低頻度の更新と高頻度の読み込みがある場合・・・

gistfile1.scala

import java.util.concurrent.atomic.AtomicReference

class LowUpdateHighReadList[T] {
  val aList = new AtomicReference[List[T]]
  aList.set(List())

  def list() : List[T] = aList.get()

  def add(t : T) : List[T] = {
    listUpdate(t::_)
  }

  def remove(t : T) : List[T] = {
    listUpdate(_.filter(_ != t))
  }

  protected def listUpdate(f : (List[T]) => List[T]) : List[T] = {
    val list = aList.get()
    val newList = f(list)
    if( aList.compareAndSet(list,newList) ) {
      newList
    } else {
      listUpdate(f)
    }
  }

}