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Prevent Vec::drain_filter from double dropping on panic

Fixes: #60977
This commit is contained in:
Aaron Loucks 2019-05-26 22:41:34 -04:00
parent 5187be620c
commit 84ae9699c6
2 changed files with 162 additions and 10 deletions

View file

@ -2120,6 +2120,7 @@ impl<T> Vec<T> {
del: 0,
old_len,
pred: filter,
panic_flag: false,
}
}
}
@ -2751,6 +2752,7 @@ pub struct DrainFilter<'a, T, F>
del: usize,
old_len: usize,
pred: F,
panic_flag: bool,
}
#[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
@ -2760,21 +2762,34 @@ 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 {
while self.idx < self.old_len {
let i = self.idx;
self.idx += 1;
let v = slice::from_raw_parts_mut(self.vec.as_mut_ptr(), self.old_len);
if (self.pred)(&mut v[i]) {
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;
if drained {
self.del += 1;
return Some(ptr::read(&v[i]));
} else if self.del > 0 {
}
else if self.del > 0 {
let del = self.del;
let src: *const T = &v[i];
let dst: *mut T = &mut v[i - del];
// This is safe because self.vec has length 0
// thus its elements will not have Drop::drop
// called on them in the event of a panic.
ptr::copy_nonoverlapping(src, dst, 1);
}
}
@ -2792,9 +2807,47 @@ impl<T, F> Drop for DrainFilter<'_, T, F>
where F: FnMut(&mut T) -> bool,
{
fn drop(&mut self) {
self.for_each(drop);
unsafe {
self.vec.set_len(self.old_len - self.del);
// 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,
{
drain: &'b mut DrainFilter<'a, T, F>,
}
impl<'a, 'b, T, F> Drop for BackshiftOnDrop<'a, 'b, T, F>
where
F: FnMut(&mut T) -> bool
{
fn drop(&mut self) {
unsafe {
while self.drain.idx < self.drain.old_len {
let i = self.drain.idx;
self.drain.idx += 1;
let v = slice::from_raw_parts_mut(
self.drain.vec.as_mut_ptr(),
self.drain.old_len,
);
if self.drain.del > 0 {
let del = self.drain.del;
let src: *const T = &v[i];
let dst: *mut T = &mut v[i - del];
ptr::copy_nonoverlapping(src, dst, 1);
}
}
self.drain.vec.set_len(self.drain.old_len - self.drain.del);
}
}
}
let backshift = BackshiftOnDrop {
drain: self
};
if !backshift.drain.panic_flag {
backshift.drain.for_each(drop);
}
}
}