[scala] DynamicVariable 예제

스칼라의 DynamicVariable은 Java의 Thread Local State 변수와 동일한 효과를 가진다. 

import scala.concurrent.ExecutionContext
import scala.util.DynamicVariable

object DynamicVariableExample extends App {

  def execute(body: =>Unit) = ExecutionContext.global.execute(new Runnable {
    def run() = body
  })

  val dyn = new DynamicVariable[Int](10)

  def doSomething = println(Thread.currentThread().getName() + ":" + dyn.value)

  dyn.withValue(1) {  execute(doSomething) }
  dyn.withValue(50) {  execute(doSomething) }
  println

}

결과

scala-execution-context-global-11:1

scala-execution-context-global-12:50

내부 코드를 살펴보면,java.lang.InheritableThreadLocal을 사용하고 있다. 

class DynamicVariable[T](init: T) {
  private val tl = new InheritableThreadLocal[T] {
    override def initialValue = init.asInstanceOf[T with AnyRef]
  }

public class InheritableThreadLocal<T> extends ThreadLocal<T> {