os: improve loadavg() performance

PR-URL: #11516
Reviewed-By: Jackson Tian <shyvo1987@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>

benchmark/os/loadavg.js

@@ -0,0 +1,17 @@
+'use strict';
+
+const common = require('../common.js');
+const loadavg = require('os').loadavg;
+
+const bench = common.createBenchmark(main, {
+  n: [5e6]
+});
+
+function main(conf) {
+  const n = +conf.n;
+
+  bench.start();
+  for (var i = 0; i < n; ++i)
+    loadavg();
+  bench.end(n);
+}

lib/os.js

@@ -1,12 +1,12 @@
 'use strict';
 
 const binding = process.binding('os');
+const getLoadAvg = binding.getLoadAvg;
 const constants = process.binding('constants').os;
 const internalUtil = require('internal/util');
 const isWindows = process.platform === 'win32';
 
 exports.hostname = binding.getHostname;
-exports.loadavg = binding.getLoadAvg;
 exports.uptime = binding.getUptime;
 exports.freemem = binding.getFreeMem;
 exports.totalmem = binding.getTotalMem;
@@ -17,6 +17,12 @@ exports.networkInterfaces = binding.getInterfaceAddresses;
 exports.homedir = binding.getHomeDirectory;
 exports.userInfo = binding.getUserInfo;
 
+const avgValues = new Float64Array(3);
+exports.loadavg = function loadavg() {
+  getLoadAvg(avgValues);
+  return [avgValues[0], avgValues[1], avgValues[2]];
+};
+
 Object.defineProperty(exports, 'constants', {
   configurable: false,
   enumerable: true,

src/node_os.cc

@@ -28,8 +28,10 @@ namespace node {
 namespace os {
 
 using v8::Array;
+using v8::ArrayBuffer;
 using v8::Boolean;
 using v8::Context;
+using v8::Float64Array;
 using v8::FunctionCallbackInfo;
 using v8::Integer;
 using v8::Local;
@@ -182,14 +184,12 @@ static void GetUptime(const FunctionCallbackInfo<Value>& args) {
 
 
 static void GetLoadAvg(const FunctionCallbackInfo<Value>& args) {
-  Environment* env = Environment::GetCurrent(args);
-  double loadavg[3];
+  CHECK(args[0]->IsFloat64Array());
+  Local<Float64Array> array = args[0].As<Float64Array>();
+  CHECK_EQ(array->Length(), 3);
+  Local<ArrayBuffer> ab = array->Buffer();
+  double* loadavg = static_cast<double*>(ab->GetContents().Data());
   uv_loadavg(loadavg);
-  Local<Array> loads = Array::New(env->isolate(), 3);
-  loads->Set(0, Number::New(env->isolate(), loadavg[0]));
-  loads->Set(1, Number::New(env->isolate(), loadavg[1]));
-  loads->Set(2, Number::New(env->isolate(), loadavg[2]));
-  args.GetReturnValue().Set(loads);
 }