Added ability to lock strings to prevent their representation or encoding from changing.

src/handles.h

 // Copyright 2011 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 145 matching lines @@
   // Zaps the handles in the half-open interval [start, end).
   static void ZapRange(internal::Object** start, internal::Object** end);
 
   friend class v8::HandleScope;
   friend class v8::ImplementationUtilities;
 };
 
 
 // ----------------------------------------------------------------------------
 // Handle operations.
-// They might invoke garbage collection. The result is an handle to
-// an object of expected type, or the handle is an error if running out
-// of space or encountering an internal error.
+// They might invoke garbage collection. The result is an handle to an
+// object of expected type, or the handle is a null handle if encountering
+// an internal error. Will not return a null handle due to out-of-memory
+// unless otherwise stated, but will instead try to do GC and die fatally
+// if that doesn't help.
 
 void NormalizeProperties(Handle<JSObject> object,
                          PropertyNormalizationMode mode,
                          int expected_additional_properties);
 Handle<NumberDictionary> NormalizeElements(Handle<JSObject> object);
 void TransformToFastProperties(Handle<JSObject> object,
                                int unused_property_fields);
 MUST_USE_RESULT Handle<NumberDictionary> NumberDictionarySet(
     Handle<NumberDictionary> dictionary,
     uint32_t index,
     Handle<Object> value,
     PropertyDetails details);
 
 // Flattens a string.
 void FlattenString(Handle<String> str);
 
 // Flattens a string and returns the underlying external or sequential
-// string.
+// string. Never returns a null handle.
 Handle<String> FlattenGetString(Handle<String> str);
 
 Handle<Object> SetProperty(Handle<JSReceiver> object,
                            Handle<String> key,
                            Handle<Object> value,
                            PropertyAttributes attributes,
                            StrictModeFlag strict_mode);
 
 Handle<Object> SetProperty(Handle<Object> object,
                            Handle<Object> key,
@@ skipping 175 matching lines @@
   NoHandleAllocation() {}
   ~NoHandleAllocation() {}
 #else
   inline NoHandleAllocation();
   inline ~NoHandleAllocation();
  private:
   int level_;
 #endif
 };
 
+
+// Prevents a (non-cons, non-slice) string from having its representation
+// changed. This is just a Handle based wrapper around Heap::LockString.
+// Use Heap::UnlockString to unlock (that one can't cause allocation, so
+// it doesn't need a Handle wrapper).
+void LockString(Handle<String> string);
+
+// Scoped lock on a string.
+class StringLock {
+ public:
+  explicit StringLock(Handle<String> string);
+  ~StringLock();
+ private:
+  Handle<String> string_;
+};
+
 } }  // namespace v8::internal
 
 #endif  // V8_HANDLES_H_