VM thread shutdown.

runtime/vm/thread.cc

Index: runtime/vm/thread.cc
diff --git a/runtime/vm/thread.cc b/runtime/vm/thread.cc
index 3b3eb3308d30b292147168449f670ba1f62033f5..b1fd5765bb9b3afa5ebc240bef026f331c5ae23d 100644
--- a/runtime/vm/thread.cc
+++ b/runtime/vm/thread.cc
@@ -134,11 +134,15 @@ void Thread::EnterIsolate(Isolate* isolate) {
   ASSERT(thread->thread_state() == NULL);
   InterruptableThreadState* thread_state =
       ThreadInterrupter::GetCurrentThreadState();
-#if defined(DEBUG)
-  thread->set_thread_state(NULL);  // Exclude thread itself from the dupe check.
-  Isolate::CheckForDuplicateThreadState(thread_state);
-  thread->set_thread_state(thread_state);
-#endif
+  // TODO(koda): Calling Isolate::CheckForDuplicateThreadState(thread_state)
+  // here can lead to deadlock. Isolate::KillAllIsolates(), takes the isolate
+  // list lock and posts the kill message to the target isolate, entering the
+  // monitor at the top of MessageHandler::PostMessage() to do so. That monitor
+  // is also entered before calling MessageHandler::HandleMessages(), which
+  // enters a StartIsolateScope, which calls Thread::EnterIsolate(), which would
+  // call Isolate::CheckForDuplicateThreadState(), which attempts to take the
+  // isolate list lock, potentially creating a cycle.
+  // Evaluate doing this check some other way.
   ASSERT(thread_state != NULL);
   // TODO(koda): Migrate profiler interface to use Thread.
   Profiler::BeginExecution(isolate);