o3 0.40.0

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
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256

use std::{marker, num, ptr};

use crate::{
    buffer::{
        pool,
        pool::{owners::Key, state},
        storage::regions,
    },
    mem::rc,
};

#[repr(C, align(8))]
pub(in crate::buffer) struct Slot<K: crate::buffer::raw::Backing = super::Plain> {
    prefix: regions::Prefix,
    pub(super) link: K::Link,
}

// SAFETY: Slot retains its exact initialized prefix and embedded reference domain.
unsafe impl<K: crate::buffer::raw::Backing> crate::mem::raw::Edge for Slot<K> {
    fn count(&self) -> &crate::mem::raw::Count {
        crate::mem::raw::Edge::count(&self.prefix)
    }
}

// SAFETY: each slot edge retains its exact published pool until terminal release.
unsafe impl<K: crate::buffer::raw::Backing> crate::mem::raw::Target for Slot<K> {
    unsafe fn destroy(pointer: ptr::NonNull<Self>) {
        // SAFETY: Last transfers this slot before its live key is replaced.
        unsafe { Retired::<K, super::Any>::from_owner(pointer.cast()) }.finish();
    }
}

/// One freshly initialized nonempty slot list before its first acquisition.
#[repr(transparent)]
pub(in crate::buffer::pool) struct Seed<K, S> {
    slots: super::Ptr<K, S>,
}

/// One newly activated slot edge still carrying its exact pool identity.
#[repr(C)]
pub(in crate::buffer::pool) struct Active<K: crate::buffer::raw::Backing, S> {
    pub(in crate::buffer::pool) slots: super::Ptr<K, S>,
    pub(in crate::buffer::pool) key: Key,
}

/// Exact terminal slot state produced only by the last live edge.
#[repr(C)]
pub(super) struct Retired<K, S> {
    slots: super::Ptr<K, S>,
    key: Key,
}

impl<K: crate::buffer::raw::Backing, S> Active<K, S> {
    pub(in crate::buffer::pool) fn acquire(slots: super::Ptr<K, S>) -> Option<Self> {
        let key = slots.header().free.head()?;
        // SAFETY: this exact vacant head is consumed without intervening reentry.
        Some(unsafe { Self::take(slots, key) })
    }

    /// # Safety
    /// `key` is this pool's exclusively claimed, initialized free-list head.
    unsafe fn take(slots: super::Ptr<K, S>, key: Key) -> Self {
        use crate::mem::raw::Edge;

        let slot = slots.slot(key);
        let header = slots.header();
        // SAFETY: the caller owns this exact vacant head; publish its live key
        // before creating the first edge. Any resident association is already empty.
        unsafe {
            header.free.pop(slot.prefix.word());
            slot.prefix.write(key.get());
            slot.activate();
        }
        header.available.set(header.available.get() - 1);
        Self { slots, key }
    }
}

impl<K: crate::buffer::raw::Backing, S> Seed<K, S> {
    /// # Safety
    /// The core must have just published a nonempty Slot list initialized in
    /// index order and must not have exposed any acquisition capability.
    pub(super) const unsafe fn from_ptr(core: super::Ptr<K, S>) -> Self {
        Self { slots: core }
    }

    pub(in crate::buffer::pool) fn take(self) -> (super::Ptr<K, S>, Active<K, S>) {
        let core = self.slots;
        // SAFETY: Seed proves index zero belongs to this exact freshly
        // initialized nonempty list and is its current free-list head.
        let key = unsafe { Key::new(0) };
        // SAFETY: Seed owns this initialized head until the first acquisition.
        let active = unsafe { Active::take(core, key) };
        (core, active)
    }
}

impl<K: crate::buffer::raw::Backing, S> Active<K, S> {
    /// # Safety
    /// The caller must transfer one live edge for this exact pool slot.
    pub(super) unsafe fn release(slots: super::Ptr<K, S>, key: Key) {
        use crate::mem::raw::Edge;

        // SAFETY: the caller transfers its one live edge to this exact slot.
        if unsafe { slots.slot(key).release() } != rc::Release::Last {
            return;
        }
        Retired { slots, key }.finish();
    }
}

impl<K: crate::buffer::raw::Backing, S> Drop for Active<K, S> {
    fn drop(&mut self) {
        // SAFETY: Active transfers its one live edge to this exact slot.
        unsafe { Self::release(self.slots, self.key) };
    }
}

impl<K: crate::buffer::raw::Backing, S> Retired<K, S> {
    pub(super) fn finish(self) {
        {
            let header = self.slots.header();
            let slot = self.slots.slot(self.key);
            // SAFETY: Retired owns this exact detached slot until publication.
            unsafe {
                header
                    .free
                    .push(self.key, |next| slot.prefix.write(Key::encode(next)))
            };
            header.available.set(header.available.get() + 1);
        }
        super::Header::retire(self.slots);
    }
}

impl<K: crate::buffer::raw::Backing> Retired<K, super::Any> {
    /// # Safety
    /// The caller must transfer the terminal edge for this exact slot owner.
    pub(super) unsafe fn from_owner(owner: ptr::NonNull<()>) -> Self {
        // SAFETY: the terminal owner is an active Slot prefix from its live pool.
        let super::Binding { slots, key } =
            unsafe { super::Ptr::<K, super::Any>::from_owner(owner) };
        Self { slots, key }
    }
}

/// One ephemeral projection of an exact live pool slot.
pub(in crate::buffer) struct Entry<'span, K: crate::buffer::raw::Backing, S = state::Uninit> {
    slots: super::Ptr<K, S>,
    pub(in crate::buffer::pool) key: Key,
    live: marker::PhantomData<&'span ()>,
}

impl<'span, K: crate::buffer::raw::Backing, S> Entry<'span, K, S> {
    pub(in crate::buffer::pool) const fn new<M>(span: &'span pool::Span<K, M, S>) -> Self {
        Self {
            slots: span.slots,
            key: span.key,
            live: marker::PhantomData,
        }
    }

    pub(in crate::buffer::pool) fn capacity(self) -> num::NonZero<u32> {
        self.slots.header().capacity()
    }

    pub(in crate::buffer) fn data(self) -> *mut u8 {
        self.slots.data(self.key)
    }

    pub(in crate::buffer::pool) fn owner(self) -> ptr::NonNull<regions::Prefix> {
        self.slots.owner(self.key)
    }

    pub(in crate::buffer::pool) fn is_unique(self) -> bool {
        self.slots.is_unique(self.key)
    }

    pub(in crate::buffer::pool) fn try_retain(self) -> Result<Active<K, S>, rc::Error> {
        use crate::mem::raw::Edge;

        // SAFETY: the borrowed Span owns this exact active slot throughout admission.
        unsafe { self.slot().prefix.try_retain() }?;
        Ok(Active {
            slots: self.slots,
            key: self.key,
        })
    }

    /// # Safety
    /// The caller must transfer the Span edge projected by this Entry.
    pub(in crate::buffer::pool) unsafe fn release(self) {
        // SAFETY: Entry keeps the exact pool and key paired by its live Span.
        unsafe { Active::release(self.slots, self.key) };
    }

    pub(super) const fn core(self) -> super::Ptr<K, S> {
        self.slots
    }

    pub(super) fn slot(self) -> &'span Slot<K> {
        // SAFETY: Entry is constructed only from a live Span borrow; that span
        // retains this exact slot and its pool for the complete `'span` domain.
        unsafe { self.slots.ptr(self.key).as_ref() }
    }
}

impl<K: crate::buffer::raw::Backing, S> Clone for Entry<'_, K, S> {
    fn clone(&self) -> Self {
        *self
    }
}

impl<K: crate::buffer::raw::Backing, S> Copy for Entry<'_, K, S> {}

const _: () = {
    assert!(size_of::<Slot>() == 8);
    assert!(size_of::<Slot<super::Resident<'static>>>() == 16);
    assert!(align_of::<Slot>() == 8);
    assert!(size_of::<Seed<super::Plain, state::Uninit>>() == size_of::<usize>());
    assert!(size_of::<Active<super::Plain, state::Uninit>>() == 2 * size_of::<usize>());
    assert!(size_of::<Retired<super::Plain, state::Uninit>>() == 2 * size_of::<usize>());
    assert!(size_of::<super::Binding<super::Plain>>() == 2 * size_of::<usize>());
    assert!(size_of::<super::Binding<super::Resident<'static>>>() == 2 * size_of::<usize>());
};

impl<K: crate::buffer::raw::Backing> Slot<K> {
    pub(super) unsafe fn initialize(base: super::Base<K>, slots: u32, link: K::Link) {
        // SAFETY: Layout places exactly `slots` Slot cells immediately after
        // the Header cell owned by this unpublished allocation base.
        let base = unsafe { base.slots().as_ptr() };
        for index in 0..slots {
            let next = if index + 1 == slots {
                None
            } else {
                // SAFETY: index + 1 remains within this exact Slot array.
                Some(unsafe { Key::new(index + 1) })
            };
            // SAFETY: every index is in the allocated Slot array and is
            // initialized exactly once before the pool is published.
            unsafe {
                base.add(index as usize).write(Self {
                    prefix: regions::Prefix::empty(Key::<false>::encode(next)),
                    link: link.clone(),
                });
            }
        }
    }

    /// # Safety
    /// The slot still contains its live key, before free-list publication.
    pub(super) unsafe fn key(&self) -> Key {
        // SAFETY: the caller retains the exact key published at activation.
        unsafe { Key::new(self.prefix.word()) }
    }
}