Clear EventHandler on Stop, to avoid future usages.

runtime/bin/eventhandler.cc

Index: runtime/bin/eventhandler.cc
diff --git a/runtime/bin/eventhandler.cc b/runtime/bin/eventhandler.cc
index d4d8a285bc40ffa5e74845fbe827fa7327ea61b3..6c431dbe915c883cb723dfad1c96f1e230c93ca0 100644
--- a/runtime/bin/eventhandler.cc
+++ b/runtime/bin/eventhandler.cc
@@ -62,17 +62,11 @@ void TimeoutQueue::UpdateTimeout(Dart_Port port, int64_t timeout) {
 }
 
 
-/*
- * 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;
 }
 
 
@@ -95,20 +89,22 @@ void FUNCTION_NAME(EventHandler_Start)(Dart_NativeArguments args) {
  */
 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();
 }