[翻译]AKKA笔记 - DEATHWATCH -7
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当我们说Actor生命周期的时候,我们能看到Actor能被很多种方式停掉(用ActorSystem.stop或ActorContext.stop或发送一个PoisonPill - 也有一个kill和gracefulstop)。
无论Actor是怎么死的,有些情况一些系统中的其他actor想要知道。让我们举一个Actor与数据库交互的例子 - 我们叫它RepositoryActor。很明显,会有一些其他actor会向这个RepositoryActor发送消息。这些有“兴趣”的Actor很愿意留个eye或者看(watch)这个actor关闭时的消息。这个在Actor里面叫DeathWatch。这个用来watch和unwatch的方法就是ActorContext.watch和ActorContext.unwatch。如果已经监视了,这些watcher会在Actor关闭时收到一个Terminated消息,并可以很舒服的加到他们的receive功能中。
不像Supervision有一个严格的父子继承关系,任何Actor都可以watch任何ActorSystem中的Actor。
让我们看下。
代码
QUOTEREPOSITORYACTOR
1.我们的QueryRepositoryActor格言查询Actor保存了一个quote的列表并且在收到一个QuoteRepositoryRequest时随机返回一条。
- 他记录了收到消息的个数,如果收到超过3个消息,他用PoisonPill把自己杀掉
这没啥神奇的。
package me.rerun.akkanotes.deathwatchimport akka.actor.{PoisonPill, Actor, ActorLogging, actorRef2Scala} import me.rerun.akkanotes.protocols.QuoteRepositoryProtocol._ import scala.util.Randomclass QuoteRepositoryActor() extends Actor with ActorLogging { val quotes = List( "Moderation is for cowards", "Anything worth doing is worth overdoing", "The trouble is you think you have time", "You never gonna know if you never even try") var repoRequestCount:Int=1 def receive = { case QuoteRepositoryRequest => { if (repoRequestCount>3){ self!PoisonPill } else { //Get a random Quote from the list and construct a response val quoteResponse = QuoteRepositoryResponse(quotes(Random.nextInt(quotes.size))) log.info(s"QuoteRequest received in QuoteRepositoryActor. Sending response to Teacher Actor $quoteResponse") repoRequestCount=repoRequestCount+1 sender ! quoteResponse } } }}
TEACHERACTORWATCHER
一样的,TeacherActorWatcher也没啥神奇的,除了他创建了一个QuoteRepositoryActor并且用context.watch观察。
package me.rerun.akkanotes.deathwatchimport akka.actor.{Terminated, Props, Actor, ActorLogging} import me.rerun.akkanotes.protocols.TeacherProtocol.QuoteRequest import me.rerun.akkanotes.protocols.QuoteRepositoryProtocol.QuoteRepositoryRequestclass TeacherActorWatcher extends Actor with ActorLogging { val quoteRepositoryActor=context.actorOf(Props[QuoteRepositoryActor], "quoteRepositoryActor") context.watch(quoteRepositoryActor) def receive = { case QuoteRequest => { quoteRepositoryActor ! QuoteRepositoryRequest } case Terminated(terminatedActorRef)=>{ log.error(s"Child Actor {$terminatedActorRef} Terminated") } }}
测试CASE
这里会有点意思。我从来没想过这个可以被测试。akka-testkit。我们会分析下这三个测试CASE:
1. 断言如果观察到已经收到Terminated消息
QuoteRepositoryActor应该在收到第四条消息时给测试case发送一条Terminated消息。前三条应该是可以的。
"A QuoteRepositoryActor" must { ... ... ... "send back a termination message to the watcher on 4th message" in { val quoteRepository=TestActorRef[QuoteRepositoryActor] val testProbe=TestProbe() testProbe.watch(quoteRepository) //Let's watch the Actor within (1000 millis) { var receivedQuotes = List[String]() (1 to 3).foreach(_ => quoteRepository ! QuoteRepositoryRequest) receiveWhile() { case QuoteRepositoryResponse(quoteString) => { receivedQuotes = receivedQuotes :+ quoteString } } receivedQuotes.size must be (3) println(s"receiveCount ${receivedQuotes.size}") //4th message quoteRepository!QuoteRepositoryRequest testProbe.expectTerminated(quoteRepository) //Expect a Terminated Message } }
2.如果没有观察(watched/unwatched)到则断言没收到Terminated消息
事实上,我们做这个只是演示下context.unwatch。如果我们移掉testProbe.watch和testProbe.unwatch这行,则测试case会运行的很正常。
"not send back a termination message on 4th message if not watched" in { val quoteRepository=TestActorRef[QuoteRepositoryActor] val testProbe=TestProbe() testProbe.watch(quoteRepository) //watching within (1000 millis) { var receivedQuotes = List[String]() (1 to 3).foreach(_ => quoteRepository ! QuoteRepositoryRequest) receiveWhile() { case QuoteRepositoryResponse(quoteString) => { receivedQuotes = receivedQuotes :+ quoteString } } testProbe.unwatch(quoteRepository) //not watching anymore receivedQuotes.size must be (3) println(s"receiveCount ${receivedQuotes.size}") //4th message quoteRepository!QuoteRepositoryRequest testProbe.expectNoMsg() //Not Watching. No Terminated Message } }
3. 在TeacherActorWatcher中断言收到了Terminated消息
我们订阅了EventStream并通过检查一个特殊的日志消息来断言termination。
"end back a termination message to the watcher on 4th message to the TeacherActor" in { //This just subscribes to the EventFilter for messages. We have asserted all that we need against the QuoteRepositoryActor in the previous testcase val teacherActor=TestActorRef[TeacherActorWatcher] within (1000 millis) { (1 to 3).foreach (_=>teacherActor!QuoteRequest) //this sends a message to the QuoteRepositoryActor EventFilter.error (pattern="""Child Actor .* Terminated""", occurrences = 1).intercept{ teacherActor!QuoteRequest //Send the dangerous 4th message } } }
EventFilter中的pattern属性,没啥奇怪的,需要一个正则表达式。正则pattern=”“”Child Actor .* Terminated”“”用来匹配一条格式是Child Actor {Actor[akka://TestUniversityMessageSystem/user/$$d/quoteRepositoryActor#-1905987636]} Terminated日志信息。
Github
与往常一样,代码在github。看下deathwatch的包。
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