node: improve GetActiveRequests performance

v8 is faster at setting object properties in JS than C++. Even when it
requires calling into JS from native code. Make
process._getActiveRequests() faster by doing this when populating the
array containing request objects.

Simple benchmark:

    for (let i = 0; i < 22; i++)
      fs.open(__filename, 'r', function() { });
    let t = process.hrtime();
    for (let i = 0; i < 1e6; i++)
      process._getActiveRequests();
    t = process.hrtime(t);
    console.log((t[0] * 1e9 + t[1]) / 1e6);

Results between the two:

    Previous:  4406 ns/op
    Patched:    690 ns/op     5.4x faster

PR-URL: https://github.com/nodejs/node/pull/3375
Reviewed-By: James Snell <jasnell@gmail.com>
Reviewed-By: Ben Noordhuis <ben@strongloop.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/test/parallel/test-process-getactiverequests.js b/test/parallel/test-process-getactiverequests.js
new file mode 100644
index 0000000000..4b7e0df1a5
--- /dev/null
+++ b/test/parallel/test-process-getactiverequests.js
@@ -0,0 +1,10 @@
+'use strict';
+
+const common = require('../common');
+const assert = require('assert');
+const fs = require('fs');
+
+for (let i = 0; i < 12; i++)
+  fs.open(__filename, 'r', function() { });
+
+assert.equal(12, process._getActiveRequests().length);