- Prevent interrupting the NULL thread when the isolate is

runtime/vm/isolate.cc

 // Copyright (c) 2013, 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 "vm/isolate.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "platform/json.h"
 #include "vm/code_observers.h"
@@ skipping 1748 matching lines @@
     // Paused at breakpoint. Don't tick.
     return 0;
   }
   MessageHandler* msg_handler = message_handler();
   if ((msg_handler != NULL) &&
       (msg_handler->paused_on_start() ||
        msg_handler->paused_on_exit())) {
     // Paused at start / exit . Don't tick.
     return 0;
   }
-  if (mutator_thread_ == NULL) {
+  // Make sure that the isolate's mutator thread does not change behind our
+  // backs. Otherwise we find the entry in the registry and end up reading
+  // the field again. Only by that time it has been reset to NULL because the
+  // thread was in process of exiting the isolate.
+  Thread* mutator = mutator_thread_;
+  if (mutator == NULL) {
     // No active mutator.
     ProfileIdle();
     return 1;
   }
 
   // TODO(johnmccutchan): Sample all threads, not just the mutator thread.
   // TODO(johnmccutchan): Keep a global list of threads and use that
   // instead of Isolate.
   ThreadRegistry::EntryIterator it(thread_registry());
   while (it.HasNext()) {
     const ThreadRegistry::Entry& entry = it.Next();
-    if (entry.thread == mutator_thread_) {
-      ThreadInterrupter::InterruptThread(mutator_thread_);
+    if (entry.thread == mutator) {
+      ThreadInterrupter::InterruptThread(mutator);
       break;
     }
   }
   return 1;
 }
 
 
 void Isolate::ProfileIdle() {
   vm_tag_counters_.Increment(vm_tag());
 }
@@ skipping 349 matching lines @@
                            serialized_message_, serialized_message_len_);
 }
 
 
 void IsolateSpawnState::Cleanup() {
   SwitchIsolateScope switch_scope(I);
   Dart::ShutdownIsolate();
 }
 
 }  // namespace dart