To avoid recreating WebCore::String objects constantly, we now transform V8 strings to external strings when they get handed out to WebKit the first time.

Review URL: http://codereview.chromium.org/20121

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@9871 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 28 insertions, 6 deletions

diff --git a/webkit/port/bindings/v8/v8_binding.h b/webkit/port/bindings/v8/v8_binding.h
index 4a011cf..553364c 100644
--- a/webkit/port/bindings/v8/v8_binding.h
+++ b/webkit/port/bindings/v8/v8_binding.h
@@ -7,6 +7,7 @@
 
 #include "config.h"
 
+#include "AtomicString.h"
 #include "CString.h"
 #include "MathExtras.h"
 #include "PlatformString.h"
@@ -43,10 +44,12 @@ class WebCoreStringResource: public v8::String::ExternalStringResource {
   // Keeps the string buffer alive until the V8 engine garbage collects it.
   String external_string_;
 };
-
-// TODO: converting between WebCore::String and V8 string is expensive.
-// Optimize it !!!
-inline String ToWebCoreString(v8::Handle<v8::Value> obj) {
+  
+// Convert a v8::String to a WebCore::String. If the V8 string is not already
+// an external string then it is transformed into an external string at this
+// point to avoid repeated conversions.
+inline String ToWebCoreString(v8::Handle<v8::Value> obj,
+                              bool atomic = false) {
   v8::TryCatch block;
   v8::Local<v8::String> v8_str = obj->ToString();
   if (v8_str.IsEmpty())
@@ -59,9 +62,28 @@ inline String ToWebCoreString(v8::Handle<v8::Value> obj) {
   }
 
   int length = v8_str->Length();
+  if (length == 0) {
+    // Avoid trying to morph empty strings, as they do not have enough room to
+    // contain the external reference.
+    return "";
+  }
+
+  // Copy the characters from the v8::String into a WebCore::String and allocate
+  // an external resource which will be attached to the v8::String.
   StringBuffer buf(length);
   v8_str->Write(reinterpret_cast<uint16_t*>(buf.characters()), 0, length);
-  return String::adopt(buf);
+  String result;
+  if (atomic) {
+    result = AtomicString(buf.characters(), length);
+  } else {
+    result = StringImpl::adopt(buf);
+  }
+  WebCoreStringResource* resource = new WebCoreStringResource(result);
+  if (!v8_str->MakeExternal(resource)) {
+    // In case of a failure delete the external resource as it was not used.
+    delete resource;
+  }
+  return result;
 }
 
 inline String valueToStringWithNullCheck(v8::Handle<v8::Value> value) {
@@ -78,7 +100,7 @@ inline String valueToStringWithNullOrUndefinedCheck(
 // Convert a value to a 32-bit integer.  The conversion fails if the
 // value cannot be converted to an integer or converts to nan or to an
 // infinity.
-// FIXME: Rename to toWebCorString() once V8 bindings migration is complete.
+// FIXME: Rename to toInt32() once V8 bindings migration is complete.
 inline int ToInt32(v8::Handle<v8::Value> value, bool& ok) {
   ok = true;