Allow the morphing of strings to external strings to avoid having to...

src/api.cc

Index: src/api.cc
===================================================================
--- src/api.cc	(revision 1251)
+++ src/api.cc	(working copy)
@@ -2440,22 +2440,58 @@
 
 static void DisposeExternalString(v8::Persistent<v8::Value> obj,
                                   void* parameter) {
-  v8::String::ExternalStringResource* resource =
-    reinterpret_cast<v8::String::ExternalStringResource*>(parameter);
-  const size_t total_size = resource->length() * sizeof(*resource->data());
-  i::Counters::total_external_string_memory.Decrement(total_size);
-  delete resource;
+  i::ExternalTwoByteString* str =
+      i::ExternalTwoByteString::cast(*Utils::OpenHandle(*obj));
+
+  // External symbols are deleted when they are pruned out of the symbol
+  // table. Generally external symbols are not registered with the weak handle
+  // callbacks unless they are upgraded to a symbol after being externalized.
+  if (!str->IsSymbol()) {
+    v8::String::ExternalStringResource* resource =
+        reinterpret_cast<v8::String::ExternalStringResource*>(parameter);
+    if (resource != NULL) {
+      const size_t total_size = resource->length() * sizeof(*resource->data());
+      i::Counters::total_external_string_memory.Decrement(total_size);
+
+      // The object will continue to live in the JavaScript heap until the
+      // handle is entirely cleaned out by the next GC. For example the
+      // destructor for the resource below could bring it back to life again.
+      // Which is why we make sure to not have a dangling pointer here.
+      str->set_resource(NULL);
+      delete resource;
+    }
+  }
+
+  // In any case we do not need this handle any longer.
   obj.Dispose();
 }
 
 
 static void DisposeExternalAsciiString(v8::Persistent<v8::Value> obj,
                                        void* parameter) {
-  v8::String::ExternalAsciiStringResource* resource =
-    reinterpret_cast<v8::String::ExternalAsciiStringResource*>(parameter);
-  const size_t total_size = resource->length() * sizeof(*resource->data());
-  i::Counters::total_external_string_memory.Decrement(total_size);
-  delete resource;
+  i::ExternalAsciiString* str =
+      i::ExternalAsciiString::cast(*Utils::OpenHandle(*obj));
+
+  // External symbols are deleted when they are pruned out of the symbol
+  // table. Generally external symbols are not registered with the weak handle
+  // callbacks unless they are upgraded to a symbol after being externalized.
+  if (!str->IsSymbol()) {
+    v8::String::ExternalAsciiStringResource* resource =
+        reinterpret_cast<v8::String::ExternalAsciiStringResource*>(parameter);
+    if (resource != NULL) {
+      const size_t total_size = resource->length() * sizeof(*resource->data());
+      i::Counters::total_external_string_memory.Decrement(total_size);
+
+      // The object will continue to live in the JavaScript heap until the
+      // handle is entirely cleaned out by the next GC. For example the
+      // destructor for the resource below could bring it back to life again.
+      // Which is why we make sure to not have a dangling pointer here.
+      str->set_resource(NULL);
+      delete resource;
+    }
+  }
+
+  // In any case we do not need this handle any longer.
   obj.Dispose();
 }
 
@@ -2475,6 +2511,24 @@
 }
 
 
+bool v8::String::MakeExternal(v8::String::ExternalStringResource* resource) {
+  if (IsDeadCheck("v8::String::MakeExternal()")) return false;
+  if (this->IsExternal()) return false;  // Already an external string.
+  i::Handle <i::String> obj = Utils::OpenHandle(this);
+  bool result = obj->MakeExternal(resource);
+  if (result && !obj->IsSymbol()) {
+    // Operation was successful and the string is not a symbol. In this case
+    // we need to make sure that the we call the destructor for the external
+    // resource when no strong references to the string remain.
+    i::Handle<i::Object> handle = i::GlobalHandles::Create(*obj);
+    i::GlobalHandles::MakeWeak(handle.location(),
+                               resource,
+                               &DisposeExternalString);
+  }
+  return result;
+}
+
+
 Local<String> v8::String::NewExternal(
       v8::String::ExternalAsciiStringResource* resource) {
   EnsureInitialized("v8::String::NewExternal()");
@@ -2490,6 +2544,25 @@
 }
 
 
+bool v8::String::MakeExternal(
+    v8::String::ExternalAsciiStringResource* resource) {
+  if (IsDeadCheck("v8::String::MakeExternal()")) return false;
+  if (this->IsExternal()) return false;  // Already an external string.
+  i::Handle <i::String> obj = Utils::OpenHandle(this);
+  bool result = obj->MakeExternal(resource);
+  if (result && !obj->IsSymbol()) {
+    // Operation was successful and the string is not a symbol. In this case
+    // we need to make sure that the we call the destructor for the external
+    // resource when no strong references to the string remain.
+    i::Handle<i::Object> handle = i::GlobalHandles::Create(*obj);
+    i::GlobalHandles::MakeWeak(handle.location(),
+                               resource,
+                               &DisposeExternalAsciiString);
+  }
+  return result;
+}
+
+
 Local<v8::Object> v8::Object::New() {
   EnsureInitialized("v8::Object::New()");
   LOG_API("Object::New");