使用 DeathWatch 杀死 Akka 演员时未发送消息

Question

我试图在演员被杀时发送消息。

这是基于 Akka 死亡观察文档： http ://doc.akka.io/docs/akka/2.3.6/java/untyped-actors.html#deathwatch-java

在 serviceActor 中，我正在等待“杀死”消息，但实际上我从未发送过此消息。 所以要在 ServiceActor 中接收消息，我使用：

else if (msg instanceof Terminated) {
        final Terminated t = (Terminated) msg;
        if (t.getActor() == child) {
            lastSender.tell(Msg.TERMINATED, getSelf());
        }
    } else {
        unhandled(msg);
    }

我已将持续时间设置为 10 毫秒：

Duration.create(10, TimeUnit.MILLISECONDS)

但消息Msg.TERMINATED从未在 onReceive 方法中收到：

@Override
    public void onReceive(Object msg) {
        if (msg == ServiceActor.Msg.SUCCESS) {
            System.out.println("Success");
            getContext().stop(getSelf());
        } else if (msg == ServiceActor.Msg.TERMINATED) {
            System.out.println("Terminated");
        } else
            unhandled(msg);
    }

当 ServiceActor 失败时，如何向 HelloWorld 发送消息？

整个代码：

package terminatetest;
import akka.Main;

public class Launcher {

    public static void main(String args[]) {

        String[] akkaArgsArray = new String[1];

        akkaArgsArray[0] = "terminatetest.HelloWorld";

        Main.main(akkaArgsArray);

    }

}

package terminatetest;


import java.util.concurrent.TimeUnit;

import scala.concurrent.duration.Duration;
import akka.actor.ActorRef;
import akka.actor.PoisonPill;
import akka.actor.Props;
import akka.actor.UntypedActor;

public class HelloWorld extends UntypedActor {

    @Override
    public void preStart() {

        int counter = 0;

        akka.actor.ActorSystem system = getContext().system();

        final ActorRef greeter = getContext().actorOf(
                Props.create(ServiceActor.class), String.valueOf(counter));

        system.scheduler().scheduleOnce(
                Duration.create(10, TimeUnit.MILLISECONDS), new Runnable() {
                    public void run() {
                        greeter.tell(PoisonPill.getInstance(), getSelf());
                    }
                }, system.dispatcher());

        greeter.tell("http://www.google.com", getSelf());

        counter = counter + 1;
    }

    @Override
    public void onReceive(Object msg) {
        if (msg == ServiceActor.Msg.SUCCESS) {
            System.out.println("Success");
            getContext().stop(getSelf());
        } else if (msg == ServiceActor.Msg.TERMINATED) {
            System.out.println("Terminated");
        } else
            unhandled(msg);
    }
}

package terminatetest;

import static com.utils.PrintUtils.println;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;

import akka.actor.ActorRef;
import akka.actor.Props;
import akka.actor.Terminated;
import akka.actor.UntypedActor;

public class ServiceActor extends UntypedActor {

    final ActorRef child = this.getContext().actorOf(Props.empty(), "child");
    {
        this.getContext().watch(child);
    }

    ActorRef lastSender = getContext().system().deadLetters();

    public static enum Msg {
        SUCCESS, FAIL, TERMINATED;
    }

    @Override
    public void onReceive(Object msg) {

        if (msg instanceof String) {
            String urlName = (String) msg;

            try {
                long startTime = System.currentTimeMillis();
                URL url = new URL(urlName);
                HttpURLConnection conn = (HttpURLConnection) url.openConnection();
                conn.connect();

                BufferedReader reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));
                StringBuilder out = new StringBuilder();
                String line;
                while ((line = reader.readLine()) != null) {
                    out.append(line);
                }
                System.out.println("Connection successful to " + url);
                System.out.println("Content is " + out);
                long endTime = System.currentTimeMillis();
                System.out.println("Total Time : " + (endTime - startTime) + " milliseconds");

            } catch (MalformedURLException mue) {
                println("URL Name " + urlName);
                System.out.println("MalformedURLException");
                System.out.println(mue.getMessage());
                mue.printStackTrace();
                getSender().tell(Msg.FAIL, getSelf());
            } catch (IOException ioe) {
                println("URL Name " + urlName);
                System.out.println("IOException");
                System.out.println(ioe.getMessage());
                ioe.printStackTrace();
                System.out.println("Now exiting");
                getSender().tell(Msg.FAIL, getSelf());
            }
        }

        else if (msg instanceof Terminated) {
                final Terminated t = (Terminated) msg;
                if (t.getActor() == child) {
                    lastSender.tell(Msg.TERMINATED, getSelf());
                }
            } else {
                unhandled(msg);
            }
    }

}

更新：我现在正在使用以下方法从子演员本身启动毒药：

更新到 ServiceActor ：

if (urlName.equalsIgnoreCase("poisonPill")) {   
    this.getSelf().tell(PoisonPill.getInstance(), getSelf());
    getSender().tell(Msg.TERMINATED, getSelf());
}

更新到 HelloWorld ：

system.scheduler().scheduleOnce(
        Duration.create(10, TimeUnit.MILLISECONDS), new Runnable() {
            public void run() {
                greeter.tell("poisonPill", getSelf());
            }
        }, system.dispatcher());

这将显示以下输出：

startTime : 1412777375414
Connection successful to http://www.google.com
Content is ....... (I'veremoved the content for brevity)
Total Time : 1268 milliseconds
Terminated

毒丸消息在 10 毫秒后发送，在这个例子中，actor 存活了 1268 毫秒。 那么为什么在发送毒药时演员没有终止？ 这是因为时间太短了吗？

更新代码：

package terminatetest;


import java.util.concurrent.TimeUnit;

import scala.concurrent.duration.Duration;
import akka.actor.ActorRef;
import akka.actor.Props;
import akka.actor.UntypedActor;

public class HelloWorld extends UntypedActor {

    @Override
    public void preStart() {

        int counter = 0;

        akka.actor.ActorSystem system = getContext().system();

        final ActorRef greeter = getContext().actorOf(
                Props.create(ServiceActor.class), String.valueOf(counter));

        system.scheduler().scheduleOnce(
                Duration.create(10, TimeUnit.MILLISECONDS), new Runnable() {
                    public void run() {
                        greeter.tell("poisonPill", getSelf());
                    }
                }, system.dispatcher());

        greeter.tell("http://www.google.com", getSelf());

        counter = counter + 1;
    }

    @Override
    public void onReceive(Object msg) {
        if (msg == ServiceActor.Msg.SUCCESS) {
            System.out.println("Success");
            getContext().stop(getSelf());
        } else if (msg == ServiceActor.Msg.TERMINATED) {
            System.out.println("Terminated");
        } else
            unhandled(msg);
    }
}


package terminatetest;

import static com.utils.PrintUtils.println;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;

import akka.actor.ActorRef;
import akka.actor.PoisonPill;
import akka.actor.UntypedActor;

public class ServiceActor extends UntypedActor {

    ActorRef lastSender = getSender();

    public static enum Msg {
        SUCCESS, FAIL, TERMINATED;
    }

    @Override
    public void onReceive(Object msg) {

        if (msg instanceof String) {
            String urlName = (String) msg;

            if (urlName.equalsIgnoreCase("poisonPill")) {   
                this.getSelf().tell(PoisonPill.getInstance(), getSelf());
                getSender().tell(Msg.TERMINATED, getSelf());
            }

            else {

                try {
                    long startTime = System.currentTimeMillis();
                    System.out.println("startTime : "+startTime);
                    URL url = new URL(urlName);
                    HttpURLConnection conn = (HttpURLConnection) url.openConnection();
                    conn.connect();

                    BufferedReader reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));
                    StringBuilder out = new StringBuilder();
                    String line;
                    while ((line = reader.readLine()) != null) {
                        out.append(line);
                    }
                    System.out.println("Connection successful to " + url);
                    System.out.println("Content is " + out);
                    long endTime = System.currentTimeMillis();
                    System.out.println("Total Time : " + (endTime - startTime) + " milliseconds");

                } catch (MalformedURLException mue) {
                    println("URL Name " + urlName);
                    System.out.println("MalformedURLException");
                    System.out.println(mue.getMessage());
                    mue.printStackTrace();
                    getSender().tell(Msg.FAIL, getSelf());
                } catch (IOException ioe) {
                    println("URL Name " + urlName);
                    System.out.println("IOException");
                    System.out.println(ioe.getMessage());
                    ioe.printStackTrace();
                    System.out.println("Now exiting");
                    getSender().tell(Msg.FAIL, getSelf());
                }
            }
        }
    }

}

Answer 1

我认为您的问题源于这样一个事实，即您在ServiceActor构建过程中只设置了lastSender一次，并且您明确地将其设置为死信。 如果您想将消息发送回给您发送String消息的演员，那么您需要将lastSender设置lastSender sender() 。 不这样做将导致您的Msg.TERMINATED总是死信。

编辑

我现在在这里看到真正的问题。 在HelloWorld演员中，您正在向ServiceActor发送一个PoisonPill 。 ServiceActor将因此停止自身，从而也停止child ref（因为它是ServiceActor的子actor）。 在这一点上，您会认为Terminated消息会被传递给ServiceActor因为它明确地PoisonPill child （并且它可能确实被传递了），但是您已经向ServiceActor发送了一个PoisonPill ，因此它不会处理在该消息之后收到的任何消息（这将是Terminate ）所以这就是块的原因：

else if (msg instanceof Terminated) {

在ServiceActor永远不会被击中。

编辑2

您的演员收到首先点击 google 的请求，然后第二次收到"poisonPill"消息（10 毫秒后）。 当actor按顺序处理它的邮箱时，actor会在处理消息以停止自身之前完全处理命中google的请求。 这就是演员在 10 毫秒后不会停止的原因。 你不能在演员正在做的事情中阻止它。