Rehash and clear deleted entries in weak collections during GC

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/heap/mark-compact.h"
 
 #include "src/base/atomicops.h"
 #include "src/base/bits.h"
 #include "src/base/sys-info.h"
 #include "src/code-stubs.h"
@@ skipping 2532 matching lines @@
         reinterpret_cast<JSWeakCollection*>(weak_collection_obj);
     DCHECK(MarkCompactCollector::IsMarked(weak_collection));
     if (weak_collection->table()->IsHashTable()) {
       ObjectHashTable* table = ObjectHashTable::cast(weak_collection->table());
       for (int i = 0; i < table->Capacity(); i++) {
         HeapObject* key = HeapObject::cast(table->KeyAt(i));
         if (!MarkCompactCollector::IsMarked(key)) {
           table->RemoveEntry(i);
         }
       }
+      // Rehash if more than 25% of the entries are deleted entries.
+      // TODO(jochen): Consider to shrink the fixed array in place.
+      if ((table->NumberOfDeletedElements() << kJSWeakCollectionLoadFactorExp) >
+          table->NumberOfElements()) {
+        HandleScope scope(heap()->isolate());
+        table->Rehash(heap()->isolate()->factory()->undefined_value());
+      }
     }
     weak_collection_obj = weak_collection->next();
     weak_collection->set_next(heap()->undefined_value());
   }
   heap()->set_encountered_weak_collections(Smi::FromInt(0));
 }
 
 
 void MarkCompactCollector::AbortWeakCollections() {
   Object* weak_collection_obj = heap()->encountered_weak_collections();
@@ skipping 1333 matching lines @@
     MarkBit mark_bit = Marking::MarkBitFrom(host);
     if (Marking::IsBlack(mark_bit)) {
       RelocInfo rinfo(isolate(), pc, RelocInfo::CODE_TARGET, 0, host);
       RecordRelocSlot(host, &rinfo, target);
     }
   }
 }
 
 }  // namespace internal
 }  // namespace v8