Weak Cells

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 280 matching lines @@
 void MarkCompactCollector::CollectGarbage() {
   // Make sure that Prepare() has been called. The individual steps below will
   // update the state as they proceed.
   DCHECK(state_ == PREPARE_GC);
 
   MarkLiveObjects();
   DCHECK(heap_->incremental_marking()->IsStopped());
 
   if (FLAG_collect_maps) ClearNonLiveReferences();
 
+  ProcessAndClearWeakCells();
+
   ClearWeakCollections();
 
+  heap_->set_encountered_weak_cells(heap_->undefined_value());
+
 #ifdef VERIFY_HEAP
   if (FLAG_verify_heap) {
     VerifyMarking(heap_);
   }
 #endif
 
   SweepSpaces();
 
 #ifdef VERIFY_HEAP
   if (heap()->weak_embedded_objects_verification_enabled()) {
@@ skipping 502 matching lines @@
   if (sweeping_in_progress()) {
     // Instead of waiting we could also abort the sweeper threads here.
     EnsureSweepingCompleted();
   }
 
   // Clear marking bits if incremental marking is aborted.
   if (was_marked_incrementally_ && abort_incremental_marking_) {
     heap()->incremental_marking()->Abort();
     ClearMarkbits();
     AbortWeakCollections();
+    AbortWeakCells();
     AbortCompaction();
     was_marked_incrementally_ = false;
   }
 
   // Don't start compaction if we are in the middle of incremental
   // marking cycle. We did not collect any slots.
   if (!FLAG_never_compact && !was_marked_incrementally_) {
     StartCompaction(NON_INCREMENTAL_COMPACTION);
   }
 
@@ skipping 1885 matching lines @@
   while (weak_collection_obj != Smi::FromInt(0)) {
     JSWeakCollection* weak_collection =
         reinterpret_cast<JSWeakCollection*>(weak_collection_obj);
     weak_collection_obj = weak_collection->next();
     weak_collection->set_next(heap()->undefined_value());
   }
   heap()->set_encountered_weak_collections(Smi::FromInt(0));
 }
 
 
+void MarkCompactCollector::ProcessAndClearWeakCells() {
+  HeapObject* undefined = heap()->undefined_value();
+  Object* weak_cell_obj = heap()->encountered_weak_cells();
+  while (weak_cell_obj != undefined) {
+    WeakCell* weak_cell = reinterpret_cast<WeakCell*>(weak_cell_obj);
+    HeapObject* value = weak_cell->value();
+    if (!MarkCompactCollector::IsMarked(value)) {
+      weak_cell->update_value_from_gc(undefined);
+    } else {
+      Object** slot = HeapObject::RawField(weak_cell, WeakCell::kValueOffset);
+      heap()->mark_compact_collector()->RecordSlot(slot, slot, value);
+    }
+    weak_cell_obj = weak_cell->next();
+    weak_cell->set_next(undefined);

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

No write barrier needed.

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

Done.

+  }
+  heap()->set_encountered_weak_cells(undefined);
+}
+
+
+void MarkCompactCollector::AbortWeakCells() {
+  Object* undefined = heap()->undefined_value();
+  Object* weak_cell_obj = heap()->encountered_weak_cells();
+  while (weak_cell_obj != undefined) {
+    WeakCell* weak_cell = reinterpret_cast<WeakCell*>(weak_cell_obj);
+    weak_cell_obj = weak_cell->next();
+    weak_cell->set_next(undefined);

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

No write barrier needed

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

Done.

+  }
+  heap()->set_encountered_weak_cells(undefined);
+}
+
+
 void MarkCompactCollector::RecordMigratedSlot(Object* value, Address slot) {
   if (heap_->InNewSpace(value)) {
     heap_->store_buffer()->Mark(slot);
   } else if (value->IsHeapObject() && IsOnEvacuationCandidate(value)) {
     SlotsBuffer::AddTo(&slots_buffer_allocator_, &migration_slots_buffer_,
                        reinterpret_cast<Object**>(slot),
                        SlotsBuffer::IGNORE_OVERFLOW);
   }
 }
 
 
 // We scavange new space simultaneously with sweeping. This is done in two

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

scavange -> scavenge

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

Done.

 // passes.
 //
 // The first pass migrates all alive objects from one semispace to another or
 // promotes them to old space.  Forwarding address is written directly into
 // first word of object without any encoding.  If object is dead we write
 // NULL as a forwarding address.
 //
 // The second pass updates pointers to new space in all spaces.  It is possible
 // to encounter pointers to dead new space objects during traversal of pointers
 // to new space.  We should clear them to avoid encountering them during next
@@ skipping 1650 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