process: improve memoryUsage() performance

Creating an object in JS and using a typed array to transfer values
from C++ to JS is faster than creating an object and setting
properties in C++.

The included benchmark shows ~34% increase in performance with this
change.

PR-URL: https://github.com/nodejs/node/pull/11497
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

benchmark/process/memoryUsage.js

@@ -0,0 +1,16 @@
+'use strict';
+
+var common = require('../common.js');
+var bench = common.createBenchmark(main, {
+  n: [1e5]
+});
+
+function main(conf) {
+  var n = +conf.n;
+
+  bench.start();
+  for (var i = 0; i < n; i++) {
+    process.memoryUsage();
+  }
+  bench.end(n);
+}

lib/internal/bootstrap_node.js

@@ -38,6 +38,7 @@
 
     _process.setup_hrtime();
     _process.setup_cpuUsage();
+    _process.setupMemoryUsage();
     _process.setupConfig(NativeModule._source);
     NativeModule.require('internal/process/warning').setup();
     NativeModule.require('internal/process/next_tick').setup();

lib/internal/process.js

@@ -11,6 +11,7 @@ function lazyConstants() {
 
 exports.setup_cpuUsage = setup_cpuUsage;
 exports.setup_hrtime = setup_hrtime;
+exports.setupMemoryUsage = setupMemoryUsage;
 exports.setupConfig = setupConfig;
 exports.setupKillAndExit = setupKillAndExit;
 exports.setupSignalHandlers = setupSignalHandlers;
@@ -98,6 +99,20 @@ function setup_hrtime() {
   };
 }
 
+function setupMemoryUsage() {
+  const memoryUsage_ = process.memoryUsage;
+  const memValues = new Float64Array(4);
+
+  process.memoryUsage = function memoryUsage() {
+    memoryUsage_(memValues);
+    return {
+      rss: memValues[0],
+      heapTotal: memValues[1],
+      heapUsed: memValues[2],
+      external: memValues[3]
+    };
+  };
+}
 
 function setupConfig(_source) {
   // NativeModule._source

src/env.h

@@ -106,7 +106,6 @@ namespace node {
   V(exponent_string, "exponent")                                              \
   V(exports_string, "exports")                                                \
   V(ext_key_usage_string, "ext_key_usage")                                    \
-  V(external_string, "external")                                              \
   V(external_stream_string, "_externalStream")                                \
   V(family_string, "family")                                                  \
   V(fatal_exception_string, "_fatalException")                                \
@@ -117,8 +116,6 @@ namespace node {
   V(get_string, "get")                                                        \
   V(gid_string, "gid")                                                        \
   V(handle_string, "handle")                                                  \
-  V(heap_total_string, "heapTotal")                                           \
-  V(heap_used_string, "heapUsed")                                             \
   V(homedir_string, "homedir")                                                \
   V(hostmaster_string, "hostmaster")                                          \
   V(ignore_string, "ignore")                                                  \
@@ -186,7 +183,6 @@ namespace node {
   V(rename_string, "rename")                                                  \
   V(replacement_string, "replacement")                                        \
   V(retry_string, "retry")                                                    \
-  V(rss_string, "rss")                                                        \
   V(serial_string, "serial")                                                  \
   V(scopeid_string, "scopeid")                                                \
   V(sent_shutdown_string, "sentShutdown")                                     \

src/node.cc

@@ -2247,25 +2247,22 @@ void MemoryUsage(const FunctionCallbackInfo<Value>& args) {
     return env->ThrowUVException(err, "uv_resident_set_memory");
   }
 
+  Isolate* isolate = env->isolate();
   // V8 memory usage
   HeapStatistics v8_heap_stats;
-  env->isolate()->GetHeapStatistics(&v8_heap_stats);
-
-  Local<Number> heap_total =
-      Number::New(env->isolate(), v8_heap_stats.total_heap_size());
-  Local<Number> heap_used =
-      Number::New(env->isolate(), v8_heap_stats.used_heap_size());
-  Local<Number> external_mem =
-      Number::New(env->isolate(),
-                  env->isolate()->AdjustAmountOfExternalAllocatedMemory(0));
-
-  Local<Object> info = Object::New(env->isolate());
-  info->Set(env->rss_string(), Number::New(env->isolate(), rss));
-  info->Set(env->heap_total_string(), heap_total);
-  info->Set(env->heap_used_string(), heap_used);
-  info->Set(env->external_string(), external_mem);
-
-  args.GetReturnValue().Set(info);
+  isolate->GetHeapStatistics(&v8_heap_stats);
+
+  // Get the double array pointer from the Float64Array argument.
+  CHECK(args[0]->IsFloat64Array());
+  Local<Float64Array> array = args[0].As<Float64Array>();
+  CHECK_EQ(array->Length(), 4);
+  Local<ArrayBuffer> ab = array->Buffer();
+  double* fields = static_cast<double*>(ab->GetContents().Data());
+
+  fields[0] = rss;
+  fields[1] = v8_heap_stats.total_heap_size();
+  fields[2] = v8_heap_stats.used_heap_size();
+  fields[3] = isolate->AdjustAmountOfExternalAllocatedMemory(0);
 }