Scala中的多个Actors实现有何不同？

Question

随着Scala 2.9.0的发布,Typesafe Stack也被宣布,它结合了Scala语言和Akka框架.现在,虽然Scala在其标准库中有演员,但Akka使用自己的实现.而且,如果我们寻找其他实现,我们也会发现Lift和Scalaz也有实现!

那么,这些实现之间有什么区别？

Answer 1

这个答案不是我的.它由Viktor Klang(Akka成名)在David Pollak(电梯名望),Jason Zaugg(Scalaz成名),Philipp Haller(Scala Actors成名)的帮助下制作.

我在这里所做的就是格式化它(如果Stack Overflow支持表格会更容易).

当我有更多时间时,我会稍后填写几个地方.

设计理念

• Scalaz演员

  最小的复杂性.最大的通用性,模块性和可扩展性.

• 举起演员

  最小的复杂性,JVM的垃圾收集,而不是担心明确的生命周期,与其他Scala和Java程序一致的错误处理行为,轻量/小内存占用,邮箱,静态类似于Scala Actors和Erlang actor,高性能.

• 斯卡拉演员

  在Scala中提供完整的Erlang actor模型,轻量级/小内存占用.

• Akka演员

  简单,透明,可分配,高性能,轻量级和高适应性.

版本

                    Scalaz Actors   Lift Actors     Scala Actors    Akka Actors
Current stable ver. 5               2.1             2.9.0           0.10
Minimum Scala ver.  2.8             2.7.7                           2.8
Minimum Java ver.                   1.5             1.5             1.6

演员模型支持

                    Scalaz Actors   Lift Actors     Scala Actors    Akka Actors
Spawn new actors    Yes             Yes             Yes             Yes
inside of actor
Send messages to    Yes             Yes             Yes             Yes
known actor 
Change behavior     Actors are      Yes             Yes: nested     Yes:
for next message    immutable                       react/receive   become/unbecome
Supervision         Not provided    No              Actor: Yes,     Yes
(link/trapExit)                                     Reactor: No

国家层面的隔离

如果用户在其Actors上定义公共方法,它们是否可以从外部调用？

• Scalaz演员:不适用.演员是一个密封的特质.
• 电梯演员:是的
• 斯卡拉演员:是的
• Akka Actors:不,演员实例被屏蔽在ActorRef后面.

演员类型

• Scalaz演员: Actor[A] extends A => ()
• 电梯演员:LiftActor,SpecializeLiftActor[T]
• 斯卡拉演员:Reactor[T],Actor extends Reactor[Any]
• Akka演员: Actor[Any]

演员生命周期管理

                    Scalaz Actors   Lift Actors     Scala Actors    Akka Actors
Manual start        No              No              Yes             Yes
Manual stop         No              No              No              Yes
Restart-on-failure  n/a             Yes             Yes             Configurable per actor instance
Restart semantics                   n/a             Rerun actor     Restore actor to stable state by re-allocating it and
                                                    behavior        throw away the old instance
Restart configurability             n/a             n/a             X times, X times within Y time
Lifecycle hooks provided            No lifecycle    act             preStart, postStop, preRestart, postRestart

消息发送模式

                    Scalaz Actors   Lift Actors     Scala Actors    Akka Actors
Fire-forget         a ! message     actor ! msg     actor ! msg     actorRef ! msg
                    a(message)
Send-receive-reply  (see 1)         actor !? msg    actor !? msg    actorRef !! msg
                                    actor !! msg
Send-receive-future (see 2)                         actor !! msg    actorRef !!! msg
Send-result-of-     promise(message).                               future.onComplete( f => to ! f.result )
future              to(actor)
Compose actor with  actor comap f   No              No              No
function            (see 3)

(1)任何函数f都成为这样一个角色:

val a: Msg => Promise[Rep] = f.promise
val reply: Rep = a(msg).get

(2)任何函数f都成为这样一个角色:

val a = f.promise
val replyFuture = a(message)

(3)逆变函子:actor comap f.也是Kleisli的成分Promise.

消息回复模式

TBD

                    Scalaz Actors   Lift Actors     Scala Actors    Akka Actors
reply-to-sender-in-message
reply-to-message

消息处理

支持嵌套接收？

• Scalaz演员: -
• 提升演员:是的(用一点手编码).
• Scala Actors:是的,基于线程的接收和基于事件的响应.
• Akka Actors:不,嵌套接收可能会导致内存泄漏并导致性能下降.

消息执行机制

TBD

                    Scalaz Actors   Lift Actors     Scala Actors    Akka Actors
Name for Execution Mechanism
Execution Mechanism is
configurable
Execution Mechanism can be
specified on a per-actor basis
Lifecycle of Execution Mechanism
must be explicitly managed
Thread-per-actor execution
mechanism
Event-driven execution mechanism
Mailbox type
Supports transient mailboxes
Supports persistent mailboxes

分配/远程演员

                    Scalaz Actors   Lift Actors     Scala Actors    Akka Actors
Transparent remote  n/a             No              Yes             Yes
actors
Transport protocol  n/a             n/a             Java            Akka Remote Protocol
                                                    serialization   (Protobuf on top of TCP)
                                                    on top of TCP
Dynamic clustering  n/a             n/a             n/a             In commercial offering

HOWTO文档

TBD

                    Scalaz Actors   Lift Actors     Scala Actors    Akka Actors
Define an actor
Create an actor instance
Start an actor instance
Stop an actor instance

Answer 2

• scala.actors是第一个在Scala中实现Erlang风格的并发性的重要尝试,它激发了其他库设计者在更好(在某些情况下)和更高性能的实现.最大的问题(至少对我而言)是,与Erlang进程不同,补充了OTP(允许构建容错系统),scala.actors只提供了一个良好的基础,一组必须用于构建的稳定基元更高层次的框架 - 在一天结束时,你必须在演员之上编写自己的主管,演员目录,有限状态机等.

• 在这里,Akka开始拯救,为基于演员的开发提供了一个功能齐全的堆栈:更多惯用的角色,一套用于协调的高级抽象(负载平衡器,演员池等)和构建容错系统(主管) ,从OTP移植等),易于配置的调度程序(调度程序)等.对不起,如果我听起来很粗鲁,但我认为,2.9.0+中不会合并- 我宁愿期待Akka演员逐渐取代stdlib实现.

• 斯卡拉兹.通常我在所有项目的依赖项列表中都有这个库,当由于某种原因,我无法使用Akka时,非阻塞的Scalaz Promises(具有所有优点,如果sequence)与标准actor一起保存天.但是,我从未使用Scalaz actor代替scala.actors或Akka.