How make Java 8 Nashorn fast?

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I'm using Java 8 Nashorn to render CommonMark to HTML server side. If I compile and cache and reuse a CompiledScript, a certain page takes 5 minutes to render. However, if I instead use eval, and cache and reuse the script engine, rendering the same page takes 3 seconds.

Why is CompiledScript so slow? (sample code follows)

What's a good approach for running Javascript code in Nashorn, over and over again as quickly as possible? And avoiding compiling the Javascript code more than once?

This is the server side Scala code snippet that calls Nashorn in a way that takes 5 minutes: (when run 200 times; I'm compiling many comments from CommonMark to HTML.)

if (engine == null) {
  val script = scala.io.Source.fromFile("public/res/remarkable.min.js").mkString
  engine = new js.ScriptEngineManager(null).getEngineByName("nashorn")
  compiledScript = engine.asInstanceOf[js.Compilable].compile(s"""
    var global = this;
    $script;
    remarkable = new Remarkable({});
    remarkable.render(__source__);""");
}
engine.put("__source__", "**bold**")
val htmlText = compiledScript.eval()

Whereas this takes 2.7 seconds: (when run 200 times)

if (engine == null) {
  engine = new js.ScriptEngineManager(null).getEngineByName("nashorn")
  engine.eval("var global = this;")
  engine.eval(new jio.FileReader("public/res/remarkable.min.js"))
  engine.eval("remarkable = new Remarkable({});")
}
engine.put("source", "**bold**")
val htmlText = engine.eval("remarkable.render(source)")

I would actually have guessed that the CompiledScript version (the topmost snippet) would have been faster. Anyway, I suppose I'll have to cache the rendered HTML server side.

(Linux Mint & Java 8 u20)

asked 15 secs ago

KajMagnus

2,759

How make Java 8 Nashorn fast?