Add optional max elements limit for Map/Set mirror iterator preview.

src/runtime/runtime-collections.cc

 // Copyright 2014 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/arguments.h"
 #include "src/runtime/runtime-utils.h"
 
 
@@ skipping 209 matching lines @@
   result->set_table(holder->table());
   result->set_index(Smi::FromInt(Smi::cast(holder->index())->value()));
   result->set_kind(Smi::FromInt(Smi::cast(holder->kind())->value()));
 
   return *result;
 }
 
 
 RUNTIME_FUNCTION(Runtime_GetWeakMapEntries) {
   HandleScope scope(isolate);
-  DCHECK(args.length() == 1);
+  DCHECK(args.length() == 2);
   CONVERT_ARG_HANDLE_CHECKED(JSWeakCollection, holder, 0);
+  CONVERT_NUMBER_CHECKED(int, max_entries, Int32, args[1]);
+  RUNTIME_ASSERT(max_entries >= 0);
+
   Handle<ObjectHashTable> table(ObjectHashTable::cast(holder->table()));
+  if (max_entries == 0 || max_entries > table->NumberOfElements()) {
+    max_entries = table->NumberOfElements();
+  }
   Handle<FixedArray> entries =
-      isolate->factory()->NewFixedArray(table->NumberOfElements() * 2);
+      isolate->factory()->NewFixedArray(max_entries * 2);
   {
     DisallowHeapAllocation no_gc;
-    int number_of_non_hole_elements = 0;
-    for (int i = 0; i < table->Capacity(); i++) {
+    int count = 0;
+    for (int i = 0; count / 2 < max_entries && i < table->Capacity(); i++) {
       Handle<Object> key(table->KeyAt(i), isolate);
       if (table->IsKey(*key)) {
-        entries->set(number_of_non_hole_elements++, *key);
+        entries->set(count++, *key);
         Object* value = table->Lookup(key);
-        entries->set(number_of_non_hole_elements++, value);
+        entries->set(count++, value);
       }
     }
-    DCHECK_EQ(table->NumberOfElements() * 2, number_of_non_hole_elements);
+    DCHECK_EQ(max_entries * 2, count);
   }
   return *isolate->factory()->NewJSArrayWithElements(entries);
 }
 
 
 RUNTIME_FUNCTION(Runtime_MapIteratorNext) {
   SealHandleScope shs(isolate);
   DCHECK(args.length() == 2);
   CONVERT_ARG_CHECKED(JSMapIterator, holder, 0);
   CONVERT_ARG_CHECKED(JSArray, value_array, 1);
@@ skipping 82 matching lines @@
   if (*table != *new_table) {
     // Zap the old table since we didn't record slots for its elements.
     table->FillWithHoles(0, table->length());
   }
   return *weak_collection;
 }
 
 
 RUNTIME_FUNCTION(Runtime_GetWeakSetValues) {
   HandleScope scope(isolate);
-  DCHECK(args.length() == 1);
+  DCHECK(args.length() == 2);
   CONVERT_ARG_HANDLE_CHECKED(JSWeakCollection, holder, 0);
+  CONVERT_NUMBER_CHECKED(int, max_values, Int32, args[1]);
+  RUNTIME_ASSERT(max_values >= 0);
+
   Handle<ObjectHashTable> table(ObjectHashTable::cast(holder->table()));
-  Handle<FixedArray> values =
-      isolate->factory()->NewFixedArray(table->NumberOfElements());
+  if (max_values == 0 || max_values > table->NumberOfElements()) {
+    max_values = table->NumberOfElements();
+  }
+  Handle<FixedArray> values = isolate->factory()->NewFixedArray(max_values);
   {
     DisallowHeapAllocation no_gc;
-    int number_of_non_hole_elements = 0;
-    for (int i = 0; i < table->Capacity(); i++) {
+    int count = 0;
+    for (int i = 0; count < max_values && i < table->Capacity(); i++) {
       Handle<Object> key(table->KeyAt(i), isolate);
-      if (table->IsKey(*key)) {
-        values->set(number_of_non_hole_elements++, *key);
-      }
+      if (table->IsKey(*key)) values->set(count++, *key);
     }
-    DCHECK_EQ(table->NumberOfElements(), number_of_non_hole_elements);
+    DCHECK_EQ(max_values, count);
   }
   return *isolate->factory()->NewJSArrayWithElements(values);
 }
 
 
 RUNTIME_FUNCTION(Runtime_ObservationWeakMapCreate) {
   HandleScope scope(isolate);
   DCHECK(args.length() == 0);
   // TODO(adamk): Currently this runtime function is only called three times per
   // isolate. If it's called more often, the map should be moved into the
   // strong root list.
   Handle<Map> map =
       isolate->factory()->NewMap(JS_WEAK_MAP_TYPE, JSWeakMap::kSize);
   Handle<JSWeakMap> weakmap =
       Handle<JSWeakMap>::cast(isolate->factory()->NewJSObjectFromMap(map));
   return *WeakCollectionInitialize(isolate, weakmap);
 }
 }
 }  // namespace v8::internal