thesix 0.3.0

Policy-driven six-tier cache orchestration for Rust
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

#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub enum TierId {
    L0,
    L1,
    L2,
    L3,
    L4,
    L5,
    /// Authority. Not a cache rung: it is never blind-written and never
    /// invalidated. Writes reach it through the owning repository, which then
    /// invalidates downward.
    L6,
}

impl TierId {
    /// Every rung, in ladder order. `capabilities()` iterates this so a new
    /// rung cannot be forgotten by a hand-written list.
    pub const ALL: [TierId; 7] = [
        TierId::L0,
        TierId::L1,
        TierId::L2,
        TierId::L3,
        TierId::L4,
        TierId::L5,
        TierId::L6,
    ];

    pub fn as_usize(&self) -> usize {
        match self {
            TierId::L0 => 0,
            TierId::L1 => 1,
            TierId::L2 => 2,
            TierId::L3 => 3,
            TierId::L4 => 4,
            TierId::L5 => 5,
            TierId::L6 => 6,
        }
    }

    pub fn from_usize(idx: usize) -> Option<Self> {
        match idx {
            0 => Some(TierId::L0),
            1 => Some(TierId::L1),
            2 => Some(TierId::L2),
            3 => Some(TierId::L3),
            4 => Some(TierId::L4),
            5 => Some(TierId::L5),
            6 => Some(TierId::L6),
            _ => None,
        }
    }
}

impl std::fmt::Display for TierId {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            TierId::L0 => write!(f, "L0"),
            TierId::L1 => write!(f, "L1"),
            TierId::L2 => write!(f, "L2"),
            TierId::L3 => write!(f, "L3"),
            TierId::L4 => write!(f, "L4"),
            TierId::L5 => write!(f, "L5"),
            TierId::L6 => write!(f, "L6"),
        }
    }
}

#[derive(Debug)]
pub struct TierRegistry {
    tiers: Vec<TierId>,
    health: Vec<std::sync::RwLock<TierHealth>>,
}

impl TierRegistry {
    pub fn new() -> Self {
        // Fixed tier set; no fallible operation, so no unwrap is needed.
        let tiers: Vec<TierId> = vec![
            TierId::L0,
            TierId::L1,
            TierId::L2,
            TierId::L3,
            TierId::L4,
            TierId::L5,
            TierId::L6,
        ];
        // One health slot per tier. Sized from the tier list rather than a
        // literal so adding a rung cannot desynchronise the two.
        let health = (0..tiers.len())
            .map(|_| std::sync::RwLock::new(TierHealth::default()))
            .collect();
        TierRegistry { tiers, health }
    }

    pub fn all(&self) -> &[TierId] {
        &self.tiers
    }

    pub fn len(&self) -> usize {
        self.tiers.len()
    }

    pub fn is_empty(&self) -> bool {
        self.tiers.is_empty()
    }

    pub fn tier_health(&self, tier: TierId) -> TierHealth {
        self.health[tier.as_usize()]
            .read()
            .map(|h| h.clone())
            .unwrap_or_default()
    }

    /// Record a failure against a tier; increments the consecutive-failure
    /// counter and degrades the health score. Used by the circuit breaker.
    pub fn fail(&self, tier: TierId) {
        if let Ok(mut h) = self.health[tier.as_usize()].write() {
            h.consecutive_failures += 1;
            h.last_failure_timestamp = Some(std::time::SystemTime::now());
            h.health_score = (h.health_score - 0.1).max(0.0);
        }
    }

    /// Reset a tier's health after a successful operation.
    pub fn recover(&self, tier: TierId) {
        if let Ok(mut h) = self.health[tier.as_usize()].write() {
            h.consecutive_failures = 0;
            h.health_score = 1.0;
            h.last_failure_timestamp = None;
        }
    }

    pub fn is_circuit_open(&self, tier: TierId) -> bool {
        self.health[tier.as_usize()]
            .read()
            .map_or(true, |h| h.is_circuit_open())
    }

    pub fn try_fallback_tier(&self, exclude: TierId) -> Option<TierId> {
        for &tier in &self.tiers {
            if tier == exclude {
                continue;
            }
            if !self.is_circuit_open(tier) {
                return Some(tier);
            }
        }
        None
    }
}

impl Default for TierRegistry {
    fn default() -> Self {
        Self::new()
    }
}

pub mod fixed_tier_stub;
pub mod l0;
pub mod l1;
pub mod l2;
pub mod l3;
pub mod l4;
pub mod l5;
pub mod sharded_stub;
pub mod test;

pub mod backends;

#[path = "trait.rs"]
pub mod tier_trait;

pub use tier_trait::{BackendKind, CacheTier, TierHealth};