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use rustc_index::bit_set::BitSet;
use rustc_index::vec::Idx;
use std::collections::VecDeque;
/// A work queue is a handy data structure for tracking work left to
/// do. (For example, basic blocks left to process.) It is basically a
/// de-duplicating queue; so attempting to insert X if X is already
/// enqueued has no effect. This implementation assumes that the
/// elements are dense indices, so it can allocate the queue to size
/// and also use a bit set to track occupancy.
pub struct WorkQueue<T: Idx> {
deque: VecDeque<T>,
set: BitSet<T>,
}
impl<T: Idx> WorkQueue<T> {
/// Creates a new work queue with all the elements from (0..len).
#[inline]
pub fn with_all(len: usize) -> Self {
WorkQueue { deque: (0..len).map(T::new).collect(), set: BitSet::new_filled(len) }
}
/// Creates a new work queue that starts empty, where elements range from (0..len).
#[inline]
pub fn with_none(len: usize) -> Self {
WorkQueue { deque: VecDeque::with_capacity(len), set: BitSet::new_empty(len) }
}
/// Attempt to enqueue `element` in the work queue. Returns false if it was already present.
#[inline]
pub fn insert(&mut self, element: T) -> bool {
if self.set.insert(element) {
self.deque.push_back(element);
true
} else {
false
}
}
/// Attempt to pop an element from the work queue.
#[inline]
pub fn pop(&mut self) -> Option<T> {
if let Some(element) = self.deque.pop_front() {
self.set.remove(element);
Some(element)
} else {
None
}
}
/// Returns `true` if nothing is enqueued.
#[inline]
pub fn is_empty(&self) -> bool {
self.deque.is_empty()
}
}