v8: optimize `getHeapStatistics`

Since setting object properties in C++ can be slow, pass
data to JS using preallocated smalloc buffer and create
object in JS instead.

PR-URL: https://github.com/iojs/io.js/pull/469
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>

1 files changed, 47 insertions, 13 deletions

diff --git a/src/node_v8.cc b/src/node_v8.cc
index 47e802e41b..f3bdda409d 100644
--- a/src/node_v8.cc
+++ b/src/node_v8.cc
@@ -8,6 +8,7 @@
 namespace node {
 
 using v8::Context;
+using v8::ExternalArrayType;
 using v8::Function;
 using v8::FunctionCallbackInfo;
 using v8::Handle;
@@ -20,25 +21,41 @@ using v8::Uint32;
 using v8::V8;
 using v8::Value;
 
+#define HEAP_STATISTICS_PROPERTIES(V)                                         \
+  V(0, total_heap_size, kTotalHeapSizeIndex)                                  \
+  V(1, total_heap_size_executable, kTotalHeapSizeExecutableIndex)             \
+  V(2, total_physical_size, kTotalPhysicalSizeIndex)                          \
+  V(3, used_heap_size, kUsedHeapSizeIndex)                                    \
+  V(4, heap_size_limit, kHeapSizeLimitIndex)
+
+#define V(a, b, c) +1
+static const size_t kHeapStatisticsBufferLength = HEAP_STATISTICS_PROPERTIES(V);
+#undef V
+
+static const ExternalArrayType kHeapStatisticsBufferType =
+    v8::kExternalUint32Array;
 
 void GetHeapStatistics(const FunctionCallbackInfo<Value>& args) {
-  Environment* env = Environment::GetCurrent(args);
+  CHECK(args.Length() == 1 && args[0]->IsObject());
+
   Isolate* isolate = args.GetIsolate();
   HeapStatistics s;
   isolate->GetHeapStatistics(&s);
-  Local<Object> info = Object::New(isolate);
-  // TODO(trevnorris): Setting many object properties in C++ is a significant
-  // performance hit. Redo this to pass the results to JS and create/set the
-  // properties there.
-#define V(name)                                                               \
-  info->Set(env->name ## _string(), Uint32::NewFromUnsigned(isolate, s.name()))
-  V(total_heap_size);
-  V(total_heap_size_executable);
-  V(total_physical_size);
-  V(used_heap_size);
-  V(heap_size_limit);
+  Local<Object> obj = args[0].As<Object>();
+  uint32_t* data =
+      static_cast<uint32_t*>(obj->GetIndexedPropertiesExternalArrayData());
+
+  CHECK_NE(data, nullptr);
+  ASSERT_EQ(obj->GetIndexedPropertiesExternalArrayDataType(),
+            kHeapStatisticsBufferType);
+  ASSERT_EQ(obj->GetIndexedPropertiesExternalArrayDataLength(),
+            kHeapStatisticsBufferLength);
+
+#define V(i, name, _)                                                         \
+  data[i] = static_cast<uint32_t>(s.name());
+
+  HEAP_STATISTICS_PROPERTIES(V)
 #undef V
-  args.GetReturnValue().Set(info);
 }
 
 
@@ -54,6 +71,23 @@ void InitializeV8Bindings(Handle<Object> target,
   Environment* env = Environment::GetCurrent(context);
   env->SetMethod(target, "getHeapStatistics", GetHeapStatistics);
   env->SetMethod(target, "setFlagsFromString", SetFlagsFromString);
+
+  target->Set(FIXED_ONE_BYTE_STRING(env->isolate(),
+                                    "kHeapStatisticsBufferLength"),
+              Uint32::NewFromUnsigned(env->isolate(),
+                                      kHeapStatisticsBufferLength));
+
+  target->Set(FIXED_ONE_BYTE_STRING(env->isolate(),
+                                    "kHeapStatisticsBufferType"),
+              Uint32::NewFromUnsigned(env->isolate(),
+                                      kHeapStatisticsBufferType));
+
+#define V(i, _, name)                                                         \
+  target->Set(FIXED_ONE_BYTE_STRING(env->isolate(), #name),                   \
+              Uint32::NewFromUnsigned(env->isolate(), i));
+
+  HEAP_STATISTICS_PROPERTIES(V)
+#undef V
 }
 
 }  // namespace node