Change handling of debugger unloading

src/debug.h

 // Copyright 2006-2008 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 @@
   // Send the JSON message for a debug event.
   static bool SendEventMessage(Handle<Object> event_data);
 
   // Add a debugger command to the command queue.
   static void ProcessCommand(Vector<const uint16_t> command);
 
   // Check whether there are commands in the command queue.
   static bool HasCommands();
 
   static void ProcessHostDispatch(void* dispatch);
-  static void UpdateActiveDebugger();
   static Handle<Object> Call(Handle<JSFunction> fun,
                              Handle<Object> data,
                              bool* pending_exception);
 
   // Start the debugger agent listening on the provided port.
   static bool StartAgent(const char* name, int port);
 
   // Stop the debugger agent.
   static void StopAgent();
 
+  // Unload the debugger if possible. Only called when no debugger is currently
+  // active.
+  static void UnloadDebugger();
+
   inline static bool EventActive(v8::DebugEvent event) {
+    ScopedLock with(debugger_access_);
+
+    // Check whether the message handler was been cleared.
+    if (message_handler_cleared_) {
+      UnloadDebugger();
+    }
+
     // Currently argument event is not used.
-    return !Debugger::compiling_natives_ && Debugger::debugger_active_;
+    return !compiling_natives_ && Debugger::IsDebuggerActive();
   }
 
-  static void set_debugger_active(bool debugger_active) {
-    Debugger::debugger_active_ = debugger_active;
-  }
-  static bool debugger_active() { return Debugger::debugger_active_; }
   static void set_compiling_natives(bool compiling_natives) {
     Debugger::compiling_natives_ = compiling_natives;
   }
   static bool compiling_natives() { return Debugger::compiling_natives_; }
   static void set_loading_debugger(bool v) { is_loading_debugger_ = v; }
   static bool is_loading_debugger() { return Debugger::is_loading_debugger_; }
 
  private:
-  static Handle<Object> event_listener_;  // Global handle to listener
+  static bool IsDebuggerActive();
+
+  static Mutex* debugger_access_;  // Mutex guarding debugger variables.
+  static Handle<Object> event_listener_;  // Global handle to listener.
   static Handle<Object> event_listener_data_;
-  static bool debugger_active_;  // Are there any active debugger?
   static bool compiling_natives_;  // Are we compiling natives?
   static bool is_loading_debugger_;  // Are we loading the debugger?
+  static bool never_unload_debugger_;  // Can we unload the debugger?
   static DebugMessageThread* message_thread_;
   static v8::DebugMessageHandler message_handler_;
+  static bool message_handler_cleared_;  // Was message handler cleared?
   static void* message_handler_data_;
   static v8::DebugHostDispatchHandler host_dispatch_handler_;
   static void* host_dispatch_handler_data_;
 
   static DebuggerAgent* agent_;
 
   static const int kQueueInitialSize = 4;
   static LockingMessageQueue command_queue_;
   static LockingMessageQueue message_queue_;
   static Semaphore* command_received_;  // Signaled for each command received.
   static Semaphore* message_received_;  // Signalled for each message send.
 
+  friend class EnterDebugger;
   friend class DebugMessageThread;
 };
 
 
 // Thread to read messages from the message queue and invoke the debug message
 // handler in another thread as the V8 thread. This thread is started if the
 // registration of the debug message handler requested to be called in a thread
 // seperate from the V8 thread.
 class DebugMessageThread: public Thread {
  public:
@@ skipping 56 matching lines @@
       StackGuard::Preempt();
       Debug::set_preemption_pending(false);
     }
 
     // If there are commands in the queue when leaving the debugger request that
     // these commands are processed.
     if (prev_ == NULL && Debugger::HasCommands()) {
       StackGuard::DebugCommand();
     }
 
+    // If leaving the debugger with the debugger no longer active unload it.
+    if (prev_ == NULL) {
+      if (!Debugger::IsDebuggerActive()) {
+        Debugger::UnloadDebugger();
+      }
+    }
+
     // Leaving this debugger entry.
     Debug::set_debugger_entry(prev_);
   }
 
   // Check whether the debugger could be entered.
   inline bool FailedToEnter() { return load_failed_; }
 
   // Check whether there are any JavaScript frames on the stack.
   inline bool HasJavaScriptFrames() { return has_js_frames_; }
 
@@ skipping 64 matching lines @@
   }
  private:
   Debug::AddressId id_;
   int reg_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_V8_DEBUG_H_