Fix data race on Debug::thread_local_.current_debug_scope_

src/debug.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_DEBUG_H_
 #define V8_DEBUG_H_
 
 #include "src/allocation.h"
 #include "src/arguments.h"
 #include "src/assembler.h"
+#include "src/base/atomicops.h"
 #include "src/base/platform/platform.h"
 #include "src/execution.h"
 #include "src/factory.h"
 #include "src/flags.h"
 #include "src/frames-inl.h"
 #include "src/hashmap.h"
 #include "src/liveedit.h"
 #include "src/string-stream.h"
 #include "src/v8threads.h"
 
@@ skipping 431 matching lines @@
   void FreeThreadResources() { }
 
   // Record function from which eval was called.
   static void RecordEvalCaller(Handle<Script> script);
 
   bool CheckExecutionState(int id) {
     return !debug_context().is_null() && break_id() != 0 && break_id() == id;
   }
 
   // Flags and states.
-  DebugScope* debugger_entry() { return thread_local_.current_debug_scope_; }
+  DebugScope* debugger_entry() {
+    return reinterpret_cast<DebugScope*>(
+        base::NoBarrier_Load(&thread_local_.current_debug_scope_));
+  }
   inline Handle<Context> debug_context() { return debug_context_; }
   void set_live_edit_enabled(bool v) { live_edit_enabled_ = v; }
   bool live_edit_enabled() const {
     return FLAG_enable_liveedit && live_edit_enabled_ ;
   }
 
   inline bool is_active() const { return is_active_; }
   inline bool is_loaded() const { return !debug_context_.is_null(); }
   inline bool has_break_points() const { return has_break_points_; }
   inline bool in_debug_scope() const {
-    return thread_local_.current_debug_scope_ != NULL;
+    return !!base::NoBarrier_Load(&thread_local_.current_debug_scope_);
   }
   void set_disable_break(bool v) { break_disabled_ = v; }
 
   StackFrame::Id break_frame_id() { return thread_local_.break_frame_id_; }
   int break_id() { return thread_local_.break_id_; }
 
   // Support for embedding into generated code.
   Address is_active_address() {
     return reinterpret_cast<Address>(&is_active_);
   }
@@ skipping 108 matching lines @@
 
   // Storage location for jump when exiting debug break calls.
   // Note that this address is not GC safe.  It should be computed immediately
   // before returning to the DebugBreakCallHelper.
   Address after_break_target_;
 
   // Per-thread data.
   class ThreadLocal {
    public:
     // Top debugger entry.
-    DebugScope* current_debug_scope_;
+    base::AtomicWord current_debug_scope_;
 
     // Counter for generating next break id.
     int break_count_;
 
     // Current break id.
     int break_id_;
 
     // Frame id for the frame of the current break.
     StackFrame::Id break_frame_id_;
 
@@ skipping 129 matching lines @@
   // several frames above.
   // There is no calling conventions here, because it never actually gets
   // called, it only gets returned to.
   static void GenerateFrameDropperLiveEdit(MacroAssembler* masm);
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_DEBUG_H_