Clojure
has an Atom for
changing state between threads in a synchronous and independent manner,that is not part of the STM.你
use it like this：
user=> (def my-atom (atom 0)) #'user/my-atom user=> @my-atom 0 user=> (swap! my-atom inc) 1 user=> @my-atom 1 user=> (swap! my-atom (fn [n] (* (+ n n) 2))) 4
我的问题是：Scala等同于Clojure的Atom是什么？
解决方法
正如@Shepmaster和@ om-nom-nom所说,它是java.util.concurrent.atomic.Atomic的封装.
一个等效的包装器可能如下所示：
import java.util.concurrent.atomic._
import scala.annotation.tailrec
object Atom {
def apply[A](init: A): Atom[A] = new Impl(new AtomicReference(init))
private class Impl[A](state: AtomicReference[A]) extends Atom[A] {
def apply(): A = state.get()
def update(value: A): Unit = state.set(value)
def transformAndGet(f: A => A): A = transformImpl(f)
@tailrec private final def transformImpl(fun: A => A): A = {
val v = state.get()
val newv = fun(v)
if (state.compareAndSet(v,newv)) newv
else transformImpl(fun)
}
}
}
trait Atom[A] {
def apply(): A
def update(value: A): Unit
def transformAndGet(f: A => A): A
}
例如：
val myAtom = Atom(0) myAtom() // --> 0 myAtom.transformAndGet(_ + 1) // --> 1 myAtom() // --> 1 myAtom.transformAndGet(_ * 4) // --> 4
如果使用Scala-STM,该功能内置于STM引用中,通过使用.single视图：
scala> import scala.concurrent.stm._
import scala.concurrent.stm._
scala> val myAtom = Ref(0).single
myAtom: scala.concurrent.stm.Ref.View[Int] =
scala.concurrent.stm.ccstm.CCSTMRefs$IntRef@52f463b0
scala> myAtom()
res0: Int = 0
scala> myAtom.transformAndGet(_ + 1)
res1: Int = 1
scala> myAtom()
res2: Int = 1
scala> myAtom.transformAndGet(_ * 4)
res3: Int = 4
优点是Ref.apply已经为您提供了原始类型的专用单元格,例如Int而不是AnyRef(Boxed).
