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
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@@ 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.
+  //
+  // The sign of the offset corresponds to the generator state: positive is
+  // "suspended", negative is "executing" and 0 is "closed".
   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)
 

[Michael Starzinger, 2013/04/19 13:15:56]

Can we add constants here for the magic sentinel values used in the
continuation? I assume that you just need two values (i.e. one for "executing"
and one for "closed") right? I was thinking along the lines of ...

static const int kGeneratorExecuting = -1;
static const int kGeneratorClosed = 0;

This would allow us to track statically where those magic values are set and
used. Also I don't think we need the full range of negative numbers.

[wingo, 2013/04/19 13:57:41]

Good point; done.

   // 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_