Object.oberve: assertions to narrow down flaky crashes with array length mutation.

src/runtime.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 4358 matching lines @@
                                     strict_mode);
 }
 
 
 RUNTIME_FUNCTION(MaybeObject*, Runtime_TransitionElementsSmiToDouble) {
   NoHandleAllocation ha;
   RUNTIME_ASSERT(args.length() == 1);
   Handle<Object> object = args.at<Object>(0);
   if (object->IsJSObject()) {
     Handle<JSObject> js_object(Handle<JSObject>::cast(object));
+    ASSERT(!js_object->map()->is_observed());
     ElementsKind new_kind = js_object->HasFastHoleyElements()
         ? FAST_HOLEY_DOUBLE_ELEMENTS
         : FAST_DOUBLE_ELEMENTS;
     return TransitionElements(object, new_kind, isolate);
   } else {
     return *object;
   }
 }
 
 
 RUNTIME_FUNCTION(MaybeObject*, Runtime_TransitionElementsDoubleToObject) {
   NoHandleAllocation ha;
   RUNTIME_ASSERT(args.length() == 1);
   Handle<Object> object = args.at<Object>(0);
   if (object->IsJSObject()) {
     Handle<JSObject> js_object(Handle<JSObject>::cast(object));
+    ASSERT(!js_object->map()->is_observed());
     ElementsKind new_kind = js_object->HasFastHoleyElements()
         ? FAST_HOLEY_ELEMENTS
         : FAST_ELEMENTS;
     return TransitionElements(object, new_kind, isolate);
   } else {
     return *object;
   }
 }
 
 
@@ skipping 9075 matching lines @@
 RUNTIME_FUNCTION(MaybeObject*, Runtime_SetIsObserved) {
   ASSERT(args.length() == 2);
   CONVERT_ARG_CHECKED(JSReceiver, obj, 0);
   CONVERT_BOOLEAN_ARG_CHECKED(is_observed, 1);
   if (obj->IsJSGlobalProxy()) {
     Object* proto = obj->GetPrototype();
     if (obj->IsNull()) return isolate->heap()->undefined_value();
     ASSERT(proto->IsJSGlobalObject());
     obj = JSReceiver::cast(proto);
   }
+  ASSERT(!(obj->map()->is_observed() && obj->IsJSObject() &&
+           JSObject::cast(obj)->HasFastElements()));
   if (obj->map()->is_observed() != is_observed) {
+    if (is_observed && obj->IsJSObject() &&
+        !JSObject::cast(obj)->HasExternalArrayElements()) {
+      // Go to dictionary mode, so that we don't skip map checks.
+      MaybeObject* maybe = JSObject::cast(obj)->NormalizeElements();
+      if (maybe->IsFailure()) return maybe;
+      ASSERT(!JSObject::cast(obj)->HasFastElements());
+    }
     MaybeObject* maybe = obj->map()->Copy();
     Map* map;
     if (!maybe->To(&map)) return maybe;
     map->set_is_observed(is_observed);
     obj->set_map(map);
-    if (is_observed && obj->IsJSObject() &&
-        !JSObject::cast(obj)->HasExternalArrayElements()) {
-      // Go to dictionary mode, so that we don't skip map checks.
-      maybe = JSObject::cast(obj)->NormalizeElements();
-      if (maybe->IsFailure()) return maybe;
-      ASSERT(!JSObject::cast(obj)->HasFastElements());
-    }
   }
   return isolate->heap()->undefined_value();
 }
 
 
 RUNTIME_FUNCTION(MaybeObject*, Runtime_SetObserverDeliveryPending) {
   ASSERT(args.length() == 0);
   isolate->set_observer_delivery_pending(true);
   return isolate->heap()->undefined_value();
 }
@@ skipping 118 matching lines @@
     // Handle last resort GC and make sure to allow future allocations
     // to grow the heap without causing GCs (if possible).
     isolate->counters()->gc_last_resort_from_js()->Increment();
     isolate->heap()->CollectAllGarbage(Heap::kNoGCFlags,
                                        "Runtime::PerformGC");
   }
 }
 
 
 } }  // namespace v8::internal