Link all global contexts into a weak list.

src/contexts.h

Index: src/contexts.h
diff --git a/src/contexts.h b/src/contexts.h
index 78dda6a64a6d73df78be031acb4b7f50148b05e4..e55c64c59f0bd3a487d0b95ae52101f57dd6b933 100644
--- a/src/contexts.h
+++ b/src/contexts.h
@@ -225,7 +225,14 @@ class Context: public FixedArray {
     OUT_OF_MEMORY_INDEX,
     MAP_CACHE_INDEX,
     CONTEXT_DATA_INDEX,
-    GLOBAL_CONTEXT_SLOTS
+
+    // Properties from here get weak reference treatment by the GC.
+    NEXT_CONTEXT_LINK,  // Weak.
+
+    // Total number of slots.
+    GLOBAL_CONTEXT_SLOTS,
+
+    FIRST_WEAK_SLOT = NEXT_CONTEXT_LINK
   };
 
   // Direct slot access.
@@ -333,6 +340,17 @@ class Context: public FixedArray {
     return kHeaderSize + index * kPointerSize - kHeapObjectTag;
   }
 
+  static const int kSize = kHeaderSize + GLOBAL_CONTEXT_SLOTS * kPointerSize;
+
+  // GC support.

[Søren Thygesen Gjesse, 2010/10/18 14:31:10]

Maybe extend the comment to say that during scavenge all slots are strong and
only during mark sweep/mark compact does the weak slots receive weak treatment.

+  typedef FixedBodyDescriptor<
+      kHeaderSize, kSize, kSize> ScavengeBodyDescriptor;
+
+  typedef FixedBodyDescriptor<
+      kHeaderSize,
+      kHeaderSize + FIRST_WEAK_SLOT * kPointerSize,
+      kSize> MarkCompactBodyDescriptor;
+
  private:
   // Unchecked access to the slots.
   Object* unchecked_previous() { return get(PREVIOUS_INDEX); }