[Bindings] Create and use V8 context snapshots

third_party/WebKit/Source/platform/bindings/V8PerIsolateData.cpp

Index: third_party/WebKit/Source/platform/bindings/V8PerIsolateData.cpp
diff --git a/third_party/WebKit/Source/platform/bindings/V8PerIsolateData.cpp b/third_party/WebKit/Source/platform/bindings/V8PerIsolateData.cpp
index 19eee733f61eadc76f64c8a9cac86fa1179742cb..5b5c60fe5ccefb324a89048f826ac8491264a367 100644
--- a/third_party/WebKit/Source/platform/bindings/V8PerIsolateData.cpp
+++ b/third_party/WebKit/Source/platform/bindings/V8PerIsolateData.cpp
@@ -27,6 +27,7 @@
 
 #include <memory>
 
+#include "platform/RuntimeEnabledFeatures.h"
 #include "platform/ScriptForbiddenScope.h"
 #include "platform/WebTaskRunner.h"
 #include "platform/bindings/DOMDataStore.h"
@@ -51,12 +52,17 @@ static void MicrotasksCompletedCallback(v8::Isolate* isolate) {
   V8PerIsolateData::From(isolate)->RunEndOfScopeTasks();
 }
 
-V8PerIsolateData::V8PerIsolateData(WebTaskRunner* task_runner)
+V8PerIsolateData::V8PerIsolateData(
+    WebTaskRunner* task_runner,
+    intptr_t* table,
+    gin::IsolateHolder::V8ContextMode context_mode)
     : isolate_holder_(
           task_runner ? task_runner->ToSingleThreadTaskRunner() : nullptr,
           gin::IsolateHolder::kSingleThread,
           IsMainThread() ? gin::IsolateHolder::kDisallowAtomicsWait
-                         : gin::IsolateHolder::kAllowAtomicsWait),
+                         : gin::IsolateHolder::kAllowAtomicsWait,
+          table,
+          context_mode),
       string_cache_(WTF::WrapUnique(new StringCache(GetIsolate()))),
       private_property_(V8PrivateProperty::Create()),
       constructor_mode_(ConstructorMode::kCreateNewObject),
@@ -78,8 +84,19 @@ v8::Isolate* V8PerIsolateData::MainThreadIsolate() {
   return g_main_thread_per_isolate_data->GetIsolate();
 }
 
-v8::Isolate* V8PerIsolateData::Initialize(WebTaskRunner* task_runner) {
-  V8PerIsolateData* data = new V8PerIsolateData(task_runner);
+v8::Isolate* V8PerIsolateData::Initialize(
+    WebTaskRunner* task_runner,
+    intptr_t* table,
+    gin::IsolateHolder::V8ContextMode context_mode) {
+  CHECK(context_mode == gin::IsolateHolder::kUseSnapshot ||
+        context_mode == gin::IsolateHolder::kTakeSnapshot);
+  if (context_mode == gin::IsolateHolder::kUseSnapshot &&
+      !RuntimeEnabledFeatures::v8ContextSnapshotEnabled()) {
+    context_mode = gin::IsolateHolder::kDefault;
+  }
+
+  V8PerIsolateData* data =
+      new V8PerIsolateData(task_runner, table, context_mode);
   v8::Isolate* isolate = data->GetIsolate();
   isolate->SetData(gin::kEmbedderBlink, data);
   return isolate;
@@ -163,6 +180,14 @@ v8::Local<v8::FunctionTemplate> V8PerIsolateData::FindOrCreateOperationTemplate(
 v8::Local<v8::FunctionTemplate> V8PerIsolateData::FindInterfaceTemplate(
     const DOMWrapperWorld& world,
     const void* key) {
+  if (GetV8ContextMode() == gin::IsolateHolder::kTakeSnapshot) {

[haraken, 2017/05/20 19:10:03]

I don't fully understand this code. Would you help me understand why we need to
use interface_template_persistent_map_ when taking a snapshot?

[peria, 2017/05/30 08:25:44]

We have to remove all references from the embedder (=Blink) to V8 objects, and
we can't do it with v8::Eternal<>.

+    auto& map = interface_template_persistent_map_;
+    auto result = map.find(key);
+    if (result != map.end())
+      return result->value.Get(GetIsolate());
+    return v8::Local<v8::FunctionTemplate>();
+  }
+
   auto& map = SelectInterfaceTemplateMap(world);
   auto result = map.find(key);
   if (result != map.end())
@@ -174,8 +199,18 @@ void V8PerIsolateData::SetInterfaceTemplate(
     const DOMWrapperWorld& world,
     const void* key,
     v8::Local<v8::FunctionTemplate> value) {
-  auto& map = SelectInterfaceTemplateMap(world);
-  map.insert(key, v8::Eternal<v8::FunctionTemplate>(GetIsolate(), value));
+  if (GetV8ContextMode() == gin::IsolateHolder::kTakeSnapshot) {
+    auto& map = interface_template_persistent_map_;
+    map.insert(key, CopyablePersistent(GetIsolate(), value));
+  } else {
+    auto& map = SelectInterfaceTemplateMap(world);
+    map.insert(key, v8::Eternal<v8::FunctionTemplate>(GetIsolate(), value));
+  }
+}
+
+void V8PerIsolateData::ClearPersistents() {
+  interface_template_persistent_map_.clear();
+  private_property_.reset();

[haraken, 2017/05/20 19:10:03]

Why do we need to clear private_property_?

[peria, 2017/05/30 08:25:44]

To clear WindowDocumentCachedAccessor.
https://chromium.googlesource.com/chromium/src/+/74b864441c2ce011435c511f23ea...

 }
 
 const v8::Eternal<v8::Name>* V8PerIsolateData::FindOrCreateEternalNameCache(