聊聊flink的FencedAkkaInvocationHandler

序

本文主要研究一下flink的FencedAkkaInvocationHandler

FencedRpcGateway

flink-release-1.7.2/flink-runtime/src/main/java/org/apache/flink/runtime/rpc/FencedRpcGateway.java

public interface FencedRpcGateway<F extends Serializable> extends RpcGateway {

    /**
     * Get the current fencing token.
     *
     * @return current fencing token
     */
    F getFencingToken();
}

• FencedRpcGateway接口繼承了RpcGateway接口，它定義一個泛型F，即爲fencing token的泛型

FencedMainThreadExecutable

flink-release-1.7.2/flink-runtime/src/main/java/org/apache/flink/runtime/rpc/FencedMainThreadExecutable.java

public interface FencedMainThreadExecutable extends MainThreadExecutable {

    /**
     * Run the given runnable in the main thread without attaching a fencing token.
     *
     * @param runnable to run in the main thread without validating the fencing token.
     */
    void runAsyncWithoutFencing(Runnable runnable);

    /**
     * Run the given callable in the main thread without attaching a fencing token.
     *
     * @param callable to run in the main thread without validating the fencing token.
     * @param timeout for the operation
     * @param <V> type of the callable result
     * @return Future containing the callable result
     */
    <V> CompletableFuture<V> callAsyncWithoutFencing(Callable<V> callable, Time timeout);
}

• FencedMainThreadExecutable接口繼承了MainThreadExecutable，它定義了runAsyncWithoutFencing、callAsyncWithoutFencing方法用於運行unfenced runnable或者unfenced callable，之因此這樣定義主要是由於FencedMainThreadExecutable繼承了MainThreadExecutable，於是MainThreadExecutable裏頭定義的runAsync、callAsync、scheduleRunAsync方法的語義就變成是Fenced

FencedAkkaInvocationHandler

flink-release-1.7.2/flink-runtime/src/main/java/org/apache/flink/runtime/rpc/akka/FencedAkkaInvocationHandler.java

public class FencedAkkaInvocationHandler<F extends Serializable> extends AkkaInvocationHandler implements FencedMainThreadExecutable, FencedRpcGateway<F> {

    private final Supplier<F> fencingTokenSupplier;

    public FencedAkkaInvocationHandler(
            String address,
            String hostname,
            ActorRef rpcEndpoint,
            Time timeout,
            long maximumFramesize,
            @Nullable CompletableFuture<Void> terminationFuture,
            Supplier<F> fencingTokenSupplier) {
        super(address, hostname, rpcEndpoint, timeout, maximumFramesize, terminationFuture);

        this.fencingTokenSupplier = Preconditions.checkNotNull(fencingTokenSupplier);
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        Class<?> declaringClass = method.getDeclaringClass();

        if (declaringClass.equals(FencedMainThreadExecutable.class) ||
            declaringClass.equals(FencedRpcGateway.class)) {
            return method.invoke(this, args);
        } else {
            return super.invoke(proxy, method, args);
        }
    }

    @Override
    public void runAsyncWithoutFencing(Runnable runnable) {
        checkNotNull(runnable, "runnable");

        if (isLocal) {
            getActorRef().tell(
                new UnfencedMessage<>(new RunAsync(runnable, 0L)), ActorRef.noSender());
        } else {
            throw new RuntimeException("Trying to send a Runnable to a remote actor at " +
                getActorRef().path() + ". This is not supported.");
        }
    }

    @Override
    public <V> CompletableFuture<V> callAsyncWithoutFencing(Callable<V> callable, Time timeout) {
        checkNotNull(callable, "callable");
        checkNotNull(timeout, "timeout");

        if (isLocal) {
            @SuppressWarnings("unchecked")
            CompletableFuture<V> resultFuture = (CompletableFuture<V>) FutureUtils.toJava(
                Patterns.ask(
                    getActorRef(),
                    new UnfencedMessage<>(new CallAsync(callable)),
                    timeout.toMilliseconds()));

            return resultFuture;
        } else {
            throw new RuntimeException("Trying to send a Runnable to a remote actor at " +
                getActorRef().path() + ". This is not supported.");
        }
    }

    @Override
    public void tell(Object message) {
        super.tell(fenceMessage(message));
    }

    @Override
    public CompletableFuture<?> ask(Object message, Time timeout) {
        return super.ask(fenceMessage(message), timeout);
    }

    @Override
    public F getFencingToken() {
        return fencingTokenSupplier.get();
    }

    private <P> FencedMessage<F, P> fenceMessage(P message) {
        if (isLocal) {
            return new LocalFencedMessage<>(fencingTokenSupplier.get(), message);
        } else {
            if (message instanceof Serializable) {
                @SuppressWarnings("unchecked")
                FencedMessage<F, P> result = (FencedMessage<F, P>) new RemoteFencedMessage<>(fencingTokenSupplier.get(), (Serializable) message);

                return result;
            } else {
                throw new RuntimeException("Trying to send a non-serializable message " + message + " to a remote " +
                    "RpcEndpoint. Please make sure that the message implements java.io.Serializable.");
            }
        }
    }
}

• FencedAkkaInvocationHandler繼承了AkkaInvocationHandler，實現了FencedMainThreadExecutable、FencedRpcGateway接口；runAsyncWithoutFencing、callAsyncWithoutFencing發送的均爲UnfencedMessage
• FencedAkkaInvocationHandler的invoke方法針對FencedRpcGateway、FencedMainThreadExecutable的方法則對當前對象進行對應方法調用，其餘的就轉爲調用父類的invoke方法
• 父類的runAsync、scheduleRunAsync、callAsync最後調用的是tell或者ask方法，而FencedAkkaInvocationHandler覆蓋了父類的tell及ask方法，將runAsync、scheduleRunAsync、callAsync方法的語義變爲Fenced；這裏的tell及ask方法經過fenceMessage方法構造FencedMessage，而fenceMessage方法經過getFencingToken方法獲取fencing token；getFencingToken方法調用的是fencingTokenSupplier.get()，fencingTokenSupplier由構造器傳入

UnfencedMessage

flink-release-1.7.2/flink-runtime/src/main/java/org/apache/flink/runtime/rpc/messages/UnfencedMessage.java

public class UnfencedMessage<P> {
    private final P payload;

    public UnfencedMessage(P payload) {
        this.payload = Preconditions.checkNotNull(payload);
    }

    public P getPayload() {
        return payload;
    }

    @Override
    public String toString() {
        return "UnfencedMessage(" + payload + ')';
    }
}

• UnfencedMessage即不須要fencing token的message

FencedMessage

flink-release-1.7.2/flink-runtime/src/main/java/org/apache/flink/runtime/rpc/messages/FencedMessage.java

public interface FencedMessage<F extends Serializable, P> {

    F getFencingToken();

    P getPayload();
}

• FencedMessage接口定義了getFencingToken及getPayload方法；它有兩個子類，分別是LocalFencedMessage及RemoteFencedMessage

LocalFencedMessage

flink-release-1.7.2/flink-runtime/src/main/java/org/apache/flink/runtime/rpc/messages/LocalFencedMessage.java

public class LocalFencedMessage<F extends Serializable, P> implements FencedMessage<F, P> {

    private final F fencingToken;
    private final P payload;

    public LocalFencedMessage(@Nullable F fencingToken, P payload) {
        this.fencingToken = fencingToken;
        this.payload = Preconditions.checkNotNull(payload);
    }

    @Override
    public F getFencingToken() {
        return fencingToken;
    }

    @Override
    public P getPayload() {
        return payload;
    }

    @Override
    public String toString() {
        return "LocalFencedMessage(" + fencingToken + ", " + payload + ')';
    }
}

• LocalFencedMessage實現了FencedMessage接口，其中fencingToken的類型要求實現Serializable接口，它有fencingToken及payload兩個屬性

RemoteFencedMessage

flink-release-1.7.2/flink-runtime/src/main/java/org/apache/flink/runtime/rpc/messages/RemoteFencedMessage.java

public class RemoteFencedMessage<F extends Serializable, P extends Serializable> implements FencedMessage<F, P>, Serializable {
    private static final long serialVersionUID = 4043136067468477742L;

    private final F fencingToken;
    private final P payload;

    public RemoteFencedMessage(@Nullable F fencingToken, P payload) {
        this.fencingToken = fencingToken;
        this.payload = Preconditions.checkNotNull(payload);
    }

    @Override
    public F getFencingToken() {
        return fencingToken;
    }

    @Override
    public P getPayload() {
        return payload;
    }

    @Override
    public String toString() {
        return "RemoteFencedMessage(" + fencingToken + ", " + payload + ')';
    }
}

• RemoteFencedMessage實現了FencedMessage及Serializable接口，同時payload的類型也要求實現Serializable接口，它有fencingToken及payload兩個屬性

小結

• FencedRpcGateway接口繼承了RpcGateway接口，它定義一個泛型F，即爲fencing token的泛型；FencedMainThreadExecutable接口繼承了MainThreadExecutable，它定義了runAsyncWithoutFencing、callAsyncWithoutFencing方法用於運行unfenced runnable或者unfenced callable
• FencedAkkaInvocationHandler繼承了AkkaInvocationHandler，實現了FencedMainThreadExecutable、FencedRpcGateway接口；runAsyncWithoutFencing、callAsyncWithoutFencing發送的均爲UnfencedMessage；父類的runAsync、scheduleRunAsync、callAsync最後調用的是tell或者ask方法，而FencedAkkaInvocationHandler覆蓋了父類的tell及ask方法，將runAsync、scheduleRunAsync、callAsync方法的語義變爲Fenced；這裏的tell及ask方法經過fenceMessage方法構造FencedMessage
• UnfencedMessage即不須要fencing token的message；FencedMessage接口定義了getFencingToken及getPayload方法；它有兩個子類，分別是LocalFencedMessage及RemoteFencedMessage；LocalFencedMessage與RemoteFencedMessage的區別在於RemoteFencedMessage實現了Serializable接口，同時payload的類型也要求實現Serializable接口

doc

• FencedAkkaInvocationHandler