node: improve performance of hrtime()

process.hrtime() was performing too many operations in C++ that could be
done faster in JS. Move those operations over by creating a length 4
Uint32Array and perform bitwise operations on the seconds so that it was
unnecessary for the native API to do any object creation or set any
fields.

This has improved performance from ~350 ns/op to ~65 ns/op. Light
benchmark included to demonstrate the performance change.

PR-URL: nodejs#3780
Reviewed-By: Fedor Indutny <fedor@indutny.com>

benchmark/misc/bench-hrtime.js

@@ -0,0 +1,18 @@
+'use strict';
+
+const common = require('../common');
+
+const bench = common.createBenchmark(main, {
+  n: [1e6]
+});
+
+
+function main(conf) {
+  const n = conf.n >>> 0;
+
+  bench.start();
+  for (var i = 0; i < n; i++) {
+    process.hrtime();
+  }
+  bench.end(n);
+}

src/node.cc

@@ -2132,22 +2132,23 @@ void Hrtime(const FunctionCallbackInfo<Value>& args) {
 
   uint64_t t = uv_hrtime();
 
-  if (args.Length() > 0) {
-    // return a time diff tuple
-    if (!args[0]->IsArray()) {
+  if (!args[1]->IsUndefined()) {
+    if (!args[1]->IsArray()) {
       return env->ThrowTypeError(
-          "process.hrtime() only accepts an Array tuple.");
+          "process.hrtime() only accepts an Array tuple");
     }
-    Local<Array> inArray = Local<Array>::Cast(args[0]);
-    uint64_t seconds = inArray->Get(0)->Uint32Value();
-    uint64_t nanos = inArray->Get(1)->Uint32Value();
-    t -= (seconds * NANOS_PER_SEC) + nanos;
+    args.GetReturnValue().Set(true);
   }
 
-  Local<Array> tuple = Array::New(env->isolate(), 2);
-  tuple->Set(0, Integer::NewFromUnsigned(env->isolate(), t / NANOS_PER_SEC));
-  tuple->Set(1, Integer::NewFromUnsigned(env->isolate(), t % NANOS_PER_SEC));
-  args.GetReturnValue().Set(tuple);
+  Local<ArrayBuffer> ab = args[0].As<Uint32Array>()->Buffer();
+  uint32_t* fields = static_cast<uint32_t*>(ab->GetContents().Data());
+
+  // These three indices will contain the values for the hrtime tuple. The
+  // seconds value is broken into the upper/lower 32 bits and stored in two
+  // uint32 fields to be converted back in JS.
+  fields[0] = (t / NANOS_PER_SEC) >> 32;
+  fields[1] = (t / NANOS_PER_SEC) & 0xffffffff;
+  fields[2] = t % NANOS_PER_SEC;
 }
 
 extern "C" void node_module_register(void* m) {

src/node.js

@@ -181,12 +181,27 @@
   }
 
   startup.setupProcessObject = function() {
+    const _hrtime = process.hrtime;
+    const hrValues = new Uint32Array(3);
+
     process._setupProcessObject(pushValueToArray);
 
     function pushValueToArray() {
       for (var i = 0; i < arguments.length; i++)
         this.push(arguments[i]);
     }
+
+    process.hrtime = function hrtime(ar) {
+      const ret = [0, 0];
+      if (_hrtime(hrValues, ar)) {
+        ret[0] = (hrValues[0] * 0x100000000 + hrValues[1]) - ar[0];
+        ret[1] = hrValues[2] - ar[1];
+      } else {
+        ret[0] = hrValues[0] * 0x100000000 + hrValues[1];
+        ret[1] = hrValues[2];
+      }
+      return ret;
+    };
   };
 
   startup.globalVariables = function() {