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// This Source Code Form is subject to the terms of the Mozilla Public // License, v. 2.0. If a copy of the MPL was not distributed with this // file, You can obtain one at https://mozilla.org/MPL/2.0/. #![feature(iter_advance_by)] #![forbid(unsafe_code)] #![warn(missing_docs, broken_intra_doc_links)] //! This library provides a bitvec struct which uses atomic integers as its backing representation. //! //! This allows the bitvec to be used without external synchronization, though the perils //! of improper use of atomics can come into play. use std::sync::atomic::AtomicU64; use std::sync::atomic::Ordering; use std::borrow::Borrow; use std::marker::PhantomData; /// AtomicBitVec is build atop a standard [`Vec`], and uses [`AtomicU64`] for its backing store. /// The ordering for atomic operations is left to the user to decide. /// /// The term "blocks" is used throughout this documentation to refer to the number of atomic /// integers are stored in the backing storage. All resizing and allocation is done in block-sized /// units; this means that the bit-length of these bitvecs will *always* be a multiple of 64. pub struct AtomicBitVec { data: Vec<AtomicU64> } const fn next_mul_64(v: usize) -> usize { (v + 64) & !63 } impl AtomicBitVec { /// Creates an empty [`AtomicBitVec`]. /// /// This does not allocate; you'll need to call one of [`with_bit_capacity`], [`with_capacity`], /// [`resize_blocks_with`], or [`resize_bits_with`] to actually allocate memory and initialize /// the backing store. /// /// [`with_bit_capacity`]: #method.with_bit_capacity /// [`with_capacity`]: #method.with_capacity /// [`resize_blocks_with`]: #method.resize_blocks_with /// [`resize_bits_with`]: #method.resize_bits_with /// /// # Examples /// Basic usage: /// ``` /// use atomic_bitvec::AtomicBitVec; /// let s = AtomicBitVec::new(); /// ``` pub const fn new() -> Self { Self { data: Vec::new() } } /// Returns the size of this bitvec in memory in bytes. /// /// This value is calculated from the size of the allocated backing store and the size of the /// vector itself. This does not take into account potential reserve overhead; it is based /// purely on the current length of the bitvec. pub fn size_in_mem(&self) -> usize { std::mem::size_of::<Vec<AtomicU64>>() + self.data.len() * std::mem::size_of::<AtomicU64>() } /// Creates a new bitvec with capacity to hold at least `bit_cap` many bits. /// /// This implementation will allocate as many bits as is necessary to hold a multiple of 64 bits. pub fn with_bit_capacity(bit_cap: usize) -> Self { let blocks = next_mul_64(bit_cap) / 64; Self::with_capacity(blocks) } /// Creates a new bitvec with capacity to hold at least `blocks` many blocks. /// /// Each block holds 64 bits. pub fn with_capacity(blocks: usize) -> Self { Self { data: Vec::with_capacity(blocks) } } /// Resizes a bitvec to contain `new_blocks` many blocks, using `f` to generate new elements if /// extending the bitvec. If `new_blocks` is less than [`block_cnt`], this truncates instead. /// /// [`block_cnt`]: #method.block_cnt /// /// # Examples /// ``` /// # use atomic_bitvec::AtomicBitVec; /// # use std::sync::atomic::AtomicU64; /// let mut s = AtomicBitVec::with_capacity(2); /// assert_eq!(s.block_cnt(), 0); /// s.resize_blocks_with(4, AtomicU64::default); /// assert_eq!(s.block_cnt(), 4); /// ``` pub fn resize_blocks_with(&mut self, new_blocks: usize, f: impl FnMut() -> AtomicU64) { self.data.resize_with(new_blocks, f) } /// Resizes a bitvec to contain at least `new_bits` many bits, using `f` to generate new blocks if /// extending the bitvec. If `new_bits` is less than [`len`], this truncates instead. /// /// This will extend the bitvec to the next multiple of 64 bits if `new_bits` is not a multiple of 64. /// /// [`len`]: #method.len /// /// # Examples /// ``` /// # use atomic_bitvec::AtomicBitVec; /// # use std::sync::atomic::AtomicU64; /// let mut s = AtomicBitVec::with_bit_capacity(128); /// assert_eq!(s.len(), 0); /// s.resize_bits_with(200, AtomicU64::default); /// // Note that the next multiple of 64 bits was allocated. /// assert_eq!(s.block_cnt(), 4); /// assert_eq!(s.len(), 256); /// ``` pub fn resize_bits_with(&mut self, new_bits: usize, f: impl FnMut() -> AtomicU64) { let blocks = next_mul_64(new_bits) / 64; self.data.resize_with(blocks, f) } /// Returns the current block count of the bitvec. This is equivalent to the bit-length /// of the bitvec divided by 64. /// /// # Examples /// ``` /// # use atomic_bitvec::AtomicBitVec; /// # use std::sync::atomic::AtomicU64; /// let mut s = AtomicBitVec::with_bit_capacity(128); /// s.resize_bits_with(200, AtomicU64::default); /// assert_eq!(s.block_cnt(), 4); /// ``` pub fn block_cnt(&self) -> usize { self.data.len() } /// Returns the current bit-length of the bitvec. This is equivalent to the current block count /// times 64. /// /// # Examples /// ``` /// # use atomic_bitvec::AtomicBitVec; /// # use std::sync::atomic::AtomicU64; /// let mut s = AtomicBitVec::with_bit_capacity(128); /// s.resize_bits_with(200, AtomicU64::default); /// // Note that the next multiple of 64 bits was allocated. /// assert_eq!(s.len(), 256); /// ``` pub fn len(&self) -> usize { self.block_cnt() * 64 } /// Sets the bit at `idx` to `value`, using the atomic ordering provided by `ordering`. /// Returns the previous value at the specified bit. /// /// The bit will be set atomically, allowing this bitvec to be used from multiple threads. /// /// # Examples /// ``` /// # use atomic_bitvec::AtomicBitVec; /// # use std::sync::atomic::{AtomicU64, Ordering}; /// let mut s = AtomicBitVec::with_bit_capacity(128); /// s.resize_bits_with(256, AtomicU64::default); /// s.set(3, true, Ordering::AcqRel); /// assert!(s.get(3, Ordering::Acquire)); /// ``` /// /// # Panics /// Panics if `idx` is out of bounds. pub fn set(&self, idx: usize, value: bool, ordering: Ordering) -> bool { let (loc, mask) = Self::loc_and_mask(idx); let dest: &AtomicU64 = &self.data[loc]; if value { let prev = dest.fetch_or(mask, ordering); prev & mask != 0 } else { let unset_mask = !mask; let prev = dest.fetch_and(unset_mask, ordering); prev & mask != 0 } } /// Returns the bit at the specified index according to the given atomic ordering. /// /// # Examples /// ``` /// # use atomic_bitvec::AtomicBitVec; /// # use std::sync::atomic::{AtomicU64, Ordering}; /// let mut s = AtomicBitVec::with_bit_capacity(128); /// s.resize_bits_with(256, AtomicU64::default); /// s.set(3, true, Ordering::AcqRel); /// assert!(s.get(3, Ordering::Acquire)); /// ``` /// /// # Panics /// Panics if `idx` is out of bounds or if `ordering` is not valid for [`AtomicU64::load`] pub fn get(&self, idx: usize, ordering: Ordering) -> bool { let (loc, mask) = Self::loc_and_mask(idx); let dest: &AtomicU64 = &self.data[loc]; dest.load(ordering) & mask != 0 } /// Returns an iterator over the bits of this bitvec. /// /// # Examples /// ``` /// # use atomic_bitvec::AtomicBitVec; /// # use std::sync::atomic::{AtomicU64, Ordering}; /// let mut s = AtomicBitVec::with_bit_capacity(128); /// s.resize_bits_with(64, AtomicU64::default); /// s.set(3, true, Ordering::AcqRel); /// let i = s.iter(Ordering::Acquire); /// let v: Vec<bool> = i.take(5).collect(); /// assert_eq!(v, [false, false, false, true, false]); /// ``` /// # Panics /// Panics if `ordering` is not valid for [`AtomicU64::load`] /// # Warning /// Because this struct can be updated atomically, if this function is called while other threads /// are updating this bitvec, the result may not be equivalent to if this function had been called /// when this thread had unique ownership. /// ```no_run /// # use atomic_bitvec::AtomicBitVec; /// # use std::sync::atomic::{AtomicU64, Ordering}; /// # use std::sync::Arc; /// /// let mut s = AtomicBitVec::with_bit_capacity(128); /// s.resize_bits_with(64, AtomicU64::default); /// s.set(3, true, Ordering::AcqRel); /// let a = Arc::new(s); /// let ta = a.clone(); /// # let h = /// std::thread::spawn(move || ta.set(4, true, Ordering::AcqRel)); /// let i = a.iter(Ordering::Acquire); /// let v: Vec<bool> = i.take(5).collect(); /// assert_eq!(v, [false, false, false, true, false]); // May or may not panic! /// # h.join().unwrap(); /// ``` pub fn iter<'a>(&'a self, ordering: Ordering) -> impl Iterator<Item=bool> + 'a { Iter::new(self, ordering) } const fn loc_and_mask(idx: usize) -> (usize, u64) { let mask = 1u64 << (idx & (64 - 1)); let block = idx >> (64u64.trailing_zeros()); (block, mask) } /// Counts all of the set bits in this bitvec. /// /// # Examples /// ``` /// # use atomic_bitvec::AtomicBitVec; /// # use std::sync::atomic::{AtomicU64, Ordering}; /// let mut s = AtomicBitVec::with_bit_capacity(128); /// s.resize_bits_with(64, AtomicU64::default); /// s.set(3, true, Ordering::AcqRel); /// s.set(5, true, Ordering::AcqRel); /// assert_eq!(s.count_ones(Ordering::Acquire), 2); /// ``` /// # Panics /// Panics if `ordering` is not valid for [`AtomicU64::load`] /// /// # Warning /// Because this struct can be updated atomically, if this function is called while other threads /// are updating this bitvec, the result may not be equivalent to if this function had been called /// when this thread had unique ownership. /// ```no_run /// # use atomic_bitvec::AtomicBitVec; /// # use std::sync::atomic::{AtomicU64, Ordering}; /// # use std::sync::Arc; /// let mut s = AtomicBitVec::with_bit_capacity(128); /// s.resize_bits_with(64, AtomicU64::default); /// s.set(3, true, Ordering::AcqRel); /// s.set(5, true, Ordering::AcqRel); /// let a = Arc::new(s); /// let ta = a.clone(); /// # let h = /// std::thread::spawn(move || ta.set(5, false, Ordering::AcqRel)); /// assert_eq!(a.count_ones(Ordering::Acquire), 2); // May or may not panic! /// # h.join().unwrap(); /// ``` pub fn count_ones(&self, ordering: Ordering) -> u64 { self.data.iter() .map(|n| n.load(ordering).count_ones() as u64) .sum() } } /// The iterator for an [`AtomicBitVec`]. This implementation pulls double duty as the struct /// used for [`Iterator`] and [`IntoIterator`]. pub struct Iter<'a, Inner> where Inner: Borrow<AtomicBitVec> + 'a { src: Inner, order: Ordering, idx: usize, back_idx: usize, phony: PhantomData<&'a AtomicBitVec>, } impl<'a, Inner> Iter<'a, Inner> where Inner: Borrow<AtomicBitVec> + 'a { pub(crate) fn src(&self) -> &AtomicBitVec { self.src.borrow() } } impl<'a> Iter<'a, &'a AtomicBitVec> { pub(crate) fn new(orig: &'a AtomicBitVec, order: Ordering) -> Self { let bit_size = orig.len(); Self { src: orig, order, idx: 0, back_idx: bit_size, phony: PhantomData::default(), } } } impl IntoIterator for AtomicBitVec { type Item = bool; type IntoIter = Iter<'static, AtomicBitVec>; fn into_iter(self) -> Self::IntoIter { let bs = self.len(); Iter { src: self, order: Ordering::Acquire, idx: 0, back_idx: bs, phony: Default::default(), } } } impl<'a, Inner> Iterator for Iter<'a, Inner> where Inner: Borrow<AtomicBitVec> + 'a { type Item = bool; fn next(&mut self) -> Option<Self::Item> { if self.idx < self.back_idx { let o = self.src().get(self.idx, self.order); self.idx += 1; Some(o) } else { None } } fn size_hint(&self) -> (usize, Option<usize>) { let hint = self.back_idx - self.idx; (hint, Some(hint)) } fn advance_by(&mut self, n: usize) -> Result<(), usize> { if self.idx + n <= self.back_idx { self.idx += n; Ok(()) } else { let e = self.back_idx - self.idx; self.idx += n; Err(e) } } } impl<'a, Inner> ExactSizeIterator for Iter<'a, Inner> where Inner: Borrow<AtomicBitVec> + 'a {} impl<'a, Inner> DoubleEndedIterator for Iter<'a, Inner> where Inner: Borrow<AtomicBitVec> + 'a { fn next_back(&mut self) -> Option<Self::Item> { if self.idx < self.back_idx { let o = self.src().get(self.back_idx - 1, self.order); self.back_idx = self.back_idx.saturating_sub(1); Some(o) } else { None } } } #[cfg(test)] mod tests { use super::*; static_assertions::assert_impl_all!(AtomicBitVec: Sync); }