Struct AllocationOptionsHolder

struct AllocationOptionsHolder {
    alloc_options: RefCell<AllocationOptions>,
}

A wrapper for AllocatorContext to hold a AllocationOptions that can be modified by the same mutator thread.

All Allocator instances in Allocators share one AllocationOptions instance, and it will only be accessed by the mutator (via Mutator::allocators) or the GC worker (via GCWorker::copy) that owns it. Rust doesn’t like multiple mutable references pointing to a shared data structure. We cannot use [atomic::Atomic] because AllocationOptions has multiple fields. We wrap it in a RefCell to make it internally mutable.

Note: The allocation option is called every time Allocator::alloc_with_options is called. Because API functions should only be called on allocation slow paths, we believe that RefCell should be good enough for performance. If this is too slow, we may consider UnsafeCell. If that’s still too slow, we should consider changing the API to make the allocation options a persistent per-mutator value, and allow the VM binding set its value via a new API function.

Fields

alloc_options: RefCell<AllocationOptions>

Implementations

impl AllocationOptionsHolder

pub fn new(alloc_options: AllocationOptions) -> Self

pub fn set_alloc_options(&self, options: AllocationOptions)

pub fn clear_alloc_options(&self)

pub fn get_alloc_options(&self) -> AllocationOptions

Trait Implementations

impl Sync for AllocationOptionsHolder

Strictly speaking, AllocationOptionsHolder isn’t Sync. Two threads cannot set or clear the same AllocationOptionsHolder at the same time. However, both Mutator and GCWorker are Send, and both of which own Allocators and require its field Arc<AllocationContext> to be Send, which requires AllocationContext to be Sync, which requires AllocationOptionsHolder to be Sync. (Note that Arc<T> can be cloned and given to another thread, and Rust expects T to be Sync, too. But we never share AllocationContext between threads, but only between multiple Allocator instances within the same Allocators instance. Rust can’t figure this out.)