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// Implementation taken partly from https://docs.rs/hashbrown/0.14.0/src/hashbrown/lib.rs.html,
// but with some adjustments to use `Ephemeron<K,V>` instead of `(K,V)`
use hashbrown::{
hash_map::DefaultHashBuilder,
raw::{RawIter, RawTable},
TryReserveError,
};
use crate::{custom_trace, Allocator, Ephemeron, Finalize, Gc, GcRefCell, Trace};
use std::{fmt, hash::BuildHasher, marker::PhantomData, mem};
/// A map that holds weak references to its keys and is traced by the garbage collector.
#[derive(Clone, Debug, Default, Finalize)]
pub struct WeakMap<K: Trace + ?Sized + 'static, V: Trace + 'static> {
pub(crate) inner: Gc<GcRefCell<RawWeakMap<K, V>>>,
}
unsafe impl<K: Trace + ?Sized + 'static, V: Trace + 'static> Trace for WeakMap<K, V> {
custom_trace!(this, mark, {
mark(&this.inner);
});
}
impl<K: Trace + ?Sized, V: Trace + Clone> WeakMap<K, V> {
/// Creates a new `WeakMap`.
#[must_use]
#[inline]
pub fn new() -> Self {
Allocator::alloc_weak_map()
}
/// Inserts a key-value pair into the map.
#[inline]
pub fn insert(&mut self, key: &Gc<K>, value: V) {
self.inner.borrow_mut().insert(key, value);
}
/// Removes a key from the map, returning the value at the key if the key was previously in the map.
#[inline]
pub fn remove(&mut self, key: &Gc<K>) -> Option<V> {
self.inner.borrow_mut().remove(key)
}
/// Returns `true` if the map contains a value for the specified key.
#[must_use]
#[inline]
pub fn contains_key(&self, key: &Gc<K>) -> bool {
self.inner.borrow().contains_key(key)
}
/// Returns a reference to the value corresponding to the key.
#[must_use]
#[inline]
pub fn get(&self, key: &Gc<K>) -> Option<V> {
self.inner.borrow().get(key)
}
}
/// A hash map where the bucket type is an <code>[Ephemeron]\<K, V\></code>.
///
/// This data structure allows associating a <code>[Gc]\<K\></code> with a value `V` that will be
/// invalidated when the `Gc<K>` gets collected. In other words, all key entries on the map are weakly
/// held.
pub(crate) struct RawWeakMap<K, V, S = DefaultHashBuilder>
where
K: Trace + ?Sized + 'static,
V: Trace + 'static,
{
hash_builder: S,
table: RawTable<Ephemeron<K, V>>,
}
impl<K, V, S> Finalize for RawWeakMap<K, V, S>
where
K: Trace + ?Sized + 'static,
V: Trace + 'static,
{
}
// SAFETY: The implementation correctly marks all ephemerons inside the map.
unsafe impl<K, V, S> Trace for RawWeakMap<K, V, S>
where
K: Trace + ?Sized + 'static,
V: Trace + 'static,
{
custom_trace!(this, mark, {
for eph in this.iter() {
mark(eph);
}
});
}
impl<K, V, S> Default for RawWeakMap<K, V, S>
where
S: Default,
K: Trace + ?Sized + 'static,
V: Trace + 'static,
{
fn default() -> Self {
Self::with_hasher(Default::default())
}
}
impl<K, V> RawWeakMap<K, V, DefaultHashBuilder>
where
K: Trace + ?Sized + 'static,
V: Trace + 'static,
{
/// Creates an empty `RawWeakMap`.
///
/// The map is initially created with a capacity of 0, so it will not allocate until it
/// is first inserted into.
pub(crate) fn new() -> Self {
Self::default()
}
/// Creates an empty `RawWeakMap` with the specified capacity.
///
/// The map will be able to hold at least `capacity` elements without reallocating.
/// If `capacity` is 0, the map will not allocate.
#[allow(unused)]
pub(crate) fn with_capacity(capacity: usize) -> Self {
Self::with_capacity_and_hasher(capacity, DefaultHashBuilder::default())
}
}
impl<K, V, S> RawWeakMap<K, V, S>
where
K: Trace + ?Sized + 'static,
V: Trace + 'static,
{
/// Creates an empty `RawWeakMap` which will use the given hash builder to hash
/// keys.
///
/// The map is initially created with a capacity of 0, so it will not allocate until it is first
/// inserted into.
pub(crate) const fn with_hasher(hash_builder: S) -> Self {
Self {
hash_builder,
table: RawTable::new(),
}
}
/// Creates an empty `RawWeakMap` with the specified capacity, using `hash_builder`
/// to hash the keys.
///
/// The map will be able to hold at least `capacity` elements without reallocating.
/// If `capacity` is 0, the map will not allocate.
pub(crate) fn with_capacity_and_hasher(capacity: usize, hash_builder: S) -> Self {
Self {
hash_builder,
table: RawTable::with_capacity(capacity),
}
}
/// Returns a reference to the map's [`BuildHasher`].
#[allow(unused)]
pub(crate) const fn hasher(&self) -> &S {
&self.hash_builder
}
/// Returns the number of elements the map can hold without reallocating.
///
/// This number is a lower bound; the map might be able to hold more, but is guaranteed to be
/// able to hold at least this many.
#[allow(unused)]
pub(crate) fn capacity(&self) -> usize {
self.table.capacity()
}
/// An iterator visiting all entries in arbitrary order.
/// The iterator element type is <code>[Ephemeron]<K, V></code>.
pub(crate) fn iter(&self) -> Iter<'_, K, V> {
// SAFETY: The returned iterator is tied to the lifetime of self.
unsafe {
Iter {
inner: self.table.iter(),
marker: PhantomData,
}
}
}
/// Returns the number of elements in the map.
///
/// This is an upper bound; the map might contain some expired keys which haven't been
/// removed.
#[allow(unused)]
pub(crate) fn len(&self) -> usize {
self.table.len()
}
/// Returns `true` if the map contains no elements.
///
/// This might return `false` if the map has expired keys that are still pending to be
/// cleaned up.
#[allow(unused)]
pub(crate) fn is_empty(&self) -> bool {
self.len() == 0
}
/// Retains only the elements specified by the predicate. Keeps the
/// allocated memory for reuse.
///
/// In other words, remove all ephemerons <code>[Ephemeron]<K, V></code> such that
/// `f(&eph)` returns `false`.
/// The elements are visited in unsorted (and unspecified) order.
pub(crate) fn retain<F>(&mut self, mut f: F)
where
F: FnMut(&Ephemeron<K, V>) -> bool,
{
// SAFETY:
// - `item` is only used internally, which means it outlives self.
// - `item` pointer is not used after the call to `erase`.
unsafe {
for item in self.table.iter() {
let eph = item.as_ref();
if !f(eph) {
self.table.erase(item);
}
}
}
}
/// Clears the map, removing all key-value pairs. Keeps the allocated memory
/// for reuse.
#[allow(unused)]
pub(crate) fn clear(&mut self) {
self.table.clear();
}
}
impl<K, V, S> RawWeakMap<K, V, S>
where
K: Trace + ?Sized + 'static,
V: Trace + Clone + 'static,
S: BuildHasher,
{
/// Reserves capacity for at least `additional` more elements to be inserted
/// in the `RawWeakMap`. The collection may reserve more space to avoid
/// frequent reallocations.
///
/// # Panics
///
/// Panics if the new capacity exceeds [`isize::MAX`] bytes and [`abort`](std::process::abort)
/// the program in case of allocation error. Use [`try_reserve`](RawWeakMap::try_reserve) instead
/// if you want to handle memory allocation failure.
#[allow(unused)]
pub(crate) fn reserve(&mut self, additional: usize) {
self.table
.reserve(additional, make_hasher(&self.hash_builder));
}
/// Tries to reserve capacity for at least `additional` more elements to be inserted
/// in the given `RawWeakMap<K,V>`. The collection may reserve more space to avoid
/// frequent reallocations.
///
/// # Errors
///
/// If the capacity overflows, or the allocator reports a failure, then an error
/// is returned.
#[allow(unused)]
pub(crate) fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
self.table
.try_reserve(additional, make_hasher(&self.hash_builder))
}
/// Shrinks the capacity of the map as much as possible. It will drop
/// down as much as possible while maintaining the internal rules
/// and possibly leaving some space in accordance with the resize policy.
#[allow(unused)]
pub(crate) fn shrink_to_fit(&mut self) {
self.table
.shrink_to(0, make_hasher::<_, V, S>(&self.hash_builder));
}
/// Shrinks the capacity of the map with a lower limit. It will drop
/// down no lower than the supplied limit while maintaining the internal rules
/// and possibly leaving some space in accordance with the resize policy.
///
/// This function does nothing if the current capacity is smaller than the
/// supplied minimum capacity.
#[allow(unused)]
pub(crate) fn shrink_to(&mut self, min_capacity: usize) {
self.table
.shrink_to(min_capacity, make_hasher::<_, V, S>(&self.hash_builder));
}
/// Returns the value corresponding to the supplied key.
// TODO: make this return a reference instead of cloning.
pub(crate) fn get(&self, k: &Gc<K>) -> Option<V> {
if self.table.is_empty() {
None
} else {
let hash = make_hash_from_gc(&self.hash_builder, k);
self.table.get(hash, equivalent_key(k))?.value()
}
}
/// Returns `true` if the map contains a value for the specified key.
pub(crate) fn contains_key(&self, k: &Gc<K>) -> bool {
self.get(k).is_some()
}
// Inserts a key-value pair into the map.
///
/// If the map did not have this key present, [`None`] is returned.
///
/// If the map did have this key present, the value is updated, and the old
/// value is returned. The key is not updated.
pub(crate) fn insert(&mut self, k: &Gc<K>, v: V) -> Option<Ephemeron<K, V>> {
let hash = make_hash_from_gc(&self.hash_builder, k);
let hasher = make_hasher(&self.hash_builder);
let eph = Ephemeron::new(k, v);
match self
.table
.find_or_find_insert_slot(hash, equivalent_key(k), hasher)
{
// SAFETY: `bucket` is only used inside the replace call, meaning it doesn't
// outlive self.
Ok(bucket) => Some(mem::replace(unsafe { bucket.as_mut() }, eph)),
Err(slot) => {
// SAFETY: `slot` comes from a call to `find_or_find_insert_slot`, and `self`
// is not mutated until the call to `insert_in_slot`.
unsafe {
self.table.insert_in_slot(hash, slot, eph);
}
None
}
}
}
/// Removes a key from the map, returning the value at the key if the key
/// was previously in the map. Keeps the allocated memory for reuse.
pub(crate) fn remove(&mut self, k: &Gc<K>) -> Option<V> {
let hash = make_hash_from_gc(&self.hash_builder, k);
self.table.remove_entry(hash, equivalent_key(k))?.value()
}
/// Clears all the expired keys in the map.
pub(crate) fn clear_expired(&mut self) {
self.retain(|eph| eph.value().is_some());
}
}
pub(crate) struct Iter<'a, K, V>
where
K: Trace + ?Sized + 'static,
V: Trace + 'static,
{
inner: RawIter<Ephemeron<K, V>>,
marker: PhantomData<&'a Ephemeron<K, V>>,
}
impl<K, V> Clone for Iter<'_, K, V>
where
K: Trace + ?Sized + 'static,
V: Trace + 'static,
{
#[inline]
fn clone(&self) -> Self {
Iter {
inner: self.inner.clone(),
marker: PhantomData,
}
}
}
impl<K, V> fmt::Debug for Iter<'_, K, V>
where
K: Trace + ?Sized + 'static + fmt::Debug,
V: Trace + 'static + fmt::Debug,
{
#[inline]
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_list().entries(self.clone()).finish()
}
}
impl<'a, K, V> Iterator for Iter<'a, K, V>
where
K: Trace + ?Sized + 'static,
V: Trace + 'static,
{
type Item = &'a Ephemeron<K, V>;
#[inline]
fn next(&mut self) -> Option<Self::Item> {
// SAFETY: The original map outlives the iterator thanks to the lifetime parameter,
// and since the returned ephemeron carries that information, the call to `as_ref` is safe.
unsafe { self.inner.next().map(|b| b.as_ref()) }
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
self.inner.size_hint()
}
}
impl<K, V, S> fmt::Debug for RawWeakMap<K, V, S>
where
K: fmt::Debug + ?Sized + Trace + Finalize,
V: fmt::Debug + Trace + Finalize,
{
#[inline]
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
self.iter().fmt(f)
}
}
fn make_hasher<K, V, S>(hash_builder: &S) -> impl Fn(&Ephemeron<K, V>) -> u64 + '_
where
S: BuildHasher,
K: Trace + ?Sized + 'static,
V: Trace + 'static,
{
move |val| make_hash_from_eph::<K, V, S>(hash_builder, val)
}
fn make_hash_from_eph<K, V, S>(hash_builder: &S, eph: &Ephemeron<K, V>) -> u64
where
S: BuildHasher,
K: Trace + ?Sized + 'static,
V: Trace + 'static,
{
use std::hash::Hasher;
let mut state = hash_builder.build_hasher();
// TODO: Is this true for custom hashers? if not, rewrite `key` to be safe.
// SAFETY: The return value of `key` is only used to hash it, which
// cannot trigger a garbage collection,
unsafe {
if let Some(val) = eph.inner().key() {
std::ptr::hash(val, &mut state);
} else {
std::ptr::hash(eph.inner_ptr().as_ptr(), &mut state);
}
}
state.finish()
}
fn make_hash_from_gc<K, S>(hash_builder: &S, gc: &Gc<K>) -> u64
where
S: BuildHasher,
K: Trace + ?Sized + 'static,
{
use std::hash::Hasher;
let mut state = hash_builder.build_hasher();
std::ptr::hash(gc.inner_ptr().as_ptr(), &mut state);
state.finish()
}
fn equivalent_key<K, V>(k: &Gc<K>) -> impl Fn(&Ephemeron<K, V>) -> bool + '_
where
K: Trace + ?Sized + 'static,
V: Trace + 'static,
{
// SAFETY: The return value of `key` is only used inside eq, which
// cannot trigger a garbage collection.
move |eph| unsafe {
eph.inner().key().is_some_and(|val| {
let val: *const _ = val;
std::ptr::eq(val, k.inner_ptr().as_ptr())
})
}
}