Skip write barriers when updating the weak hash table.

src/heap.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 "v8.h"
 
 #include "accessors.h"
 #include "api.h"
 #include "bootstrapper.h"
 #include "codegen.h"
@@ skipping 5442 matching lines @@
   }
   UNREACHABLE();
 }
 
 
 // TODO(ishell): Find a better place for this.
 void Heap::AddWeakObjectToCodeDependency(Handle<Object> obj,
                                          Handle<DependentCode> dep) {
   ASSERT(!InNewSpace(*obj));
   ASSERT(!InNewSpace(*dep));
+  // This handle scope keeps the table handle local to this function, which
+  // allows us to safely skip write barriers in table update operations.
   HandleScope scope(isolate());
   Handle<WeakHashTable> table(WeakHashTable::cast(weak_object_to_code_table_),
                               isolate());
   table = WeakHashTable::Put(table, obj, dep);
 
   if (ShouldZapGarbage() && weak_object_to_code_table_ != *table) {
     WeakHashTable::cast(weak_object_to_code_table_)->Zap(the_hole_value());
   }
   set_weak_object_to_code_table(*table);
   ASSERT_EQ(*dep, table->Lookup(obj));
@@ skipping 992 matching lines @@
       static_cast<int>(object_sizes_last_time_[index]));
   CODE_AGE_LIST_COMPLETE(ADJUST_LAST_TIME_OBJECT_COUNT)
 #undef ADJUST_LAST_TIME_OBJECT_COUNT
 
   OS::MemCopy(object_counts_last_time_, object_counts_, sizeof(object_counts_));
   OS::MemCopy(object_sizes_last_time_, object_sizes_, sizeof(object_sizes_));
   ClearObjectStats();
 }
 
 } }  // namespace v8::internal