After moving unreachable weak global handles only process harmony collections

src/heap/mark-compact.cc

Index: src/heap/mark-compact.cc
diff --git a/src/heap/mark-compact.cc b/src/heap/mark-compact.cc
index 847bdac1263db4c9de13aa624e934bb5edcbcdba..c98b433144d192dc2b6056c789f409eceb29b7e7 100644
--- a/src/heap/mark-compact.cc
+++ b/src/heap/mark-compact.cc
@@ -2078,13 +2078,16 @@ void MarkCompactCollector::ProcessMarkingDeque() {
 
 // Mark all objects reachable (transitively) from objects on the marking
 // stack including references only considered in the atomic marking pause.
-void MarkCompactCollector::ProcessEphemeralMarking(ObjectVisitor* visitor) {
+void MarkCompactCollector::ProcessEphemeralMarking(
+    ObjectVisitor* visitor, bool only_process_harmony_weak_collections) {
   bool work_to_do = true;
   DCHECK(marking_deque_.IsEmpty());
   while (work_to_do) {
-    isolate()->global_handles()->IterateObjectGroups(
-        visitor, &IsUnmarkedHeapObjectWithHeap);
-    MarkImplicitRefGroups();
+    if (!only_process_harmony_weak_collections) {
+      isolate()->global_handles()->IterateObjectGroups(
+          visitor, &IsUnmarkedHeapObjectWithHeap);
+      MarkImplicitRefGroups();
+    }
     ProcessWeakCollections();
     work_to_do = !marking_deque_.IsEmpty();
     ProcessMarkingDeque();
@@ -2196,26 +2199,24 @@ void MarkCompactCollector::MarkLiveObjects() {
   // The objects reachable from the roots are marked, yet unreachable
   // objects are unmarked.  Mark objects reachable due to host
   // application specific logic or through Harmony weak maps.
-  ProcessEphemeralMarking(&root_visitor);
+  ProcessEphemeralMarking(&root_visitor, false);
 
   // The objects reachable from the roots, weak maps or object groups
-  // are marked, yet unreachable objects are unmarked.  Mark objects
+  // are marked. Objects pointed to only by weak global handles cannot be
+  // immediately reclaimed. Instead, we have to mark them as pending and mark
+  // objects reachable from them.
   // reachable only from weak global handles.

[Michael Starzinger, 2014/12/02 10:22:42]

nit: This dangling part of the sentence looks like a left-over, can we drop it?

[jochen (gone - plz use gerrit), 2014/12/02 10:37:18]

done

   //
   // First we identify nonlive weak handles and mark them as pending
   // destruction.
   heap()->isolate()->global_handles()->IdentifyWeakHandles(
       &IsUnmarkedHeapObject);
-  // Then we mark the objects and process the transitive closure.
+  // Then we mark the objects.
   heap()->isolate()->global_handles()->IterateWeakRoots(&root_visitor);
-  while (marking_deque_.overflowed()) {
-    RefillMarkingDeque();
-    EmptyMarkingDeque();
-  }
 
-  // Repeat host application specific and Harmony weak maps marking to
-  // mark unmarked objects reachable from the weak roots.
-  ProcessEphemeralMarking(&root_visitor);
+  // Repeat Harmony weak maps marking to mark unmarked objects reachable from
+  // the weak roots we just marked as pending destruction.

[Michael Starzinger, 2014/12/02 10:22:42]

This requires more explanation as to why we can skip other embedder-specific
marking here, e.g. all objects groups have been fully processed and no weakly
reachable node can discover new object groups.

[jochen (gone - plz use gerrit), 2014/12/02 10:37:18]

done

+  ProcessEphemeralMarking(&root_visitor, true);
 
   AfterMarking();