Fix race condition when posting debugger messages to the message queue

bin/dbg_message.h

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef BIN_DBG_MESSAGE_H_
 #define BIN_DBG_MESSAGE_H_
 
 #include "bin/builtin.h"
 #include "bin/utils.h"
 
@@ skipping 194 matching lines @@
 
   // Initialize the message queue processing by setting up the appropriate
   // handlers.
   static void Initialize();
 
   // Parses the input message and returns the command index if the message
   // contains a valid isolate specific command.
   // It returns kInvalidCommand otherwise.
   static int32_t LookupIsolateCommand(const char* buf, int32_t buflen);
 
+  // Queue debugger message targetted for the isolate.
+  static bool AddIsolateMessage(Dart_IsolateId isolate_id,
+                                int32_t cmd_idx,
+                                const char* start,
+                                const char* end,
+                                int debug_fd);
+
+  // Interrupt isolate.
+  static bool InterruptIsolate(Dart_IsolateId isolate_id);
+
   // Add Debugger Message Queue corresponding to the Isolate.
   static DbgMsgQueue* AddIsolateMsgQueue(Dart_IsolateId isolate_id);
 
   // Get Debugger Message Queue corresponding to the Isolate.
   static DbgMsgQueue* GetIsolateMsgQueue(Dart_IsolateId isolate_id);
 
   // Remove Debugger Message Queue corresponding to the Isolate.
   static void RemoveIsolateMsgQueue(Dart_IsolateId isolate_id);
 
   // Generic handlers for breakpoints, exceptions and delayed breakpoint
   // resolution.
   static void BptResolvedHandler(Dart_IsolateId isolate_id,
                                  intptr_t bp_id,
                                  Dart_Handle url,
                                  intptr_t line_number);
   static void BreakpointHandler(Dart_IsolateId isolate_id,
                                 Dart_Breakpoint bpt,
                                 Dart_StackTrace trace);
   static void ExceptionThrownHandler(Dart_IsolateId isolate_id,
                                      Dart_Handle exception,
                                      Dart_StackTrace stack_trace);
   static void IsolateEventHandler(Dart_IsolateId isolate_id,
                                   Dart_IsolateEvent kind);
 
  private:
+  static DbgMsgQueue* GetIsolateMsgQueueLocked(Dart_IsolateId isolate_id);
+
   static DbgMsgQueue* list_;
   static dart::Mutex msg_queue_list_lock_;
 
   DISALLOW_ALLOCATION();
   DISALLOW_IMPLICIT_CONSTRUCTORS(DbgMsgQueueList);
 };
 
 #endif  // BIN_DBG_MESSAGE_H_