events: improve once() performance

This commit takes advantage of the performance improvements V8 has
made to function.bind() in V8 5.4 and uses it to avoid constant
recompilation/reoptimization of the wrapper closure used in once().
This change results in ~27% performance increase for once().

PR-URL: https://github.com/nodejs/node/pull/10445
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Teddy Katz <teddy.katz@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

1 files changed, 20 insertions, 0 deletions

diff --git a/benchmark/events/ee-once.js b/benchmark/events/ee-once.js
new file mode 100644
index 0000000000..29ea562c40
--- /dev/null
+++ b/benchmark/events/ee-once.js
@@ -0,0 +1,20 @@
+'use strict';
+var common = require('../common.js');
+var EventEmitter = require('events').EventEmitter;
+
+var bench = common.createBenchmark(main, {n: [2e7]});
+
+function main(conf) {
+  var n = conf.n | 0;
+
+  var ee = new EventEmitter();
+
+  function listener() {}
+
+  bench.start();
+  for (var i = 0; i < n; i += 1) {
+    ee.once('dummy', listener);
+    ee.emit('dummy');
+  }
+  bench.end(n);
+}