Thread-safe weak-keys hash map

Question

How doe I get a concurrent or thread-safe Map in Scala whose keys are weak? For example, there is collection.mutable.WeakHashMap but it doesn't seem to support concurrent access/update. A cheap solution would be to hide it behind a regular Java synchronized lock?

Answer 1

Use Guava's MapMaker.

An example from the doc shows exactly what you need (translated into Scala):

import java.util.concurrent.ConcurrentMap

val timers: ConcurrentMap[Request, Stopwatch] = 
    new MapMaker().concurrencyLevel(4).weakKeys.makeMap

This is, of course, Java map, but you can easily wrap it into Scala map:

import java.{util => ju}
import scala.collection.JavaConverters._
import scala.collection.mutable

val javaMap: ju.Map[String,String] = ...
val scalaMap: mutable.Map[String,String] = javaMap.asScala