Edge trait

We make the representation of edges VM-specific.  The MMTk core only
depends on the abstract Edge trait.  This allows VM bindings to custom
the behaviour of loading/storing of edges, and support features like
compressed OOPs.

Author: wks

docs/tutorial/code/mygc_semispace/gc_work.rs

@@ -42,7 +42,7 @@ impl<VM:VMBinding> ProcessEdgesWork for MyGCProcessEdges<VM> {
     type VM = VM;
     type ScanObjectsWorkType = ScanObjects<Self>;
 
-    fn new(edges: Vec<Address>, roots: bool, mmtk: &'static MMTK<VM>) -> Self {
+    fn new(edges: Vec<EdgeOf<Self>>, roots: bool, mmtk: &'static MMTK<VM>) -> Self {
         let base = ProcessEdgesBase::new(edges, roots, mmtk);
         let plan = base.plan().downcast_ref::<MyGC<VM>>().unwrap();
         Self { base, plan }

src/mmtk.rs

@@ -2,6 +2,9 @@
 use crate::plan::Plan;
 use crate::policy::space::SFTMap;
 use crate::scheduler::GCWorkScheduler;
+
+#[cfg(feature = "extreme_assertions")]
+use crate::util::edge_logger::EdgeLogger;
 use crate::util::finalizable_processor::FinalizableProcessor;
 use crate::util::heap::layout::heap_layout::Mmapper;
 use crate::util::heap::layout::heap_layout::VMMap;
@@ -86,7 +89,9 @@ pub struct MMTK<VM: VMBinding> {
         Mutex<FinalizableProcessor<<VM::VMReferenceGlue as ReferenceGlue<VM>>::FinalizableType>>,
     pub(crate) scheduler: Arc<GCWorkScheduler<VM>>,
     #[cfg(feature = "sanity")]
-    pub(crate) sanity_checker: Mutex<SanityChecker>,
+    pub(crate) sanity_checker: Mutex<SanityChecker<VM::VMEdge>>,
+    #[cfg(feature = "extreme_assertions")]
+    pub(crate) edge_logger: EdgeLogger<VM::VMEdge>,
     inside_harness: AtomicBool,
 }
 
@@ -130,6 +135,8 @@ impl<VM: VMBinding> MMTK<VM> {
             #[cfg(feature = "sanity")]
             sanity_checker: Mutex::new(SanityChecker::new()),
             inside_harness: AtomicBool::new(false),
+            #[cfg(feature = "extreme_assertions")]
+            edge_logger: EdgeLogger::new(),
         }
     }
 

src/plan/generational/gc_work.rs

@@ -1,7 +1,8 @@
 use crate::plan::generational::global::Gen;
 use crate::policy::space::Space;
 use crate::scheduler::gc_work::*;
-use crate::util::{Address, ObjectReference};
+use crate::util::ObjectReference;
+use crate::vm::edge_shape::Edge;
 use crate::vm::*;
 use crate::MMTK;
 use std::ops::{Deref, DerefMut};
@@ -18,7 +19,7 @@ impl<VM: VMBinding> ProcessEdgesWork for GenNurseryProcessEdges<VM> {
     type VM = VM;
     type ScanObjectsWorkType = ScanObjects<Self>;
 
-    fn new(edges: Vec<Address>, roots: bool, mmtk: &'static MMTK<VM>) -> Self {
+    fn new(edges: Vec<EdgeOf<Self>>, roots: bool, mmtk: &'static MMTK<VM>) -> Self {
         let base = ProcessEdgesBase::new(edges, roots, mmtk);
         let gen = base.plan().generational();
         Self { gen, base }
@@ -34,11 +35,11 @@ impl<VM: VMBinding> ProcessEdgesWork for GenNurseryProcessEdges<VM> {
             .trace_object_nursery(&mut self.base.nodes, object, worker)
     }
     #[inline]
-    fn process_edge(&mut self, slot: Address) {
-        let object = unsafe { slot.load::<ObjectReference>() };
+    fn process_edge(&mut self, slot: EdgeOf<Self>) {
+        let object = slot.load();
         let new_object = self.trace_object(object);
         debug_assert!(!self.gen.nursery.in_space(new_object));
-        unsafe { slot.store(new_object) };
+        slot.store(new_object);
     }
 
     #[inline(always)]

src/plan/markcompact/gc_work.rs

@@ -43,7 +43,7 @@ impl<VM: VMBinding> GCWork<VM> for UpdateReferences<VM> {
         VM::VMScanning::prepare_for_roots_re_scanning();
         mmtk.plan.base().prepare_for_stack_scanning();
         #[cfg(feature = "extreme_assertions")]
-        crate::util::edge_logger::reset();
+        mmtk.edge_logger.reset();
 
         // TODO investigate why the following will create duplicate edges
         // scheduler.work_buckets[WorkBucketStage::RefForwarding]

src/plan/tracing.rs

@@ -3,9 +3,9 @@
 
 use std::mem;
 
-use crate::scheduler::gc_work::ProcessEdgesWork;
+use crate::scheduler::gc_work::{EdgeOf, ProcessEdgesWork};
 use crate::scheduler::{GCWorker, WorkBucketStage};
-use crate::util::{Address, ObjectReference};
+use crate::util::ObjectReference;
 use crate::vm::EdgeVisitor;
 
 /// This trait represents an object queue to enqueue objects during tracing.
@@ -63,7 +63,7 @@ impl ObjectQueue for VectorObjectQueue {
 
 /// A transitive closure visitor to collect all the edges of an object.
 pub struct ObjectsClosure<'a, E: ProcessEdgesWork> {
-    buffer: Vec<Address>,
+    buffer: Vec<EdgeOf<E>>,
     worker: &'a mut GCWorker<E::VM>,
 }
 
@@ -85,9 +85,9 @@ impl<'a, E: ProcessEdgesWork> ObjectsClosure<'a, E> {
     }
 }
 
-impl<'a, E: ProcessEdgesWork> EdgeVisitor for ObjectsClosure<'a, E> {
+impl<'a, E: ProcessEdgesWork> EdgeVisitor<EdgeOf<E>> for ObjectsClosure<'a, E> {
     #[inline(always)]
-    fn visit_edge(&mut self, slot: Address) {
+    fn visit_edge(&mut self, slot: EdgeOf<E>) {
         if self.buffer.is_empty() {
             self.buffer.reserve(E::CAPACITY);
         }

src/scheduler/gc_work.rs

@@ -5,6 +5,7 @@ use crate::plan::ObjectsClosure;
 use crate::plan::VectorObjectQueue;
 use crate::util::metadata::*;
 use crate::util::*;
+use crate::vm::edge_shape::Edge;
 use crate::vm::*;
 use crate::*;
 use std::marker::PhantomData;
@@ -227,7 +228,7 @@ impl<VM: VMBinding> GCWork<VM> for EndOfGC {
         #[cfg(feature = "extreme_assertions")]
         if crate::util::edge_logger::should_check_duplicate_edges(&*mmtk.plan) {
             // reset the logging info at the end of each GC
-            crate::util::edge_logger::reset();
+            mmtk.edge_logger.reset();
         }
 
         if <VM as VMBinding>::VMCollection::COORDINATOR_ONLY_STW {
@@ -331,7 +332,7 @@ impl<E: ProcessEdgesWork> GCWork<E::VM> for ScanVMSpecificRoots<E> {
 }
 
 pub struct ProcessEdgesBase<VM: VMBinding> {
-    pub edges: Vec<Address>,
+    pub edges: Vec<VM::VMEdge>,
     pub nodes: VectorObjectQueue,
     mmtk: &'static MMTK<VM>,
     // Use raw pointer for fast pointer dereferencing, instead of using `Option<&'static mut GCWorker<E::VM>>`.
@@ -345,12 +346,12 @@ unsafe impl<VM: VMBinding> Send for ProcessEdgesBase<VM> {}
 impl<VM: VMBinding> ProcessEdgesBase<VM> {
     // Requires an MMTk reference. Each plan-specific type that uses ProcessEdgesBase can get a static plan reference
     // at creation. This avoids overhead for dynamic dispatch or downcasting plan for each object traced.
-    pub fn new(edges: Vec<Address>, roots: bool, mmtk: &'static MMTK<VM>) -> Self {
+    pub fn new(edges: Vec<VM::VMEdge>, roots: bool, mmtk: &'static MMTK<VM>) -> Self {
         #[cfg(feature = "extreme_assertions")]
         if crate::util::edge_logger::should_check_duplicate_edges(&*mmtk.plan) {
             for edge in &edges {
                 // log edge, panic if already logged
-                crate::util::edge_logger::log_edge(*edge);
+                mmtk.edge_logger.log_edge(*edge);
             }
         }
         Self {
@@ -388,6 +389,9 @@ impl<VM: VMBinding> ProcessEdgesBase<VM> {
     }
 }
 
+/// A short-hand for `<E::VM as VMBinding>::VMEdge`.
+pub type EdgeOf<E> = <<E as ProcessEdgesWork>::VM as VMBinding>::VMEdge;
+
 /// Scan & update a list of object slots
 //
 // Note: be very careful when using this trait. process_node() will push objects
@@ -407,7 +411,8 @@ pub trait ProcessEdgesWork:
     const CAPACITY: usize = 4096;
     const OVERWRITE_REFERENCE: bool = true;
     const SCAN_OBJECTS_IMMEDIATELY: bool = true;
-    fn new(edges: Vec<Address>, roots: bool, mmtk: &'static MMTK<Self::VM>) -> Self;
+
+    fn new(edges: Vec<EdgeOf<Self>>, roots: bool, mmtk: &'static MMTK<Self::VM>) -> Self;
 
     /// Trace an MMTk object. The implementation should forward this call to the policy-specific
     /// `trace_object()` methods, depending on which space this object is in.
@@ -463,11 +468,11 @@ pub trait ProcessEdgesWork:
     }
 
     #[inline]
-    fn process_edge(&mut self, slot: Address) {
-        let object = unsafe { slot.load::<ObjectReference>() };
+    fn process_edge(&mut self, slot: EdgeOf<Self>) {
+        let object = slot.load();
         let new_object = self.trace_object(object);
         if Self::OVERWRITE_REFERENCE {
-            unsafe { slot.store(new_object) };
+            slot.store(new_object);
         }
     }
 
@@ -511,7 +516,7 @@ impl<VM: VMBinding> ProcessEdgesWork for SFTProcessEdges<VM> {
     type VM = VM;
     type ScanObjectsWorkType = ScanObjects<Self>;
 
-    fn new(edges: Vec<Address>, roots: bool, mmtk: &'static MMTK<VM>) -> Self {
+    fn new(edges: Vec<EdgeOf<Self>>, roots: bool, mmtk: &'static MMTK<VM>) -> Self {
         let base = ProcessEdgesBase::new(edges, roots, mmtk);
         Self { base }
     }
@@ -552,8 +557,8 @@ impl<E: ProcessEdgesWork> Clone for ProcessEdgesWorkRootsWorkFactory<E> {
     }
 }
 
-impl<E: ProcessEdgesWork> RootsWorkFactory for ProcessEdgesWorkRootsWorkFactory<E> {
-    fn create_process_edge_roots_work(&mut self, edges: Vec<Address>) {
+impl<E: ProcessEdgesWork> RootsWorkFactory<EdgeOf<E>> for ProcessEdgesWorkRootsWorkFactory<E> {
+    fn create_process_edge_roots_work(&mut self, edges: Vec<EdgeOf<E>>) {
         crate::memory_manager::add_work_packet(
             self.mmtk,
             WorkBucketStage::Closure,
@@ -827,7 +832,7 @@ impl<VM: VMBinding, P: PlanTraceObject<VM> + Plan<VM = VM>, const KIND: TraceKin
     type VM = VM;
     type ScanObjectsWorkType = PlanScanObjects<Self, P>;
 
-    fn new(edges: Vec<Address>, roots: bool, mmtk: &'static MMTK<VM>) -> Self {
+    fn new(edges: Vec<EdgeOf<Self>>, roots: bool, mmtk: &'static MMTK<VM>) -> Self {
         let base = ProcessEdgesBase::new(edges, roots, mmtk);
         let plan = base.plan().downcast_ref::<P>().unwrap();
         Self { plan, base }
@@ -854,11 +859,11 @@ impl<VM: VMBinding, P: PlanTraceObject<VM> + Plan<VM = VM>, const KIND: TraceKin
     }
 
     #[inline]
-    fn process_edge(&mut self, slot: Address) {
-        let object = unsafe { slot.load::<ObjectReference>() };
+    fn process_edge(&mut self, slot: EdgeOf<Self>) {
+        let object = slot.load();
         let new_object = self.trace_object(object);
         if P::may_move_objects::<KIND>() {
-            unsafe { slot.store(new_object) };
+            slot.store(new_object);
         }
     }
 }

src/util/edge_logger.rs

@@ -5,39 +5,53 @@
 //!
 
 use crate::plan::Plan;
-use crate::util::Address;
+use crate::vm::edge_shape::Edge;
 use crate::vm::VMBinding;
 use std::collections::HashSet;
 use std::sync::RwLock;
 
-lazy_static! {
+pub struct EdgeLogger<ES: Edge> {
     // A private hash-set to keep track of edges.
-    static ref EDGE_LOG: RwLock<HashSet<Address>> = RwLock::new(HashSet::new());
+    edge_log: RwLock<HashSet<ES>>,
+}
+
+unsafe impl<ES: Edge> Sync for EdgeLogger<ES> {}
+
+impl<ES: Edge> EdgeLogger<ES> {
+    pub fn new() -> Self {
+        Self {
+            edge_log: Default::default(),
+        }
+    }
+
+    /// Logs an edge.
+    /// Panics if the edge was already logged.
+    ///
+    /// # Arguments
+    ///
+    /// * `edge` - The edge to log.
+    ///
+    pub fn log_edge(&self, edge: ES) {
+        trace!("log_edge({:?})", edge);
+        let mut edge_log = self.edge_log.write().unwrap();
+        assert!(
+            edge_log.insert(edge),
+            "duplicate edge ({:?}) detected",
+            edge
+        );
+    }
+
+    /// Reset the edge logger by clearing the hash-set of edges.
+    /// This function is called at the end of each GC iteration.
+    ///
+    pub fn reset(&self) {
+        let mut edge_log = self.edge_log.write().unwrap();
+        edge_log.clear();
+    }
 }
 
 /// Whether we should check duplicate edges. This depends on the actual plan.
 pub fn should_check_duplicate_edges<VM: VMBinding>(plan: &dyn Plan<VM = VM>) -> bool {
     // If a plan allows tracing duplicate edges, we should not run this check.
     !plan.constraints().may_trace_duplicate_edges
 }
-
-/// Logs an edge.
-/// Panics if the edge was already logged.
-///
-/// # Arguments
-///
-/// * `edge` - The edge to log.
-///
-pub fn log_edge(edge: Address) {
-    trace!("log_edge({})", edge);
-    let mut edge_log = EDGE_LOG.write().unwrap();
-    assert!(edge_log.insert(edge), "duplicate edge ({}) detected", edge);
-}
-
-/// Reset the edge logger by clearing the hash-set of edges.
-/// This function is called at the end of each GC iteration.
-///
-pub fn reset() {
-    let mut edge_log = EDGE_LOG.write().unwrap();
-    edge_log.clear();
-}

src/util/sanity/sanity_checker.rs

@@ -1,6 +1,7 @@
 use crate::plan::Plan;
 use crate::scheduler::gc_work::*;
-use crate::util::{Address, ObjectReference};
+use crate::util::ObjectReference;
+use crate::vm::edge_shape::Edge;
 use crate::vm::*;
 use crate::MMTK;
 use crate::{scheduler::*, ObjectQueue};
@@ -9,20 +10,20 @@ use std::ops::{Deref, DerefMut};
 use std::sync::atomic::Ordering;
 
 #[allow(dead_code)]
-pub struct SanityChecker {
+pub struct SanityChecker<ES: Edge> {
     /// Visited objects
     refs: HashSet<ObjectReference>,
     /// Cached root edges for sanity root scanning
-    roots: Vec<Vec<Address>>,
+    roots: Vec<Vec<ES>>,
 }
 
-impl Default for SanityChecker {
+impl<ES: Edge> Default for SanityChecker<ES> {
     fn default() -> Self {
         Self::new()
     }
 }
 
-impl SanityChecker {
+impl<ES: Edge> SanityChecker<ES> {
     pub fn new() -> Self {
         Self {
             refs: HashSet::new(),
@@ -31,7 +32,7 @@ impl SanityChecker {
     }
 
     /// Cache a list of root edges to the sanity checker.
-    pub fn add_roots(&mut self, roots: Vec<Address>) {
+    pub fn add_roots(&mut self, roots: Vec<ES>) {
         self.roots.push(roots)
     }
 
@@ -164,7 +165,7 @@ impl<VM: VMBinding> ProcessEdgesWork for SanityGCProcessEdges<VM> {
     type ScanObjectsWorkType = ScanObjects<Self>;
 
     const OVERWRITE_REFERENCE: bool = false;
-    fn new(edges: Vec<Address>, roots: bool, mmtk: &'static MMTK<VM>) -> Self {
+    fn new(edges: Vec<EdgeOf<Self>>, roots: bool, mmtk: &'static MMTK<VM>) -> Self {
         Self {
             base: ProcessEdgesBase::new(edges, roots, mmtk),
             // ..Default::default()