111 lines
4.5 KiB
Rust
111 lines
4.5 KiB
Rust
//! This is a "monotonic `FxHashMap`": A `FxHashMap` that, when shared, can be pushed to but not
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//! otherwise mutated. We also box items in the map. This means we can safely provide
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//! shared references into existing items in the `FxHashMap`, because they will not be dropped
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//! (from being removed) or moved (because they are boxed).
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//! The API is is completely tailored to what `memory.rs` needs. It is still in
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//! a separate file to minimize the amount of code that has to care about the unsafety.
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use std::borrow::Borrow;
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use std::cell::RefCell;
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use std::collections::hash_map::Entry;
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use std::hash::Hash;
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use rustc_data_structures::fx::FxHashMap;
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use crate::AllocMap;
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#[derive(Debug, Clone)]
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pub struct MonoHashMap<K: Hash + Eq, V>(RefCell<FxHashMap<K, Box<V>>>);
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impl<K: Hash + Eq, V> MonoHashMap<K, V> {
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/// This function exists for priroda to be able to iterate over all evaluator memory.
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///
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/// The function is somewhat roundabout with the closure argument because internally the
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/// `MonoHashMap` uses a `RefCell`. When iterating over the `FxHashMap` inside the `RefCell`,
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/// we need to keep a borrow to the `FxHashMap` inside the iterator. The borrow is only alive
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/// as long as the `Ref` returned by `RefCell::borrow()` is alive. So we can't return the
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/// iterator, as that would drop the `Ref`. We can't return both, as it's not possible in Rust
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/// to have a struct/tuple with a field that refers to another field.
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pub fn iter<T>(&self, f: impl FnOnce(&mut dyn Iterator<Item = (&K, &V)>) -> T) -> T {
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f(&mut self.0.borrow().iter().map(|(k, v)| (k, &**v)))
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}
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}
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impl<K: Hash + Eq, V> Default for MonoHashMap<K, V> {
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fn default() -> Self {
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MonoHashMap(RefCell::new(Default::default()))
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}
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}
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impl<K: Hash + Eq, V> AllocMap<K, V> for MonoHashMap<K, V> {
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#[inline(always)]
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fn contains_key<Q: ?Sized + Hash + Eq>(&mut self, k: &Q) -> bool
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where
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K: Borrow<Q>,
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{
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self.0.get_mut().contains_key(k)
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}
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#[inline(always)]
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fn insert(&mut self, k: K, v: V) -> Option<V> {
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self.0.get_mut().insert(k, Box::new(v)).map(|x| *x)
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}
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#[inline(always)]
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fn remove<Q: ?Sized + Hash + Eq>(&mut self, k: &Q) -> Option<V>
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where
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K: Borrow<Q>,
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{
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self.0.get_mut().remove(k).map(|x| *x)
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}
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#[inline(always)]
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fn filter_map_collect<T>(&self, mut f: impl FnMut(&K, &V) -> Option<T>) -> Vec<T> {
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self.0.borrow().iter().filter_map(move |(k, v)| f(k, &*v)).collect()
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}
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/// The most interesting method: Providing a shared reference without
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/// holding the `RefCell` open, and inserting new data if the key
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/// is not used yet.
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/// `vacant` is called if the key is not found in the map;
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/// if it returns a reference, that is used directly, if it
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/// returns owned data, that is put into the map and returned.
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#[inline(always)]
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fn get_or<E>(&self, k: K, vacant: impl FnOnce() -> Result<V, E>) -> Result<&V, E> {
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// We cannot hold borrow_mut while calling `vacant`, since that might have to do lookups in this very map.
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if let Some(v) = self.0.borrow().get(&k) {
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let val: *const V = &**v;
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// This is safe because `val` points into a `Box`, that we know will not move and
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// will also not be dropped as long as the shared reference `self` is live.
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return unsafe { Ok(&*val) };
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}
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let new_val = Box::new(vacant()?);
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let val: *const V = &**self.0.borrow_mut().try_insert(k, new_val).ok().unwrap();
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// This is safe because `val` points into a `Box`, that we know will not move and
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// will also not be dropped as long as the shared reference `self` is live.
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unsafe { Ok(&*val) }
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}
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/// Read-only lookup (avoid read-acquiring the RefCell).
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fn get(&self, k: K) -> Option<&V> {
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let val: *const V = match self.0.borrow().get(&k) {
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Some(v) => &**v,
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None => return None,
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};
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// This is safe because `val` points into a `Box`, that we know will not move and
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// will also not be dropped as long as the shared reference `self` is live.
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unsafe { Some(&*val) }
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}
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#[inline(always)]
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fn get_mut_or<E>(&mut self, k: K, vacant: impl FnOnce() -> Result<V, E>) -> Result<&mut V, E> {
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match self.0.get_mut().entry(k) {
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Entry::Occupied(e) => Ok(e.into_mut()),
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Entry::Vacant(e) => {
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let v = vacant()?;
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Ok(e.insert(Box::new(v)))
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}
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}
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}
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}
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