一、介绍
Flink是分布式大数据处理框架，那么网络通信就离不开了，从目前来看，几乎所有的开源的大型软件，尤其是Java的，基本已经不再倾向于自己写底层网络通信，毕竟有很多可以使用的Rpc网络通信框架可以来完善使用，Flink也是如此，它是基本Akka Rpc这款Rpc通信框架的。
二、分析
1、服务端
先看一下测试代码的最基础的通信代码（RpcEndPointTest.java）：
public interface BaseGateway extends RpcGateway {
CompletableFuture<Integer> foobar();
}
//基础的通信协议接口
public interface ExtendedGateway extends BaseGateway {
CompletableFuture<Integer> barfoo();
}
public interface DifferentGateway extends RpcGateway {
CompletableFuture<String> foo();
}
public static class BaseEndpoint extends RpcEndpoint implements BaseGateway {
private final int foobarValue;
protected BaseEndpoint(RpcService rpcService, int foobarValue) {
super(rpcService);
this.foobarValue = foobarValue;
}
@Override
public CompletableFuture<Integer> foobar() {
return CompletableFuture.completedFuture(foobarValue);
}
}
在Flink中，Rpc的网关接口非常简单，代码如下：
public interface RpcGateway {
/**
* Returns the fully qualified address under which the associated rpc endpoint is reachable.
*
* @return Fully qualified (RPC) address under which the associated rpc endpoint is reachable
*/
String getAddress();
/**
* Returns the fully qualified hostname under which the associated rpc endpoint is reachable.
*
* @return Fully qualified hostname under which the associated rpc endpoint is reachable
*/
String getHostname();
}
这两方法太简单了，不解释。在Akka的服务中要获得相关的Actor，地址是必须的，而在网络通信中既可以直接获取地址，又可以通过HostName来获得。在flink中，网络的服务端是由RpcService这个接口来控制：
public interface RpcService {
/**
* Return the hostname or host address under which the rpc service can be reached.
* If the rpc service cannot be contacted remotely, then it will return an empty string.
*
* @return Address of the rpc service or empty string if local rpc service
*/
String getAddress();
/**
* Return the port under which the rpc service is reachable. If the rpc service cannot be
* contacted remotely, then it will return -1.
*
* @return Port of the rpc service or -1 if local rpc service
*/
int getPort();
/**
* Connect to a remote rpc server under the provided address. Returns a rpc gateway which can
* be used to communicate with the rpc server. If the connection failed, then the returned
* future is failed with a {@link RpcConnectionException}.
*
* @param address Address of the remote rpc server
* @param clazz Class of the rpc gateway to return
* @param <C> Type of the rpc gateway to return
* @return Future containing the rpc gateway or an {@link RpcConnectionException} if the
* connection attempt failed
*/
<C extends RpcGateway> CompletableFuture<C> connect(
String address,
Class<C> clazz);
/**
* Connect to a remote fenced rpc server under the provided address. Returns a fenced rpc gateway
* which can be used to communicate with the rpc server. If the connection failed, then the
* returned future is failed with a {@link RpcConnectionException}.
*
* @param address Address of the remote rpc server
* @param fencingToken Fencing token to be used when communicating with the server
* @param clazz Class of the rpc gateway to return
* @param <F> Type of the fencing token
* @param <C> Type of the rpc gateway to return
* @return Future containing the fenced rpc gateway or an {@link RpcConnectionException} if the
* connection attempt failed
*/
<F extends Serializable, C extends FencedRpcGateway<F>> CompletableFuture<C> connect(
String address,
F fencingToken,
Class<C> clazz);
/**
* Start a rpc server which forwards the remote procedure calls to the provided rpc endpoint.
*
* @param rpcEndpoint Rpc protocol to dispatch the rpcs to
* @param <C> Type of the rpc endpoint
* @return Self gateway to dispatch remote procedure calls to oneself
*/
<C extends RpcEndpoint & RpcGateway> RpcServer startServer(C rpcEndpoint);
/**
* Fence the given RpcServer with the given fencing token.
*
* <p>Fencing the RpcServer means that we fix the fencing token to the provided value.
* All RPCs will then be enriched with this fencing token. This expects that the receiving
* RPC endpoint extends {@link FencedRpcEndpoint}.
*
* @param rpcServer to fence with the given fencing token
* @param fencingToken to fence the RpcServer with
* @param <F> type of the fencing token
* @return Fenced RpcServer
*/
<F extends Serializable> RpcServer fenceRpcServer(RpcServer rpcServer, F fencingToken);
/**
* Stop the underlying rpc server of the provided self gateway.
*
* @param selfGateway Self gateway describing the underlying rpc server
*/
void stopServer(RpcServer selfGateway);
/**
* Trigger the asynchronous stopping of the {@link RpcService}.
*
* @return Future which is completed once the {@link RpcService} has been
* fully stopped.
*/
CompletableFuture<Void> stopService();
/**
* Returns a future indicating when the RPC service has been shut down.
*
* @return Termination future
*/
CompletableFuture<Void> getTerminationFuture();
/**
* Gets the executor, provided by this RPC service. This executor can be used for example for
* the {@code handleAsync(...)} or {@code thenAcceptAsync(...)} methods of futures.
*
* <p><b>IMPORTANT:</b> This executor does not isolate the method invocations against
* any concurrent invocations and is therefore not suitable to run completion methods of futures
* that modify state of an {@link RpcEndpoint}. For such operations, one needs to use the
* {@link RpcEndpoint#getMainThreadExecutor() MainThreadExecutionContext} of that
* {@code RpcEndpoint}.
*
* @return The execution context provided by the RPC service
*/
Executor getExecutor();
/**
* Gets a scheduled executor from the RPC service. This executor can be used to schedule
* tasks to be executed in the future.
*
* <p><b>IMPORTANT:</b> This executor does not isolate the method invocations against
* any concurrent invocations and is therefore not suitable to run completion methods of futures
* that modify state of an {@link RpcEndpoint}. For such operations, one needs to use the
* {@link RpcEndpoint#getMainThreadExecutor() MainThreadExecutionContext} of that
* {@code RpcEndpoint}.
*
* @return The RPC service provided scheduled executor
*/
ScheduledExecutor getScheduledExecutor();
/**
* Execute the runnable in the execution context of this RPC Service, as returned by
* {@link #getExecutor()}, after a scheduled delay.
*
* @param runnable Runnable to be executed
* @param delay The delay after which the runnable will be executed
*/
ScheduledFuture<?> scheduleRunnable(Runnable runnable, long delay, TimeUnit unit);
/**
* Execute the given runnable in the executor of the RPC service. This method can be used to run
* code outside of the main thread of a {@link RpcEndpoint}.
*
* <p><b>IMPORTANT:</b> This executor does not isolate the method invocations against
* any concurrent invocations and is therefore not suitable to run completion methods of futures
* that modify state of an {@link RpcEndpoint}. For such operations, one needs to use the
* {@link RpcEndpoint#getMainThreadExecutor() MainThreadExecutionContext} of that
* {@code RpcEndpoint}.
*
* @param runnable to execute
*/
void execute(Runnable runnable);
/**
* Execute the given callable and return its result as a {@link CompletableFuture}. This method can be used
* to run code outside of the main thread of a {@link RpcEndpoint}.
*
* <p><b>IMPORTANT:</b> This executor does not isolate the method invocations against
* any concurrent invocations and is therefore not suitable to run completion methods of futures
* that modify state of an {@link RpcEndpoint}. For such operations, one needs to use the
* {@link RpcEndpoint#getMainThreadExecutor() MainThreadExecutionContext} of that
* {@code RpcEndpoint}.
*
* @param callable to execute
* @param <T> is the return value type
* @return Future containing the callable's future result
*/
<T> CompletableFuture<T> execute(Callable<T> callable);
}
由他来控制着相关的服务端节点的启动，即RpcEndPoint：
public abstract class RpcEndpoint implements RpcGateway, AutoCloseableAsync {
protected final Logger log = LoggerFactory.getLogger(getClass());
// ------------------------------------------------------------------------
/** RPC service to be used to start the RPC server and to obtain rpc gateways. */
private final RpcService rpcService;
/** Unique identifier for this rpc endpoint. */
private final String endpointId;
/** Interface to access the underlying rpc server. */
protected final RpcServer rpcServer;
/** A reference to the endpoint's main thread, if the current method is called by the main thread. */
final AtomicReference<Thread> currentMainThread = new AtomicReference<>(null);
/** The main thread executor to be used to execute future callbacks in the main thread
* of the executing rpc server. */
private final MainThreadExecutor mainThreadExecutor;
/**
* Initializes the RPC endpoint.
*
* @param rpcService The RPC server that dispatches calls to this RPC endpoint.
* @param endpointId Unique identifier for this endpoint
*/
protected RpcEndpoint(final RpcService rpcService, final String endpointId) {
this.rpcService = checkNotNull(rpcService, "rpcService");
this.endpointId = checkNotNull(endpointId, "endpointId");
this.rpcServer = rpcService.startServer(this);
this.mainThreadExecutor = new MainThreadExecutor(rpcServer, this::validateRunsInMainThread);
}
/**
* Initializes the RPC endpoint with a random endpoint id.
*
* @param rpcService The RPC server that dispatches calls to this RPC endpoint.
*/
protected RpcEndpoint(final RpcService rpcService) {
this(rpcService, UUID.randomUUID().toString());
}
/**
* Returns the rpc endpoint's identifier.
*
* @return Rpc endpoint's identifier.
*/
public String getEndpointId() {
return endpointId;
}
// ------------------------------------------------------------------------
// Start & shutdown & lifecycle callbacks
// ------------------------------------------------------------------------
/**
* Starts the rpc endpoint. This tells the underlying rpc server that the rpc endpoint is ready
* to process remote procedure calls.
*
* @throws Exception indicating that something went wrong while starting the RPC endpoint
*/
public final void start() {
rpcServer.start();
}
/**
* User overridable callback.
*
* <p>This method is called when the RpcEndpoint is being started. The method is guaranteed
* to be executed in the main thread context and can be used to start the rpc endpoint in the
* context of the rpc endpoint's main thread.
*
* <p>IMPORTANT: This method should never be called directly by the user.
* @throws Exception indicating that the rpc endpoint could not be started. If an exception occurs,
* then the rpc endpoint will automatically terminate.
*/
public void onStart() throws Exception {}
/**
* Stops the rpc endpoint. This tells the underlying rpc server that the rpc endpoint is
* no longer ready to process remote procedure calls.
*/
protected final void stop() {
rpcServer.stop();
}
/**
* User overridable callback.
*
* <p>This method is called when the RpcEndpoint is being shut down. The method is guaranteed
* to be executed in the main thread context and can be used to clean up internal state.
*
* <p>IMPORTANT: This method should never be called directly by the user.
*
* @return Future which is completed once all post stop actions are completed. If an error
* occurs this future is completed exceptionally
*/
public CompletableFuture<Void> onStop() {
return CompletableFuture.completedFuture(null);
}
/**
* Triggers the shut down of the rpc endpoint. The shut down is executed asynchronously.
*
* <p>In order to wait on the completion of the shut down, obtain the termination future
* via {@link #getTerminationFuture()}} and wait on its completion.
*/
@Override
public final CompletableFuture<Void> closeAsync() {
rpcService.stopServer(rpcServer);
return getTerminationFuture();
}
// ------------------------------------------------------------------------
// Basic RPC endpoint properties
// ------------------------------------------------------------------------
/**
* Returns a self gateway of the specified type which can be used to issue asynchronous
* calls against the RpcEndpoint.
*
* <p>IMPORTANT: The self gateway type must be implemented by the RpcEndpoint. Otherwise
* the method will fail.
*
* @param selfGatewayType class of the self gateway type
* @param <C> type of the self gateway to create
* @return Self gateway of the specified type which can be used to issue asynchronous rpcs
*/
public <C extends RpcGateway> C getSelfGateway(Class<C> selfGatewayType) {
if (selfGatewayType.isInstance(rpcServer)) {
@SuppressWarnings("unchecked")
C selfGateway = ((C) rpcServer);
return selfGateway;
} else {
throw new RuntimeException("RpcEndpoint does not implement the RpcGateway interface of type " + selfGatewayType + '.');
}
}
/**
* Gets the address of the underlying RPC endpoint. The address should be fully qualified so that
* a remote system can connect to this RPC endpoint via this address.
*
* @return Fully qualified address of the underlying RPC endpoint
*/
@Override
public String getAddress() {
return rpcServer.getAddress();
}
/**
* Gets the hostname of the underlying RPC endpoint.
*
* @return Hostname on which the RPC endpoint is running
*/
@Override
public String getHostname() {
return rpcServer.getHostname();
}
/**
* Gets the main thread execution context. The main thread execution context can be used to
* execute tasks in the main thread of the underlying RPC endpoint.
*
* @return Main thread execution context
*/
protected MainThreadExecutor getMainThreadExecutor() {
return mainThreadExecutor;
}
/**
* Gets the endpoint's RPC service.
*
* @return The endpoint's RPC service
*/
public RpcService getRpcService() {
return rpcService;
}
/**
* Return a future which is completed with true when the rpc endpoint has been terminated.
* In case of a failure, this future is completed with the occurring exception.
*
* @return Future which is completed when the rpc endpoint has been terminated.
*/
public CompletableFuture<Void> getTerminationFuture() {
return rpcServer.getTerminationFuture();
}
// ------------------------------------------------------------------------
// Asynchronous executions
// ------------------------------------------------------------------------
/**
* Execute the runnable in the main thread of the underlying RPC endpoint.
*
* @param runnable Runnable to be executed in the main thread of the underlying RPC endpoint
*/
protected void runAsync(Runnable runnable) {
rpcServer.runAsync(runnable);
}
/**
* Execute the runnable in the main thread of the underlying RPC endpoint, with
* a delay of the given number of milliseconds.
*
* @param runnable Runnable to be executed
* @param delay The delay after which the runnable will be executed
*/
protected void scheduleRunAsync(Runnable runnable, Time delay) {
scheduleRunAsync(runnable, delay.getSize(), delay.getUnit());
}
/**
* Execute the runnable in the main thread of the underlying RPC endpoint, with
* a delay of the given number of milliseconds.
*
* @param runnable Runnable to be executed
* @param delay The delay after which the runnable will be executed
*/
protected void scheduleRunAsync(Runnable runnable, long delay, TimeUnit unit) {
rpcServer.scheduleRunAsync(runnable, unit.toMillis(delay));
}
/**
* Execute the callable in the main thread of the underlying RPC service, returning a future for
* the result of the callable. If the callable is not completed within the given timeout, then
* the future will be failed with a {@link TimeoutException}.
*
* @param callable Callable to be executed in the main thread of the underlying rpc server
* @param timeout Timeout for the callable to be completed
* @param <V> Return type of the callable
* @return Future for the result of the callable.
*/
protected <V> CompletableFuture<V> callAsync(Callable<V> callable, Time timeout) {
return rpcServer.callAsync(callable, timeout);
}
// ------------------------------------------------------------------------
// Main Thread Validation
// ------------------------------------------------------------------------
/**
* Validates that the method call happens in the RPC endpoint's main thread.
*
* <p><b>IMPORTANT:</b> This check only happens when assertions are enabled,
* such as when running tests.
*
* <p>This can be used for additional checks, like
* <pre>{@code
* protected void concurrencyCriticalMethod() {
* validateRunsInMainThread();
*
* // some critical stuff
* }
* }</pre>
*/
public void validateRunsInMainThread() {
assert MainThreadValidatorUtil.isRunningInExpectedThread(currentMainThread.get());
}
// ------------------------------------------------------------------------
// Utilities
// ------------------------------------------------------------------------
/**
* Executor which executes runnables in the main thread context.
*/
protected static class MainThreadExecutor implements ComponentMainThreadExecutor {
private final MainThreadExecutable gateway;
private final Runnable mainThreadCheck;
MainThreadExecutor(MainThreadExecutable gateway, Runnable mainThreadCheck) {
this.gateway = Preconditions.checkNotNull(gateway);
this.mainThreadCheck = Preconditions.checkNotNull(mainThreadCheck);
}
public void runAsync(Runnable runnable) {
gateway.runAsync(runnable);
}
public void scheduleRunAsync(Runnable runnable, long delayMillis) {
gateway.scheduleRunAsync(runnable, delayMillis);
}
public void execute(@Nonnull Runnable command) {
runAsync(command);
}
@Override
public ScheduledFuture<?> schedule(Runnable command, long delay, TimeUnit unit) {
final long delayMillis = TimeUnit.MILLISECONDS.convert(delay, unit);
FutureTask<Void> ft = new FutureTask<>(command, null);
scheduleRunAsync(ft, delayMillis);
return new ScheduledFutureAdapter<>(ft, delayMillis, TimeUnit.MILLISECONDS);
}
@Override
public <V> ScheduledFuture<V> schedule(Callable<V> callable, long delay, TimeUnit unit) {
throw new UnsupportedOperationException("Not implemented because the method is currently not required.");
}
@Override
public ScheduledFuture<?> scheduleAtFixedRate(Runnable command, long initialDelay, long period, TimeUnit unit) {
throw new UnsupportedOperationException("Not implemented because the method is currently not required.");
}
@Override
public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command, long initialDelay, long delay, TimeUnit unit) {
throw new UnsupportedOperationException("Not implemented because the method is currently not required.");
}
@Override
public void assertRunningInMainThread() {
mainThreadCheck.run();
}
}
}
一系列的启动，是由前面提到过的StartService中启动的，如果不太清楚可以回去翻一翻。启动endpoint就意味着服务端启动了。
2、客户端
有了服务端自然要有客户端，代码如下：
class AkkaInvocationHandler implements InvocationHandler, AkkaBasedEndpoint, RpcServer {
private static final Logger LOG = LoggerFactory.getLogger(AkkaInvocationHandler.class);
/**
* The Akka (RPC) address of {@link #rpcEndpoint} including host and port of the ActorSystem in
* which the actor is running.
*/
private final String address;
/**
* Hostname of the host, {@link #rpcEndpoint} is running on.
*/
private final String hostname;
private final ActorRef rpcEndpoint;
// whether the actor ref is local and thus no message serialization is needed
protected final boolean isLocal;
// default timeout for asks
private final Time timeout;
private final long maximumFramesize;
// null if gateway; otherwise non-null
@Nullable
private final CompletableFuture<Void> terminationFuture;
AkkaInvocationHandler(
String address,
String hostname,
ActorRef rpcEndpoint,
Time timeout,
long maximumFramesize,
@Nullable CompletableFuture<Void> terminationFuture) {
this.address = Preconditions.checkNotNull(address);
this.hostname = Preconditions.checkNotNull(hostname);
this.rpcEndpoint = Preconditions.checkNotNull(rpcEndpoint);
this.isLocal = this.rpcEndpoint.path().address().hasLocalScope();
this.timeout = Preconditions.checkNotNull(timeout);
this.maximumFramesize = maximumFramesize;
this.terminationFuture = terminationFuture;
}
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
Class<?> declaringClass = method.getDeclaringClass();
Object result;
if (declaringClass.equals(AkkaBasedEndpoint.class) ||
declaringClass.equals(Object.class) ||
declaringClass.equals(RpcGateway.class) ||
declaringClass.equals(StartStoppable.class) ||
declaringClass.equals(MainThreadExecutable.class) ||
declaringClass.equals(RpcServer.class)) {
result = method.invoke(this, args);
} else if (declaringClass.equals(FencedRpcGateway.class)) {
throw new UnsupportedOperationException("AkkaInvocationHandler does not support the call FencedRpcGateway#" +
method.getName() + ". This indicates that you retrieved a FencedRpcGateway without specifying a " +
"fencing token. Please use RpcService#connect(RpcService, F, Time) with F being the fencing token to " +
"retrieve a properly FencedRpcGateway.");
} else {
result = invokeRpc(method, args);
}
return result;
}
@Override
public ActorRef getActorRef() {
return rpcEndpoint;
}
@Override
public void runAsync(Runnable runnable) {
scheduleRunAsync(runnable, 0L);
}
@Override
public void scheduleRunAsync(Runnable runnable, long delayMillis) {
checkNotNull(runnable, "runnable");
checkArgument(delayMillis >= 0, "delay must be zero or greater");
if (isLocal) {
long atTimeNanos = delayMillis == 0 ? 0 : System.nanoTime() + (delayMillis * 1_000_000);
tell(new RunAsync(runnable, atTimeNanos));
} else {
throw new RuntimeException("Trying to send a Runnable to a remote actor at " +
rpcEndpoint.path() + ". This is not supported.");
}
}
@Override
public <V> CompletableFuture<V> callAsync(Callable<V> callable, Time callTimeout) {
if (isLocal) {
@SuppressWarnings("unchecked")
CompletableFuture<V> resultFuture = (CompletableFuture<V>) ask(new CallAsync(callable), callTimeout);
return resultFuture;
} else {
throw new RuntimeException("Trying to send a Callable to a remote actor at " +
rpcEndpoint.path() + ". This is not supported.");
}
}
@Override
public void start() {
rpcEndpoint.tell(ControlMessages.START, ActorRef.noSender());
}
@Override
public void stop() {
rpcEndpoint.tell(ControlMessages.STOP, ActorRef.noSender());
}
// ------------------------------------------------------------------------
// Private methods
// ------------------------------------------------------------------------
/**
* Invokes a RPC method by sending the RPC invocation details to the rpc endpoint.
*
* @param method to call
* @param args of the method call
* @return result of the RPC
* @throws Exception if the RPC invocation fails
*/
private Object invokeRpc(Method method, Object[] args) throws Exception {
String methodName = method.getName();
Class<?>[] parameterTypes = method.getParameterTypes();
Annotation[][] parameterAnnotations = method.getParameterAnnotations();
Time futureTimeout = extractRpcTimeout(parameterAnnotations, args, timeout);
final RpcInvocation rpcInvocation = createRpcInvocationMessage(methodName, parameterTypes, args);
Class<?> returnType = method.getReturnType();
final Object result;
if (Objects.equals(returnType, Void.TYPE)) {
tell(rpcInvocation);
result = null;
} else {
// execute an asynchronous call
CompletableFuture<?> resultFuture = ask(rpcInvocation, futureTimeout);
CompletableFuture<?> completableFuture = resultFuture.thenApply((Object o) -> {
if (o instanceof SerializedValue) {
try {
return ((SerializedValue<?>) o).deserializeValue(getClass().getClassLoader());
} catch (IOException | ClassNotFoundException e) {
throw new CompletionException(
new RpcException("Could not deserialize the serialized payload of RPC method : "
+ methodName, e));
}
} else {
return o;
}
});
if (Objects.equals(returnType, CompletableFuture.class)) {
result = completableFuture;
} else {
try {
result = completableFuture.get(futureTimeout.getSize(), futureTimeout.getUnit());
} catch (ExecutionException ee) {
throw new RpcException("Failure while obtaining synchronous RPC result.", ExceptionUtils.stripExecutionException(ee));
}
}
}
return result;
}
/**
* Create the RpcInvocation message for the given RPC.
*
* @param methodName of the RPC
* @param parameterTypes of the RPC
* @param args of the RPC
* @return RpcInvocation message which encapsulates the RPC details
* @throws IOException if we cannot serialize the RPC invocation parameters
*/
protected RpcInvocation createRpcInvocationMessage(
final String methodName,
final Class<?>[] parameterTypes,
final Object[] args) throws IOException {
final RpcInvocation rpcInvocation;
if (isLocal) {
rpcInvocation = new LocalRpcInvocation(
methodName,
parameterTypes,
args);
} else {
try {
RemoteRpcInvocation remoteRpcInvocation = new RemoteRpcInvocation(
methodName,
parameterTypes,
args);
if (remoteRpcInvocation.getSize() > maximumFramesize) {
throw new IOException("The rpc invocation size exceeds the maximum akka framesize.");
} else {
rpcInvocation = remoteRpcInvocation;
}
} catch (IOException e) {
LOG.warn("Could not create remote rpc invocation message. Failing rpc invocation because...", e);
throw e;
}
}
return rpcInvocation;
}
// ------------------------------------------------------------------------
// Helper methods
// ------------------------------------------------------------------------
/**
* Extracts the {@link RpcTimeout} annotated rpc timeout value from the list of given method
* arguments. If no {@link RpcTimeout} annotated parameter could be found, then the default
* timeout is returned.
*
* @param parameterAnnotations Parameter annotations
* @param args Array of arguments
* @param defaultTimeout Default timeout to return if no {@link RpcTimeout} annotated parameter
* has been found
* @return Timeout extracted from the array of arguments or the default timeout
*/
private static Time extractRpcTimeout(Annotation[][] parameterAnnotations, Object[] args, Time defaultTimeout) {
if (args != null) {
Preconditions.checkArgument(parameterAnnotations.length == args.length);
for (int i = 0; i < parameterAnnotations.length; i++) {
if (isRpcTimeout(parameterAnnotations[i])) {
if (args[i] instanceof Time) {
return (Time) args[i];
} else {
throw new RuntimeException("The rpc timeout parameter must be of type " +
Time.class.getName() + ". The type " + args[i].getClass().getName() +
" is not supported.");
}
}
}
}
return defaultTimeout;
}
/**
* Checks whether any of the annotations is of type {@link RpcTimeout}.
*
* @param annotations Array of annotations
* @return True if {@link RpcTimeout} was found; otherwise false
*/
private static boolean isRpcTimeout(Annotation[] annotations) {
for (Annotation annotation : annotations) {
if (annotation.annotationType().equals(RpcTimeout.class)) {
return true;
}
}
return false;
}
/**
* Sends the message to the RPC endpoint.
*
* @param message to send to the RPC endpoint.
*/
protected void tell(Object message) {
rpcEndpoint.tell(message, ActorRef.noSender());
}
/**
* Sends the message to the RPC endpoint and returns a future containing
* its response.
*
* @param message to send to the RPC endpoint
* @param timeout time to wait until the response future is failed with a {@link TimeoutException}
* @return Response future
*/
protected CompletableFuture<?> ask(Object message, Time timeout) {
return FutureUtils.toJava(
Patterns.ask(rpcEndpoint, message, timeout.toMilliseconds()));
}
@Override
public String getAddress() {
return address;
}
@Override
public String getHostname() {
return hostname;
}
@Override
public CompletableFuture<Void> getTerminationFuture() {
return terminationFuture;
}
}
这个客户继承了三个类或者说接口。InvocationHandler, AkkaBasedEndpoint, RpcServer，分别提供了操作，节点控制和相关通信传输协议。在获得客户端后就可以通过相关的接口来发送消息了。
3.Rpc的通信
客户端继承了InvocationHandler：
public interface InvocationHandler {
public Object invoke(Object proxy, Method method, Object[] args)
throws Throwable;
}
这个接口只有一个函数，invoke，如果编程时间稍微长一些的，都会明白类似这种名字的函数，基本都是调用相关接口函数的。在前面的RpcInvocation中会有LocalRpcInvocation和RemoteRpcInvocation的选择性生成，本地的调用本地的，远端的调用远端的。通过这二者对RPC方法的封装，在调用invokeRpc这个函数时，即可通过类型判断来决定调用tell还是ask的任一个。而这个类型的判断是通过二者是否在同一个JVM中，这个在上面的invokeRpc函数中有所体现，下面是删减后的代码：
private Object invokeRpc(Method method, Object[] args) throws Exception {
......
Class<?> returnType = method.getReturnType();
final Object result;
if (Objects.equals(returnType, Void.TYPE)) {
tell(rpcInvocation);
result = null;
} else {
// execute an asynchronous call
CompletableFuture<?> resultFuture = ask(rpcInvocation, futureTimeout);
......
});
......
return result;
}
protected void tell(Object message) {
rpcEndpoint.tell(message, ActorRef.noSender());
}
protected CompletableFuture<?> ask(Object message, Time timeout) {
return FutureUtils.toJava(
Patterns.ask(rpcEndpoint, message, timeout.toMilliseconds()));
}
再向下，就开始调用Akka的相关Rpc操作了。在前面的StartServer函数中：
final Props akkaRpcActorProps;
if (rpcEndpoint instanceof FencedRpcEndpoint) {
akkaRpcActorProps = Props.create(
FencedAkkaRpcActor.class,
rpcEndpoint,
terminationFuture,
getVersion(),
configuration.getMaximumFramesize());
} else {
akkaRpcActorProps = Props.create(
AkkaRpcActor.class,
rpcEndpoint,
terminationFuture,
getVersion(),
configuration.getMaximumFramesize());
}
ActorRef actorRef;
synchronized (lock) {
checkState(!stopped, "RpcService is stopped");
actorRef = actorSystem.actorOf(akkaRpcActorProps, rpcEndpoint.getEndpointId());
actors.put(actorRef, rpcEndpoint);
}
可以跳到tell函数中，发现就是调用的actor包中的ActorRef来实现的。
三、总结
这里分析还是比较粗糙的，并发模型中有两个一个是CSP（典型的是GO），另外一个是这Actor,现在这个用的就是这个。为什么没有详细的分析RpcServer和client的实现，主要原因是这个调用确实简单，而且前面虽然不是系统的但也把重点已经分析过了(比如JobMaster、Dispatcher、TaskExecutor等，这些都RpcEndpoint的子类)，这里再说一次也没有什么必要。包括序列化部分，其实也有些纠结是不是分析。但是这其实又是另外一个部分，到时候儿再说。
