o3 0.23.0

shared-nothing primitives
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160

use std::mem;

pub(in crate::buffer) use built::Built;

use crate::{
    buffer,
    buffer::{
        segments,
        segments::{Chain, Key, Pool, handles},
        storage,
    },
    depot::arena::linked::{fifo::ends, slots},
};

mod built;

/// Fresh, unaliased metadata capacity owned by one prepared build.
pub struct Exact<T, S> {
    handle: Pool<T>,
    source: S,
}

pub(in crate::buffer) struct Writer<'a, T> {
    nodes: &'a slots::Store<segments::Item<T>>,
    links: ends::Exclusive<slots::Index>,
}

impl<T: buffer::raw::Segment, S: buffer::raw::Sequence<T>> Exact<T, S> {
    pub fn try_new(source: S) -> Result<Self, S::Error> {
        let count = source.count();
        let handle = Pool::try_new(segments::Plan {
            segments: count.into_raw() as usize,
            chains: usize::from(count.is_many()),
        });
        Self::try_build(source, handle)
    }

    pub(in crate::buffer::segments) fn try_reserve(
        source: S,
        current: segments::Count,
    ) -> Result<Self, S::Error> {
        let handle = Pool::try_reserve(current, source.count());
        Self::try_build(source, handle)
    }

    fn try_build(
        source: S,
        handle: Result<Pool<T>, crate::alloc::Error>,
    ) -> Result<Self, S::Error> {
        let handle = match handle {
            Ok(handle) => handle,
            Err(error) => return Err(source.reject(error)),
        };
        Ok(Self { handle, source })
    }
}

impl<T: buffer::raw::Segment, S: buffer::raw::Sequence<T>> Exact<T, S> {
    pub fn collect(self) -> S::Output
    where
        S: buffer::raw::Sequence<T, Item = segments::Item<T>>,
    {
        let Self { handle, source } = self;
        let mut source = source.owners();
        let nodes = handles::nodes(&handle);
        let mut writer = Writer::new(nodes);
        for value in source.by_ref() {
            let claim = unsafe { slots::Vacant::reserve(nodes) };
            unsafe { writer.push_claim(claim, value) };
        }
        let links = writer.into_links();
        Self::finish(handle, links, source)
    }

    pub fn try_collect<E>(self) -> Result<S::Output, E>
    where
        S: buffer::raw::Sequence<T, Item = Result<segments::Item<T>, E>>,
    {
        let Self { handle, source } = self;
        let mut source = source.owners();
        let nodes = handles::nodes(&handle);
        let mut writer = Writer::new(nodes);
        for value in source.by_ref() {
            let value = value?;
            let claim = unsafe { slots::Vacant::reserve(nodes) };
            unsafe { writer.push_claim(claim, value) };
        }
        let links = writer.into_links();
        Ok(Self::finish(handle, links, source))
    }

    fn finish(
        handle: Pool<T>,
        links: ends::Exclusive<slots::Index>,
        total: impl buffer::raw::Total,
    ) -> S::Output {
        let key = match buffer::raw::Total::count(&total).kind() {
            segments::Kind::Empty => Key::EMPTY,
            segments::Kind::One => Key::single(links.head_raw()),
            segments::Kind::Many(count) => {
                let descs = handles::descriptors(&handle);
                // SAFETY: `Exact` is constructed with one private descriptor
                // whenever its admitted source contains at least two owners;
                // Sequence preserves that total throughout iteration.
                let claim =
                    unsafe { slots::Vacant::reserve(descs) }.insert(handles::Descriptor::new(
                        links,
                        count.nonzero(),
                        buffer::raw::Total::len(&total),
                        buffer::raw::Total::resident(&total),
                    ));
                let key = Key::multi(claim.index());
                unsafe { claim.publish() };
                key
            }
        };
        let mut sequence = Chain::new(handle);
        sequence.key = key;
        buffer::raw::Assemble::finish::<S>(Built::new(sequence))
    }
}

impl<T: buffer::raw::Segment> Writer<'_, T> {
    /// # Safety
    /// `index` is an outstanding vacancy in this writer's exact node store.
    pub(in crate::buffer::segments::handles::pool) unsafe fn push_claim(
        &mut self,
        claim: slots::Vacant<segments::Item<T>, &'_ slots::Store<segments::Item<T>>>,
        value: segments::Item<T>,
    ) {
        unsafe { claim.insert(value).append(&mut self.links) };
    }

    pub(in crate::buffer) fn into_links(mut self) -> ends::Exclusive<slots::Index> {
        mem::replace(&mut self.links, ends::Exclusive::empty())
    }
}

impl<'a, T> Writer<'a, T> {
    pub(in crate::buffer::segments::handles::pool) fn new(
        nodes: &'a slots::Store<segments::Item<T>>,
    ) -> Self {
        Self {
            nodes,
            links: ends::Exclusive::empty(),
        }
    }
}

impl<T> Drop for Writer<'_, T> {
    fn drop(&mut self) {
        // SAFETY: this writer owns its exact initialized node-store partition.
        let mut links = unsafe { ends::Bound::new(self.nodes, &mut self.links) };
        links.clear();
    }
}

const _: () = assert!(
    size_of::<Exact<storage::Shared, &segments::Many<storage::Shared>>>() == 2 * size_of::<usize>()
);