Add a second kind of HandleScope that ties the lifetime of Handles created in its scope to the life…

src/api.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 391 matching lines @@
 // so that the currently executing thread always has its own copy of this
 // data.
 class HandleScopeImplementer {
  public:
   explicit HandleScopeImplementer(Isolate* isolate)
       : isolate_(isolate),
         blocks_(0),
         entered_contexts_(0),
         saved_contexts_(0),
         spare_(NULL),
-        call_depth_(0) { }
+        call_depth_(0),
+        last_block_before_compilation_(NULL),
+        last_valid_handle_before_compilation_(NULL),
+        hidden_extensions_head_(NULL) { }

[Erik Corry, 2012/06/22 11:08:36]

Instead of 'hidden' may I suggest 'persistent'.  That is what we have used other
places where we have non-stack based handles that do not have a scope based
lifetime.

[sanjoy, 2012/06/22 20:08:10]

Done.

 
   ~HandleScopeImplementer() {
     DeleteArray(spare_);
   }
 
   // Threading support for handle data.
   static int ArchiveSpacePerThread();
   char* RestoreThread(char* from);
   char* ArchiveThread(char* to);
   void FreeThreadResources();
 
   // Garbage collection support.
   void Iterate(v8::internal::ObjectVisitor* v);
   static char* Iterate(v8::internal::ObjectVisitor* v, char* data);
 
+  struct HiddenExtensions {
+    List<Object**> blocks;
+    Object** last_block_end;
+    HiddenExtensions* previous;
+    HiddenExtensions* next;
+  };
 
   inline internal::Object** GetSpareOrNewBlock();
   inline void DeleteExtensions(internal::Object** prev_limit);
 
+  // HideExtensions must be called _before_ the next field in
+  // HandleScopeData is reverted.
+  HiddenExtensions* HideExtensions(internal::Object** prev_limit);
+  void DeleteHiddenExtensions(HiddenExtensions* extension);
+
   inline void IncrementCallDepth() {call_depth_++;}
   inline void DecrementCallDepth() {call_depth_--;}
   inline bool CallDepthIsZero() { return call_depth_ == 0; }
 
   inline void EnterContext(Handle<Object> context);
   inline bool LeaveLastContext();
 
   // Returns the last entered context or an empty handle if no
   // contexts have been entered.
   inline Handle<Object> LastEnteredContext();
 
   inline void SaveContext(Context* context);
   inline Context* RestoreContext();
   inline bool HasSavedContexts();
 
   inline List<internal::Object**>* blocks() { return &blocks_; }
 
+  void set_last_block_before_compilation() {
+    // We only track one such special block.
+    ASSERT(!last_block_before_compilation_);
+    last_block_before_compilation_ = blocks_.last();
+    last_valid_handle_before_compilation_ = isolate_->handle_scope_data()->next;
+  }
+
+  void unset_last_block_before_compilation() {
+    ASSERT(last_block_before_compilation_);
+    last_block_before_compilation_ = NULL;
+    last_valid_handle_before_compilation_ = NULL;
+  }
+
  private:
   void ResetAfterArchive() {
     blocks_.Initialize(0);
     entered_contexts_.Initialize(0);
     saved_contexts_.Initialize(0);
     spare_ = NULL;
     call_depth_ = 0;
   }
 
   void Free() {
@@ skipping 13 matching lines @@
   Isolate* isolate_;
   List<internal::Object**> blocks_;
   // Used as a stack to keep track of entered contexts.
   List<Handle<Object> > entered_contexts_;
   // Used as a stack to keep track of saved contexts.
   List<Context*> saved_contexts_;
   Object** spare_;
   int call_depth_;
   // This is only used for threading support.
   v8::ImplementationUtilities::HandleScopeData handle_scope_data_;
+  Object** last_block_before_compilation_;
+  Object** last_valid_handle_before_compilation_;
+  HiddenExtensions* hidden_extensions_head_;
 
+  template<bool HasCompilationBlock>
   void IterateThis(ObjectVisitor* v);
   char* RestoreThreadHelper(char* from);
   char* ArchiveThreadHelper(char* to);
 
   DISALLOW_COPY_AND_ASSIGN(HandleScopeImplementer);
 };
 
 
 const int kHandleBlockSize = v8::internal::KB - 2;  // fit in one page
 
@@ skipping 73 matching lines @@
     stress_type_ = stress_type;
   }
 
  private:
   static v8::Testing::StressType stress_type_;
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_API_H_