masstree 0.9.5

A high-performance concurrent ordered map (trie of B+trees)
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

use loom::sync::Arc;
use loom::sync::atomic::{AtomicU8, AtomicU64, AtomicUsize, Ordering};
use loom::thread;
use std::array as StdArray;

use super::WIDTH;

/// Simplified internode for loom testing.
///
/// Uses loom atomics to enable deterministic interleaving exploration.
struct LoomInternode {
    nkeys: AtomicU8,
    ikey0: [AtomicU64; WIDTH],
}

impl LoomInternode {
    fn new() -> Self {
        Self {
            nkeys: AtomicU8::new(0),
            ikey0: StdArray::from_fn(|_| AtomicU64::new(0)),
        }
    }

    fn nkeys(&self) -> usize {
        self.nkeys.load(Ordering::Acquire) as usize
    }

    fn set_nkeys(&self, n: u8) {
        self.nkeys.store(n, Ordering::Release);
    }

    fn ikey(&self, idx: usize) -> u64 {
        self.ikey0[idx].load(Ordering::Acquire)
    }

    fn set_ikey(&self, idx: usize, key: u64) {
        self.ikey0[idx].store(key, Ordering::Release);
    }

    fn find_insert_position(&self, insert_ikey: u64) -> usize {
        let n: usize = self.nkeys();

        for i in 0..n {
            if self.ikey(i) >= insert_ikey {
                return i;
            }
        }

        n
    }

    fn insert_key(&self, pos: usize, key: u64) {
        let n = self.nkeys();

        for i in (pos..n).rev() {
            let k = self.ikey(i);
            self.set_ikey(i + 1, k);
        }

        self.set_ikey(pos, key);
        self.set_nkeys((n + 1) as u8);
    }
}

#[test]
fn test_loom_find_position_concurrent_reads() {
    loom::model(|| {
        let node = Arc::new(LoomInternode::new());

        // Setup: insert keys 10, 20, 30
        node.set_ikey(0, 10);
        node.set_ikey(1, 20);
        node.set_ikey(2, 30);
        node.set_nkeys(3);

        let n1 = Arc::clone(&node);
        let t1 = thread::spawn(move || n1.find_insert_position(25));

        let n2 = Arc::clone(&node);
        let t2 = thread::spawn(move || n2.find_insert_position(15));

        let pos1 = t1.join().unwrap();
        let pos2 = t2.join().unwrap();

        assert!(pos1 <= 3, "pos1={} should be <= 3", pos1);
        assert!(pos2 <= 3, "pos2={} should be <= 3", pos2);
    });
}

#[test]
fn test_loom_find_position_during_insert() {
    loom::model(|| {
        let node = Arc::new(LoomInternode::new());

        node.set_ikey(0, 20);
        node.set_nkeys(1);

        let results = Arc::new(AtomicUsize::new(0));

        let n1 = Arc::clone(&node);
        let t1 = thread::spawn(move || {
            n1.insert_key(0, 10);
        });

        let n2 = Arc::clone(&node);
        let r2 = Arc::clone(&results);
        let t2 = thread::spawn(move || {
            let pos = n2.find_insert_position(15);
            r2.store(pos, Ordering::Relaxed);
        });

        t1.join().unwrap();
        t2.join().unwrap();

        let pos = results.load(Ordering::Relaxed);
        assert!(pos <= 2, "pos={} should be <= 2", pos);
    });
}

#[test]
fn test_loom_concurrent_reads_different_keys() {
    loom::model(|| {
        let node = Arc::new(LoomInternode::new());

        // Setup: insert keys 10, 20, 30, 40
        node.set_ikey(0, 10);
        node.set_ikey(1, 20);
        node.set_ikey(2, 30);
        node.set_ikey(3, 40);
        node.set_nkeys(4);

        let n1 = Arc::clone(&node);
        let t1 = thread::spawn(move || n1.find_insert_position(5)); // Before all

        let n2 = Arc::clone(&node);
        let t2 = thread::spawn(move || n2.find_insert_position(25)); // Middle

        let n3 = Arc::clone(&node);
        let t3 = thread::spawn(move || n3.find_insert_position(50)); // After all

        let pos1 = t1.join().unwrap();
        let pos2 = t2.join().unwrap();
        let pos3 = t3.join().unwrap();

        // All should get deterministic results (no concurrent writes)
        assert_eq!(pos1, 0, "5 should go at position 0");
        assert_eq!(pos2, 2, "25 should go at position 2");
        assert_eq!(pos3, 4, "50 should go at position 4");
    });
}