterator<Item=Self::ItemRef<'a>>;
/// Returns an iterator that reads the contents of this container.
fn iter(&self) -> Self::Iter<'_>;
/// Iterator type when draining the container.
type DrainIter<'a>: Iterator<Item=Self::Item<'a>>;
/// Returns an iterator that drains the contents of this container.
/// Drain leaves the container in an undefined state.
fn drain(&mut self) -> Self::DrainIter<'_>;
}
/// A container that can be sized and reveals its capacity.
pub trait SizableContainer: Container {
/// Return the capacity of the container.
fn capacity(&self) -> usize;
/// Return the preferred capacity of the container.
fn preferred_capacity() -> usize;
/// Reserve space for `additional` elements, possibly increasing the capacity of the container.
fn reserve(&mut self, additional: usize);
}
/// A container that can absorb items of a specific type.
pub trait PushInto<T> {
/// Push item into self.
fn push_into(&mut self, item: T);
}
/// A type that can build containers from items.
///
/// An implementation needs to absorb elements, and later reveal equivalent information
/// chunked into individual containers, but is free to change the data representation to
/// better fit the properties of the container.
///
/// Types implementing this trait should provide appropriate [`PushInto`] implementations such
/// that users can push the expected item types.
///
/// The owner extracts data in two ways. The opportunistic [`Self::extract`] method returns
/// any ready data, but doesn't need to produce partial outputs. In contrast, [`Self::finish`]
/// needs to produce all outputs, even partial ones. Caller should repeatedly call the functions
/// to drain pending or finished data.
///
/// The caller should consume the containers returned by [`Self::extract`] and
/// [`Self::finish`]. Implementations can recycle buffers, but should ensure that they clear
/// any remaining elements.
///
/// For example, a consolidating builder can aggregate differences in-place, but it has
/// to ensure that it preserves the intended information.
///
/// The trait does not prescribe any specific ordering guarantees, and each implementation can
/// decide to represent a push order for `extract` and `finish`, or not.
pub trait ContainerBuilder: Default + 'static {
/// The container type we're building.
type Container: Container;
/// Extract assembled containers, potentially leaving unfinished data behind. Can
/// be called repeatedly, for example while the caller can send data.
///
/// Returns a `Some` if there is data ready to be shipped, and `None` otherwise.
#[must_use]
fn extract(&mut self) -> Option<&mut Self::Container>;
/// Extract assembled containers and any unfinished data. Should
/// be called repeatedly until it returns `None`.
#[must_use]
fn finish(&mut self) -> Option<&mut Self::Container>;
}
/// A default container builder that uses length and preferred capacity to chunk data.
///
/// Maintains a single empty allocation between [`Self::push_into`] and [`Self::extract`], but not
/// across [`Self::finish`] to maintain a low memory footprint.
///
/// Maintains FIFO order.
#[derive(Default, Debug)]
pub struct CapacityContainerBuilder<C>{
/// Container that we're writing to.
current: C,
/// Emtpy allocation.
empty: Option<C>,
/// Completed containers pending to be sent.
pending: VecDeque<C>,
}
impl<T, C: SizableContainer + PushInto<T>> PushInto<T> for CapacityContainerBuilder<C> {
#[inline]
fn push_into(&mut self, item: T) {
if self.current.capacity() == 0 {
self.current = self.empty.take().unwrap_or_default();
// Discard any non-uniform capacity container.
if self.current.capacity() != C::preferred_capacity() {
self.current = C::default();
}
// Protect against non-emptied containers.
self.current.clear();
}
// Ensure capacity
if self.current.capacity() < C::preferred_capacity() {
self.current.reserve(C::preferred_capacity() - self.current.len());
}
// Push item
self.current.push(item);
// Maybe flush
if self.current.len() == self.current.capacity() {
self.pending.push_back(std::mem::take(&mut self.current));
}
}
}
impl<C: Container> ContainerBuilder for CapacityContainerBuilder<C> {
type Container = C;
#[inline]
fn extract(&mut self) -> Option<&mut C> {
if let Some(container) = self.pending.pop_front() {
self.empty = Some(container);
self.empty.as_mut()
} else {
None
}
}
#[inline]
fn finish(&mut self) -> Option<&mut C> {
if !self.current.is_empty() {
self.pending.push_back(std::mem::take(&mut self.current));
}
self.empty = self.pending.pop_front();
self.empty.as_mut()
}
}
impl<C: Container> CapacityContainerBuilder<C> {
/// Push a pre-formed container at this builder. This exists to maintain
/// API compatibility.
#[inline]
pub fn push_container(&mut self, container: &mut C) {
if !container.is_empty() {
// Flush to maintain FIFO ordering.
if self.current.len() > 0 {
self.pending.push_back(std::mem::take(&mut self.current));
}
let mut empty = self.empty.take().unwrap_or_default();
// Ideally, we'd discard non-uniformly sized containers, but we don't have
// access to `len`/`capacity` of the container.
empty.clear();
self.pending.push_back(std::mem::replace(container, empty));
}
}
}
impl<T: Clone + 'static> Container for Vec<T> {
type ItemRef<'a> = &'a T where T: 'a;
type Item<'a> = T where T: 'a;
fn len(&self) -> usize {
Vec::len(self)
}
fn is_empty(&self) -> bool {
Vec::is_empty(self)
}
fn clear(&mut self) { Vec::clear(self) }
type Iter<'a> = std::slice::Iter<'a, T>;
fn iter(&self) -> Self::Iter<'_> {
self.as_slice().iter()
}
type DrainIter<'a> = std::vec::Drain<'a, T>;
fn drain(&mut self) -> Self::DrainIter<'_> {
self.drain(..)
}
}
impl<T: Clone + 'static> SizableContainer for Vec<T> {
fn capacity(&self) -> usize {
self.capacity()
}
fn preferred_capacity() -> usize {
buffer::default_capacity::<T>()
}
fn reserve(&mut self, additional: usize) {
self.reserve(additional);
}
}
impl<T> PushInto<T> for Vec<T> {
#[inline]
fn push_into(&mut self, item: T) {
self.push(item)
}
}
impl<T: Clone> PushInto<&T> for Vec<T> {
#[inline]
fn push_into(&mut self, item: &T) {
self.push(item.clone())
}
}
impl<T: Clone> PushInto<&&T> for Vec<T> {
#[inline]
fn push_into(&mut self, item: &&T) {
self.push_into(*item)
}
}
mod rc {
use std::ops::Deref;
use std::rc::Rc;
use crate::Container;
impl<T: Container> Container for Rc<T> {
type ItemRef<'a> = T::ItemRef<'a> where Self: 'a;
type Item<'a> = T::ItemRef<'a> where Self: 'a;
fn len(&self) -> usize {
std::ops::Deref::deref(self).len()
}
fn is_empty(&self) -> bool {
std::ops::Deref::deref(self).is_empty()
}
fn clear(&mut self) {
// Try to reuse the allocation if possible
if let Some(inner) = Rc::get_mut(self) {
inner.clear();
} else {
*self = Self::default();
}
}
type Iter<'a> = T::Iter<'a>;
fn iter(&self) -> Self::Iter<'_> {
self.deref().iter()
}
type DrainIter<'a> = T::Iter<'a>;
fn drain(&mut self) -> Self::DrainIter<'_> {
self.iter()
}
}
}
mod arc {
use std::ops::Deref;
use std::sync::Arc;
use crate::Container;
impl<T: Container> Container for Arc<T> {
type ItemRef<'a> = T::ItemRef<'a> where Self: 'a;
type Item<'a> = T::ItemRef<'a> where Self: 'a;
fn len(&self) -> usize {
std::ops::Deref::deref(self).len()
}
fn is_empty(&self) -> bool {
std::ops::Deref::deref(self).is_empty()
}
fn clear(&mut self) {
// Try to reuse the allocation if possible
if let Some(inner) = Arc::get_mut(self) {
inner.clear();
} else {
*self = Self::default();
}
}
type Iter<'a> = T::Iter<'a>;
fn iter(&self) -> Self::Iter<'_> {
self.deref().iter()
}
type DrainIter<'a> = T::Iter<'a>;
fn drain(&mut self) -> Self::DrainIter<'_> {
self.iter()
}
}
}
/// A container that can partition itself into pieces.
pub trait PushPartitioned: SizableContainer {
/// Partition and push this container.
///
/// Drain all elements from `self`, and use the function `index` to determine which `buffer` to
/// append an element to. Call `flush` with an index and a buffer to send the data downstream.
fn push_partitioned<I, F>(&mut self, buffers: &mut [Self], index: I, flush: F)
where
for<'a> I: FnMut(&Self::Item<'a>) -> usize,
F: FnMut(usize, &mut Self);
}
impl<C: SizableContainer> PushPartitioned for C where for<'a> C: PushInto<C::Item<'a>> {
fn push_partitioned<I, F>(&mut self, buffers: &mut [Self], mut index: I, mut flush: F)
where
for<'a> I: FnMut(&Self::Item<'a>) -> usize,
F: FnMut(usize, &mut Self),
{
let ensure_capacity = |this: &mut Self| {
let capacity = this.capacity();
let desired_capacity = Self::preferred_capacity();
if capacity < desired_capacity {
this.reserve(desired_capacity - capacity);
}
};
for datum in self.drain() {
let index = index(&datum);
ensure_capacity(&mut buffers[index]);
buffers[index].push(datum);
if buffers[index].len() >= buffers[index].capacity() {
flush(index, &mut buffers[index]);
}
}
self.clear();
}
}
pub mod buffer {
//! Functionality related to calculating default buffer sizes
/// The upper limit for buffers to allocate, size in bytes. [default_capacity] converts
/// this to size in elements.
pub const BUFFER_SIZE_BYTES: usize = 1 << 13;
/// The maximum buffer capacity in elements. Returns a number between [BUFFER_SIZE_BYTES]
/// and 1, inclusively.
pub const fn default_capacity<T>() -> usize {
let size = std::mem::size_of::<T>();
if size == 0 {
BUFFER_SIZE_BYTES
} else if size <= BUFFER_SIZE_BYTES {
BUFFER_SIZE_BYTES / size
} else {
1
}
}
}