Scala中有SoftHashMap吗？ [英] Is there a SoftHashMap in Scala?

问题描述

我知道这个java的问题，但没有一个这些实现似乎很好用 scala.collection.JavaConversions 。

I'm aware of this question for java, but none of those implementations seem to play well with scala.collection.JavaConversions.

我正在寻找简单的东西（例如单个文件，不是整个库），实现 SoftHashMap ，使其与Scala Map （即支持 getOrElseUpdate ，解压缩，剩余的Scala Map 方法）

I'm looking for something simple (e.g. single file, not a whole library) that implements SoftHashMap such that it plays well with Scala Map (i.e. supports getOrElseUpdate, unzip, and the remaining Scala Map methods).

推荐答案

实现灵感来自这个java WeakHashMap ：

import scala.collection.mutable.{Map, HashMap}
import scala.ref._


class SoftMap[K, V <: AnyRef] extends Map[K, V]
{
  class SoftValue[K, +V <: AnyRef](val key:K, value:V, queue:ReferenceQueue[V]) extends SoftReference(value, queue)

  private val map = new HashMap[K, SoftValue[K, V]]

  private val queue = new ReferenceQueue[V]

  override def += (kv: (K, V)): this.type =
  {
    processQueue
    val sv = new SoftValue(kv._1, kv._2, queue)
    map(kv._1) = sv
    this
  }

  private def processQueue
  {
    while (true)
    {
      queue.poll match
      {   
        case Some(sv:SoftValue[K, _]) => map.remove(sv.key)
        case _ => return
      }
    }
  }


  override def get(key: K): Option[V] = map.get(key) match
  {
    case Some(sv) => sv.get match
      { case v:Some[_] => v
        case None => {map.remove(key); None} }
    case None => None
  }



  override def -=(key: K):this.type =
  {
    processQueue
    map.remove(key)
    this
  }

  override def iterator: Iterator[(K, V)] =
  {
    processQueue
    map.iterator.collect{ case (key, sv) if sv.get.isDefined => (key, sv.get.get) }
  }

  override def empty:SoftMap[K, V] = new SoftMap[K, V]

  override def size = {processQueue; map.size}
}

这篇关于Scala中有SoftHashMap吗？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！