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Fix SharedArray length in bytes to be a multiple of pointer alignment

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This commit is contained in:
Simon Hausmann 2020-07-07 16:00:00 +02:00
parent f646809ff4
commit 89a05245f9
1 changed files with 18 additions and 16 deletions
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36
sixtyfps_runtime/corelib/abi/sharedarray.rs
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@ -15,25 +15,27 @@ struct PaddingFillingIter<'a, U> {
iter: &'a mut dyn Iterator<Item = MaybeUninit<U>>,
pos: usize,
len: usize,
padding_elements: usize,
}
impl<'a, U> PaddingFillingIter<'a, U> {
fn new(len: usize, iter: &'a mut dyn Iterator<Item = MaybeUninit<U>>) -> Self {
Self { iter, pos: 0, len }
let alignment = core::mem::align_of::<usize>();
let mut padding_elements = if len == 0 { 1 } else { 0 }; // ThinArc can't deal with empty arrays, so add padding for empty arrays.
// Add padding to ensure that the size in bytes is a multiple of the pointer alignment. This can mean different
// increments depending on whether sizeof(U) is less or greater than align_of(usize).
loop {
let size_in_bytes = (len + padding_elements) * core::mem::size_of::<U>();
let byte_aligned_size = (size_in_bytes + alignment - 1) & !(alignment - 1);
let padding_bytes = byte_aligned_size - size_in_bytes;
if padding_bytes == 0 {
break;
}
padding_elements += 1;
}
fn padded_length(&self) -> usize {
// add some padding at the end since the size of the inner will anyway have to be padded
let align = core::mem::align_of::<usize>() / core::mem::size_of::<U>();
if self.len > 0 {
if align > 0 {
(self.len + align - 1) & !(align - 1)
} else {
self.len
}
} else {
align
}
Self { iter, pos: 0, len, padding_elements }
}
}
@ -44,14 +46,14 @@ impl<'a, U: Clone> Iterator for PaddingFillingIter<'a, U> {
self.pos += 1;
if pos < self.len {
self.iter.next()
} else if pos < self.padded_length() {
} else if pos < self.len + self.padding_elements {
Some(MaybeUninit::uninit())
} else {
None
}
}
fn size_hint(&self) -> (usize, Option<usize>) {
let l = self.padded_length() - self.pos;
let l = self.len + self.padding_elements;
(l, Some(l))
}
}
@ -80,7 +82,7 @@ impl<T: Clone> SharedArray<T> {
SharedArray {
inner: servo_arc::Arc::into_thin(servo_arc::Arc::from_header_and_iter(
servo_arc::HeaderWithLength::new(len, iter.padded_length()),
servo_arc::HeaderWithLength::new(len, iter.size_hint().0),
iter,
)),
}
@ -109,7 +111,7 @@ impl<T: Clone + Copy + Default + Sized + 'static> StaticNull for T {
let iter = PaddingFillingIter::new(len, null_iter);
servo_arc::Arc::into_thin(servo_arc::Arc::from_header_and_iter(
servo_arc::HeaderWithLength::new(len, iter.padded_length()),
servo_arc::HeaderWithLength::new(len, iter.size_hint().0),
iter,
))
});