Avoid verifying heap while sweeper is running.

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 991 matching lines @@
   }
 
  private:
   DISALLOW_COPY_AND_ASSIGN(FinalizeWeakPersistentHandlesVisitor);
 };
 
 
 void Isolate::Shutdown() {
   ASSERT(this == Isolate::Current());
   ASSERT(top_resource() == NULL);
-  ASSERT((heap_ == NULL) || heap_->Verify());
+#if defined(DEBUG)
+  if (heap_ != NULL) {
+    // Wait for concurrent GC tasks to finish before final verification.
+    PageSpace* old_space = heap_->old_space();
+    MonitorLocker ml(old_space->tasks_lock());
+    while (old_space->tasks() > 0) {
+      ml.Wait();
+    }
+    heap_->Verify(kForbidMarked);
+  }
+#endif  // DEBUG
 
   // Remove this isolate from the list *before* we start tearing it down, to
   // avoid exposing it in a state of decay.
   RemoveIsolateFromList(this);
 
   // Create an area where we do have a zone and a handle scope so that we can
   // call VM functions while tearing this isolate down.
   {
     StackZone stack_zone(this);
     HandleScope handle_scope(this);
@@ skipping 548 matching lines @@
                            serialized_message_, serialized_message_len_);
 }
 
 
 void IsolateSpawnState::Cleanup() {
   SwitchIsolateScope switch_scope(I);
   Dart::ShutdownIsolate();
 }
 
 }  // namespace dart