Struct mozjs::jsapi::JS::TenuredHeap
source · #[repr(C)]pub struct TenuredHeap {
pub bits: usize,
}
Expand description
The TenuredHeap
-
Pointers which are statically known to only reference “tenured” objects can avoid the extra overhead of SpiderMonkey’s write barriers.
-
Objects in the “tenured” heap have stronger alignment restrictions than those in the “nursery”, so it is possible to store flags in the lower bits of pointers known to be tenured. TenuredHeap wraps a normal tagged pointer with a nice API for accessing the flag bits and adds various assertions to ensure that it is not mis-used.
GC things are said to be “tenured” when they are located in the long-lived heap: e.g. they have gained tenure as an object by surviving past at least one GC. For performance, SpiderMonkey allocates some things which are known to normally be long lived directly into the tenured generation; for example, global objects. Additionally, SpiderMonkey does not visit individual objects when deleting non-tenured objects, so object with finalizers are also always tenured; for instance, this includes most DOM objects.
The considerations to keep in mind when using a TenuredHeap
- It is invalid for a TenuredHeap
to refer to a non-tenured thing. - It is however valid for a Heap
to refer to a tenured thing. - It is not possible to store flag bits in a Heap
.
Fields§
§bits: usize
Trait Implementations§
source§impl Clone for TenuredHeap
impl Clone for TenuredHeap
source§fn clone(&self) -> TenuredHeap
fn clone(&self) -> TenuredHeap
1.0.0 · source§fn clone_from(&mut self, source: &Self)
fn clone_from(&mut self, source: &Self)
source
. Read moresource§impl Debug for TenuredHeap
impl Debug for TenuredHeap
source§impl PartialEq<TenuredHeap> for TenuredHeap
impl PartialEq<TenuredHeap> for TenuredHeap
source§fn eq(&self, other: &TenuredHeap) -> bool
fn eq(&self, other: &TenuredHeap) -> bool
self
and other
values to be equal, and is used
by ==
.