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.deathwatch
import akka.actor.{PoisonPill, Actor, ActorLogging, actorRef2Scala}
import me.rerun.akkanotes.protocols.QuoteRepositoryProtocol._
import scala.util.Random
class 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 $quoteResponse")
repoRequestCount=repoRequestCount+1
sender ! quoteResponse
}
}
}
}TEACHERACTORWATCHER
一样的，TeacherActorWatcher也没啥神奇的，除了他创建了一个QuoteRepositoryActor并且用context.watch观察。
package me.rerun.akkanotes.deathwatch
import akka.actor.{Terminated, Props, Actor, ActorLogging}
import me.rerun.akkanotes.protocols.TeacherProtocol.QuoteRequest
import me.rerun.akkanotes.protocols.QuoteRepositoryProtocol.QuoteRepositoryRequest
class TeacherActorWatcher extends Actor with ActorLogging {
val quoteRepositoryActor=context.actorOf(Props[QuoteRepositoryActor], "quoteRepositoryActor")
context.watch(quoteRepositoryActor)
def receive = {
case QuoteRequest => {
quoteRepositoryActor ! QuoteRepositoryRequest
}
case Terminated(terminatedActorRef)=>{
log.error(s"Child Actor {$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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