Clear EventHandler on Stop, to avoid future usages.

runtime/bin/eventhandler.cc

 // 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.
 
 #include "bin/dartutils.h"
 #include "bin/eventhandler.h"
 #include "bin/socket.h"
 #include "bin/thread.h"
 
 #include "include/dart_api.h"
@@ skipping 44 matching lines @@
   while (current != NULL) {
     if (next_timeout_ == NULL ||
         current->timeout() < next_timeout_->timeout()) {
       next_timeout_ = current;
     }
     current = current->next();
   }
 }
 
 
-/*
- * Returns the reference of the EventHandler stored in the native field.
- */
-static EventHandler* GetEventHandler(Dart_Handle handle) {
-  ASSERT(event_handler != NULL);
-  return event_handler;
-}
-
 void EventHandler::Stop() {
+  MutexLocker locker(mutex_);
   if (event_handler == NULL) return;
   event_handler->Shutdown();
+  event_handler = NULL;
 }
 
 
 /*
  * Starts the EventHandler thread and stores its reference in the dart
  * EventHandler object. args[0] holds the reference to the dart EventHandler
  * object.
  */
 void FUNCTION_NAME(EventHandler_Start)(Dart_NativeArguments args) {
   MutexLocker locker(mutex_);
   if (event_handler != NULL) return;
   event_handler = EventHandler::Start();
 }
 
 
 /*
  * Send data to the EventHandler thread to register for a given instance
  * args[1] a ReceivePort args[2] with a notification event args[3]. args[0]
  * holds the reference to the dart EventHandler object.
  */
 void FUNCTION_NAME(EventHandler_SendData)(Dart_NativeArguments args) {
   Dart_EnterScope();
-  Dart_Handle handle = Dart_GetNativeArgument(args, 0);
-  EventHandler* event_handler = GetEventHandler(handle);
-  Dart_Handle sender = Dart_GetNativeArgument(args, 1);
-  intptr_t id = kInvalidId;
-  if (Dart_IsNull(sender)) {
-    id = kTimerId;
-  } else {
-    Socket::GetSocketIdNativeField(sender, &id);
+  MutexLocker locker(mutex_);
+  // Only send if the event handler is active.
+  if (event_handler) {
+    Dart_Handle sender = Dart_GetNativeArgument(args, 1);
+    intptr_t id = kInvalidId;
+    if (Dart_IsNull(sender)) {
+      id = kTimerId;
+    } else {
+      Socket::GetSocketIdNativeField(sender, &id);
+    }
+    Dart_Handle handle = Dart_GetNativeArgument(args, 2);
+    Dart_Port dart_port =
+        DartUtils::GetIntegerField(handle, DartUtils::kIdFieldName);
+    int64_t data = DartUtils::GetIntegerValue(Dart_GetNativeArgument(args, 3));
+    event_handler->SendData(id, dart_port, data);

[kustermann, 2013/07/17 08:58:03]

As you/fschneider proposed, you could just do:
...
{
  MutexLocker locker(mutex_);
  event_handler->SendData(id, dart_port, data);
}
to narrow the critical area.

   }
-  handle = Dart_GetNativeArgument(args, 2);
-  Dart_Port dart_port =
-      DartUtils::GetIntegerField(handle, DartUtils::kIdFieldName);
-  int64_t data = DartUtils::GetIntegerValue(Dart_GetNativeArgument(args, 3));
-  event_handler->SendData(id, dart_port, data);
   Dart_ExitScope();
 }
 
 }  // namespace bin
 }  // namespace dart