lazy instantiation of the default isolate

src/isolate.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 477 matching lines @@
   // True if at least one thread Enter'ed this isolate.
   bool IsInUse() { return entry_stack_ != NULL; }
 
   // Destroys the non-default isolates.
   // Sets default isolate into "has_been_disposed" state rather then destroying,
   // for legacy API reasons.
   void TearDown();
 
   static void GlobalTearDown();
 
-  bool IsDefaultIsolate() const { return this == default_isolate_; }
+  bool IsDefaultIsolate() const { return is_default_isolate_; }
 
   static void SetCrashIfDefaultIsolateInitialized();
   // Ensures that process-wide resources and the default isolate have been
   // allocated. It is only necessary to call this method in rare cases, for
   // example if you are using V8 from within the body of a static initializer.
   // Safe to call multiple times.
-  static void EnsureDefaultIsolate();
+  static Isolate* EnsureDefaultIsolate();
+
+  // Initialize all thread local variables
+  static void InitializeThreadLocalStorage();
 
   // Find the PerThread for this particular (isolate, thread) combination
   // If one does not yet exist, return null.
   PerIsolateThreadData* FindPerThreadDataForThisThread();
 
   // Find the PerThread for given (isolate, thread) combination
   // If one does not yet exist, return null.
   PerIsolateThreadData* FindPerThreadDataForThread(ThreadId thread_id);
 
 #ifdef ENABLE_DEBUGGER_SUPPORT
@@ skipping 609 matching lines @@
     function_entry_hook_ = function_entry_hook;
   }
 
   void* stress_deopt_count_address() { return &stress_deopt_count_; }
 
   inline RandomNumberGenerator* random_number_generator();
 
   // Given an address occupied by a live code object, return that object.
   Object* FindCodeObject(Address a);
 
+  static Atomic32 GetLivingIsolates() {
+    return Acquire_Load(&living_isolates_);
+  }
+
  private:
-  Isolate();
+  explicit Isolate(bool is_default_isolate = false);
 
   friend struct GlobalState;
   friend struct InitializeGlobalState;
 
   enum State {
     UNINITIALIZED,    // Some components may not have been allocated.
     INITIALIZED       // All components are fully initialized.
   };
 
   // These fields are accessed through the API, offsets must be kept in sync
@@ skipping 44 matching lines @@
     DISALLOW_COPY_AND_ASSIGN(EntryStackItem);
   };
 
   // This mutex protects highest_thread_id_, thread_data_table_ and
   // default_isolate_.
   static Mutex process_wide_mutex_;
 
   static Thread::LocalStorageKey per_isolate_thread_data_key_;
   static Thread::LocalStorageKey isolate_key_;
   static Thread::LocalStorageKey thread_id_key_;
-  static Isolate* default_isolate_;
   static ThreadDataTable* thread_data_table_;
 
   // A global counter for all generated Isolates, might overflow.
   static Atomic32 isolate_counter_;
+  static Atomic32 living_isolates_;
 
   void Deinit();
 
   static void SetIsolateThreadLocals(Isolate* isolate,
                                      PerIsolateThreadData* data);
 
   // Find the PerThread for this particular (isolate, thread) combination.
   // If one does not yet exist, allocate a new one.
   PerIsolateThreadData* FindOrAllocatePerThreadDataForThisThread();
 
@@ skipping 21 matching lines @@
   void FillCache();
 
   void PropagatePendingExceptionToExternalTryCatch();
 
   void InitializeDebugger();
 
   // Traverse prototype chain to find out whether the object is derived from
   // the Error object.
   bool IsErrorObject(Handle<Object> obj);
 
+  bool is_default_isolate_;

[Michael Starzinger, 2013/10/01 14:19:08]

nit: Let's move this down to the other boolean flags around line 1316, easier to
find.

   Atomic32 id_;
   EntryStackItem* entry_stack_;
   int stack_trace_nesting_level_;
   StringStream* incomplete_message_;
   // The preallocated memory thread singleton.
   PreallocatedMemoryThread* preallocated_memory_thread_;
   Address isolate_addresses_[kIsolateAddressCount + 1];  // NOLINT
   NoAllocationStringAllocator* preallocated_message_space_;
   Bootstrapper* bootstrapper_;
   RuntimeProfiler* runtime_profiler_;
@@ skipping 267 matching lines @@
 
 // Mark the native context with out of memory.
 inline void Context::mark_out_of_memory() {
   native_context()->set_out_of_memory(GetIsolate()->heap()->true_value());
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_ISOLATE_H_