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

extern crate crossbeam_epoch;

use crossbeam_epoch::{Atomic, Owned};
use std::sync::atomic::Ordering;
use std::ops::Deref;
use std::fmt;

pub struct Stm<T: 'static + Send> {
    inner: Atomic<T>,
}

impl<T: 'static + Send> Stm<T> {
    pub fn new(data: T) -> Stm<T> {
        Stm {
            inner: Atomic::new(data),
        }
    }

    pub fn update<F>(&self, f: F)
    where
        F: Fn(&T) -> T,
    {
        let guard = crossbeam_epoch::pin();
        guard.flush();
        loop {
            let shared = self.inner.load(Ordering::Acquire, &guard);
            let data = unsafe { shared.as_ref().unwrap() };
            let t = f(data);
            let r = self.inner
                .compare_and_set(shared, Owned::new(t), Ordering::AcqRel, &guard);
            if let Ok(r) = r {
                unsafe { guard.defer(move || r.into_owned()) }
                break;
            }
        }
    }

    pub fn load(&self) -> StmGuard<T> {
        StmGuard {
            parent: self,
            inner: crossbeam_epoch::pin(),
        }
    }
}

impl<T: 'static + Send + fmt::Debug> fmt::Debug for Stm<T> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.debug_struct("StmGuard")
            .field("data", self.load().deref())
            .finish()
    }
}

impl<T: 'static + Send + fmt::Display> fmt::Display for Stm<T> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        self.load().deref().fmt(f)
    }
}

pub struct StmGuard<'a, T: 'static + Send> {
    parent: &'a Stm<T>,
    inner: crossbeam_epoch::Guard,
}

impl<'a, T: 'static + Send> Deref for StmGuard<'a, T> {
    type Target = T;
    fn deref(&self) -> &T {
        let shared = self.parent.inner.load(Ordering::Acquire, &self.inner);
        unsafe { shared.as_ref().unwrap() }
    }
}

impl<'a, T: 'static + Send + fmt::Debug> fmt::Debug for StmGuard<'a, T> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.debug_struct("StmGuard")
            .field("data", &self.deref())
            .finish()
    }
}

impl<'a, T: 'static + Send + fmt::Display> fmt::Display for StmGuard<'a, T> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        self.deref().fmt(f)
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    #[test]
    fn stm_test() {
        let stm = Stm::new(vec![1, 2, 3]);
        {
            let data = stm.load();
            println!("{:?}", data);
        }

        stm.update(|v| {
            let mut v = v.clone();
            v.push(4);
            v
        });

        {
            let data = stm.load();
            println!("{:?}", data);
        }

        stm.update(|_| vec![1]);

        {
            let data = stm.load();
            println!("{:?}", data);
        }
    }
}