Store script's line ends in copy-on-write fixed array.

This allows to remove explicit copy from line ends JS accessor which is used for formatting of stack traces.

Eager copying of line ends array might cause multiple full GC collections for huge scripts (e.g. scripts generated by GWT compiler with PRETY preset).

Review URL: http://codereview.chromium.org/5148002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@5839 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

diff --git a/src/accessors.cc b/src/accessors.cc
index 7c21659ebc4d95d5fc5a2a07ba98f9ef356a07c3..08ef41b9f7ea60d95911fd4caa97d299d7bee20c 100644 (file)
--- a/src/accessors.cc
+++ b/src/accessors.cc
@@ -316,8 +316,10 @@ MaybeObject* Accessors::ScriptGetLineEnds(Object* object, void*) {
   InitScriptLineEnds(script);
   ASSERT(script->line_ends()->IsFixedArray());
   Handle<FixedArray> line_ends(FixedArray::cast(script->line_ends()));
-  Handle<FixedArray> copy = Factory::CopyFixedArray(line_ends);
-  Handle<JSArray> js_array = Factory::NewJSArrayWithElements(copy);
+  // We do not want anyone to modify this array from JS.
+  ASSERT(*line_ends == Heap::empty_fixed_array() ||
+         line_ends->map() == Heap::fixed_cow_array_map());
+  Handle<JSArray> js_array = Factory::NewJSArrayWithElements(line_ends);
   return *js_array;
 }
 

diff --git a/src/handles.cc b/src/handles.cc
index 7a46bc3ea251fc6232b769ee0c4232c279306ae2..1364951b714ceb2c87731312f77ff1427ad98f5f 100644 (file)
--- a/src/handles.cc
+++ b/src/handles.cc
@@ -499,6 +499,10 @@ void InitScriptLineEnds(Handle<Script> script) {
 
   Handle<FixedArray> array = CalculateLineEnds(src, true);
 
+  if (*array != Heap::empty_fixed_array()) {
+    array->set_map(Heap::fixed_cow_array_map());
+  }
+
   script->set_line_ends(*array);
   ASSERT(script->line_ends()->IsFixedArray());
 }