聊聊flink的ActorGateway

序

本文主要研究一下flink的ActorGateway

ActorGateway

flink-1.7.2/flink-runtime/src/main/java/org/apache/flink/runtime/instance/ActorGateway.java

public interface ActorGateway extends Serializable {

    /**
     * Sends a message asynchronously and returns its response. The response to the message is
     * returned as a future.
     *
     * @param message Message to be sent
     * @param timeout Timeout until the Future is completed with an AskTimeoutException
     * @return Future which contains the response to the sent message
     */
    Future<Object> ask(Object message, FiniteDuration timeout);

    /**
     * Sends a message asynchronously without a result.
     *
     * @param message Message to be sent
     */
    void tell(Object message);

    /**
     * Sends a message asynchronously without a result with sender being the sender.
     *
     * @param message Message to be sent
     * @param sender Sender of the message
     */
    void tell(Object message, ActorGateway sender);

    /**
     * Forwards a message. For the receiver of this message it looks as if sender has sent the
     * message.
     *
     * @param message Message to be sent
     * @param sender Sender of the forwarded message
     */
    void forward(Object message, ActorGateway sender);

    /**
     * Retries to send asynchronously a message up to numberRetries times. The response to this
     * message is returned as a future. The message is re-sent if the number of retries is not yet
     * exceeded and if an exception occurred while sending it.
     *
     * @param message Message to be sent
     * @param numberRetries Number of times to retry sending the message
     * @param timeout Timeout for each sending attempt
     * @param executionContext ExecutionContext which is used to send the message multiple times
     * @return Future of the response to the sent message
     */
    Future<Object> retry(
            Object message,
            int numberRetries,
            FiniteDuration timeout,
            ExecutionContext executionContext);

    /**
     * Returns the path of the remote instance.
     *
     * @return Path of the remote instance.
     */
    String path();

    /**
     * Returns the underlying actor with which is communicated
     *
     * @return ActorRef of the target actor
     */
    ActorRef actor();

    /**
     * Returns the leaderSessionID associated with the remote actor or null.
     *
     * @return Leader session ID if its associated with this gateway, otherwise null
     */
    UUID leaderSessionID();
}

• ActorGateway接口定义了ask、tell、forward、retry、path、actor、leaderSessionID方法；它有一个实现类为AkkaActorGateway

AkkaActorGateway

flink-1.7.2/flink-runtime/src/main/java/org/apache/flink/runtime/instance/AkkaActorGateway.java

public class AkkaActorGateway implements ActorGateway, Serializable {

    private static final long serialVersionUID = 42L;

    // ActorRef of the remote instance
    private final ActorRef actor;

    // Associated leader session ID, which is used for RequiresLeaderSessionID messages
    private final UUID leaderSessionID;

    // Decorator for messages
    private final MessageDecorator decorator;

    public AkkaActorGateway(ActorRef actor, UUID leaderSessionID) {
        this.actor = Preconditions.checkNotNull(actor);
        this.leaderSessionID = Preconditions.checkNotNull(leaderSessionID);
        // we want to wrap RequiresLeaderSessionID messages in a LeaderSessionMessage
        this.decorator = new LeaderSessionMessageDecorator(leaderSessionID);
    }

    /**
     * Sends a message asynchronously and returns its response. The response to the message is
     * returned as a future.
     *
     * @param message Message to be sent
     * @param timeout Timeout until the Future is completed with an AskTimeoutException
     * @return Future which contains the response to the sent message
     */
    @Override
    public Future<Object> ask(Object message, FiniteDuration timeout) {
        Object newMessage = decorator.decorate(message);
        return Patterns.ask(actor, newMessage, new Timeout(timeout));
    }

    /**
     * Sends a message asynchronously without a result.
     *
     * @param message Message to be sent
     */
    @Override
    public void tell(Object message) {
        Object newMessage = decorator.decorate(message);
        actor.tell(newMessage, ActorRef.noSender());
    }

    /**
     * Sends a message asynchronously without a result with sender being the sender.
     *
     * @param message Message to be sent
     * @param sender Sender of the message
     */
    @Override
    public void tell(Object message, ActorGateway sender) {
        Object newMessage = decorator.decorate(message);
        actor.tell(newMessage, sender.actor());
    }

    /**
     * Forwards a message. For the receiver of this message it looks as if sender has sent the
     * message.
     *
     * @param message Message to be sent
     * @param sender Sender of the forwarded message
     */
    @Override
    public void forward(Object message, ActorGateway sender) {
        Object newMessage = decorator.decorate(message);
        actor.tell(newMessage, sender.actor());
    }

    /**
     * Retries to send asynchronously a message up to numberRetries times. The response to this
     * message is returned as a future. The message is re-sent if the number of retries is not yet
     * exceeded and if an exception occurred while sending it.
     *
     * @param message Message to be sent
     * @param numberRetries Number of times to retry sending the message
     * @param timeout Timeout for each sending attempt
     * @param executionContext ExecutionContext which is used to send the message multiple times
     * @return Future of the response to the sent message
     */
    @Override
    public Future<Object> retry(
            Object message,
            int numberRetries,
            FiniteDuration timeout,
            ExecutionContext executionContext) {

        Object newMessage = decorator.decorate(message);

        return AkkaUtils.retry(
            actor,
            newMessage,
            numberRetries,
            executionContext,
            timeout);
    }

    /**
     * Returns the ActorPath of the remote instance.
     *
     * @return ActorPath of the remote instance.
     */
    @Override
    public String path() {
        return actor.path().toString();
    }

    /**
     * Returns {@link ActorRef} of the target actor
     *
     * @return ActorRef of the target actor
     */
    @Override
    public ActorRef actor() {
        return actor;
    }

    @Override
    public UUID leaderSessionID() {
        return leaderSessionID;
    }

    @Override
    public String toString() {
        return String.format("AkkaActorGateway(%s, %s)", actor.path(), leaderSessionID);
    }
}

• AkkaActorGateway实现了ActorGateway接口，它的构造器要求输入ActorRef及leaderSessionID，同时基于leaderSessionID创建了LeaderSessionMessageDecorator；ask、tell、forward、retry方法均首先调用LeaderSessionMessageDecorator.decorate方法包装message参数，然后再去调用ActorRef的相应方法

MessageDecorator

flink-1.7.2/flink-runtime/src/main/java/org/apache/flink/runtime/messages/MessageDecorator.java

public interface MessageDecorator extends java.io.Serializable {

    /**
     * Decorates a message
     *
     * @param message Message to decorate
     * @return Decorated message
     */
    Object decorate(Object message);
}

• MessageDecorator接口定义了decorate方法用于包装message，它有一个实现类为LeaderSessionMessageDecorator

LeaderSessionMessageDecorator

flink-1.7.2/flink-runtime/src/main/java/org/apache/flink/runtime/messages/LeaderSessionMessageDecorator.java

public class LeaderSessionMessageDecorator implements MessageDecorator {

    private static final long serialVersionUID = 5359618147408392706L;
    
    /** Leader session ID with which the RequiresLeaderSessionID messages will be decorated */
    private final UUID leaderSessionID;

    /**
     * Sets the leader session ID with which the messages will be decorated.
     *
     * @param leaderSessionID Leader session ID to be used for decoration
     */
    public LeaderSessionMessageDecorator(UUID leaderSessionID) {
        this.leaderSessionID = leaderSessionID;
    }

    @Override
    public Object decorate(Object message) {
        if (message instanceof RequiresLeaderSessionID) {
            return new JobManagerMessages.LeaderSessionMessage(leaderSessionID, message);
        } else {
            return message;
        }
    }
}

• LeaderSessionMessageDecorator实现了MessageDecorator接口，其decorate方法判断message是RequiresLeaderSessionID类型的话，则返回JobManagerMessages.LeaderSessionMessage，否则返回原始的message

JobManagerMessages.LeaderSessionMessage

flink-1.7.2/flink-runtime/src/main/scala/org/apache/flink/runtime/messages/JobManagerMessages.scala

object JobManagerMessages {

  /** Wrapper class for leader session messages. Leader session messages implement the
    * [[RequiresLeaderSessionID]] interface and have to be wrapped in a [[LeaderSessionMessage]],
    * which also contains the current leader session ID.
    *
    * @param leaderSessionID Current leader session ID
    * @param message [[RequiresLeaderSessionID]] message to be wrapped in a [[LeaderSessionMessage]]
    */
  case class LeaderSessionMessage(leaderSessionID: UUID, message: Any)

  //......
}

• JobManagerMessages.LeaderSessionMessage是一个case class，它有两个属性，分别是leaderSessionID及message

小结

• ActorGateway接口定义了ask、tell、forward、retry、path、actor、leaderSessionID方法；它有一个实现类为AkkaActorGateway
• AkkaActorGateway实现了ActorGateway接口，它的构造器要求输入ActorRef及leaderSessionID，同时基于leaderSessionID创建了LeaderSessionMessageDecorator；ask、tell、forward、retry方法均首先调用LeaderSessionMessageDecorator.decorate方法包装message参数，然后再去调用ActorRef的相应方法
• MessageDecorator接口定义了decorate方法用于包装message，它有一个实现类为LeaderSessionMessageDecorator；LeaderSessionMessageDecorator实现了MessageDecorator接口，其decorate方法判断message是RequiresLeaderSessionID类型的话，则返回JobManagerMessages.LeaderSessionMessage，否则返回原始的message；JobManagerMessages.LeaderSessionMessage是一个case class，它有两个属性，分别是leaderSessionID及message

doc

• ActorGateway