Weak Cells

src/heap/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 "src/v8.h"
 
 #include "src/accessors.h"
 #include "src/api.h"
 #include "src/base/bits.h"
 #include "src/base/once.h"
@@ skipping 132 matching lines @@
 #endif
 
   // Ensure old_generation_size_ is a multiple of kPageSize.
   DCHECK(MB >= Page::kPageSize);
 
   memset(roots_, 0, sizeof(roots_[0]) * kRootListLength);
   set_native_contexts_list(NULL);
   set_array_buffers_list(Smi::FromInt(0));
   set_allocation_sites_list(Smi::FromInt(0));
   set_encountered_weak_collections(Smi::FromInt(0));
+  set_encountered_weak_cells(Smi::FromInt(0));
   // Put a dummy entry in the remembered pages so we can find the list the
   // minidump even if there are no real unmapped pages.
   RememberUnmappedPage(NULL, false);
 
   ClearObjectStats(true);
 }
 
 
 intptr_t Heap::Capacity() {
   if (!HasBeenSetUp()) return 0;
@@ skipping 1339 matching lines @@
       PropertyCell* cell = PropertyCell::cast(heap_object);
       Address value_address = cell->ValueAddress();
       scavenge_visitor.VisitPointer(reinterpret_cast<Object**>(value_address));
       Address type_address = cell->TypeAddress();
       scavenge_visitor.VisitPointer(reinterpret_cast<Object**>(type_address));
     }
   }
 
   // Copy objects reachable from the encountered weak collections list.
   scavenge_visitor.VisitPointer(&encountered_weak_collections_);
+  // Copy objects reachable from the encountered weak cells.
+  scavenge_visitor.VisitPointer(&encountered_weak_cells_);
 
   // Copy objects reachable from the code flushing candidates list.
   MarkCompactCollector* collector = mark_compact_collector();
   if (collector->is_code_flushing_enabled()) {
     collector->code_flusher()->IteratePointersToFromSpace(&scavenge_visitor);
   }
 
   new_space_front = DoScavenge(&scavenge_visitor, new_space_front);
 
   while (isolate()->global_handles()->IterateObjectGroups(
@@ skipping 1030 matching lines @@
 
     TYPED_ARRAYS(ALLOCATE_FIXED_TYPED_ARRAY_MAP)
 #undef ALLOCATE_FIXED_TYPED_ARRAY_MAP
 
     ALLOCATE_VARSIZE_MAP(FIXED_ARRAY_TYPE, sloppy_arguments_elements)
 
     ALLOCATE_VARSIZE_MAP(CODE_TYPE, code)
 
     ALLOCATE_MAP(CELL_TYPE, Cell::kSize, cell)
     ALLOCATE_MAP(PROPERTY_CELL_TYPE, PropertyCell::kSize, global_property_cell)
+    ALLOCATE_MAP(WEAK_CELL_TYPE, WeakCell::kSize, weak_cell)
     ALLOCATE_MAP(FILLER_TYPE, kPointerSize, one_pointer_filler)
     ALLOCATE_MAP(FILLER_TYPE, 2 * kPointerSize, two_pointer_filler)
 
 
     for (unsigned i = 0; i < arraysize(struct_table); i++) {
       const StructTable& entry = struct_table[i];
       Map* map;
       if (!AllocateMap(entry.type, entry.size).To(&map)) return false;
       roots_[entry.index] = map;
     }
@@ skipping 106 matching lines @@
   result->set_map_no_write_barrier(global_property_cell_map());
   PropertyCell* cell = PropertyCell::cast(result);
   cell->set_dependent_code(DependentCode::cast(empty_fixed_array()),
                            SKIP_WRITE_BARRIER);
   cell->set_value(the_hole_value());
   cell->set_type(HeapType::None());
   return result;
 }
 
 
+AllocationResult Heap::AllocateWeakCell(HeapObject* value) {
+  int size = WeakCell::kSize;
+  STATIC_ASSERT(WeakCell::kSize <= Page::kMaxRegularHeapObjectSize);
+  HeapObject* result;
+  {
+    AllocationResult allocation =
+        AllocateRaw(size, OLD_POINTER_SPACE, OLD_POINTER_SPACE);
+    if (!allocation.To(&result)) return allocation;
+  }
+  result->set_map_no_write_barrier(weak_cell_map());
+  WeakCell::cast(result)->update_value_from_gc(value);

[Erik Corry, 2014/10/13 15:56:17]

This is from allocation, not from GC, so probably should not call this function.

[ulan, 2014/10/14 10:17:22]

Introduced a new function "initialize" for this and renamed
"update_value_from_gc" to "clear".

+  WeakCell::cast(result)->set_next(undefined_value());

[Erik Corry, 2014/10/13 15:56:17]

There's no need to set the write barrier when setting to undefined, is there? I
think it's immovable and immortal.  So we could add SKIP_WRITE_BARRIER here.

[ulan, 2014/10/14 10:17:22]

Done.

+  return result;
+}
+
+
 void Heap::CreateApiObjects() {
   HandleScope scope(isolate());
   Factory* factory = isolate()->factory();
   Handle<Map> new_neander_map =
       factory->NewMap(JS_OBJECT_TYPE, JSObject::kHeaderSize);
 
   // Don't use Smi-only elements optimizations for objects with the neander
   // map. There are too many cases where element values are set directly with a
   // bottleneck to trap the Smi-only -> fast elements transition, and there
   // appears to be no benefit for optimize this case.
@@ skipping 2464 matching lines @@
   if (!CreateInitialMaps()) return false;
   CreateApiObjects();
 
   // Create initial objects
   CreateInitialObjects();
   CHECK_EQ(0, gc_count_);
 
   set_native_contexts_list(undefined_value());
   set_array_buffers_list(undefined_value());
   set_allocation_sites_list(undefined_value());
+  set_encountered_weak_cells(undefined_value());
   weak_object_to_code_table_ = undefined_value();
   return true;
 }
 
 
 void Heap::SetStackLimits() {
   DCHECK(isolate_ != NULL);
   DCHECK(isolate_ == isolate());
   // On 64 bit machines, pointers are generally out of range of Smis.  We write
   // something that looks like an out of range Smi to the GC.
@@ skipping 975 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
 
   MemCopy(object_counts_last_time_, object_counts_, sizeof(object_counts_));
   MemCopy(object_sizes_last_time_, object_sizes_, sizeof(object_sizes_));
   ClearObjectStats();
 }
 }
 }  // namespace v8::internal