How to reduce Scala (/ Java) startup overhead?

Question

I\'m pretty ignorant of the Java world (I do mostly C / Python) but Scala looked interesting enough to pull me in. One problem I\'m having with it is the enormous startup ov

Answer 1

You could work around the JVM start-up time by opening the Scala REPL and then loading your scripts directly into it using the :load command. This compiles (it does take some time, but I don't find it long in practice) the contents of the script and loads it for use in the REPL. For example:

scala> :load testScript.scala
Loading testScript.scala...
import scala.collection.mutable.Map
memory: scala.collection.mutable.Map[Int,Int] = Map()
fib: (Int)Int
res7: Int = 165580141

scala> fib(10)
res1: Int = 55

scala> fib(11)
res2: Int = 89

scala> fib(12)
res3: Int = 144

scala> fib(13)
res4: Int = 233

For example, a typical workflow of mine when writing different prototypes in Scala is as follows. I have a text editor open in one window, and the Scala REPL in another. I write my code and then load it (:load script.scala). The results produced by the script are immediately available (as seen in the above transcript, res7) and any functions, classes or objects defined in the script are also available. And it's faster than running scala myScript.scala as the JVM is already loaded.

If you go the compiled route, use fsc (the fast Scala compiler). The first time it's invoked it creates a daemon process that compiles the code. Therefore you will only have to pay the JVM start-up price once. Just note that if you change the value of CLASSPATH (the environment variable), you'll have to restart fsc (it's something that has bugged me for a while).

-- Flaviu Cipcigan