Use atomic operation to read the length of a fixed array.

src/elements.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #include "src/arguments.h"
 #include "src/conversions.h"
 #include "src/elements.h"
 #include "src/objects.h"
@@ skipping 866 matching lines @@
     // Check whether the backing store should be shrunk.
     if (length <= old_capacity) {
       if (array->HasFastSmiOrObjectElements()) {
         backing_store = JSObject::EnsureWritableFastElements(array);
       }
       if (2 * length <= old_capacity) {
         // If more than half the elements won't be used, trim the array.
         if (length == 0) {
           array->initialize_elements();
         } else {
-          isolate->heap()->RightTrimFixedArray<Heap::FROM_MUTATOR>(
+          isolate->heap()->RightTrimFixedArray<Heap::CONCURRENT_TO_SWEEPER>(
               *backing_store, old_capacity - length);
         }
       } else {
         // Otherwise, fill the unused tail with holes.
         int old_length = FastD2IChecked(array->length()->Number());
         for (int i = length; i < old_length; i++) {
           Handle<BackingStore>::cast(backing_store)->set_the_hole(i);
         }
       }
       return length_object;
@@ skipping 945 matching lines @@
       UNREACHABLE();
       break;
   }
 
   array->set_elements(*elms);
   array->set_length(Smi::FromInt(number_of_elements));
   return array;
 }
 
 } }  // namespace v8::internal