lockbell 0.1.1

An RwLock that rings back when contention clears.
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

use std::sync::{
    Arc,
    atomic::{AtomicBool, Ordering::Relaxed},
};

use lockbell::RwLockBell;

#[test]
fn test_dropping_flag_prevents_double_drain() {
    let lock = Arc::new(RwLockBell::new(0u64));
    let called = Arc::new(AtomicBool::new(false));
    let called2 = called.clone();

    let w = lock.write();
    assert!(
        lock.try_write_or(move || called2.store(true, Relaxed))
            .is_none()
    );
    drop(w);

    assert!(called.load(Relaxed));

    let r = lock.read();
    drop(r);
}

#[test]
fn test_write_guard_drop_then_read_guard_drop_sequence() {
    let lock = Arc::new(RwLockBell::new(0u64));
    let first = Arc::new(AtomicBool::new(false));
    let second = Arc::new(AtomicBool::new(false));
    let first2 = first.clone();
    let second2 = second.clone();

    {
        let w = lock.write();
        assert_eq!(*w, 0);
        assert!(
            lock.try_write_or(move || first2.store(true, Relaxed))
                .is_none()
        );
        drop(w);
    }
    assert!(first.load(Relaxed));

    let r = lock.read();
    assert_eq!(*r, 0);

    assert!(
        lock.try_write_or(move || second2.store(true, Relaxed))
            .is_none()
    );
    assert!(!second.load(Relaxed));
    drop(r);
    assert!(second.load(Relaxed));
}

#[test]
fn test_not_dropping_unblocked_after_read_guard_drain() {
    let lock = Arc::new(RwLockBell::new(0u64));
    let called = Arc::new(AtomicBool::new(false));
    let called2 = called.clone();

    let r = lock.read();
    assert!(lock.try_write_or(|| {}).is_none());
    drop(r);

    let r2 = lock.read();
    assert!(
        lock.try_write_or(move || called2.store(true, Relaxed))
            .is_none()
    );
    drop(r2);

    assert!(called.load(Relaxed));
}

#[test]
fn test_write_then_read_then_write_cycle() {
    use parking_lot::Mutex;

    let lock = Arc::new(RwLockBell::new(0u64));
    let order = Arc::new(Mutex::new(Vec::<&str>::new()));

    // Phase 1: write guard fires callback
    {
        let o = order.clone();
        let w = lock.write();
        assert!(lock.try_write_or(move || o.lock().push("write")).is_none());
        drop(w);
    }

    // Phase 2: read guard fires callback
    {
        let o = order.clone();
        let r = lock.read();
        assert!(lock.try_write_or(move || o.lock().push("read")).is_none());
        drop(r);
    }

    // Phase 3: write guard fires callback again
    {
        let o = order.clone();
        let w = lock.write();
        assert!(lock.try_write_or(move || o.lock().push("write2")).is_none());
        drop(w);
    }

    assert_eq!(*order.lock(), vec!["write", "read", "write2"]);
}

#[test]
fn test_read_guard_during_write_callback() {
    let lock = Arc::new(RwLockBell::new(0u64));
    let lock2 = lock.clone();
    let inner_read = Arc::new(AtomicBool::new(false));
    let inner_read2 = inner_read.clone();

    let w = lock.write();
    assert!(
        lock.try_write_or(move || {
            // The write lock is released before callbacks fire,
            // so we should be able to read.
            let r = lock2.read();
            assert_eq!(*r, 0);
            inner_read2.store(true, Relaxed);
        })
        .is_none()
    );
    drop(w);
    assert!(inner_read.load(Relaxed));
}