atomic-bitset.rs

#![cfg_attr(test, feature(test))]

#[cfg(test)]
#[macro_use] 
extern crate lazy_static;

use std::mem;
use std::sync::atomic::{ATOMIC_USIZE_INIT, AtomicUsize, Ordering};

pub const INIT: AtomicBitSet = AtomicBitSet {
    bits: ATOMIC_USIZE_INIT,
    _padding: [0; 7],
};

pub struct AtomicBitSet {
    bits: AtomicUsize,
    _padding: [usize; 7],
}

impl AtomicBitSet {
    pub fn new() -> AtomicBitSet {
        Self::from_bits(0)
    }

    pub fn from_bits(bits: usize) -> AtomicBitSet {
        AtomicBitSet {
            bits: AtomicUsize::new(bits),
            _padding: [0; 7],
        }
    }

    pub fn set(&self, idx: usize, val: bool, ord: Ordering) -> bool {
        let shift_val = 1 << idx;

        (if val {
            self.bits.fetch_or(shift_val, ord)
        } else {
            self.bits.fetch_and(!shift_val, ord)
        } & shift_val) != 0
    }

    pub fn get(&self, idx: usize, ord: Ordering) -> bool {
        self.bits.load(ord) & (1 << idx) != 0
    }

    pub fn clear_all(&self, ord: Ordering) -> AtomicBitSet {
        Self::from_bits(self.bits.swap(0, ord))
    }
}

#[inline(always)]
fn assert_idx(idx: usize) {
    assert!(idx < mem::size_of::<usize>() * 8);
}

#[cfg(test)]
mod test {

    extern crate test;

    use self::test::Bencher;

    use super::*;

    use std::mem;
    use std::sync::atomic::{ATOMIC_BOOL_INIT, AtomicBool, Ordering};

    static SHARED_BITSET: AtomicBitSet = INIT;

    lazy_static! {
        static ref SHARED_BOOLS: [AtomicBool; 64] = unsafe { mem::transmute([0usize; 64]) };
    }

    #[bench]
    fn bench_atomic_bit_set(bench: &mut Bencher) {
        bench.iter(|| for i in 0 .. 64 {
            let val = SHARED_BITSET.get(i, Ordering::Relaxed);
            SHARED_BITSET.set(i, !val, Ordering::Relaxed);
        });
    }

    #[bench]
    fn bench_atomic_bool_array(bench: &mut Bencher) {
        bench.iter(|| for i in 0 .. 64 {
            let val = SHARED_BOOLS[i].load(Ordering::Relaxed);
            SHARED_BOOLS[i].store(!val, Ordering::Relaxed);
        });
    }
}