Allow the morphing of strings to external strings to avoid having to...

src/mark-compact.cc

 // Copyright 2006-2008 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 372 matching lines @@
 
 
 // Helper class for pruning the symbol table.
 class SymbolTableCleaner : public ObjectVisitor {
  public:
   SymbolTableCleaner() : pointers_removed_(0) { }
   void VisitPointers(Object** start, Object** end) {
     // Visit all HeapObject pointers in [start, end).
     for (Object** p = start; p < end; p++) {
       if ((*p)->IsHeapObject() && !HeapObject::cast(*p)->IsMarked()) {
+        // Check if the symbol being pruned is an external symbol. We need to
+        // delete the associated external data as this symbol is going away.
+
+        // Since the object is not marked we can access its map word safely
+        // without having to worry about marking bits in the object header.
+        Map* map = HeapObject::cast(*p)->map();
+        // Since no objects have yet been moved we can safely access the map of
+        // the object.
+        uint32_t type = map->instance_type();
+        bool is_external = (type & kStringRepresentationMask) ==
+                           kExternalStringTag;
+        if (is_external) {
+          bool is_two_byte = (type & kStringEncodingMask) == kTwoByteStringTag;
+          byte* resource_addr = reinterpret_cast<byte*>(*p) +
+                                ExternalString::kResourceOffset -
+                                kHeapObjectTag;
+          if (is_two_byte) {
+            v8::String::ExternalStringResource* resource =
+                *reinterpret_cast<v8::String::ExternalStringResource**>
+                (resource_addr);
+            delete resource;
+          } else {
+            v8::String::ExternalAsciiStringResource* resource =
+                *reinterpret_cast<v8::String::ExternalAsciiStringResource**>
+                (resource_addr);
+            delete resource;
+          }
+        }
         // Set the entry to null_value (as deleted).
         *p = Heap::null_value();
         pointers_removed_++;
       }
     }
   }
 
   int PointersRemoved() {
     return pointers_removed_;
   }
@@ skipping 1324 matching lines @@
 
 void MarkCompactCollector::RebuildRSets() {
 #ifdef DEBUG
   ASSERT(state_ == RELOCATE_OBJECTS);
   state_ = REBUILD_RSETS;
 #endif
   Heap::RebuildRSets();
 }
 
 } }  // namespace v8::internal