Parallel marking.

runtime/vm/raw_object.h

Index: runtime/vm/raw_object.h
diff --git a/runtime/vm/raw_object.h b/runtime/vm/raw_object.h
index cef2223f7a70706d4c2ee0ce8684a6ef12f7864f..5ffc2ff661a66b35dd32ee52372cb29d6ee8beb2 100644
--- a/runtime/vm/raw_object.h
+++ b/runtime/vm/raw_object.h
@@ -344,6 +344,11 @@ class RawObject {
     ASSERT(IsMarked());
     UpdateTagBit<MarkBit>(false);
   }
+  // Returns false if the bit was already set.
+  // TODO(koda): Add "must use result" annotation here, after we add support.
+  bool TryAcquireMarkBit() {
+    return TryAcquireTagBit<MarkBit>();
+  }
 
   // Support for GC watched bit.
   // TODO(iposva): Get rid of this.
@@ -397,6 +402,11 @@ class RawObject {
     uword tags = ptr()->tags_;
     ptr()->tags_ = RememberedBit::update(false, tags);
   }
+  // Returns false if the bit was already set.
+  // TODO(koda): Add "must use result" annotation here, after we add support.
+  bool TryAcquireRememberedBit() {
+    return TryAcquireTagBit<RememberedBit>();
+  }
 
   bool IsDartInstance() {
     return (!IsHeapObject() || (GetClassId() >= kInstanceCid));
@@ -514,6 +524,20 @@ class RawObject {
     } while (tags != old_tags);
   }
 
+  template<class TagBitField>
+  bool TryAcquireTagBit() {
+    uword tags = ptr()->tags_;
+    uword old_tags;
+    do {
+      old_tags = tags;
+      if (TagBitField::decode(tags)) return false;
+      uword new_tags = TagBitField::update(true, old_tags);
+      tags = AtomicOperations::CompareAndSwapWord(
+          &ptr()->tags_, old_tags, new_tags);
+    } while (tags != old_tags);
+    return true;
+  }
+
   // All writes to heap objects should ultimately pass through one of the
   // methods below or their counterparts in Object, to ensure that the
   // write barrier is correctly applied.
@@ -574,7 +598,7 @@ class RawObject {
   friend class Heap;
   friend class HeapMapAsJSONVisitor;
   friend class ClassStatsVisitor;
-  friend class MarkingVisitor;
+  template<bool> friend class MarkingVisitorBase;
   friend class Mint;
   friend class Object;
   friend class OneByteString;  // StoreSmi
@@ -1047,7 +1071,7 @@ class RawCode : public RawObject {
   const int32_t* data() const { OPEN_ARRAY_START(int32_t, int32_t); }
 
   friend class Function;
-  friend class MarkingVisitor;
+  template<bool> friend class MarkingVisitorBase;
   friend class SkippedCodeFunctions;
   friend class StackFrame;
 };
@@ -1100,7 +1124,7 @@ class RawInstructions : public RawObject {
   friend class RawFunction;
   friend class Code;
   friend class StackFrame;
-  friend class MarkingVisitor;
+  template<bool> friend class MarkingVisitorBase;
   friend class SkippedCodeFunctions;
   friend class Function;
   friend class InstructionsReader;
@@ -1977,7 +2001,7 @@ class RawWeakProperty : public RawInstance {
 
   friend class DelaySet;
   friend class GCMarker;
-  friend class MarkingVisitor;
+  template<bool> friend class MarkingVisitorBase;
   friend class Scavenger;
   friend class ScavengerVisitor;
 };