salsa/
revision.rs

1use std::num::NonZeroU32;
2use std::sync::atomic::{AtomicU32, Ordering};
3
4/// Value of the initial revision, as a u32. We don't use 0
5/// because we want to use a `NonZeroU32`.
6const START: u32 = 1;
7
8/// A unique identifier for the current version of the database; each
9/// time an input is changed, the revision number is incremented.
10/// `Revision` is used internally to track which values may need to be
11/// recomputed, but is not something you should have to interact with
12/// directly as a user of salsa.
13#[derive(Copy, Clone, PartialEq, Eq, Hash, PartialOrd, Ord)]
14pub struct Revision {
15    generation: NonZeroU32,
16}
17
18impl Revision {
19    pub(crate) fn start() -> Self {
20        Self::from(START)
21    }
22
23    pub(crate) fn from(g: u32) -> Self {
24        Self {
25            generation: NonZeroU32::new(g).unwrap(),
26        }
27    }
28
29    pub(crate) fn next(self) -> Revision {
30        Self::from(self.generation.get() + 1)
31    }
32
33    fn as_u32(self) -> u32 {
34        self.generation.get()
35    }
36}
37
38impl std::fmt::Debug for Revision {
39    fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
40        write!(fmt, "R{}", self.generation)
41    }
42}
43
44#[derive(Debug)]
45pub(crate) struct AtomicRevision {
46    data: AtomicU32,
47}
48
49impl AtomicRevision {
50    pub(crate) fn start() -> Self {
51        Self {
52            data: AtomicU32::new(START),
53        }
54    }
55
56    pub(crate) fn load(&self) -> Revision {
57        Revision::from(self.data.load(Ordering::SeqCst))
58    }
59
60    pub(crate) fn store(&self, r: Revision) {
61        self.data.store(r.as_u32(), Ordering::SeqCst);
62    }
63
64    /// Increment by 1, returning previous value.
65    pub(crate) fn fetch_then_increment(&self) -> Revision {
66        let v = self.data.fetch_add(1, Ordering::SeqCst);
67        assert!(v != u32::max_value(), "revision overflow");
68        Revision::from(v)
69    }
70}
salsa/revision.rs

salsa/
revision.rs
