bendns' repos / rust-analyzer
Unnamed repository; edit this file 'description' to name the repository.
Diffstat
-rw-r--r--crates/intern/src/symbol.rs90
-rw-r--r--crates/intern/src/symbol/symbols.rs1
2 files changed, 63 insertions, 28 deletions
diff --git a/crates/intern/src/symbol.rs b/crates/intern/src/symbol.rs
index 1517f516fc..9f7a788d00 100644
--- a/crates/intern/src/symbol.rs
+++ b/crates/intern/src/symbol.rs
@@ -5,7 +5,7 @@ use std::{
borrow::Borrow,
fmt,
hash::{BuildHasherDefault, Hash, Hasher},
- mem,
+ mem::{self, ManuallyDrop},
ptr::NonNull,
sync::OnceLock,
};
@@ -25,6 +25,15 @@ const _: () = assert!(std::mem::align_of::<Box<str>>() == std::mem::align_of::<&
const _: () = assert!(std::mem::size_of::<Arc<Box<str>>>() == std::mem::size_of::<&&str>());
const _: () = assert!(std::mem::align_of::<Arc<Box<str>>>() == std::mem::align_of::<&&str>());
+const _: () =
+ assert!(std::mem::size_of::<*const *const str>() == std::mem::size_of::<TaggedArcPtr>());
+const _: () =
+ assert!(std::mem::align_of::<*const *const str>() == std::mem::align_of::<TaggedArcPtr>());
+
+const _: () = assert!(std::mem::size_of::<Arc<Box<str>>>() == std::mem::size_of::<TaggedArcPtr>());
+const _: () =
+ assert!(std::mem::align_of::<Arc<Box<str>>>() == std::mem::align_of::<TaggedArcPtr>());
+
/// A pointer that points to a pointer to a `str`, it may be backed as a `&'static &'static str` or
/// `Arc<Box<str>>` but its size is that of a thin pointer. The active variant is encoded as a tag
/// in the LSB of the alignment niche.
@@ -40,19 +49,24 @@ impl TaggedArcPtr {
const BOOL_BITS: usize = true as usize;
const fn non_arc(r: &'static &'static str) -> Self {
- Self {
- // SAFETY: The pointer is non-null as it is derived from a reference
- // Ideally we would call out to `pack_arc` but for a `false` tag, unfortunately the
- // packing stuff requires reading out the pointer to an integer which is not supported
- // in const contexts, so here we make use of the fact that for the non-arc version the
- // tag is false (0) and thus does not need touching the actual pointer value.ext)
- packed: unsafe {
- NonNull::new_unchecked((r as *const &str).cast::<*const str>().cast_mut())
- },
- }
+ assert!(
+ mem::align_of::<&'static &'static str>().trailing_zeros() as usize > Self::BOOL_BITS
+ );
+ // SAFETY: The pointer is non-null as it is derived from a reference
+ // Ideally we would call out to `pack_arc` but for a `false` tag, unfortunately the
+ // packing stuff requires reading out the pointer to an integer which is not supported
+ // in const contexts, so here we make use of the fact that for the non-arc version the
+ // tag is false (0) and thus does not need touching the actual pointer value.ext)
+
+ let packed =
+ unsafe { NonNull::new_unchecked((r as *const &str).cast::<*const str>().cast_mut()) };
+ Self { packed }
}
fn arc(arc: Arc<Box<str>>) -> Self {
+ assert!(
+ mem::align_of::<&'static &'static str>().trailing_zeros() as usize > Self::BOOL_BITS
+ );
Self {
packed: Self::pack_arc(
// Safety: `Arc::into_raw` always returns a non null pointer
@@ -63,12 +77,14 @@ impl TaggedArcPtr {
/// Retrieves the tag.
#[inline]
- pub(crate) fn try_as_arc_owned(self) -> Option<Arc<Box<str>>> {
+ pub(crate) fn try_as_arc_owned(self) -> Option<ManuallyDrop<Arc<Box<str>>>> {
// Unpack the tag from the alignment niche
let tag = Strict::addr(self.packed.as_ptr()) & Self::BOOL_BITS;
if tag != 0 {
// Safety: We checked that the tag is non-zero -> true, so we are pointing to the data offset of an `Arc`
- Some(unsafe { Arc::from_raw(self.pointer().as_ptr().cast::<Box<str>>()) })
+ Some(ManuallyDrop::new(unsafe {
+ Arc::from_raw(self.pointer().as_ptr().cast::<Box<str>>())
+ }))
} else {
None
}
@@ -122,10 +138,11 @@ impl TaggedArcPtr {
}
}
-#[derive(PartialEq, Eq, Hash, Clone, Debug)]
+#[derive(PartialEq, Eq, Hash, Debug)]
pub struct Symbol {
repr: TaggedArcPtr,
}
+
const _: () = assert!(std::mem::size_of::<Symbol>() == std::mem::size_of::<NonNull<()>>());
const _: () = assert!(std::mem::align_of::<Symbol>() == std::mem::align_of::<NonNull<()>>());
@@ -185,19 +202,27 @@ impl Symbol {
fn drop_slow(arc: &Arc<Box<str>>) {
let (mut shard, hash) = Self::select_shard(arc);
- if Arc::count(arc) != 2 {
- // Another thread has interned another copy
- return;
+ match Arc::count(arc) {
+ 0 => unreachable!(),
+ 1 => unreachable!(),
+ 2 => (),
+ _ => {
+ // Another thread has interned another copy
+ return;
+ }
}
- match shard.raw_entry_mut().from_key_hashed_nocheck::<str>(hash, arc.as_ref()) {
- RawEntryMut::Occupied(occ) => occ.remove_entry(),
- RawEntryMut::Vacant(_) => unreachable!(),
- }
- .0
- .0
- .try_as_arc_owned()
- .unwrap();
+ ManuallyDrop::into_inner(
+ match shard.raw_entry_mut().from_key_hashed_nocheck::<str>(hash, arc.as_ref()) {
+ RawEntryMut::Occupied(occ) => occ.remove_entry(),
+ RawEntryMut::Vacant(_) => unreachable!(),
+ }
+ .0
+ .0
+ .try_as_arc_owned()
+ .unwrap(),
+ );
+ debug_assert_eq!(Arc::count(&arc), 1);
// Shrink the backing storage if the shard is less than 50% occupied.
if shard.len() * 2 < shard.capacity() {
@@ -219,7 +244,13 @@ impl Drop for Symbol {
Self::drop_slow(&arc);
}
// decrement the ref count
- drop(arc);
+ ManuallyDrop::into_inner(arc);
+ }
+}
+
+impl Clone for Symbol {
+ fn clone(&self) -> Self {
+ Self { repr: increase_arc_refcount(self.repr) }
}
}
@@ -228,8 +259,7 @@ fn increase_arc_refcount(repr: TaggedArcPtr) -> TaggedArcPtr {
return repr;
};
// increase the ref count
- mem::forget(arc.clone());
- mem::forget(arc);
+ mem::forget(Arc::clone(&arc));
repr
}
@@ -265,6 +295,7 @@ mod tests {
let base_len = MAP.get().unwrap().len();
let hello = Symbol::intern("hello");
let world = Symbol::intern("world");
+ let more_worlds = world.clone();
let bang = Symbol::intern("!");
let q = Symbol::intern("?");
assert_eq!(MAP.get().unwrap().len(), base_len + 4);
@@ -275,6 +306,7 @@ mod tests {
drop(q);
assert_eq!(MAP.get().unwrap().len(), base_len + 3);
let default = Symbol::intern("default");
+ let many_worlds = world.clone();
assert_eq!(MAP.get().unwrap().len(), base_len + 3);
assert_eq!(
"hello default world!",
@@ -285,6 +317,8 @@ mod tests {
"hello world!",
format!("{} {}{}", hello.as_str(), world.as_str(), bang.as_str())
);
+ drop(many_worlds);
+ drop(more_worlds);
drop(hello);
drop(world);
drop(bang);
diff --git a/crates/intern/src/symbol/symbols.rs b/crates/intern/src/symbol/symbols.rs
index 04bf4dff50..af1af0536c 100644
--- a/crates/intern/src/symbol/symbols.rs
+++ b/crates/intern/src/symbol/symbols.rs
@@ -10,6 +10,7 @@ use crate::{
symbol::{SymbolProxy, TaggedArcPtr},
Symbol,
};
+
macro_rules! define_symbols {
(@WITH_NAME: $($alias:ident = $value:literal),* $(,)? @PLAIN: $($name:ident),* $(,)?) => {
$(