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Edit rustc_arena::DropArena docs

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- Add a "Safety" section, edit formatting for clarity
- Add missing punctuation in code comments
This commit is contained in:
pierwill 2021-02-13 15:18:42 -08:00
parent 3c10a880ec
commit 1c3841ebf2
1 changed files with 9 additions and 6 deletions
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15
compiler/rustc_arena/src/lib.rs
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@ -568,10 +568,13 @@ impl Drop for DropType {
} }
/// An arena which can be used to allocate any type. /// An arena which can be used to allocate any type.
///
/// # Safety
///
/// Allocating in this arena is unsafe since the type system /// Allocating in this arena is unsafe since the type system
/// doesn't know which types it contains. In order to /// doesn't know which types it contains. In order to
/// allocate safely, you must store a PhantomData<T> /// allocate safely, you must store a `PhantomData<T>`
/// alongside this arena for each type T you allocate. /// alongside this arena for each type `T` you allocate.
#[derive(Default)] #[derive(Default)]
pub struct DropArena { pub struct DropArena {
/// A list of destructors to run when the arena drops. /// A list of destructors to run when the arena drops.
@ -589,7 +592,7 @@ impl DropArena {
ptr::write(mem, object); ptr::write(mem, object);
let result = &mut *mem; let result = &mut *mem;
// Record the destructor after doing the allocation as that may panic // Record the destructor after doing the allocation as that may panic
// and would cause `object`'s destructor to run twice if it was recorded before // and would cause `object`'s destructor to run twice if it was recorded before.
self.destructors self.destructors
.borrow_mut() .borrow_mut()
.push(DropType { drop_fn: drop_for_type::<T>, obj: result as *mut T as *mut u8 }); .push(DropType { drop_fn: drop_for_type::<T>, obj: result as *mut T as *mut u8 });
@ -607,16 +610,16 @@ impl DropArena {
let start_ptr = self.arena.alloc_raw(Layout::array::<T>(len).unwrap()) as *mut T; let start_ptr = self.arena.alloc_raw(Layout::array::<T>(len).unwrap()) as *mut T;
let mut destructors = self.destructors.borrow_mut(); let mut destructors = self.destructors.borrow_mut();
// Reserve space for the destructors so we can't panic while adding them // Reserve space for the destructors so we can't panic while adding them.
destructors.reserve(len); destructors.reserve(len);
// Move the content to the arena by copying it and then forgetting // Move the content to the arena by copying it and then forgetting
// the content of the SmallVec // the content of the SmallVec.
vec.as_ptr().copy_to_nonoverlapping(start_ptr, len); vec.as_ptr().copy_to_nonoverlapping(start_ptr, len);
mem::forget(vec.drain(..)); mem::forget(vec.drain(..));
// Record the destructors after doing the allocation as that may panic // Record the destructors after doing the allocation as that may panic
// and would cause `object`'s destructor to run twice if it was recorded before // and would cause `object`'s destructor to run twice if it was recorded before.
for i in 0..len { for i in 0..len {
destructors destructors
.push(DropType { drop_fn: drop_for_type::<T>, obj: start_ptr.add(i) as *mut u8 }); .push(DropType { drop_fn: drop_for_type::<T>, obj: start_ptr.add(i) as *mut u8 });