lazy instantiation of the default isolate

src/isolate.cc

Index: src/isolate.cc
diff --git a/src/isolate.cc b/src/isolate.cc
index 90bcb0f5f6201d21734ab73d4600662b82dda1ce..7e0c36aca3c27f1885a34517114f86046f3131e2 100644
--- a/src/isolate.cc
+++ b/src/isolate.cc
@@ -330,7 +330,6 @@ void Isolate::PreallocatedStorageDelete(void* p) {
   storage->LinkTo(&free_list_);
 }
 
-Isolate* Isolate::default_isolate_ = NULL;
 Thread::LocalStorageKey Isolate::isolate_key_;
 Thread::LocalStorageKey Isolate::thread_id_key_;
 Thread::LocalStorageKey Isolate::per_isolate_thread_data_key_;
@@ -348,6 +347,7 @@ static DefaultIsolateStatus default_isolate_status_
     = kDefaultIsolateUninitialized;
 Isolate::ThreadDataTable* Isolate::thread_data_table_ = NULL;
 Atomic32 Isolate::isolate_counter_ = 0;
+Atomic32 Isolate::living_isolates_ = 0;
 
 Isolate::PerIsolateThreadData*
     Isolate::FindOrAllocatePerThreadDataForThisThread() {
@@ -390,61 +390,72 @@ void Isolate::SetCrashIfDefaultIsolateInitialized() {
 }
 
 
-void Isolate::EnsureDefaultIsolate() {
+Isolate* Isolate::EnsureDefaultIsolate() {
+  static Isolate* default_isolate_ = NULL;
   LockGuard<Mutex> lock_guard(&process_wide_mutex_);
   CHECK(default_isolate_status_ != kDefaultIsolateCrashIfInitialized);
   if (default_isolate_ == NULL) {
-    isolate_key_ = Thread::CreateThreadLocalKey();
-    thread_id_key_ = Thread::CreateThreadLocalKey();
-    per_isolate_thread_data_key_ = Thread::CreateThreadLocalKey();
-#ifdef DEBUG
-    PerThreadAssertScopeBase::thread_local_key = Thread::CreateThreadLocalKey();
-#endif  // DEBUG
-    thread_data_table_ = new Isolate::ThreadDataTable();
-    default_isolate_ = new Isolate();
+    default_isolate_ = new Isolate(true);
   }
   // Can't use SetIsolateThreadLocals(default_isolate_, NULL) here
   // because a non-null thread data may be already set.
   if (Thread::GetThreadLocal(isolate_key_) == NULL) {
     Thread::SetThreadLocal(isolate_key_, default_isolate_);
   }
+
+  return default_isolate_;
+}
+
+
+void Isolate::InitializeThreadLocalStorage() {
+  // Double checked locking on existence of thread_data_table_.
+  if (thread_data_table_ != NULL) return;
+  LockGuard<Mutex> lock_guard(&process_wide_mutex_);
+  if (thread_data_table_ != NULL) return;
+  isolate_key_ = Thread::CreateThreadLocalKey();
+  thread_id_key_ = Thread::CreateThreadLocalKey();
+  per_isolate_thread_data_key_ = Thread::CreateThreadLocalKey();
+#ifdef DEBUG
+  PerThreadAssertScopeBase::thread_local_key = Thread::CreateThreadLocalKey();
+#endif  // DEBUG
+  thread_data_table_ = new Isolate::ThreadDataTable();
+  CHECK(thread_data_table_ != NULL);
 }
 
+
+// TODO(dcarney): Remove this with default_isolate_ and Isolate::Current.
 struct StaticInitializer {
   StaticInitializer() {
-    Isolate::EnsureDefaultIsolate();
+    Isolate::InitializeThreadLocalStorage();
   }
 } static_initializer;
 
 #ifdef ENABLE_DEBUGGER_SUPPORT
 Debugger* Isolate::GetDefaultIsolateDebugger() {
-  EnsureDefaultIsolate();
-  return default_isolate_->debugger();
+  return EnsureDefaultIsolate()->debugger();
 }
 #endif
 
 
 StackGuard* Isolate::GetDefaultIsolateStackGuard() {
-  EnsureDefaultIsolate();
-  return default_isolate_->stack_guard();
+  return EnsureDefaultIsolate()->stack_guard();
 }
 
 
 void Isolate::EnterDefaultIsolate() {
-  EnsureDefaultIsolate();
-  ASSERT(default_isolate_ != NULL);
+  Isolate* default_isolate = EnsureDefaultIsolate();
+  ASSERT(default_isolate != NULL);
 
   PerIsolateThreadData* data = CurrentPerIsolateThreadData();
   // If not yet in default isolate - enter it.
-  if (data == NULL || data->isolate() != default_isolate_) {
-    default_isolate_->Enter();
+  if (data == NULL || data->isolate() != default_isolate) {
+    default_isolate->Enter();
   }
 }
 
 
 v8::Isolate* Isolate::GetDefaultIsolateForLocking() {
-  EnsureDefaultIsolate();
-  return reinterpret_cast<v8::Isolate*>(default_isolate_);
+  return reinterpret_cast<v8::Isolate*>(EnsureDefaultIsolate());
 }
 
 
@@ -1734,7 +1745,7 @@ void Isolate::ThreadDataTable::RemoveAllThreads(Isolate* isolate) {
 #endif
 
 
-Isolate::Isolate()
+Isolate::Isolate(bool is_default_isolate)
     : state_(UNINITIALIZED),
       embedder_data_(NULL),
       entry_stack_(NULL),
@@ -1784,6 +1795,7 @@ Isolate::Isolate()
       has_fatal_error_(false),
       use_crankshaft_(true),
       initialized_from_snapshot_(false),
+      is_default_isolate_(is_default_isolate),
       cpu_profiler_(NULL),
       heap_profiler_(NULL),
       function_entry_hook_(NULL),
@@ -1791,7 +1803,10 @@ Isolate::Isolate()
       optimizing_compiler_thread_(NULL),
       sweeper_thread_(NULL),
       stress_deopt_count_(0) {
+  InitializeThreadLocalStorage();
+
   id_ = NoBarrier_AtomicIncrement(&isolate_counter_, 1);
+  NoBarrier_AtomicIncrement(&living_isolates_, 1);
   TRACE_ISOLATE(constructor);
 
   memset(isolate_addresses_, 0,
@@ -1974,7 +1989,7 @@ Isolate::~Isolate() {
   // The entry stack must be empty when we get here,
   // except for the default isolate, where it can
   // still contain up to one entry stack item
-  ASSERT(entry_stack_ == NULL || this == default_isolate_);
+  ASSERT(entry_stack_ == NULL || is_default_isolate_);
   ASSERT(entry_stack_ == NULL || entry_stack_->previous_item == NULL);
 
   delete entry_stack_;
@@ -2059,6 +2074,8 @@ Isolate::~Isolate() {
   delete debug_;
   debug_ = NULL;
 #endif
+
+  NoBarrier_AtomicIncrement(&living_isolates_, -1);
 }