Subj : Re: Rhino speed
To   : Dave Thorn
From : Igor Bukanov
Date : Tue Feb 15 2005 09:39 am

Dave Thorn wrote:
> Hello,
> 
> I've been investigating rhino as one of the engines to add scripting
> to a java application.  I've got it running scripts in three ways:
> 
> 1) "Standalone" - Context cx = Context.enter(); (version 1.6R1)
> 2) Via Apache's BSF (Bean Scripting Framework)  (version 1.5R3)
> 3) using jsc - the javascript compiler (version 1.6R1)

The compiler was part of Rhino since 1.5R1 release.

> 
> Doing some performance comparisons with native Java code, I found the
> rhino scripts were running rather slowly in comparison.  Some
> operations that took subsecond times in java were taking up to 14
> seconds in any rhino implementation.  This was relatively
> straightforward code, just a large number of iterations, adding
> integers to an ArrayList, and integer comparison.
> 
> The speed difference did surprise me somewhat, but especially so with
> the jsc version.  I don't know much about bytecode or compilers, but
> if jsc compiled it to bytecode, then I was expecting similar speeds to
> native Java.

JavaScript is dynamically typed language so even operations like x + y 
goes through special runtime code to check types of x and y and perform 
  operation accordingly. In addition numbers are represented as objects 
so x + y when x and y are numbers would eventually be evaluated as
new Double(((Number)x).doubleValue() + ((Number)y).doubleValue()).

In few cases Rhino can optimize that away and generates JVM bytecode 
similar to what a Java compiler generates for x + y. But as long as x 
and y comes from object properties or global variables and the result 
would be stored as a property or in a global variable, the execution 
would be like the above code.

Also all access to Java objects goes through reflection which slows 
things down.

> 
> Do I simply have naive expectations?  Am I perhaps doing something
> wrong?  Any and all suggestions and comments appreciated.

Do not write numerically intense code in JS. And if you need to do that 
then http://www.mozilla.org/rhino/perf.html may help.

Regards, Igor

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