Help with Scala parsing classes and JSON

[Sean Rhea]

scala.util.parsing.json.JSON isn't thread safe, according to the following link:

https://issues.scala-lang.org/browse/SI-4929

In a comment in that same thread, Jason Zaugg suggests instead creating a separate scala.util.parsing.json.Parser for each thread and using that. Can anyone reply with a code example that implements that suggestion? I can't figure out how to knit all of the required pieces together. (Perhaps I'm missing some subtle difference between StdTokenParsers and StandardTokenParsers?)

Thanks,

Sean

-- 

I lived for a time in New York City. Just a little bit north of that urban prison, I knew of a beautiful flat spot among the trees, just big enough for me to lie down. It was easy to get to from the confines of my apartment, and I slept there often, alone under the stars. It can be done. --Mike Clelland

[Matthew Neeley]

You could do something like this:

import scala.util.parsing.json._

// copied implementation of JSON object from standard lib, but make it a class
class SafeJSON extends Parser {

private def unRaw (in : Any) : Any = in match {
case JSONObject(obj) => obj.map({ case (k,v) => (k,unRaw(v))}).toList
case JSONArray(list) => list.map(unRaw)
case x => x
}

def parseRaw(input : String) : Option[JSONType] =
phrase(root)(new lexical.Scanner(input)) match {
case Success(result, _) => Some(result)
case _ => None
}

def parseFull(input: String): Option[Any] =
parseRaw(input) match {
case Some(data) => Some(resolveType(data))
case None => None
}

def resolveType(input: Any): Any = input match {
case JSONObject(data) => data.transform {
case (k,v) => resolveType(v)
}
case JSONArray(data) => data.map(resolveType)
case x => x
}

def perThreadNumberParser_=(f : NumericParser) { numberParser.set(f) }
def perThreadNumberParser : NumericParser = numberParser.get()
}

// SafeJSON behaves like JSON from standard lib, but stores per-thread
parser instances
// in a thread-local variable and then delegates method calls to the
appropriate parser instance.
object SafeJSON {
private parser = new ThreadLocal[SafeJSON] {
override def initialValue = new SafeJSON
}

def parseRaw(input: String): Option[JSONType] = parser.get.parseRaw(input)
def parseFull(input: String): Option[Any] = parser.get.parseFull(input)

def resolveType(input: Any): Any = parser.get.resolveType(input)

// additional methods can be similarly proxied here...
}

--Matthew

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[Sean Rhea]

That's perfect. Thanks, Matthew!

Sean