src: make IsolateData creation explicit

Make it easier to reason about the lifetime and the ownership of the
IsolateData instance by making its creation explicit and by removing
reference counting logic.

The creator of the Environment is now responsible for passing in the
IsolateData instance and for keeping it alive as long as the Environment
is alive.

PR-URL: https://github.com/nodejs/node/pull/7082
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>

5 files changed, 63 insertions, 113 deletions

diff --git a/src/debug-agent.cc b/src/debug-agent.cc
index e4e0ea061b..78eacf49ab 100644
--- a/src/debug-agent.cc
+++ b/src/debug-agent.cc
@@ -172,9 +172,15 @@ void Agent::WorkerRun() {
     Local<Context> context = Context::New(isolate);
 
     Context::Scope context_scope(context);
+
+    // FIXME(bnoordhuis) Work around V8 bug: v8::Private::ForApi() dereferences
+    // a nullptr when a context hasn't been entered first.  The symbol registry
+    // is a lazily created JS object but object instantiation does not work
+    // without a context.
+    IsolateData isolate_data(isolate, &child_loop_);
+
     Environment* env = CreateEnvironment(
-        isolate,
-        &child_loop_,
+        &isolate_data,
         context,
         arraysize(argv),
         argv,
diff --git a/src/env-inl.h b/src/env-inl.h
index a8a7d02552..cf62ca7eb4 100644
--- a/src/env-inl.h
+++ b/src/env-inl.h
@@ -15,28 +15,6 @@
 
 namespace node {
 
-inline IsolateData* IsolateData::Get(v8::Isolate* isolate) {
-  return static_cast<IsolateData*>(isolate->GetData(kIsolateSlot));
-}
-
-inline IsolateData* IsolateData::GetOrCreate(v8::Isolate* isolate,
-                                             uv_loop_t* loop) {
-  IsolateData* isolate_data = Get(isolate);
-  if (isolate_data == nullptr) {
-    isolate_data = new IsolateData(isolate, loop);
-    isolate->SetData(kIsolateSlot, isolate_data);
-  }
-  isolate_data->ref_count_ += 1;
-  return isolate_data;
-}
-
-inline void IsolateData::Put() {
-  if (--ref_count_ == 0) {
-    isolate()->SetData(kIsolateSlot, nullptr);
-    delete this;
-  }
-}
-
 // Create string properties as internalized one byte strings.
 //
 // Internalized because it makes property lookups a little faster and because
@@ -46,9 +24,8 @@ inline void IsolateData::Put() {
 //
 // One byte because our strings are ASCII and we can safely skip V8's UTF-8
 // decoding step.  It's a one-time cost, but why pay it when you don't have to?
-inline IsolateData::IsolateData(v8::Isolate* isolate, uv_loop_t* loop)
-    : event_loop_(loop),
-      isolate_(isolate),
+inline IsolateData::IsolateData(v8::Isolate* isolate, uv_loop_t* event_loop)
+    :
 #define V(PropertyName, StringValue)                                          \
     PropertyName ## _(                                                        \
         isolate,                                                              \
@@ -71,16 +48,12 @@ inline IsolateData::IsolateData(v8::Isolate* isolate, uv_loop_t* loop)
             sizeof(StringValue) - 1).ToLocalChecked()),
     PER_ISOLATE_STRING_PROPERTIES(V)
 #undef V
-    ref_count_(0) {}
+    isolate_(isolate), event_loop_(event_loop) {}
 
 inline uv_loop_t* IsolateData::event_loop() const {
   return event_loop_;
 }
 
-inline v8::Isolate* IsolateData::isolate() const {
-  return isolate_;
-}
-
 inline Environment::AsyncHooks::AsyncHooks() {
   for (int i = 0; i < kFieldsCount; i++) fields_[i] = 0;
 }
@@ -176,9 +149,9 @@ inline void Environment::ArrayBufferAllocatorInfo::reset_fill_flag() {
   fields_[kNoZeroFill] = 0;
 }
 
-inline Environment* Environment::New(v8::Local<v8::Context> context,
-                                     uv_loop_t* loop) {
-  Environment* env = new Environment(context, loop);
+inline Environment* Environment::New(IsolateData* isolate_data,
+                                     v8::Local<v8::Context> context) {
+  Environment* env = new Environment(isolate_data, context);
   env->AssignToContext(context);
   return env;
 }
@@ -212,11 +185,11 @@ inline Environment* Environment::GetCurrent(
   return static_cast<Environment*>(data.As<v8::External>()->Value());
 }
 
-inline Environment::Environment(v8::Local<v8::Context> context,
-                                uv_loop_t* loop)
+inline Environment::Environment(IsolateData* isolate_data,
+                                v8::Local<v8::Context> context)
     : isolate_(context->GetIsolate()),
-      isolate_data_(IsolateData::GetOrCreate(context->GetIsolate(), loop)),
-      timer_base_(uv_now(loop)),
+      isolate_data_(isolate_data),
+      timer_base_(uv_now(isolate_data->event_loop())),
       using_domains_(false),
       printed_error_(false),
       trace_sync_io_(false),
@@ -253,7 +226,6 @@ inline Environment::~Environment() {
 #define V(PropertyName, TypeName) PropertyName ## _.Reset();
   ENVIRONMENT_STRONG_PERSISTENT_PROPERTIES(V)
 #undef V
-  isolate_data()->Put();
 
   delete[] heap_statistics_buffer_;
   delete[] heap_space_statistics_buffer_;
@@ -541,9 +513,9 @@ inline v8::Local<v8::Object> Environment::NewInternalFieldObject() {
 #define VS(PropertyName, StringValue) V(v8::String, PropertyName, StringValue)
 #define V(TypeName, PropertyName, StringValue)                                \
   inline                                                                      \
-  v8::Local<TypeName> IsolateData::PropertyName() const {                     \
+  v8::Local<TypeName> IsolateData::PropertyName(v8::Isolate* isolate) const { \
     /* Strings are immutable so casting away const-ness here is okay. */      \
-    return const_cast<IsolateData*>(this)->PropertyName ## _.Get(isolate());  \
+    return const_cast<IsolateData*>(this)->PropertyName ## _.Get(isolate);    \
   }
   PER_ISOLATE_PRIVATE_SYMBOL_PROPERTIES(VP)
   PER_ISOLATE_STRING_PROPERTIES(VS)
@@ -555,7 +527,7 @@ inline v8::Local<v8::Object> Environment::NewInternalFieldObject() {
 #define VS(PropertyName, StringValue) V(v8::String, PropertyName, StringValue)
 #define V(TypeName, PropertyName, StringValue)                                \
   inline v8::Local<TypeName> Environment::PropertyName() const {              \
-    return isolate_data()->PropertyName();                                    \
+    return isolate_data()->PropertyName(isolate());                           \
   }
   PER_ISOLATE_PRIVATE_SYMBOL_PROPERTIES(VP)
   PER_ISOLATE_STRING_PROPERTIES(VS)
diff --git a/src/env.h b/src/env.h
index bbbd3f4b36..a6aea815fc 100644
--- a/src/env.h
+++ b/src/env.h
@@ -304,14 +304,13 @@ RB_HEAD(ares_task_list, ares_task_t);
 
 class IsolateData {
  public:
-  static inline IsolateData* GetOrCreate(v8::Isolate* isolate, uv_loop_t* loop);
-  inline void Put();
+  inline IsolateData(v8::Isolate* isolate, uv_loop_t* event_loop);
   inline uv_loop_t* event_loop() const;
 
 #define VP(PropertyName, StringValue) V(v8::Private, PropertyName, StringValue)
 #define VS(PropertyName, StringValue) V(v8::String, PropertyName, StringValue)
 #define V(TypeName, PropertyName, StringValue)                                \
-  inline v8::Local<TypeName> PropertyName() const;
+  inline v8::Local<TypeName> PropertyName(v8::Isolate* isolate) const;
   PER_ISOLATE_PRIVATE_SYMBOL_PROPERTIES(VP)
   PER_ISOLATE_STRING_PROPERTIES(VS)
 #undef V
@@ -319,15 +318,6 @@ class IsolateData {
 #undef VP
 
  private:
-  static const int kIsolateSlot = NODE_ISOLATE_SLOT;
-
-  inline static IsolateData* Get(v8::Isolate* isolate);
-  inline explicit IsolateData(v8::Isolate* isolate, uv_loop_t* loop);
-  inline v8::Isolate* isolate() const;
-
-  uv_loop_t* const event_loop_;
-  v8::Isolate* const isolate_;
-
 #define VP(PropertyName, StringValue) V(v8::Private, PropertyName, StringValue)
 #define VS(PropertyName, StringValue) V(v8::String, PropertyName, StringValue)
 #define V(TypeName, PropertyName, StringValue)                                \
@@ -338,7 +328,8 @@ class IsolateData {
 #undef VS
 #undef VP
 
-  unsigned int ref_count_;
+  v8::Isolate* const isolate_;
+  uv_loop_t* const event_loop_;
 
   DISALLOW_COPY_AND_ASSIGN(IsolateData);
 };
@@ -474,8 +465,8 @@ class Environment {
       const v8::PropertyCallbackInfo<T>& info);
 
   // See CreateEnvironment() in src/node.cc.
-  static inline Environment* New(v8::Local<v8::Context> context,
-                                 uv_loop_t* loop);
+  static inline Environment* New(IsolateData* isolate_data,
+                                 v8::Local<v8::Context> context);
   inline void CleanupHandles();
   inline void Dispose();
 
@@ -609,7 +600,7 @@ class Environment {
   static const int kContextEmbedderDataIndex = NODE_CONTEXT_EMBEDDER_DATA_INDEX;
 
  private:
-  inline Environment(v8::Local<v8::Context> context, uv_loop_t* loop);
+  inline Environment(IsolateData* isolate_data, v8::Local<v8::Context> context);
   inline ~Environment();
   inline IsolateData* isolate_data() const;
 
diff --git a/src/node.cc b/src/node.cc
index 258ebb596a..025c1a921a 100644
--- a/src/node.cc
+++ b/src/node.cc
@@ -4264,42 +4264,6 @@ int EmitExit(Environment* env) {
 }
 
 
-// Just a convenience method
-Environment* CreateEnvironment(Isolate* isolate,
-                               Local<Context> context,
-                               int argc,
-                               const char* const* argv,
-                               int exec_argc,
-                               const char* const* exec_argv) {
-  Environment* env;
-  Context::Scope context_scope(context);
-
-  env = CreateEnvironment(isolate,
-                          uv_default_loop(),
-                          context,
-                          argc,
-                          argv,
-                          exec_argc,
-                          exec_argv);
-
-  LoadEnvironment(env);
-
-  return env;
-}
-
-static Environment* CreateEnvironment(Isolate* isolate,
-                                      Local<Context> context,
-                                      NodeInstanceData* instance_data) {
-  return CreateEnvironment(isolate,
-                           instance_data->event_loop(),
-                           context,
-                           instance_data->argc(),
-                           instance_data->argv(),
-                           instance_data->exec_argc(),
-                           instance_data->exec_argv());
-}
-
-
 static void HandleCloseCb(uv_handle_t* handle) {
   Environment* env = reinterpret_cast<Environment*>(handle->data);
   env->FinishHandleCleanup(handle);
@@ -4314,17 +4278,27 @@ static void HandleCleanup(Environment* env,
 }
 
 
-Environment* CreateEnvironment(Isolate* isolate,
-                               uv_loop_t* loop,
+IsolateData* CreateIsolateData(Isolate* isolate, uv_loop_t* loop) {
+  return new IsolateData(isolate, loop);
+}
+
+
+void FreeIsolateData(IsolateData* isolate_data) {
+  delete isolate_data;
+}
+
+
+Environment* CreateEnvironment(IsolateData* isolate_data,
                                Local<Context> context,
                                int argc,
                                const char* const* argv,
                                int exec_argc,
                                const char* const* exec_argv) {
+  Isolate* isolate = context->GetIsolate();
   HandleScope handle_scope(isolate);
 
   Context::Scope context_scope(context);
-  Environment* env = Environment::New(context, loop);
+  Environment* env = Environment::New(isolate_data, context);
 
   isolate->SetAutorunMicrotasks(false);
 
@@ -4412,10 +4386,23 @@ static void StartNodeInstance(void* arg) {
     Isolate::Scope isolate_scope(isolate);
     HandleScope handle_scope(isolate);
     Local<Context> context = Context::New(isolate);
-    Environment* env = CreateEnvironment(isolate, context, instance_data);
-    array_buffer_allocator->set_env(env);
     Context::Scope context_scope(context);
 
+    // FIXME(bnoordhuis) Work around V8 bug: v8::Private::ForApi() dereferences
+    // a nullptr when a context hasn't been entered first.  The symbol registry
+    // is a lazily created JS object but object instantiation does not work
+    // without a context.
+    IsolateData isolate_data(isolate, instance_data->event_loop());
+
+    Environment* env = CreateEnvironment(&isolate_data,
+                                         context,
+                                         instance_data->argc(),
+                                         instance_data->argv(),
+                                         instance_data->exec_argc(),
+                                         instance_data->exec_argv());
+
+    array_buffer_allocator->set_env(env);
+
     isolate->SetAbortOnUncaughtExceptionCallback(
         ShouldAbortOnUncaughtException);
 
diff --git a/src/node.h b/src/node.h
index 42c5ac59d7..c1c149cdc3 100644
--- a/src/node.h
+++ b/src/node.h
@@ -190,28 +190,22 @@ NODE_EXTERN void Init(int* argc,
                       int* exec_argc,
                       const char*** exec_argv);
 
+class IsolateData;
 class Environment;
 
-NODE_EXTERN Environment* CreateEnvironment(v8::Isolate* isolate,
-                                           struct uv_loop_s* loop,
-                                           v8::Local<v8::Context> context,
-                                           int argc,
-                                           const char* const* argv,
-                                           int exec_argc,
-                                           const char* const* exec_argv);
-NODE_EXTERN void LoadEnvironment(Environment* env);
-NODE_EXTERN void FreeEnvironment(Environment* env);
+NODE_EXTERN IsolateData* CreateIsolateData(v8::Isolate* isolate,
+                                           struct uv_loop_s* loop);
+NODE_EXTERN void FreeIsolateData(IsolateData* isolate_data);
 
-// NOTE: Calling this is the same as calling
-// CreateEnvironment() + LoadEnvironment() from above.
-// `uv_default_loop()` will be passed as `loop`.
-NODE_EXTERN Environment* CreateEnvironment(v8::Isolate* isolate,
+NODE_EXTERN Environment* CreateEnvironment(IsolateData* isolate_data,
                                            v8::Local<v8::Context> context,
                                            int argc,
                                            const char* const* argv,
                                            int exec_argc,
                                            const char* const* exec_argv);
 
+NODE_EXTERN void LoadEnvironment(Environment* env);
+NODE_EXTERN void FreeEnvironment(Environment* env);
 
 NODE_EXTERN void EmitBeforeExit(Environment* env);
 NODE_EXTERN int EmitExit(Environment* env);