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cl-structures: Interning v3: ACTUALLY DO THE THING

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Here we have *real* interning, producing unique references if and only if the input is unique! Boy am I glad I invested time into this, because it's really fun to work with.

Hopefully my logic regarding Send-ness and Sync-ness aren't completely unsound.
This commit is contained in:
John 2024-04-27 20:16:36 -05:00
parent 83423f37be
commit 81cf05cc69
3 changed files with 295 additions and 0 deletions
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1
compiler/cl-structures/Cargo.toml
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@ -9,3 +9,4 @@ publish.workspace = true
[dependencies] [dependencies]
hashbrown = { version = "0.14.3", default-features = false } hashbrown = { version = "0.14.3", default-features = false }
cl-arena = { path = "../cl-arena" }

292
compiler/cl-structures/src/intern.rs Normal file
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@ -0,0 +1,292 @@
//! Interners for [strings](string_interner) and arbitrary [types](typed_interner).
//!
//! An object is [Interned][1] if it is allocated within one of the interners
//! in this module. [Interned][1] values have referential equality semantics, and
//! [Deref](std::ops::Deref) to the value within their respective intern pool.
//!
//! This means, of course, that the same value interned in two different pools will be
//! considered *not equal* by [Eq] and [Hash](std::hash::Hash).
//!
//! [1]: interned::Interned
pub mod interned {
//! An [Interned] reference asserts its wrapped value has referential equality.
use super::string_interner::StringInterner;
use std::{
fmt::{Debug, Display},
hash::Hash,
ops::Deref,
};
/// An [Interned] value is one that is *referentially comparable*.
/// That is, the interned value is unique in memory, simplifying
/// its equality and hashing implementation.
///
/// Comparing [Interned] values via [PartialOrd] or [Ord] will still
/// dereference to the wrapped pointers, and as such, may produce
/// results inconsistent with [PartialEq] or [Eq].
#[repr(transparent)]
#[derive(Eq)]
pub struct Interned<'a, T: ?Sized> {
value: &'a T,
}
impl<'a, T: ?Sized> Interned<'a, T> {
/// Gets the internal value as a pointer
pub fn as_ptr(interned: &Self) -> *const T {
interned.value
}
}
impl<'a, T: ?Sized + Debug> Debug for Interned<'a, T> {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
f.debug_struct("Interned")
.field("value", &self.value)
.finish()
}
}
impl<'a, T: ?Sized> Interned<'a, T> {
pub(super) fn new(value: &'a T) -> Self {
Self { value }
}
}
impl<'a, T: ?Sized> Deref for Interned<'a, T> {
type Target = T;
fn deref(&self) -> &Self::Target {
self.value
}
}
impl<'a, T: ?Sized> Copy for Interned<'a, T> {}
impl<'a, T: ?Sized> Clone for Interned<'a, T> {
fn clone(&self) -> Self {
*self
}
}
// TODO: These implementations are subtly incorrect, as they do not line up with `eq`
// impl<'a, T: ?Sized + PartialOrd> PartialOrd for Interned<'a, T> {
// fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
// match self == other {
// true => Some(std::cmp::Ordering::Equal),
// false => self.value.partial_cmp(other.value),
// }
// }
// }
// impl<'a, T: ?Sized + Ord> Ord for Interned<'a, T> {
// fn cmp(&self, other: &Self) -> std::cmp::Ordering {
// match self == other {
// true => std::cmp::Ordering::Equal,
// false => self.value.cmp(other.value),
// }
// }
// }
impl<'a, T: ?Sized> PartialEq for Interned<'a, T> {
fn eq(&self, other: &Self) -> bool {
std::ptr::eq(self.value, other.value)
}
}
impl<'a, T: ?Sized> Hash for Interned<'a, T> {
fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
Self::as_ptr(self).hash(state)
}
}
impl<T: ?Sized + Display> Display for Interned<'_, T> {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
self.value.fmt(f)
}
}
impl<T: AsRef<str>> From<T> for Interned<'static, str> {
/// Types which implement [AsRef<str>] will be stored in the global [StringInterner]
fn from(value: T) -> Self {
from_str(value.as_ref())
}
}
fn from_str(value: &str) -> Interned<'static, str> {
let global_interner = StringInterner::global();
global_interner.get_or_insert(value)
}
}
pub mod string_interner {
//! A [StringInterner] hands out [Interned] copies of each unique string given to it.
use super::interned::Interned;
use cl_arena::dropless_arena::DroplessArena;
use std::{
collections::HashSet,
ptr::addr_of,
sync::{OnceLock, RwLock},
};
/// A string interner hands out [Interned] copies of each unique string given to it.
pub struct StringInterner<'a> {
arena: &'a DroplessArena,
keys: RwLock<HashSet<&'a str>>,
}
impl StringInterner<'static> {
/// Gets a reference to a global string interner whose [Interned] strings are `'static`
pub fn global() -> &'static Self {
static GLOBAL_INTERNER: OnceLock<StringInterner<'static>> = OnceLock::new();
static mut ARENA: DroplessArena = DroplessArena::new();
// SAFETY: The RwLock within the interner's `keys` protects the arena
// from being modified concurrently.
GLOBAL_INTERNER.get_or_init(|| StringInterner {
arena: unsafe { &*addr_of!(ARENA) },
keys: Default::default(),
})
}
}
impl<'a> StringInterner<'a> {
/// Creates a new [StringInterner] backed by the provided [DroplessArena]
pub fn new(arena: &'a DroplessArena) -> Self {
Self { arena, keys: RwLock::new(HashSet::new()) }
}
/// Returns an [Interned] copy of the given string,
/// allocating a new one if it doesn't already exist.
///
/// # Blocks
/// This function blocks when the interner is held by another thread.
pub fn get_or_insert(&self, value: &str) -> Interned<'a, str> {
let Self { arena, keys } = self;
// Safety: Holding this write guard for the entire duration of this
// function enforces a safety invariant. See StringInterner::global.
let mut keys = keys.write().expect("should not be poisoned");
Interned::new(match keys.get(value) {
Some(value) => value,
None => {
let value = match value {
"" => "", // Arena will panic if passed an empty string
_ => arena.alloc_str(value),
};
keys.insert(value);
value
}
})
}
/// Gets a reference to the interned copy of the given value, if it exists
/// # Blocks
/// This function blocks when the interner is held by another thread.
pub fn get(&self, value: &str) -> Option<Interned<'a, str>> {
let keys = self.keys.read().expect("should not be poisoned");
keys.get(value).copied().map(Interned::new)
}
}
impl std::fmt::Debug for StringInterner<'_> {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
f.debug_struct("Interner")
.field("keys", &self.keys)
.finish()
}
}
// # Safety:
// This is fine because StringInterner::get_or_insert(v) holds a RwLock
// for its entire duration, and doesn't touch the non-(Send+Sync) arena
// unless the lock is held by a write guard.
unsafe impl<'a> Send for StringInterner<'a> {}
unsafe impl<'a> Sync for StringInterner<'a> {}
#[cfg(test)]
mod tests {
use super::StringInterner;
macro_rules! ptr_eq {
($a: expr, $b: expr $(, $($t:tt)*)?) => {
assert_eq!(std::ptr::addr_of!($a), std::ptr::addr_of!($b) $(, $($t)*)?)
};
}
macro_rules! ptr_ne {
($a: expr, $b: expr $(, $($t:tt)*)?) => {
assert_ne!(std::ptr::addr_of!($a), std::ptr::addr_of!($b) $(, $($t)*)?)
};
}
#[test]
fn empties_is_unique() {
let interner = StringInterner::global();
let empty = interner.get_or_insert("");
let empty2 = interner.get_or_insert("");
ptr_eq!(*empty, *empty2);
}
#[test]
fn non_empty_is_unique() {
let interner = StringInterner::global();
let nonempty1 = interner.get_or_insert("not empty!");
let nonempty2 = interner.get_or_insert("not empty!");
let different = interner.get_or_insert("different!");
ptr_eq!(*nonempty1, *nonempty2);
ptr_ne!(*nonempty1, *different);
}
}
}
pub mod typed_interner {
//! A [TypedInterner] hands out [Interned] references for arbitrary types.
//!
//! Note: It is a *logic error* to modify the returned reference via interior mutability
//! in a way that changes the values produced by [Eq] and [Hash].
//!
//! See the standard library [HashSet] for more details.
use super::interned::Interned;
use cl_arena::typed_arena::TypedArena;
use std::{collections::HashSet, hash::Hash, sync::RwLock};
/// A [TypedInterner] hands out [Interned] references for arbitrary types.
///
/// See the [module-level documentation](self) for more information.
pub struct TypedInterner<'a, T: Eq + Hash> {
arena: &'a TypedArena<T>,
keys: RwLock<HashSet<&'a T>>,
}
impl<'a, T: Eq + Hash> TypedInterner<'a, T> {
/// Creates a new [TypedInterner] backed by the provided [TypedArena]
pub fn new(arena: &'a TypedArena<T>) -> Self {
Self { arena, keys: RwLock::new(HashSet::new()) }
}
/// Converts the given value into an [Interned] value.
///
/// # Blocks
/// This function blocks when the interner is held by another thread.
pub fn get_or_insert(&self, value: T) -> Interned<'a, T> {
let Self { arena, keys } = self;
// Safety: Locking the keyset for the entire duration of this function
// enforces a safety invariant when the interner is stored in a global.
let mut keys = keys.write().expect("should not be poisoned");
Interned::new(match keys.get(&value) {
Some(value) => value,
None => {
let value = arena.alloc(value);
keys.insert(value);
value
}
})
}
/// Returns the [Interned] copy of the given value, if one already exists
///
/// # Blocks
/// This function blocks when the interner is being written to by another thread.
pub fn get(&self, value: &T) -> Option<Interned<'a, T>> {
let keys = self.keys.read().expect("should not be poisoned");
keys.get(value).copied().map(Interned::new)
}
}
/// # Safety
/// This should be safe because references yielded by
/// [get_or_insert](TypedInterner::get_or_insert) are unique, and the function uses
/// the [RwLock] around the [HashSet] to ensure mutual exclusion
unsafe impl<'a, T: Eq + Hash + Send> Send for TypedInterner<'a, T> where &'a T: Send {}
unsafe impl<'a, T: Eq + Hash + Send + Sync> Sync for TypedInterner<'a, T> {}
}

2
compiler/cl-structures/src/lib.rs
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@ -7,6 +7,8 @@
pub mod arena; pub mod arena;
pub mod intern;
pub mod span; pub mod span;
pub mod tree; pub mod tree;