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
//! Per-path usage counters: the refusal log's dual, the reclaim face's
//! raw material.
/// One declared path's usage counters — the refusal log's dual: that
/// log says what is missing, this says what goes unused (the reclaim
/// face's raw material). Plain relaxed atomics — the served-query
/// path pays two uncontended stores, never a lock.
///
/// The counters are atomics updated in place, so they stay private: a
/// reader takes a snapshot through [`UsageCell::read`] and
/// [`UsageCell::min_margin`].
///
/// ```
/// use kevy_index::UsageCell;
/// let c = UsageCell::declared_at(100);
/// c.hit(160);
/// c.probe(-5);
/// assert_eq!((c.read(), c.min_margin()), ((1, 160, 100), Some(-5)));
/// ```
#[derive(Debug)]
pub struct UsageCell {
/// Queries served through this path.
hits: std::sync::atomic::AtomicU64,
/// Unix seconds of the most recent hit (0 = never).
last_hit_s: std::sync::atomic::AtomicI64,
/// Unix seconds the path was first seen declared — "never hit"
/// is only meaningful with an age next to it (a path declared
/// five seconds ago is not reclaim material).
declared_s: std::sync::atomic::AtomicI64,
/// Windowed paths only: the smallest `lower_bound - boundary`
/// any query has probed (`i64::MAX` = never observed). A margin
/// that never goes non-positive means no query has touched the
/// cold side — the window-narrowing advice's whole input, no max
/// tracking needed (boundary ≈ max − span, within a bucket).
min_margin: std::sync::atomic::AtomicI64,
}
/// A zeroed cell with the margin UNOBSERVED (`i64::MAX`) — a derived
/// all-zeroes default would read as "a query probed margin 0".
impl Default for UsageCell {
fn default() -> Self {
use std::sync::atomic::{AtomicI64, AtomicU64};
Self {
hits: AtomicU64::new(0),
last_hit_s: AtomicI64::new(0),
declared_s: AtomicI64::new(0),
min_margin: AtomicI64::new(i64::MAX),
}
}
}
impl UsageCell {
/// A fresh cell for a path first seen declared at `now_s`.
#[must_use]
pub fn declared_at(now_s: i64) -> Self {
let c = Self::default();
c.declared_s.store(now_s, std::sync::atomic::Ordering::Relaxed);
c
}
/// Record one windowed query's probe depth (`lower - boundary`).
pub fn probe(&self, margin: i64) {
self.min_margin.fetch_min(margin, std::sync::atomic::Ordering::Relaxed);
}
/// Count one served query at `now_s` (unix seconds).
pub fn hit(&self, now_s: i64) {
use std::sync::atomic::Ordering::Relaxed;
self.hits.fetch_add(1, Relaxed);
self.last_hit_s.store(now_s, Relaxed);
}
/// Windowed paths only: the smallest `lower - boundary` margin any
/// query has probed, or `None` when no query has been observed.
///
/// ```
/// let c = kevy_index::UsageCell::default();
/// assert_eq!(c.min_margin(), None);
/// c.probe(40);
/// c.probe(12);
/// assert_eq!(c.min_margin(), Some(12));
/// ```
#[must_use]
pub fn min_margin(&self) -> Option<i64> {
let m = self.min_margin.load(std::sync::atomic::Ordering::Relaxed);
(m != i64::MAX).then_some(m)
}
/// `(hits, last_hit_s, declared_s)` snapshot; `last_hit_s` is 0
/// until the first hit.
#[must_use]
pub fn read(&self) -> (u64, i64, i64) {
use std::sync::atomic::Ordering::Relaxed;
(self.hits.load(Relaxed), self.last_hit_s.load(Relaxed), self.declared_s.load(Relaxed))
}
}