src: add v8.getHeapStatistics() function

Add a one-to-one binding to v8::GetHeapStatistics().  Returns info on
the current state of the JS heap, like total size and amount used.

lib/tracing.js

@@ -42,3 +42,6 @@ v8.on('removeListener', function(name) {
     binding.stopGarbageCollectionTracking();
   }
 });
+
+
+v8.getHeapStatistics = binding.getHeapStatistics;

src/node_v8.cc

@@ -35,6 +35,7 @@ using v8::GCCallbackFlags;
 using v8::GCType;
 using v8::Handle;
 using v8::HandleScope;
+using v8::HeapStatistics;
 using v8::Isolate;
 using v8::Local;
 using v8::Null;
@@ -178,6 +179,28 @@ void StartGarbageCollectionTracking(const FunctionCallbackInfo<Value>& args) {
 }
 
 
+void GetHeapStatistics(const FunctionCallbackInfo<Value>& args) {
+  Isolate* isolate = args.GetIsolate();
+  HandleScope handle_scope(isolate);
+  Environment* env = Environment::GetCurrent(isolate);
+  HeapStatistics s;
+  isolate->GetHeapStatistics(&s);
+  Local<Object> info = Object::New();
+  // 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(s.name(), isolate))
+  V(total_heap_size);
+  V(total_heap_size_executable);
+  V(total_physical_size);
+  V(used_heap_size);
+  V(heap_size_limit);
+#undef V
+  args.GetReturnValue().Set(info);
+}
+
+
 void StopGarbageCollectionTracking(const FunctionCallbackInfo<Value>& args) {
   HandleScope handle_scope(args.GetIsolate());
   Environment::GetCurrent(args.GetIsolate())->StopGarbageCollectionTracking();
@@ -193,6 +216,7 @@ void InitializeV8Bindings(Handle<Object> target,
   NODE_SET_METHOD(target,
                   "stopGarbageCollectionTracking",
                   StopGarbageCollectionTracking);
+  NODE_SET_METHOD(target, "getHeapStatistics", GetHeapStatistics);
 }
 
 }  // namespace node

test/simple/test-v8-stats.js

@@ -0,0 +1,36 @@
+// Copyright Joyent, Inc. and other Node contributors.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the
+// "Software"), to deal in the Software without restriction, including
+// without limitation the rights to use, copy, modify, merge, publish,
+// distribute, sublicense, and/or sell copies of the Software, and to permit
+// persons to whom the Software is furnished to do so, subject to the
+// following conditions:
+//
+// The above copyright notice and this permission notice shall be included
+// in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
+// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+// USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+var common = require('../common');
+var assert = require('assert');
+var v8 = require('tracing').v8;
+
+var s = v8.getHeapStatistics();
+var keys = [
+  'heap_size_limit',
+  'total_heap_size',
+  'total_heap_size_executable',
+  'total_physical_size',
+  'used_heap_size'];
+assert.deepEqual(Object.keys(s).sort(), keys);
+keys.forEach(function(key) {
+  assert.equal(typeof s[key], 'number');
+});