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

src/heap/mark-compact.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/base/atomicops.h"
 #include "src/base/bits.h"
 #include "src/code-stubs.h"
 #include "src/compilation-cache.h"
@@ skipping 2539 matching lines @@
 
   // Note that we never eliminate a transition array, though we might right-trim
   // such that number_of_transitions() == 0. If this assumption changes,
   // TransitionArray::Insert() will need to deal with the case that a transition
   // array disappeared during GC.
   int trim = TransitionArray::Capacity(transitions) - transition_index;
   if (trim > 0) {
     // Non-full-TransitionArray cases can never reach this point.
     DCHECK(TransitionArray::IsFullTransitionArray(transitions));
     TransitionArray* t = TransitionArray::cast(transitions);
-    heap_->RightTrimFixedArray<Heap::FROM_GC>(
+    heap_->RightTrimFixedArray<Heap::SEQUENTIAL_TO_SWEEPER>(
         t, trim * TransitionArray::kTransitionSize);
     t->SetNumberOfTransitions(transition_index);
     // The map still has a full transition array.
     DCHECK(TransitionArray::IsFullTransitionArray(map->raw_transitions()));
   }
 }
 
 
 void MarkCompactCollector::TrimDescriptorArray(Map* map,
                                                DescriptorArray* descriptors,
                                                int number_of_own_descriptors) {
   int number_of_descriptors = descriptors->number_of_descriptors_storage();
   int to_trim = number_of_descriptors - number_of_own_descriptors;
   if (to_trim == 0) return;
 
-  heap_->RightTrimFixedArray<Heap::FROM_GC>(
+  heap_->RightTrimFixedArray<Heap::SEQUENTIAL_TO_SWEEPER>(
       descriptors, to_trim * DescriptorArray::kDescriptorSize);
   descriptors->SetNumberOfDescriptors(number_of_own_descriptors);
 
   if (descriptors->HasEnumCache()) TrimEnumCache(map, descriptors);
   descriptors->Sort();
 
   if (FLAG_unbox_double_fields) {
     LayoutDescriptor* layout_descriptor = map->layout_descriptor();
     layout_descriptor = layout_descriptor->Trim(heap_, map, descriptors,
                                                 number_of_own_descriptors);
     SLOW_DCHECK(layout_descriptor->IsConsistentWithMap(map, true));
   }
 }
 
 
 void MarkCompactCollector::TrimEnumCache(Map* map,
                                          DescriptorArray* descriptors) {
   int live_enum = map->EnumLength();
   if (live_enum == kInvalidEnumCacheSentinel) {
     live_enum = map->NumberOfDescribedProperties(OWN_DESCRIPTORS, DONT_ENUM);
   }
   if (live_enum == 0) return descriptors->ClearEnumCache();
 
   FixedArray* enum_cache = descriptors->GetEnumCache();
 
   int to_trim = enum_cache->length() - live_enum;
   if (to_trim <= 0) return;
-  heap_->RightTrimFixedArray<Heap::FROM_GC>(descriptors->GetEnumCache(),
-                                            to_trim);
+  heap_->RightTrimFixedArray<Heap::SEQUENTIAL_TO_SWEEPER>(
+      descriptors->GetEnumCache(), to_trim);
 
   if (!descriptors->HasEnumIndicesCache()) return;
   FixedArray* enum_indices_cache = descriptors->GetEnumIndicesCache();
-  heap_->RightTrimFixedArray<Heap::FROM_GC>(enum_indices_cache, to_trim);
+  heap_->RightTrimFixedArray<Heap::SEQUENTIAL_TO_SWEEPER>(enum_indices_cache,
+                                                          to_trim);
 }
 
 
 void MarkCompactCollector::ProcessWeakCollections() {
   GCTracer::Scope gc_scope(heap()->tracer(),
                            GCTracer::Scope::MC_WEAKCOLLECTION_PROCESS);
   Object* weak_collection_obj = heap()->encountered_weak_collections();
   while (weak_collection_obj != Smi::FromInt(0)) {
     JSWeakCollection* weak_collection =
         reinterpret_cast<JSWeakCollection*>(weak_collection_obj);
@@ skipping 2111 matching lines @@
   SlotsBuffer* buffer = *buffer_address;
   while (buffer != NULL) {
     SlotsBuffer* next_buffer = buffer->next();
     DeallocateBuffer(buffer);
     buffer = next_buffer;
   }
   *buffer_address = NULL;
 }
 }
 }  // namespace v8::internal