arc-swap 0.4.7

Atomically swappable Arc
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

use std::rc::Weak as RcWeak;
use std::sync::Weak;

use crate::RefCnt;

unsafe impl<T> RefCnt for Weak<T> {
    type Base = T;
    fn as_ptr(me: &Self) -> *mut T {
        Weak::as_ptr(me) as *mut T
    }
    fn into_ptr(me: Self) -> *mut T {
        Weak::into_raw(me) as *mut T
    }
    unsafe fn from_ptr(ptr: *const T) -> Self {
        Weak::from_raw(ptr)
    }
}

unsafe impl<T> RefCnt for RcWeak<T> {
    type Base = T;
    fn as_ptr(me: &Self) -> *mut T {
        RcWeak::as_ptr(me) as *mut T
    }
    fn into_ptr(me: Self) -> *mut T {
        RcWeak::into_raw(me) as *mut T
    }
    unsafe fn from_ptr(ptr: *const T) -> Self {
        RcWeak::from_raw(ptr)
    }
}

#[cfg(test)]
mod tests {
    use std::sync::{Arc, Weak};

    use crate::ArcSwapWeak;

    // Convert to weak, push it through the shared and pull it out again.
    #[test]
    fn there_and_back() {
        let data = Arc::new("Hello");
        let shared = ArcSwapWeak::new(Arc::downgrade(&data));
        assert_eq!(1, Arc::strong_count(&data));
        assert_eq!(1, Arc::weak_count(&data));
        let weak = shared.load();
        assert_eq!("Hello", *weak.upgrade().unwrap());
        assert!(Arc::ptr_eq(&data, &weak.upgrade().unwrap()));
    }

    // Replace a weak pointer with a NULL one
    #[test]
    fn reset() {
        let data = Arc::new("Hello");
        let shared = ArcSwapWeak::new(Arc::downgrade(&data));
        assert_eq!(1, Arc::strong_count(&data));
        assert_eq!(1, Arc::weak_count(&data));

        // An empty weak (eg. NULL)
        shared.store(Weak::new());
        assert_eq!(1, Arc::strong_count(&data));
        assert_eq!(0, Arc::weak_count(&data));

        let weak = shared.load();
        assert!(weak.upgrade().is_none());
    }

    // Destroy the underlying data while the weak is still stored inside. Should make it go
    // NULL-ish
    #[test]
    fn destroy() {
        let data = Arc::new("Hello");
        let shared = ArcSwapWeak::new(Arc::downgrade(&data));

        drop(data);
        let weak = shared.load();
        assert!(weak.upgrade().is_none());
    }
}