Struct RefCountedArena 

pub struct RefCountedArena {
    state: RefCell<ArenaState>,
    _nosend: PhantomData<Rc<()>>,
}

A reference-counted arena for GC protection, backed by a BTreeMap.

This provides an alternative to R’s PROTECT stack that:

• Uses reference counting for each SEXP
• Allows releasing protections in any order
• Has no stack size limit (uses heap allocation)

Fields

state: RefCell<ArenaState>

_nosend: PhantomData<Rc<()>>

Implementations

impl RefCountedArena

pub unsafe fn new() -> Self

Create a new arena with default capacity (16 slots).

For workloads protecting many distinct SEXPs (e.g., ppsize-scale loops), prefer with_capacity to avoid backing VECSXP growth and map rehashing during operation.

Safety

Must be called from the R main thread.

pub unsafe fn with_capacity(capacity: usize) -> Self

Create a new arena with specific initial capacity.

Pre-sizing the arena avoids growth of the backing VECSXP and rehashing of the internal map. Use this when the expected number of distinct protected values is known or can be estimated.

Safety

Must be called from the R main thread.

pub unsafe fn protect(&self, x: SEXP) -> SEXP

Protect a SEXP, incrementing its reference count.

Safety

Must be called from the R main thread.

pub unsafe fn unprotect(&self, x: SEXP)

Unprotect a SEXP, decrementing its reference count.

Safety

Must be called from the R main thread.

Panics

Panics if x was not protected by this arena.

pub unsafe fn try_unprotect(&self, x: SEXP) -> bool

Try to unprotect a SEXP, returning true if it was protected.

Safety

Must be called from the R main thread.

pub fn is_protected(&self, x: SEXP) -> bool

Check if a SEXP is currently protected by this arena.

pub fn ref_count(&self, x: SEXP) -> usize

Get the reference count for a SEXP (0 if not protected).

pub fn len(&self) -> usize

Get the number of distinct SEXPs currently protected.

pub fn is_empty(&self) -> bool

Check if the arena is empty.

pub fn capacity(&self) -> usize

Get the current capacity.

pub unsafe fn clear(&self)

Clear all protections.

Safety

Must be called from the R main thread.

pub unsafe fn guard(&self, x: SEXP) -> ArenaGuard<'_>

Protect a SEXP and return an RAII guard.

Safety

Must be called from the R main thread.

Trait Implementations

impl Default for RefCountedArena

fn default() -> Self

Returns the “default value” for a type.

impl Drop for RefCountedArena

fn drop(&mut self)

Executes the destructor for this type.

fn pin_drop(self: Pin<&mut Self>)

🔬This is a nightly-only experimental API. (pin_ergonomics)

Execute the destructor for this type, but different to Drop::drop, it requires self to be pinned.

Layout

Note: Most layout information is completely unstable and may even differ between compilations. The only exception is types with certain repr(...) attributes. Please see the Rust Reference's “Type Layout” chapter for details on type layout guarantees.

Size: 88 bytes