Implement issue 549 Make V8 call DebugMessageDispatchHandler with Locker locked

src/debug.h

Index: src/debug.h
diff --git a/src/debug.h b/src/debug.h
index fe9ff3596c405d003c722917d89ebf8f1d58c067..5ea2e522465494a457e6abc6f4a413ef2b8fdbb1 100644
--- a/src/debug.h
+++ b/src/debug.h
@@ -559,6 +559,9 @@ class CommandMessageQueue BASE_EMBEDDED {
 };
 
 
+class MessageDispatchHelperThread;
+
+
 // LockingCommandMessageQueue is a thread-safe circular buffer of CommandMessage
 // messages.  The message data is not managed by LockingCommandMessageQueue.
 // Pointers to the data are passed in and out. Implemented by adding a
@@ -619,7 +622,8 @@ class Debugger {
   static void SetHostDispatchHandler(v8::Debug::HostDispatchHandler handler,
                                      int period);
   static void SetDebugMessageDispatchHandler(
-      v8::Debug::DebugMessageDispatchHandler handler);
+      v8::Debug::DebugMessageDispatchHandler handler,
+      bool provide_locker);
 
   // Invoke the message handler function.
   static void InvokeMessageHandler(MessageImpl message);
@@ -645,6 +649,8 @@ class Debugger {
   // Blocks until the agent has started listening for connections
   static void WaitForAgent();
 
+  static void CallMessageDispatchHandler();
+
   // Unload the debugger if possible. Only called when no debugger is currently
   // active.
   static void UnloadDebugger();
@@ -683,7 +689,9 @@ class Debugger {
   static v8::Debug::MessageHandler2 message_handler_;
   static bool debugger_unload_pending_;  // Was message handler cleared?
   static v8::Debug::HostDispatchHandler host_dispatch_handler_;
+  static Mutex* dispatch_handler_access_;  // Mutex guarding dispatch handler.
   static v8::Debug::DebugMessageDispatchHandler debug_message_dispatch_handler_;
+  static MessageDispatchHelperThread* message_dispatch_helper_thread_;
   static int host_dispatch_micros_;
 
   static DebuggerAgent* agent_;
@@ -860,6 +868,27 @@ class Debug_Address {
   int reg_;
 };
 
+// The optional thread that Debug Agent may use to temporary call V8 to process
+// pending debug requests if debuggee is not running V8 at the moment.
+// Techincally it does not call V8 itself, rather it asks embedding program
+// to do this via v8::Debug::HostDispatchHandler
+class MessageDispatchHelperThread: public Thread {
+ public:
+  MessageDispatchHelperThread();
+  ~MessageDispatchHelperThread();
+
+  void Schedule();
+
+ private:
+  void Run();
+
+  Semaphore* const sem_;
+  Mutex* const mutex_;
+  bool already_signalled_;
+
+  DISALLOW_COPY_AND_ASSIGN(MessageDispatchHelperThread);
+};
+
 
 } }  // namespace v8::internal