pekko/akka-docs/rst/java/code/docs/actor/japi/FaultHandlingDocSample.java

/**
 * Copyright (C) 2009-2012 Typesafe Inc. <http://www.typesafe.com>
 */
package docs.actor.japi;

//#all
//#imports
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import akka.actor.*;
import akka.dispatch.Mapper;
import akka.japi.Function;
import scala.concurrent.util.Duration;
import akka.util.Timeout;
import akka.event.Logging;
import akka.event.LoggingAdapter;
import com.typesafe.config.Config;
import com.typesafe.config.ConfigFactory;

import static akka.japi.Util.classTag;

import static akka.actor.SupervisorStrategy.*;
import static akka.pattern.Patterns.ask;
import static akka.pattern.Patterns.pipe;

import static docs.actor.japi.FaultHandlingDocSample.WorkerApi.*;
import static docs.actor.japi.FaultHandlingDocSample.CounterServiceApi.*;
import static docs.actor.japi.FaultHandlingDocSample.CounterApi.*;
import static docs.actor.japi.FaultHandlingDocSample.StorageApi.*;

//#imports

public class FaultHandlingDocSample {

  /**
   * Runs the sample
   */
  public static void main(String[] args) {
    Config config = ConfigFactory.parseString("akka.loglevel = DEBUG \n" + "akka.actor.debug.lifecycle = on");

    ActorSystem system = ActorSystem.create("FaultToleranceSample", config);
    ActorRef worker = system.actorOf(new Props(Worker.class), "worker");
    ActorRef listener = system.actorOf(new Props(Listener.class), "listener");
    // start the work and listen on progress
    // note that the listener is used as sender of the tell,
    // i.e. it will receive replies from the worker
    worker.tell(Start, listener);
  }

  /**
   * Listens on progress from the worker and shuts down the system when enough
   * work has been done.
   */
  public static class Listener extends UntypedActor {
    final LoggingAdapter log = Logging.getLogger(getContext().system(), this);

    @Override
    public void preStart() {
      // If we don't get any progress within 15 seconds then the service is unavailable
      getContext().setReceiveTimeout(Duration.parse("15 seconds"));
    }

    public void onReceive(Object msg) {
      log.debug("received message {}", msg);
      if (msg instanceof Progress) {
        Progress progress = (Progress) msg;
        log.info("Current progress: {} %", progress.percent);
        if (progress.percent >= 100.0) {
          log.info("That's all, shutting down");
          getContext().system().shutdown();
        }
      } else if (msg == ReceiveTimeout.getInstance()) {
        // No progress within 15 seconds, ServiceUnavailable
        log.error("Shutting down due to unavailable service");
        getContext().system().shutdown();
      } else {
        unhandled(msg);
      }
    }
  }

  //#messages
  public interface WorkerApi {
    public static final Object Start = "Start";
    public static final Object Do = "Do";

    public static class Progress {
      public final double percent;

      public Progress(double percent) {
        this.percent = percent;
      }

      public String toString() {
        return String.format("%s(%s)", getClass().getSimpleName(), percent);
      }
    }
  }

  //#messages

  /**
   * Worker performs some work when it receives the Start message. It will
   * continuously notify the sender of the Start message of current Progress.
   * The Worker supervise the CounterService.
   */
  public static class Worker extends UntypedActor {
    final LoggingAdapter log = Logging.getLogger(getContext().system(), this);
    final Timeout askTimeout = new Timeout(Duration.create(5, "seconds"));

    // The sender of the initial Start message will continuously be notified about progress
    ActorRef progressListener;
    final ActorRef counterService = getContext().actorOf(new Props(CounterService.class), "counter");
    final int totalCount = 51;

    // Stop the CounterService child if it throws ServiceUnavailable
    private static SupervisorStrategy strategy = new OneForOneStrategy(-1, Duration.Inf(),
        new Function<Throwable, Directive>() {
          @Override
          public Directive apply(Throwable t) {
            if (t instanceof ServiceUnavailable) {
              return stop();
            } else {
              return escalate();
            }
          }
        });

    @Override
    public SupervisorStrategy supervisorStrategy() {
      return strategy;
    }

    public void onReceive(Object msg) {
      log.debug("received message {}", msg);
      if (msg.equals(Start) && progressListener == null) {
        progressListener = getSender();
        getContext().system().scheduler().schedule(
            Duration.Zero(), Duration.create(1, "second"), getSelf(), Do, getContext().dispatcher()
        );
      } else if (msg.equals(Do)) {
        counterService.tell(new Increment(1), getSelf());
        counterService.tell(new Increment(1), getSelf());
        counterService.tell(new Increment(1), getSelf());

        // Send current progress to the initial sender
        pipe(ask(counterService, GetCurrentCount, askTimeout)
               .mapTo(classTag(CurrentCount.class))
               .map(new Mapper<CurrentCount, Progress>() {
            public Progress apply(CurrentCount c) {
                return new Progress(100.0 * c.count / totalCount);
            }
        }, getContext().dispatcher()), getContext().dispatcher())
        .to(progressListener);
      } else {
        unhandled(msg);
      }
    }
  }

  //#messages
  public interface CounterServiceApi {

    public static final Object GetCurrentCount = "GetCurrentCount";

    public static class CurrentCount {
      public final String key;
      public final long count;

      public CurrentCount(String key, long count) {
        this.key = key;
        this.count = count;
      }

      public String toString() {
        return String.format("%s(%s, %s)", getClass().getSimpleName(), key, count);
      }
    }

    public static class Increment {
      public final long n;

      public Increment(long n) {
        this.n = n;
      }

      public String toString() {
        return String.format("%s(%s)", getClass().getSimpleName(), n);
      }
    }

    public static class ServiceUnavailable extends RuntimeException {
      public ServiceUnavailable(String msg) {
        super(msg);
      }
    }

  }

  //#messages

  /**
   * Adds the value received in Increment message to a persistent counter.
   * Replies with CurrentCount when it is asked for CurrentCount. CounterService
   * supervise Storage and Counter.
   */
  public static class CounterService extends UntypedActor {

    // Reconnect message
    static final Object Reconnect = "Reconnect";

    private static class SenderMsgPair {
      final ActorRef sender;
      final Object msg;

      SenderMsgPair(ActorRef sender, Object msg) {
        this.msg = msg;
        this.sender = sender;
      }
    }

    final LoggingAdapter log = Logging.getLogger(getContext().system(), this);
    final String key = getSelf().path().name();
    ActorRef storage;
    ActorRef counter;
    final List<SenderMsgPair> backlog = new ArrayList<SenderMsgPair>();
    final int MAX_BACKLOG = 10000;

    // Restart the storage child when StorageException is thrown.
    // After 3 restarts within 5 seconds it will be stopped.
    private static SupervisorStrategy strategy = new OneForOneStrategy(3, Duration.parse("5 seconds"),
        new Function<Throwable, Directive>() {
          @Override
          public Directive apply(Throwable t) {
            if (t instanceof StorageException) {
              return restart();
            } else {
              return escalate();
            }
          }
        });

    @Override
    public SupervisorStrategy supervisorStrategy() {
      return strategy;
    }

    @Override
    public void preStart() {
      initStorage();
    }

    /**
     * The child storage is restarted in case of failure, but after 3 restarts,
     * and still failing it will be stopped. Better to back-off than
     * continuously failing. When it has been stopped we will schedule a
     * Reconnect after a delay. Watch the child so we receive Terminated message
     * when it has been terminated.
     */
    void initStorage() {
      storage = getContext().watch(getContext().actorOf(new Props(Storage.class), "storage"));
      // Tell the counter, if any, to use the new storage
      if (counter != null)
        counter.tell(new UseStorage(storage), getSelf());
      // We need the initial value to be able to operate
      storage.tell(new Get(key), getSelf());
    }

    @Override
    public void onReceive(Object msg) {
      log.debug("received message {}", msg);
      if (msg instanceof Entry && ((Entry) msg).key.equals(key) && counter == null) {
        // Reply from Storage of the initial value, now we can create the Counter
        final long value = ((Entry) msg).value;
        counter = getContext().actorOf(new Props().withCreator(new UntypedActorFactory() {
          public Actor create() {
            return new Counter(key, value);
          }
        }));
        // Tell the counter to use current storage
        counter.tell(new UseStorage(storage), getSelf());
        // and send the buffered backlog to the counter
        for (SenderMsgPair each : backlog) {
          counter.tell(each.msg, each.sender);
        }
        backlog.clear();
      } else if (msg instanceof Increment) {
        forwardOrPlaceInBacklog(msg);
      } else if (msg.equals(GetCurrentCount)) {
        forwardOrPlaceInBacklog(msg);
      } else if (msg instanceof Terminated) {
        // After 3 restarts the storage child is stopped.
        // We receive Terminated because we watch the child, see initStorage.
        storage = null;
        // Tell the counter that there is no storage for the moment
        counter.tell(new UseStorage(null), getSelf());
        // Try to re-establish storage after while
        getContext().system().scheduler().scheduleOnce(
                Duration.create(10, "seconds"), getSelf(), Reconnect, getContext().dispatcher()
        );
      } else if (msg.equals(Reconnect)) {
        // Re-establish storage after the scheduled delay
        initStorage();
      } else {
        unhandled(msg);
      }
    }

    void forwardOrPlaceInBacklog(Object msg) {
      // We need the initial value from storage before we can start delegate to the counter.
      // Before that we place the messages in a backlog, to be sent to the counter when
      // it is initialized.
      if (counter == null) {
        if (backlog.size() >= MAX_BACKLOG)
          throw new ServiceUnavailable("CounterService not available, lack of initial value");
        backlog.add(new SenderMsgPair(getSender(), msg));
      } else {
        counter.forward(msg, getContext());
      }
    }
  }

  //#messages
  public interface CounterApi {
    public static class UseStorage {
      public final ActorRef storage;

      public UseStorage(ActorRef storage) {
        this.storage = storage;
      }

      public String toString() {
        return String.format("%s(%s)", getClass().getSimpleName(), storage);
      }
    }
  }

  //#messages

  /**
   * The in memory count variable that will send current value to the Storage,
   * if there is any storage available at the moment.
   */
  public static class Counter extends UntypedActor {
    final LoggingAdapter log = Logging.getLogger(getContext().system(), this);
    final String key;
    long count;
    ActorRef storage;

    public Counter(String key, long initialValue) {
      this.key = key;
      this.count = initialValue;
    }

    @Override
    public void onReceive(Object msg) {
      log.debug("received message {}", msg);
      if (msg instanceof UseStorage) {
        storage = ((UseStorage) msg).storage;
        storeCount();
      } else if (msg instanceof Increment) {
        count += ((Increment) msg).n;
        storeCount();
      } else if (msg.equals(GetCurrentCount)) {
        getSender().tell(new CurrentCount(key, count), getSelf());
      } else {
        unhandled(msg);
      }
    }

    void storeCount() {
      // Delegate dangerous work, to protect our valuable state.
      // We can continue without storage.
      if (storage != null) {
        storage.tell(new Store(new Entry(key, count)), getSelf());
      }
    }
  }

  //#messages
  public interface StorageApi {

    public static class Store {
      public final Entry entry;

      public Store(Entry entry) {
        this.entry = entry;
      }

      public String toString() {
        return String.format("%s(%s)", getClass().getSimpleName(), entry);
      }
    }

    public static class Entry {
      public final String key;
      public final long value;

      public Entry(String key, long value) {
        this.key = key;
        this.value = value;
      }

      public String toString() {
        return String.format("%s(%s, %s)", getClass().getSimpleName(), key, value);
      }
    }

    public static class Get {
      public final String key;

      public Get(String key) {
        this.key = key;
      }

      public String toString() {
        return String.format("%s(%s)", getClass().getSimpleName(), key);
      }
    }

    public static class StorageException extends RuntimeException {
      public StorageException(String msg) {
        super(msg);
      }
    }
  }

  //#messages

  /**
   * Saves key/value pairs to persistent storage when receiving Store message.
   * Replies with current value when receiving Get message. Will throw
   * StorageException if the underlying data store is out of order.
   */
  public static class Storage extends UntypedActor {

    final LoggingAdapter log = Logging.getLogger(getContext().system(), this);
    final DummyDB db = DummyDB.instance;

    @Override
    public void onReceive(Object msg) {
      log.debug("received message {}", msg);
      if (msg instanceof Store) {
        Store store = (Store) msg;
        db.save(store.entry.key, store.entry.value);
      } else if (msg instanceof Get) {
        Get get = (Get) msg;
        Long value = db.load(get.key);
        getSender().tell(new Entry(get.key, value == null ? Long.valueOf(0L) : value), getSelf());
      } else {
        unhandled(msg);
      }
    }
  }

  //#dummydb
  public static class DummyDB {
    public static final DummyDB instance = new DummyDB();
    private final Map<String, Long> db = new HashMap<String, Long>();

    private DummyDB() {
    }

    public synchronized void save(String key, Long value) throws StorageException {
      if (11 <= value && value <= 14)
        throw new StorageException("Simulated store failure " + value);
      db.put(key, value);
    }

    public synchronized Long load(String key) throws StorageException {
      return db.get(key);
    }
  }
  //#dummydb
}
//#all