mmtk/policy/

immortalspace.rs

use atomic::Ordering;

use crate::policy::sft::SFT;
use crate::policy::space::{CommonSpace, Space};
use crate::util::address::Address;
use crate::util::heap::{MonotonePageResource, PageResource};
use crate::util::metadata::mark_bit::MarkState;

use crate::util::object_enum::{self, ObjectEnumerator};
use crate::util::{metadata, ObjectReference};

use crate::plan::{ObjectQueue, VectorObjectQueue};

use crate::policy::sft::GCWorkerMutRef;
use crate::vm::{ObjectModel, VMBinding};

/// This type implements a simple immortal collection
/// policy. Under this policy all that is required is for the
/// "collector" to propagate marks in a liveness trace.  It does not
/// actually collect.
pub struct ImmortalSpace<VM: VMBinding> {
    mark_state: MarkState,
    common: CommonSpace<VM>,
    pr: MonotonePageResource<VM>,
}

impl<VM: VMBinding> SFT for ImmortalSpace<VM> {
    fn name(&self) -> &'static str {
        self.get_name()
    }
    fn is_live(&self, _object: ObjectReference) -> bool {
        true
    }
    fn is_reachable(&self, object: ObjectReference) -> bool {
        self.mark_state.is_marked::<VM>(object)
    }
    #[cfg(feature = "object_pinning")]
    fn pin_object(&self, _object: ObjectReference) -> bool {
        false
    }
    #[cfg(feature = "object_pinning")]
    fn unpin_object(&self, _object: ObjectReference) -> bool {
        false
    }
    #[cfg(feature = "object_pinning")]
    fn is_object_pinned(&self, _object: ObjectReference) -> bool {
        true
    }
    fn is_movable(&self) -> bool {
        false
    }
    #[cfg(feature = "sanity")]
    fn is_sane(&self) -> bool {
        true
    }
    fn initialize_object_metadata(&self, object: ObjectReference, _alloc: bool) {
        self.mark_state
            .on_object_metadata_initialization::<VM>(object);
        if self.common.unlog_allocated_object {
            VM::VMObjectModel::GLOBAL_LOG_BIT_SPEC.mark_as_unlogged::<VM>(object, Ordering::SeqCst);
        }
        #[cfg(feature = "vo_bit")]
        crate::util::metadata::vo_bit::set_vo_bit(object);
    }
    #[cfg(feature = "is_mmtk_object")]
    fn is_mmtk_object(&self, addr: Address) -> Option<ObjectReference> {
        crate::util::metadata::vo_bit::is_vo_bit_set_for_addr(addr)
    }
    #[cfg(feature = "is_mmtk_object")]
    fn find_object_from_internal_pointer(
        &self,
        ptr: Address,
        max_search_bytes: usize,
    ) -> Option<ObjectReference> {
        crate::util::metadata::vo_bit::find_object_from_internal_pointer::<VM>(
            ptr,
            max_search_bytes,
        )
    }
    fn sft_trace_object(
        &self,
        queue: &mut VectorObjectQueue,
        object: ObjectReference,
        _worker: GCWorkerMutRef,
    ) -> ObjectReference {
        self.trace_object(queue, object)
    }
}

impl<VM: VMBinding> Space<VM> for ImmortalSpace<VM> {
    fn as_space(&self) -> &dyn Space<VM> {
        self
    }
    fn as_sft(&self) -> &(dyn SFT + Sync + 'static) {
        self
    }
    fn get_page_resource(&self) -> &dyn PageResource<VM> {
        &self.pr
    }
    fn maybe_get_page_resource_mut(&mut self) -> Option<&mut dyn PageResource<VM>> {
        Some(&mut self.pr)
    }
    fn common(&self) -> &CommonSpace<VM> {
        &self.common
    }

    fn initialize_sft(&self, sft_map: &mut dyn crate::policy::sft_map::SFTMap) {
        self.common().initialize_sft(self.as_sft(), sft_map)
    }

    fn release_multiple_pages(&mut self, _start: Address) {
        panic!("immortalspace only releases pages enmasse")
    }

    fn enumerate_objects(&self, enumerator: &mut dyn ObjectEnumerator) {
        object_enum::enumerate_blocks_from_monotonic_page_resource(enumerator, &self.pr);
    }

    fn clear_side_log_bits(&self) {
        let log_bit = VM::VMObjectModel::GLOBAL_LOG_BIT_SPEC.extract_side_spec();
        for (start, size) in self.pr.iterate_allocated_regions() {
            log_bit.bzero_metadata(start, size);
        }
    }

    fn set_side_log_bits(&self) {
        let log_bit = VM::VMObjectModel::GLOBAL_LOG_BIT_SPEC.extract_side_spec();
        for (start, size) in self.pr.iterate_allocated_regions() {
            log_bit.bset_metadata(start, size);
        }
    }
}

use crate::scheduler::GCWorker;
use crate::util::copy::CopySemantics;

impl<VM: VMBinding> crate::policy::gc_work::PolicyTraceObject<VM> for ImmortalSpace<VM> {
    fn trace_object<Q: ObjectQueue, const KIND: crate::policy::gc_work::TraceKind>(
        &self,
        queue: &mut Q,
        object: ObjectReference,
        _copy: Option<CopySemantics>,
        _worker: &mut GCWorker<VM>,
    ) -> ObjectReference {
        self.trace_object(queue, object)
    }
    fn may_move_objects<const KIND: crate::policy::gc_work::TraceKind>() -> bool {
        false
    }
}

impl<VM: VMBinding> ImmortalSpace<VM> {
    pub fn new(args: crate::policy::space::PlanCreateSpaceArgs<VM>) -> Self {
        let vm_map = args.vm_map;
        let is_discontiguous = args.vmrequest.is_discontiguous();
        let common = CommonSpace::new(args.into_policy_args(
            false,
            true,
            metadata::extract_side_metadata(&[*VM::VMObjectModel::LOCAL_MARK_BIT_SPEC]),
        ));
        ImmortalSpace {
            mark_state: MarkState::new(),
            pr: if is_discontiguous {
                MonotonePageResource::new_discontiguous(vm_map)
            } else {
                MonotonePageResource::new_contiguous(common.start, common.extent, vm_map)
            },
            common,
        }
    }

    pub fn prepare(&mut self) {
        self.mark_state.on_global_prepare::<VM>();
        // Reset the mark bit for the allocated regions.
        for (addr, size) in self.pr.iterate_allocated_regions() {
            debug!(
                "{:?}: reset mark bit from {} to {}",
                self.name(),
                addr,
                addr + size
            );
            self.mark_state.on_block_reset::<VM>(addr, size);
        }
    }

    pub fn release(&mut self) {
        self.mark_state.on_global_release::<VM>();
    }

    pub fn trace_object<Q: ObjectQueue>(
        &self,
        queue: &mut Q,
        object: ObjectReference,
    ) -> ObjectReference {
        #[cfg(feature = "vo_bit")]
        debug_assert!(
            crate::util::metadata::vo_bit::is_vo_bit_set(object),
            "{:x}: VO bit not set",
            object
        );
        if self.mark_state.test_and_mark::<VM>(object) {
            // Set the unlog bit if required
            if self.common.unlog_traced_object {
                VM::VMObjectModel::GLOBAL_LOG_BIT_SPEC.store_atomic::<VM, u8>(
                    object,
                    1,
                    None,
                    Ordering::SeqCst,
                );
            }
            queue.enqueue(object);
        }
        object
    }
}