use std::num::NonZero;
use handles::{Descriptor, Occupied};
use crate::{
buffer,
buffer::{
segments,
segments::{Key, Kind, Pool, handles},
},
depot::{
arena::linked::{fifo::ends, slots},
capacity,
},
};
pub(in crate::buffer::segments::chain::prefix) struct Body<'a, T> {
pub(in crate::buffer::segments::chain::prefix) handle: &'a Pool<T>,
key: &'a mut Key,
pub(in crate::buffer::segments::chain::prefix) links: ends::Exclusive<slots::Index>,
pub(in crate::buffer::segments::chain::prefix) len: usize,
pub(in crate::buffer::segments::chain::prefix) resident: usize,
}
pub(in crate::buffer::segments::chain::prefix) struct Topology<'a, T> {
pub(in crate::buffer::segments::chain::prefix) body: Body<'a, T>,
output: Output<'a>,
}
pub(in crate::buffer::segments::chain::prefix) enum Original<'a, T> {
Direct(Body<'a, T>),
Multi(Existing<'a, T>),
}
pub(in crate::buffer::segments::chain::prefix) struct Existing<'a, T> {
handle: &'a Pool<T>,
key: &'a mut Key,
index: slots::Index,
}
enum Small {
Empty,
One,
}
enum Output<'a> {
Small(Small),
Many {
count: NonZero<u32>,
claim: slots::Vacant<Descriptor, &'a slots::Store<Descriptor>>,
},
}
enum Source<'a, T> {
Direct {
body: Body<'a, T>,
state: Small,
},
Keep {
old: Existing<'a, T>,
count: NonZero<u32>,
},
Free {
old: Existing<'a, T>,
state: Small,
},
}
impl<'a, T: buffer::raw::Segment> Original<'a, T> {
pub(in crate::buffer::segments::chain::prefix) fn new(
handle: &'a Pool<T>,
key: &'a mut Key,
single: impl FnOnce(slots::Index) -> (usize, usize),
) -> Self {
let nodes = handles::nodes(handle);
let (links, len, resident) = match key.state() {
Some(Occupied::Multi(index)) => {
return Self::Multi(Existing { handle, key, index });
}
None => (ends::Exclusive::empty(), 0, 0),
Some(Occupied::Single(index)) => {
let (len, resident) = single(index);
let mut links = ends::Exclusive::empty();
unsafe { links.append_end(nodes, index) };
(links, len, resident)
}
};
Self::Direct(Body {
handle,
key,
links,
len,
resident,
})
}
pub(in crate::buffer::segments::chain::prefix) fn handle(&self) -> &'a Pool<T> {
match self {
Self::Direct(body) => body.handle,
Self::Multi(old) => old.handle,
}
}
pub(in crate::buffer::segments::chain::prefix) fn total(
&self,
) -> (segments::Count, usize, usize) {
match self {
Self::Direct(body) => (
segments::Count::new(u32::from(!body.links.is_empty())),
body.len,
body.resident,
),
Self::Multi(old) => {
let desc = unsafe { handles::descriptors(old.handle).value(old.index) };
(
segments::Count::new(desc.count.get()),
desc.len,
desc.resident_bytes,
)
}
}
}
}
impl<'a, T> Existing<'a, T> {
fn take(
self,
) -> (
Body<'a, T>,
slots::Vacant<Descriptor, &'a slots::Store<Descriptor>>,
) {
let (desc, claim) =
unsafe { handles::descriptors(self.handle).detached(self.index) }.take();
*self.key = Key::EMPTY;
(
Body {
handle: self.handle,
key: self.key,
links: desc.links,
len: desc.len,
resident: desc.resident_bytes,
},
claim,
)
}
}
impl<'a, T> Source<'a, T> {
fn new(input: Original<'a, T>, count: segments::Count) -> Self {
match input {
Original::Direct(body) => Self::Direct {
body,
state: if count == segments::Count::EMPTY {
Small::Empty
} else {
Small::One
},
},
Original::Multi(old) => match count.kind() {
Kind::Empty => Self::Free {
old,
state: Small::Empty,
},
Kind::One => Self::Free {
old,
state: Small::One,
},
Kind::Many(count) => Self::Keep {
old,
count: count.nonzero(),
},
},
}
}
fn take(self) -> Topology<'a, T> {
match self {
Self::Direct { body, state } => Topology {
body,
output: Output::Small(state),
},
Self::Free { old, state } => Topology {
body: old.take().0,
output: Output::Small(state),
},
Self::Keep { old, count } => {
let (body, claim) = old.take();
Topology {
body,
output: Output::Many { count, claim },
}
}
}
}
}
impl<'a, T: buffer::raw::Segment> Topology<'a, T> {
pub(in crate::buffer::segments::chain::prefix) fn try_pair(
source: Original<'a, T>,
target: Original<'a, T>,
remains: segments::Count,
count: segments::Count,
different_pool: &bool,
) -> Result<(Self, Self), segments::Error> {
let source = Source::new(source, remains);
let (body, output, source) = match target {
Original::Multi(old) => {
let (body, claim) = old.take();
let count = unsafe { NonZero::new_unchecked(count.into_raw()) };
(body, Output::Many { count, claim }, source)
}
Original::Direct(body) => match count.kind() {
Kind::Empty => (body, Output::Small(Small::Empty), source),
Kind::One => (body, Output::Small(Small::One), source),
Kind::Many(count) => {
let count = count.nonzero();
match (different_pool, source) {
(false, Source::Free { old, state }) => {
let (from, claim) = old.take();
return Ok((
Self {
body: from,
output: Output::Small(state),
},
Self {
body,
output: Output::Many { count, claim },
},
));
}
(_, source) => {
let claim = handles::descriptors(body.handle).vacant().ok_or(
segments::Error::ChainCapacity(capacity::Shortage {
requested: NonZero::<usize>::MIN,
available: 0,
}),
)?;
(body, Output::Many { count, claim }, source)
}
}
}
},
};
Ok((source.take(), Self { body, output }))
}
}
impl<T> Topology<'_, T> {
pub(in crate::buffer::segments::chain::prefix) fn restore(self) {
match self.output {
Output::Small(Small::Empty) => *self.body.key = Key::EMPTY,
Output::Small(Small::One) => *self.body.key = Key::single(self.body.links.head_raw()),
Output::Many { count, claim } => {
let live = claim.insert(Descriptor {
links: self.body.links,
count,
len: self.body.len,
resident_bytes: self.body.resident,
});
*self.body.key = Key::multi(live.index());
unsafe { live.publish() };
}
}
}
}