Issue #4692 - Rewrite `SetTimeout` facility to avoid `JsValuePtr` and `JsValueList`

src/JsEngine.cpp

Index: src/JsEngine.cpp
===================================================================
--- a/src/JsEngine.cpp
+++ b/src/JsEngine.cpp
@@ -18,6 +18,8 @@
 #include <AdblockPlus.h>
 #include "GlobalJsObject.h"
 #include "JsContext.h"
+#include "JsEngineInternal.h"
+#include "JsEngineTransition.h"
 #include "JsError.h"
 #include "Scheduler.h"
 #include "Utils.h"
@@ -74,6 +76,13 @@
   };
 }
 
+V8ExecutionScope::V8ExecutionScope(JsEngineInternal* engine)
+  : lock(engine->GetIsolate()),
+  isolateScope(engine->GetIsolate()),
+  handleScope(engine->GetIsolate()),
+  contextScope(engine->GetContextAsLocal())
+{}
+
 AdblockPlus::ScopedV8Isolate::ScopedV8Isolate()
 {
   V8Initializer::Init();
@@ -88,27 +97,94 @@
 
 AdblockPlus::JsEngine::JsEngine(const ScopedV8IsolatePtr& isolate)
   : isolate(isolate),
-    scheduler(new SchedulerImpl()) // use std::make_unique after we upgrade out of VS2012
+  scheduler(new SchedulerImpl()) // TODO: make_unique once available
 {}
 
+JsEngineInternal::JsEngineInternal(const AdblockPlus::ScopedV8IsolatePtr& isolate)
+  : AdblockPlus::JsEngine(isolate),
+  context(isolate->Get(),v8::Context::New(isolate->Get()))
+{
+  /*
+   * Enter v8 scope for our context so that we can initialize its global object.
+   */
+  const v8::Context::Scope contextScope(GetContextAsLocal());
+  auto globalObject = GetGlobalObject();
+  auto propertyName = AdblockPlus::Utils::ToV8String(GetIsolate(), "setTimeout");
+  globalObject->Set(propertyName, MakeCallback(::CallbackForSetTimeout));

[Eric, 2016/12/19 22:39:53]

New initialization of global object without any use of `JsEnginePtr`.

+  // TODO: Move the rest of the global object initializations here
+}
+
+/**
+ * \par Design Notes
+ * It is technically necessary to construct JsEngine instances *only* within a factory.
+ * Initialization requires that certain transient v8 scopes be set up 
+ *   before initialization and torn down afterwards.
+ * C++ has no syntax to use anything like a sentry object in the constructor itself.
+ * Thus we need to establish v8 scope within every C++ scope that constructs an object.
+ */
 AdblockPlus::JsEnginePtr AdblockPlus::JsEngine::New(const AppInfo& appInfo, const ScopedV8IsolatePtr& isolate)
 {
-  JsEnginePtr result(new JsEngine(isolate));
+  auto isolateP = isolate->Get();
+  /*
+   * TODO: Remove `locker`.
+   * Until #3595 is fixed, unit tests allocate isolates outside of this class.
+   * Once we're no longer doing that, we may assume that this class holds
+   *   exclusive access to the nascent isolate.
+   * The factory and constructor constitute a single-threaded usage,
+   *   and there will be no need to lock the isolate.
+   */
+  const v8::Locker locker(isolateP);
+  /*
+   * Set up v8 scopes for isolate and handle.
+   * We cannot set up the v8 scope for context because it doesn't exist
+   *   until after the constructor for `JsEngineInternal` returns.
+   */
+  const v8::Isolate::Scope isolateScope(isolateP);
+  const v8::HandleScope handleScope(isolateP);
 
-  const v8::Locker locker(result->GetIsolate());
-  const v8::Isolate::Scope isolateScope(result->GetIsolate());
-  const v8::HandleScope handleScope(result->GetIsolate());
+  std::shared_ptr<JsEngineInternal> engine(std::make_shared<JsEngineInternal>(isolate));
 
-  result->context.reset(new v8::Persistent<v8::Context>(result->GetIsolate(),
-    v8::Context::New(result->GetIsolate())));
+  JsEnginePtr result(engine);
+  // Establish a context scope for the legacy setup of the global object
+  const v8::Context::Scope contextScope(engine->GetContextAsLocal());
   AdblockPlus::GlobalJsObject::Setup(result, appInfo, result->GetGlobalObject());
   return result;
 }
 
+v8::Local<v8::Context> JsEngineInternal::GetContextAsLocal() const
+{
+  return v8::Local<v8::Context>::New(isolate->Get(), context);
+}
+
 AdblockPlus::JsValuePtr AdblockPlus::JsEngine::GetGlobalObject()
 {
-  JsContext context(shared_from_this());
-  return JsValuePtr(new JsValue(shared_from_this(), context.GetV8Context()->Global()));
+  return JsValuePtr(new JsValue(shared_from_this(), ToInternal(this)->GetGlobalObject()));
+}
+
+v8::Local<v8::Object> JsEngineInternal::GetGlobalObject()
+{
+  return GetContextAsLocal()->Global();
+}
+
+v8::Local<v8::Value> JsEngineInternal::ApplyFunction(
+  v8::Local<v8::Function> func,
+  AllocatedArray<v8::Local<v8::Value>> args)
+{
+  return ApplyFunction(GetGlobalObject(), func, std::move(args));
+}
+
+v8::Local<v8::Value> JsEngineInternal::ApplyFunction(
+  v8::Local<v8::Object> thisObject,
+  v8::Local<v8::Function> func,
+  AllocatedArray<v8::Local<v8::Value>> args)
+{
+  const v8::TryCatch tryCatch;
+  v8::Local<v8::Value> result = func->Call(thisObject, args.Size(), args.Get());
+  if (tryCatch.HasCaught())
+  {
+    throw AdblockPlus::JsError(tryCatch.Exception(), tryCatch.Message());
+  }
+  return result;
 }
 
 AdblockPlus::JsValuePtr AdblockPlus::JsEngine::Evaluate(const std::string& source,
@@ -199,6 +275,28 @@
   return result;
 }
 
+/**
+ * \par Implementation Notes 
+ * We initialize the `Data()` element of the callback arguments with `this`,
+ *   which raises an issue about life cycle.
+ * The result of `FunctionTemplate::New` is to create a function 
+ *   whose lifespan is the same as the context it's created in.
+ * The context is an instance member of the engine,
+ *   so as long as the engine exists, so does the context.
+ * Since evaluation in v8 only occurs during the ordinary lifespan of the engine
+ *   (i.e. after the constructor and before the destructor),
+ *   the `this` pointer will be valid whenever the callback function might be called.
+ */
+v8::Local<v8::Function> JsEngineInternal::MakeCallback(v8::InvocationCallback callback)
+{
+  return v8::FunctionTemplate::New(callback, v8::External::New(this))->GetFunction();
+}
+
+JsEngineInternal* JsEngineInternal::ExtractEngine(const v8::Arguments& arguments)
+{
+  return static_cast<JsEngineInternal*>(v8::Local<v8::External>::Cast(arguments.Data())->Value());
+}
+
 AdblockPlus::JsValueList AdblockPlus::JsEngine::ConvertArguments(const v8::Arguments& arguments)
 {
   const JsContext context(shared_from_this());
@@ -253,10 +351,10 @@
   logSystem = val;
 }
 
-
 void AdblockPlus::JsEngine::SetGlobalProperty(const std::string& name, 
                                               AdblockPlus::JsValuePtr value)
 {
+  JsContext jsContext(shared_from_this());
   auto global = GetGlobalObject();
   if (!global)
     throw std::runtime_error("Global object cannot be null");
@@ -275,3 +373,13 @@
 {
   scheduler->JoinAll();
 }
+
+JsEngineInternal* ToInternal(AdblockPlus::JsEnginePtr p)
+{
+  return static_cast<JsEngineInternal*>(p.get());
+}
+
+JsEngineInternal* ToInternal(AdblockPlus::JsEngine* p)
+{
+  return static_cast<JsEngineInternal*>(p);
+}