reduce dupliaction between mark_sweep and mark_sweep_arena2

Author: shruti2522

oscars/src/alloc/arena2/alloc.rs

@@ -133,6 +133,15 @@ impl<'arena> ErasedArenaPointer<'arena> {
         self.0.as_ptr()
     }
 
+    /// Extend the lifetime of this erased arena pointer to 'static
+    ///
+    /// SAFETY:
+    ///
+    /// safe because the gc collector owns the arena and keeps it alive
+    pub(crate) unsafe fn extend_lifetime(self) -> ErasedArenaPointer<'static> {
+        ErasedArenaPointer(self.0, PhantomData)
+    }
+
     /// Returns an [`ArenaPointer`] for the current [`ErasedArenaPointer`]
     ///
     /// # Safety
@@ -178,6 +187,15 @@ impl<'arena, T> ArenaPointer<'arena, T> {
     pub fn to_erased(self) -> ErasedArenaPointer<'arena> {
         self.0
     }
+
+    /// extend the lifetime of this arena pointer to 'static
+    ///
+    /// SAFETY:
+    ///
+    /// safe because the gc collector owns the arena and keeps it alive
+    pub(crate) unsafe fn extend_lifetime(self) -> ArenaPointer<'static, T> {
+        ArenaPointer(unsafe { self.0.extend_lifetime() }, PhantomData)
+    }
 }
 
 const FULL_MASK: u8 = 0b0100_0000;

oscars/src/collectors/mark_sweep/cell.rs

@@ -171,6 +171,14 @@ impl<T: ?Sized> GcRefCell<T> {
         }
     }
 
+    // returns a raw pointer to the inner value or `None` if currently mutably borrowed
+    pub(crate) fn get_raw(&self) -> Option<*mut T> {
+        match self.borrow.get().borrowed() {
+            BorrowState::Writing => None,
+            _ => Some(self.cell.get()),
+        }
+    }
+
     /// Mutably borrows the wrapped value, returning an error if the value is currently borrowed.
     ///
     /// The borrow lasts until the returned `GcCellRefMut` exits scope.

oscars/src/collectors/mark_sweep/internals/gc_box.rs

@@ -45,10 +45,10 @@ impl<T: Trace + Finalize + ?Sized> WeakGcBox<T> {
 
     pub(crate) fn erased_inner_ptr(&self) -> NonNull<GcBox<NonTraceable>> {
         use crate::alloc::arena3::ArenaHeapItem;
-        // SAFETY: `ArenaHeapItem` is `repr(transparent)`, use addr_of_mut! to avoid
+        // SAFETY: `ArenaHeapItem` is `repr(transparent)`, use `&raw mut` to avoid
         // creating a &mut reference during trace
         let raw: *mut ArenaHeapItem<GcBox<NonTraceable>> = self.as_heap_ptr().as_ptr();
-        unsafe { NonNull::new_unchecked(core::ptr::addr_of_mut!((*raw).0)) }
+        unsafe { NonNull::new_unchecked(&raw mut (*raw).0) }
     }
 
     pub(crate) fn as_heap_ptr(&self) -> NonNull<ArenaHeapItem<GcBox<NonTraceable>>> {

oscars/src/collectors/mark_sweep/internals/mod.rs

@@ -4,6 +4,7 @@ mod gc_header;
 mod vtable;
 
 pub(crate) use ephemeron::Ephemeron;
+pub(crate) use gc_header::{GcHeader, HeaderColor, HeaderFlags};
 pub(crate) use vtable::{DropFn, TraceFn, VTable, vtable_of};
 
 pub use self::gc_box::{GcBox, NonTraceable, WeakGcBox};

oscars/src/collectors/mark_sweep/pointers/gc.rs

@@ -44,12 +44,12 @@ impl<T: Trace> Gc<T> {
 
 impl<T: Trace + ?Sized> Gc<T> {
     pub(crate) fn as_sized_inner_ptr(&self) -> NonNull<GcBox<NonTraceable>> {
-        // SAFETY: use `addr_of_mut!` to get a raw pointer without creating
+        // SAFETY: use `&raw mut` to get a raw pointer without creating
         // a `&mut` reference, avoiding Stacked Borrows UB during GC tracing
         let raw: *mut ArenaHeapItem<GcBox<NonTraceable>> = self.as_heap_ptr().as_ptr();
         // SAFETY: `raw` is non-null because it comes from `as_heap_ptr()`
         // `ArenaHeapItem` is `#[repr(transparent)]` so it shares the same address as field 0
-        unsafe { NonNull::new_unchecked(core::ptr::addr_of_mut!((*raw).0)) }
+        unsafe { NonNull::new_unchecked(&raw mut (*raw).0) }
     }
 
     pub(crate) fn as_heap_ptr(&self) -> NonNull<ArenaHeapItem<GcBox<NonTraceable>>> {