如何在 Scala 中使用 ConcurrentLinkedQueue？

Question

val nodes = Array.fill[mutable.Buffer[Int]](numNodes){new ArrayBuffer[Int]() with mutable.SynchronizedBuffer[Int]}

def addMutualEdge(i: Int)(j: Int) {nodes(i) += j; nodes(j) += i}

当我编译这个时，我得到了弃用警告：

SynchronizedBuffer is deprecated. Synchronization via traits is deprecated as it is inherently reliable. Consider java.util.concurrent.ConcurrentLinkedQueue as an alternative

如何在上面的代码中使用java库？

Answer 1

您可以只使用ConcurrentLinkedQueue 而不是Buffer，因为它也是可变的：

scala> import java.util.concurrent._
import java.util.concurrent._

scala> val nodes = Array.fill(10){new ConcurrentLinkedQueue[Int]()}
nodes: Array[java.util.concurrent.ConcurrentLinkedQueue[Int]] = Array([], [], [], [], [], [], [], [], [], [])

scala> def addMutualEdge(i: Int)(j: Int) {nodes(i).add(j); nodes(j).add(i)}
addMutualEdge: (i: Int)(j: Int)Unit

这是最快的选择，因为此队列基于 CAS 操作，因此没有阻塞（与 SynchronizedBuffer 相比）。另一种选择是直接同步操作：

scala> val nodes = Array.fill[mutable.Buffer[Int]](10){new ArrayBuffer[Int]()}
nodes: Array[scala.collection.mutable.Buffer[Int]] = Array(ArrayBuffer(), ArrayBuffer(), ArrayBuffer(), ArrayBuffer(), ArrayBuffer(), ArrayBuffer(), ArrayBuffer(), ArrayBuffer(), ArrayBuffer(), ArrayBuffer())

scala> def addMutualEdge(i: Int)(j: Int) = this.synchronized{nodes(i) += j; nodes(j) += i}
addMutualEdge: (i: Int)(j: Int)scala.collection.mutable.Buffer[Int]

你也可以将java的Collections.synchronizedList(...)与scala.collection.JavaConverters.asScala结合使用

import java.util._
import scala.collection.JavaConverters._
scala> val nodes = Array.fill(10){Collections.synchronizedList(new ArrayBuffer[Int]().asJava).asScala}
nodes: Array[scala.collection.mutable.Buffer[Int]] = Array(Buffer(), Buffer(), Buffer(), Buffer(), Buffer(), Buffer(), Buffer(), Buffer(), Buffer(), Buffer())

或者你可以使用AtomicReferenceArray:

implicit class RichAtomic[T](a: AtomicReferenceArray[List[T]]) { def apply(i: Int) = (a,i); def update(i: Int, e: List[T]) = a.set(i, e)}
implicit class RichList[T](a: (AtomicReferenceArray[List[T]], Int)) { def ::=(e: T) = while({val lst = a._1.get(a._2);!a._1.compareAndSet(a._2, lst, e :: lst)}){}}
implicit def toList[T](a: (AtomicReferenceArray[List[T]], Int)) = a._1.get(a._2)

val nodes = new AtomicReferenceArray(Array.fill[List[Int]](10){Nil})

scala> def addMutualEdge(i: Int)(j: Int) = {nodes(i) ::= j; nodes(j) ::= i}
addMutualEdge: (i: Int)(j: Int)Unit

隐式用于提供与Array 类似的接口。请注意，::= 将元素添加到列表的开头。