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util.rs
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util.rs
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use std::cell::{Cell, UnsafeCell};
use std::marker::PhantomData;
use std::ptr::NonNull;
use crate::collect::Collect;
#[derive(Copy, Clone, Eq, PartialEq, Debug)]
pub(crate) enum GcColor {
White,
Gray,
Black,
}
pub(crate) struct GcBox<T: Collect + ?Sized> {
pub(crate) flags: GcFlags,
pub(crate) next: Cell<Option<NonNull<GcBox<Collect>>>>,
pub(crate) value: UnsafeCell<T>,
}
pub(crate) struct GcFlags(Cell<u8>);
impl GcFlags {
pub(crate) fn new() -> GcFlags {
GcFlags(Cell::new(0))
}
pub(crate) fn color(&self) -> GcColor {
match self.0.get() & 0x3 {
0x0 => GcColor::White,
0x1 => GcColor::Gray,
0x2 => GcColor::Black,
_ => unreachable!(),
}
}
pub(crate) fn set_color(&self, color: GcColor) {
self.0.set(
(self.0.get() & !0x3) | match color {
GcColor::White => 0x0,
GcColor::Gray => 0x1,
GcColor::Black => 0x2,
},
)
}
pub(crate) fn needs_trace(&self) -> bool {
self.0.get() | 0x4 != 0x0
}
pub(crate) fn set_needs_trace(&self, needs_trace: bool) {
self.0
.set((self.0.get() & !0x4) | if needs_trace { 0x4 } else { 0x0 });
}
}
// Phantom type that holds a lifetime and ensures that it is invariant.
pub(crate) type Invariant<'gc> = PhantomData<Cell<&'gc ()>>;