Document that Isolate::GetCurrent() must not be called before initialization

src/isolate.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_ISOLATE_H_
 #define V8_ISOLATE_H_
 
 #include "include/v8-debug.h"
 #include "src/allocation.h"
 #include "src/assert-scope.h"
@@ skipping 468 matching lines @@
 
   // Returns the PerIsolateThreadData for the current thread (or NULL if one is
   // not currently set).
   static PerIsolateThreadData* CurrentPerIsolateThreadData() {
     return reinterpret_cast<PerIsolateThreadData*>(
         base::Thread::GetThreadLocal(per_isolate_thread_data_key_));
   }
 
   // Returns the isolate inside which the current thread is running.
   INLINE(static Isolate* Current()) {
+    DCHECK(base::NoBarrier_Load(&isolate_key_created_) == 1);
     Isolate* isolate = reinterpret_cast<Isolate*>(
         base::Thread::GetExistingThreadLocal(isolate_key_));
     DCHECK(isolate != NULL);
     return isolate;
   }
 
   INLINE(static Isolate* UncheckedCurrent()) {
+    DCHECK(base::NoBarrier_Load(&isolate_key_created_) == 1);
     return reinterpret_cast<Isolate*>(
         base::Thread::GetThreadLocal(isolate_key_));
   }
 
   // Like UncheckedCurrent, but skips the check that |isolate_key_| was
   // initialized. Callers have to ensure that themselves.
   INLINE(static Isolate* UnsafeCurrent()) {
     return reinterpret_cast<Isolate*>(
         base::Thread::GetThreadLocal(isolate_key_));
   }
@@ skipping 664 matching lines @@
   static base::LazyMutex thread_data_table_mutex_;
 
   static base::Thread::LocalStorageKey per_isolate_thread_data_key_;
   static base::Thread::LocalStorageKey isolate_key_;
   static base::Thread::LocalStorageKey thread_id_key_;
   static ThreadDataTable* thread_data_table_;
 
   // A global counter for all generated Isolates, might overflow.
   static base::Atomic32 isolate_counter_;
 
+#if DEBUG
+  static base::Atomic32 isolate_key_created_;
+#endif
+
   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();
 
   // Initializes the current thread to run this Isolate.
@@ skipping 357 matching lines @@
   }
 
   EmbeddedVector<char, 128> filename_;
   FILE* file_;
   int scope_depth_;
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_ISOLATE_H_