avoid creating garbage when iterating over hashmaps

Author: Joel Dice

src/machine.cpp

@@ -770,12 +770,8 @@ parseInterfaceTable(Thread* t, Stream& s, object class_, object pool)
     PROTECT(t, interfaceTable);
 
     unsigned i = 0;
-    object it = hashMapIterator(t, map);
-    PROTECT(t, it);
-
-    for (; it; it = hashMapIteratorNext(t, it)) {
-      object interface = resolveClass
-        (t, tripleFirst(t, hashMapIteratorNode(t, it)));
+    for (HashMapIterator it(t, map); it.hasMore();) {
+      object interface = resolveClass(t, tripleFirst(t, it.next()));
       if (UNLIKELY(t->exception)) return;
 
       set(t, interfaceTable, ArrayBody + (i * BytesPerWord), interface);
@@ -1243,10 +1239,8 @@ parseMethodTable(Thread* t, Stream& s, object class_, object pool)
     if (classFlags(t, class_) & ACC_INTERFACE) {
       PROTECT(t, vtable);
 
-      for (object it = hashMapIterator(t, virtualMap); it;
-           it = hashMapIteratorNext(t, it))
-      {
-        object method = tripleFirst(t, hashMapIteratorNode(t, it));
+      for (HashMapIterator it(t, virtualMap); it.hasMore();) {
+        object method = tripleFirst(t, it.next());
         assert(t, arrayBody(t, vtable, methodOffset(t, method)) == 0);
         set(t, vtable, ArrayBody + (methodOffset(t, method) * BytesPerWord),
             method);

src/types.def

@@ -73,11 +73,6 @@
 (type weakHashMap
   (extends hashMap))
 
-(type hashMapIterator
-  (object map)
-  (object node)
-  (unsigned index))
-
 (type list
   (uint32_t size)
   (object front)

src/util.cpp

@@ -482,40 +482,6 @@ hashMapRemove(Thread* t, object map, object key,
   return o;
 }
 
-object
-hashMapIterator(Thread* t, object map)
-{
-  object array = hashMapArray(t, map);
-  if (array) {
-    for (unsigned i = 0; i < arrayLength(t, array); ++i) {
-      if (arrayBody(t, array, i)) {
-        return makeHashMapIterator(t, map, arrayBody(t, array, i), i + 1);
-      }
-    }
-  }
-  return 0;
-}
-
-object
-hashMapIteratorNext(Thread* t, object it)
-{
-  object map = hashMapIteratorMap(t, it);
-  object node = hashMapIteratorNode(t, it);
-  unsigned index = hashMapIteratorIndex(t, it);
-
-  if (tripleThird(t, node)) {
-    return makeHashMapIterator(t, map, tripleThird(t, node), index);
-  } else {
-    object array = hashMapArray(t, map);
-    for (unsigned i = index; i < arrayLength(t, array); ++i) {
-      if (arrayBody(t, array, i)) {
-        return makeHashMapIterator(t, map, arrayBody(t, array, i), i + 1);
-      }
-    }
-    return 0;
-  }  
-}
-
 void
 listAppend(Thread* t, object list, object value)
 {

src/util.h

@@ -93,6 +93,54 @@ treeInsertNode(Thread* t, Zone* zone, object tree, intptr_t key, object node,
                object sentinal,
                intptr_t (*compare)(Thread* t, intptr_t key, object b));
 
+class HashMapIterator: public Thread::Protector {
+ public:
+  HashMapIterator(Thread* t, object map):
+    Protector(t), map(map), node(0), index(0)
+  {
+    find();
+  }
+
+  void find() {
+    object array = hashMapArray(t, map);
+    for (unsigned i = index; i < arrayLength(t, array); ++i) {
+      if (arrayBody(t, array, i)) {
+        node = arrayBody(t, array, i);
+        index = i + 1;
+        return;
+      }
+    }
+    node = 0;
+  }
+
+  bool hasMore() {
+    return node != 0;
+  }
+
+  object next() {
+    if (node) {
+      object n = node;
+      if (tripleThird(t, node)) {
+        node = tripleThird(t, node);
+      } else {
+        find();
+      }
+      return n;
+    } else {
+      return 0;
+    }
+  }
+
+  virtual void visit(Heap::Visitor* v) {
+    v->visit(&map);
+    v->visit(&node);
+  }
+
+  object map;
+  object node;
+  unsigned index;
+};
+
 } // vm
 
 #endif//UTIL_H