Struct HeapObjectHeader

#[repr(C)]
pub struct HeapObjectHeader { /* private fields */ }

HeapObjectHeader contains meta data per object and is prepended to each object.

 +-----------------+------+------------------------------------------+
 | name            | bits |                                          |
 +-----------------+------+------------------------------------------+
 | padding         |   32 | Only present on 64-bit platform.         |
 +-----------------+------+------------------------------------------+
 | GCInfoIndex     |   14 |                                          |
 | unused          |    1 |                                          |
 | unused          |    1 | In construction encoded as |false|.      |
 +-----------------+------+------------------------------------------+
 | size            |   13 | 17 bits because allocations are aligned. |
 | unused          |    1 |                                          |
 | cell state      |    2 |                                          |
 +-----------------+------+------------------------------------------+

Notes:

• See GCInfoTable for constraints on GCInfoIndex.
• size for regular objects is encoded with 14 bits but can actually represent sizes up to |kBlinkPageSize| (2^17) because allocations are always 8 byte aligned (see kAllocationGranularity).
• size for large objects is encoded as 0. The size of a large object is stored in PreciseAllocation::cell_size.

Implementations

impl HeapObjectHeader

pub fn is_precise(&self) -> bool

Check if allocation is “precise”. Precise allocations are large allocations that have larger header stored behind HeapObjectHeader.

pub fn set_free(&mut self)

Set this header as free.

pub unsafe fn from_object(obj: *const u8) -> *mut HeapObjectHeader

Creates heap object header from object pointer. It must be valid pointer.

pub fn payload(&self) -> *const u8

Returns payload of this heap object header.

pub fn get_gc_info_index(&self) -> GCInfoIndex

Returns GCInfoIndex of allocated object.

pub fn get_size(self) -> usize

Returns size of an object. If it is allocated in large object space 0 is returned.

pub fn set_size(&mut self, size: usize)

pub fn is_grey(self) -> bool

pub fn is_white(self) -> bool

pub fn is_black(self) -> bool

pub fn set_state(&mut self, current: CellState, new: CellState) -> bool

pub fn force_set_state(&mut self, state: CellState)

pub fn set_gc_info(&mut self, index: GCInfoIndex)

pub fn is_free(&self) -> bool

pub fn state(&self) -> CellState

Trait Implementations

impl Clone for HeapObjectHeader

fn clone(&self) -> HeapObjectHeader

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for HeapObjectHeader