bjoernager/rust
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Refactor DrainFilter::next and update comments

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This commit is contained in:
Aaron Loucks 2019-05-27 12:47:47 -04:00
parent 53d46ae96e
commit b13ae65b8b
1 changed files with 13 additions and 16 deletions
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29
src/liballoc/vec.rs
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@ -2762,26 +2762,17 @@ impl<T, F> Iterator for DrainFilter<'_, T, F>
type Item = T;
fn next(&mut self) -> Option<T> {
struct SetIdxOnDrop<'a> {
idx: &'a mut usize,
new_idx: usize,
}
impl<'a> Drop for SetIdxOnDrop<'a> {
fn drop(&mut self) {
*self.idx = self.new_idx;
}
}
unsafe {
while self.idx < self.old_len {
let i = self.idx;
let v = slice::from_raw_parts_mut(self.vec.as_mut_ptr(), self.old_len);
let mut set_idx = SetIdxOnDrop { new_idx: self.idx, idx: &mut self.idx };
self.panic_flag = true;
let drained = (self.pred)(&mut v[i]);
self.panic_flag = false;
set_idx.new_idx += 1;
// Update the index *after* the predicate is called. If the index
// is updated prior and the predicate panics, the element at this
// index would be leaked.
self.idx += 1;
if drained {
self.del += 1;
return Some(ptr::read(&v[i]));
@ -2806,9 +2797,6 @@ impl<T, F> Drop for DrainFilter<'_, T, F>
where F: FnMut(&mut T) -> bool,
{
fn drop(&mut self) {
// If the predicate panics, we still need to backshift everything
// down after the last successfully drained element, but no additional
// elements are drained or checked.
struct BackshiftOnDrop<'a, 'b, T, F>
where
F: FnMut(&mut T) -> bool,
@ -2822,6 +2810,12 @@ impl<T, F> Drop for DrainFilter<'_, T, F>
{
fn drop(&mut self) {
unsafe {
// Backshift any unprocessed elements, preventing double-drop
// of any element that *should* have been previously overwritten
// but was not due to a panic in the filter predicate. This is
// implemented via drop so that it's guaranteed to run even in
// the event of a panic while consuming the remainder of the
// DrainFilter.
while self.drain.idx < self.drain.old_len {
let i = self.drain.idx;
self.drain.idx += 1;
@ -2845,6 +2839,9 @@ impl<T, F> Drop for DrainFilter<'_, T, F>
drain: self
};
// Attempt to consume any remaining elements if the filter predicate
// has not yet panicked. We'll backshift any remaining elements
// whether we've already panicked or if the consumption here panics.
if !backshift.drain.panic_flag {
backshift.drain.for_each(drop);
}