Synchronize store buffer processing and concurrent sweeping.

src/store-buffer.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 370 matching lines @@
   for (HeapObject* object = it.Next(); object != NULL; object = it.Next()) {
     if (object->IsFixedArray()) {
       Address slot_address = object->address();
       Address end = object->address() + object->Size();
 
       while (slot_address < end) {
         HeapObject** slot = reinterpret_cast<HeapObject**>(slot_address);
         // When we are not in GC the Heap::InNewSpace() predicate
         // checks that pointers which satisfy predicate point into
         // the active semispace.
-        heap_->InNewSpace(*slot);
+        Object* object = reinterpret_cast<Object*>(
+            NoBarrier_Load(reinterpret_cast<AtomicWord*>(slot)));
+        heap_->InNewSpace(object);
         slot_address += kPointerSize;
       }
     }
   }
 }
 #endif
 
 
 void StoreBuffer::Verify() {
 #ifdef VERIFY_HEAP
@@ skipping 18 matching lines @@
 
 void StoreBuffer::FindPointersToNewSpaceInRegion(
     Address start,
     Address end,
     ObjectSlotCallback slot_callback,
     bool clear_maps) {
   for (Address slot_address = start;
        slot_address < end;
        slot_address += kPointerSize) {
     Object** slot = reinterpret_cast<Object**>(slot_address);
-    if (heap_->InNewSpace(*slot)) {
-      HeapObject* object = reinterpret_cast<HeapObject*>(*slot);
-      ASSERT(object->IsHeapObject());
+    Object* object = reinterpret_cast<Object*>(
+        NoBarrier_Load(reinterpret_cast<AtomicWord*>(slot)));
+    if (heap_->InNewSpace(object)) {
+      HeapObject* heap_object = reinterpret_cast<HeapObject*>(object);
+      ASSERT(heap_object->IsHeapObject());
       // The new space object was not promoted if it still contains a map
       // pointer. Clear the map field now lazily.
-      if (clear_maps) ClearDeadObject(object);
-      slot_callback(reinterpret_cast<HeapObject**>(slot), object);
-      if (heap_->InNewSpace(*slot)) {
+      if (clear_maps) ClearDeadObject(heap_object);
+      slot_callback(reinterpret_cast<HeapObject**>(slot), heap_object);
+      object = reinterpret_cast<Object*>(
+          NoBarrier_Load(reinterpret_cast<AtomicWord*>(slot)));
+      if (heap_->InNewSpace(object)) {
         EnterDirectlyIntoStoreBuffer(slot_address);
       }
     }
   }
 }
 
 
 // Compute start address of the first map following given addr.
 static inline Address MapStartAlign(Address addr) {
   Address page = Page::FromAddress(addr)->area_start();
@@ skipping 76 matching lines @@
   Address visitable_start = page->area_start();
   Address end_of_page = page->area_end();
 
   Address visitable_end = visitable_start;
 
   Object* free_space_map = heap_->free_space_map();
   Object* two_pointer_filler_map = heap_->two_pointer_filler_map();
   Object* constant_pool_array_map = heap_->constant_pool_array_map();
 
   while (visitable_end < end_of_page) {
-    Object* o = *reinterpret_cast<Object**>(visitable_end);
+    // The sweeper thread concurrently may write free space maps and size to
+    // this page. We need acquire load here to make sure that we get a
+    // consistent view of maps and their sizes.
+    Object* o = reinterpret_cast<Object*>(
+        Acquire_Load(reinterpret_cast<AtomicWord*>(visitable_end)));
     // Skip fillers or constant pool arrays (which never contain new-space
     // pointers but can contain pointers which can be confused for fillers)
     // but not things that look like fillers in the special garbage section
     // which can contain anything.
     if (o == free_space_map ||
         o == two_pointer_filler_map ||
         o == constant_pool_array_map ||
         (visitable_end == space->top() && visitable_end != space->limit())) {
       if (visitable_start != visitable_end) {
         // After calling this the special garbage section may have moved.
@@ skipping 43 matching lines @@
     bool clear_maps) {
   Address* limit = old_top_;
   old_top_ = old_start_;
   {
     DontMoveStoreBufferEntriesScope scope(this);
     for (Address* current = old_start_; current < limit; current++) {
 #ifdef DEBUG
       Address* saved_top = old_top_;
 #endif
       Object** slot = reinterpret_cast<Object**>(*current);
-      Object* object = *slot;
+      Object* object = reinterpret_cast<Object*>(
+          NoBarrier_Load(reinterpret_cast<AtomicWord*>(slot)));
       if (heap_->InFromSpace(object)) {
         HeapObject* heap_object = reinterpret_cast<HeapObject*>(object);
         // The new space object was not promoted if it still contains a map
         // pointer. Clear the map field now lazily.
         if (clear_maps) ClearDeadObject(heap_object);
         slot_callback(reinterpret_cast<HeapObject**>(slot), heap_object);
-        if (heap_->InNewSpace(*slot)) {
+        object = reinterpret_cast<Object*>(
+            NoBarrier_Load(reinterpret_cast<AtomicWord*>(slot)));
+        if (heap_->InNewSpace(object)) {
           EnterDirectlyIntoStoreBuffer(reinterpret_cast<Address>(slot));
         }
       }
       ASSERT(old_top_ == saved_top + 1 || old_top_ == saved_top);
     }
   }
 }
 
 
 void StoreBuffer::IteratePointersToNewSpace(ObjectSlotCallback slot_callback) {
@@ skipping 115 matching lines @@
     }
     old_buffer_is_sorted_ = false;
     old_buffer_is_filtered_ = false;
     *old_top_++ = reinterpret_cast<Address>(int_addr << kPointerSizeLog2);
     ASSERT(old_top_ <= old_limit_);
   }
   heap_->isolate()->counters()->store_buffer_compactions()->Increment();
 }
 
 } }  // namespace v8::internal