Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Allow larger preallocated capacity for smaller elements #2495

Merged
merged 1 commit into from
Jul 9, 2023
Merged

Allow larger preallocated capacity for smaller elements #2495

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
19 changes: 10 additions & 9 deletions serde/src/de/impls.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -681,8 +681,8 @@ impl<'de> Visitor<'de> for CStringVisitor {
where
A: SeqAccess<'de>,
{
let len = size_hint::cautious(seq.size_hint());
let mut values = Vec::with_capacity(len);
let capacity = size_hint::cautious::<u8>(seq.size_hint());
let mut values = Vec::<u8>::with_capacity(capacity);

while let Some(value) = try!(seq.next_element()) {
values.push(value);
Expand Down Expand Up @@ -936,7 +936,7 @@ macro_rules! seq_impl {
A: SeqAccess<'de>,
{
$clear(&mut self.0);
$reserve(&mut self.0, size_hint::cautious($access.size_hint()));
$reserve(&mut self.0, size_hint::cautious::<T>($access.size_hint()));

// FIXME: try to overwrite old values here? (Vec, VecDeque, LinkedList)
while let Some(value) = try!($access.next_element()) {
Expand All @@ -962,7 +962,7 @@ seq_impl!(
BinaryHeap<T: Ord>,
seq,
BinaryHeap::clear,
BinaryHeap::with_capacity(size_hint::cautious(seq.size_hint())),
BinaryHeap::with_capacity(size_hint::cautious::<T>(seq.size_hint())),
BinaryHeap::reserve,
BinaryHeap::push
);
Expand Down Expand Up @@ -992,7 +992,7 @@ seq_impl!(
HashSet<T: Eq + Hash, S: BuildHasher + Default>,
seq,
HashSet::clear,
HashSet::with_capacity_and_hasher(size_hint::cautious(seq.size_hint()), S::default()),
HashSet::with_capacity_and_hasher(size_hint::cautious::<T>(seq.size_hint()), S::default()),
HashSet::reserve,
HashSet::insert
);
Expand All @@ -1002,7 +1002,7 @@ seq_impl!(
VecDeque<T>,
seq,
VecDeque::clear,
VecDeque::with_capacity(size_hint::cautious(seq.size_hint())),
VecDeque::with_capacity(size_hint::cautious::<T>(seq.size_hint())),
VecDeque::reserve,
VecDeque::push_back
);
Expand Down Expand Up @@ -1036,7 +1036,8 @@ where
where
A: SeqAccess<'de>,
{
let mut values = Vec::with_capacity(size_hint::cautious(seq.size_hint()));
let capacity = size_hint::cautious::<T>(seq.size_hint());
let mut values = Vec::<T>::with_capacity(capacity);

while let Some(value) = try!(seq.next_element()) {
values.push(value);
Expand Down Expand Up @@ -1072,7 +1073,7 @@ where
where
A: SeqAccess<'de>,
{
let hint = size_hint::cautious(seq.size_hint());
let hint = size_hint::cautious::<T>(seq.size_hint());
if let Some(additional) = hint.checked_sub(self.0.len()) {
self.0.reserve(additional);
}
Expand Down Expand Up @@ -1416,7 +1417,7 @@ map_impl!(BTreeMap<K: Ord, V>, map, BTreeMap::new());
map_impl!(
HashMap<K: Eq + Hash, V, S: BuildHasher + Default>,
map,
HashMap::with_capacity_and_hasher(size_hint::cautious(map.size_hint()), S::default())
HashMap::with_capacity_and_hasher(size_hint::cautious::<(K, V)>(map.size_hint()), S::default())
);

////////////////////////////////////////////////////////////////////////////////
Expand Down
13 changes: 10 additions & 3 deletions serde/src/private/de.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -474,7 +474,8 @@ mod content {
where
V: SeqAccess<'de>,
{
let mut vec = Vec::with_capacity(size_hint::cautious(visitor.size_hint()));
let mut vec =
Vec::<Content>::with_capacity(size_hint::cautious::<Content>(visitor.size_hint()));
while let Some(e) = try!(visitor.next_element()) {
vec.push(e);
}
Expand All @@ -485,7 +486,10 @@ mod content {
where
V: MapAccess<'de>,
{
let mut vec = Vec::with_capacity(size_hint::cautious(visitor.size_hint()));
let mut vec =
Vec::<(Content, Content)>::with_capacity(
size_hint::cautious::<(Content, Content)>(visitor.size_hint()),
);
while let Some(kv) = try!(visitor.next_entry()) {
vec.push(kv);
}
Expand Down Expand Up @@ -844,7 +848,10 @@ mod content {
M: MapAccess<'de>,
{
let mut tag = None;
let mut vec = Vec::with_capacity(size_hint::cautious(map.size_hint()));
let mut vec = Vec::<(Content, Content)>::with_capacity(size_hint::cautious::<(
Content,
Content,
)>(map.size_hint()));
while let Some(k) = try!(map.next_key_seed(TagOrContentVisitor::new(self.tag_name))) {
match k {
TagOrContent::Tag => {
Expand Down
14 changes: 11 additions & 3 deletions serde/src/private/size_hint.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -8,9 +8,17 @@ where
}

#[cfg(any(feature = "std", feature = "alloc"))]
#[inline]
pub fn cautious(hint: Option<usize>) -> usize {
cmp::min(hint.unwrap_or(0), 4096)
pub fn cautious<Element>(hint: Option<usize>) -> usize {
const MAX_PREALLOC_BYTES: usize = 1024 * 1024;

if mem::size_of::<Element>() == 0 {
Copy link

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

It would be good to cache the result of mem::size_of::<Element>() and reuse it at line 19 below

Copy link
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

This is the const function since 1.24 so it will be computed by the compiler

0
} else {
cmp::min(
hint.unwrap_or(0),
MAX_PREALLOC_BYTES / mem::size_of::<Element>(),
)
}
}

fn helper(bounds: (usize, Option<usize>)) -> Option<usize> {
Expand Down