Generator objects can suspend

src/objects.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 6246 matching lines @@
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(SharedFunctionInfo);
 };
 
 
 class JSGeneratorObject: public JSObject {
  public:
   // [function]: The function corresponding to this generator object.
   DECL_ACCESSORS(function, JSFunction)
 
-  // [context]: The context of the suspended computation, or undefined.
-  DECL_ACCESSORS(context, Object)
+  // [context]: The context of the suspended computation.
+  DECL_ACCESSORS(context, Context)
 
   // [continuation]: Offset into code of continuation.
+  //
+  // A positive offset indicates a suspended generator.  The special
+  // kGeneratorExecuting and kGeneratorClosed values indicate that a generator
+  // cannot be resumed.
   inline int continuation();
   inline void set_continuation(int continuation);
 
   // [operands]: Saved operand stack.
   DECL_ACCESSORS(operand_stack, FixedArray)
 
   // Casting.
   static inline JSGeneratorObject* cast(Object* obj);
 
   // Dispatched behavior.
   DECLARE_PRINTER(JSGeneratorObject)
   DECLARE_VERIFIER(JSGeneratorObject)
 
+  // Magic sentinel values for the continuation.
+  static const int kGeneratorExecuting = -1;
+  static const int kGeneratorClosed = 0;
+
   // Layout description.
   static const int kFunctionOffset = JSObject::kHeaderSize;
   static const int kContextOffset = kFunctionOffset + kPointerSize;
   static const int kContinuationOffset = kContextOffset + kPointerSize;
   static const int kOperandStackOffset = kContinuationOffset + kPointerSize;
   static const int kSize = kOperandStackOffset + kPointerSize;
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(JSGeneratorObject);
 };
@@ skipping 3062 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_