前提

前置文章:

前一篇文章简单介绍了通过动态代理完成了Client端契约接口调用转换为发送RPC协议请求的功能。这篇文章主要解决一个遗留的技术难题:请求-响应同步化处理。

需要的依赖如下:

  • JDK1.8+
  • Netty:4.1.44.Final
  • SpringBoot:2.2.2.RELEASE

简单分析Netty请求-响应的处理流程

图中已经忽略了编码解码器和其他入站出站处理器,不同颜色的线程代表完全不相同的线程,不同线程之间的处理逻辑是完全异步,也就是Netty IO线程(n-l-g-1)接收到Server端的消息并且解析完成的时候,用户调用线程(u-t-1)无法感知到解析完毕的消息包,那么这里要做的事情就是让用户调用线程(u-t-1)获取到Netty IO线程(n-l-g-1)接收并且解析完成的消息包。

这里可以用一个简单的例子来说明模拟Client端调用线程等待Netty IO线程的处理结果再同步返回的过程。

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@Slf4j
public class NettyThreadSyncTest {

@ToString
private static class ResponseFuture {

private final long beginTimestamp = System.currentTimeMillis();
@Getter
private final long timeoutMilliseconds;
@Getter
private final String requestId;
@Setter
@Getter
private volatile boolean sendRequestSucceed = false;
@Setter
@Getter
private volatile Throwable cause;
@Getter
private volatile Object response;

private final CountDownLatch latch = new CountDownLatch(1);

public ResponseFuture(String requestId, long timeoutMilliseconds) {
this.requestId = requestId;
this.timeoutMilliseconds = timeoutMilliseconds;
}

public boolean timeout() {
return System.currentTimeMillis() - beginTimestamp > timeoutMilliseconds;
}

public Object waitResponse(final long timeoutMilliseconds) throws InterruptedException {
latch.await(timeoutMilliseconds, TimeUnit.MILLISECONDS);
return response;
}

public void putResponse(Object response) throws InterruptedException {
this.response = response;
latch.countDown();
}
}

static ExecutorService REQUEST_THREAD;
static ExecutorService NETTY_IO_THREAD;
static Callable<Object> REQUEST_TASK;
static Runnable RESPONSE_TASK;

static String processBusiness(String name) {
return String.format("%s say hello!", name);
}

private static final Map<String /* request id */, ResponseFuture> RESPONSE_FUTURE_TABLE = Maps.newConcurrentMap();

@BeforeClass
public static void beforeClass() throws Exception {
String requestId = UUID.randomUUID().toString();
String requestContent = "throwable";
REQUEST_TASK = () -> {
try {
// 3秒没有得到响应认为超时
ResponseFuture responseFuture = new ResponseFuture(requestId, 3000);
RESPONSE_FUTURE_TABLE.put(requestId, responseFuture);
// 这里忽略发送请求的操作,只打印日志和模拟耗时1秒
Thread.sleep(1000);
log.info("发送请求成功,请求ID:{},请求内容:{}", requestId, requestContent);
// 更新标记属性
responseFuture.setSendRequestSucceed(true);
// 剩余2秒等待时间 - 这里只是粗略计算
return responseFuture.waitResponse(3000 - 1000);
} catch (Exception e) {
log.info("发送请求失败,请求ID:{},请求内容:{}", requestId, requestContent);
throw new RuntimeException(e);
}
};
RESPONSE_TASK = () -> {
String responseContent = processBusiness(requestContent);
try {
ResponseFuture responseFuture = RESPONSE_FUTURE_TABLE.get(requestId);
if (null != responseFuture) {
log.warn("处理响应成功,请求ID:{},响应内容:{}", requestId, responseContent);
responseFuture.putResponse(responseContent);
} else {
log.warn("请求ID[{}]对应的ResponseFuture不存在,忽略处理", requestId);
}
} catch (Exception e) {
log.info("处理响应失败,请求ID:{},响应内容:{}", requestId, responseContent);
throw new RuntimeException(e);
}
};
REQUEST_THREAD = Executors.newSingleThreadExecutor(runnable -> {
Thread thread = new Thread(runnable, "REQUEST_THREAD");
thread.setDaemon(true);
return thread;
});
NETTY_IO_THREAD = Executors.newSingleThreadExecutor(runnable -> {
Thread thread = new Thread(runnable, "NETTY_IO_THREAD");
thread.setDaemon(true);
return thread;
});
}

@Test
public void testProcessSync() throws Exception {
log.info("异步提交请求处理任务......");
Future<Object> future = REQUEST_THREAD.submit(REQUEST_TASK);
// 模拟请求耗时
Thread.sleep(1500);
log.info("异步提交响应处理任务......");
NETTY_IO_THREAD.execute(RESPONSE_TASK);
// 这里可以设置超时
log.info("同步获取请求结果:{}", future.get());
Thread.sleep(Long.MAX_VALUE);
}
}

执行testProcessSync()方法,控制台输出如下:

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2020-01-18 13:17:07 [main] INFO  c.t.client.NettyThreadSyncTest - 异步提交请求处理任务......
2020-01-18 13:17:08 [REQUEST_THREAD] INFO c.t.client.NettyThreadSyncTest - 发送请求成功,请求ID:71f47e27-c17c-458d-b271-4e74fad33a7b,请求内容:throwable
2020-01-18 13:17:09 [main] INFO c.t.client.NettyThreadSyncTest - 异步提交响应处理任务......
2020-01-18 13:17:09 [NETTY_IO_THREAD] WARN c.t.client.NettyThreadSyncTest - 处理响应成功,请求ID:71f47e27-c17c-458d-b271-4e74fad33a7b,响应内容:throwable say hello!
2020-01-18 13:17:09 [main] INFO c.t.client.NettyThreadSyncTest - 同步获取请求结果:throwable say hello!

上面这个例子里面的线程同步处理主要参考主流的Netty框架客户端部分的实现逻辑:RocketMQ(具体是NettyRemotingClient类)以及Redisson(具体是RedisExecutor类),它们就是用这种方式使得异步线程处理转化为同步处理。

Client端请求响应同步化处理

按照前面的例子,首先新增一个ResponseFuture用于承载已发送但未响应的请求:

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@ToString
public class ResponseFuture {

private final long beginTimestamp = System.currentTimeMillis();
@Getter
private final long timeoutMilliseconds;
@Getter
private final String requestId;
@Setter
@Getter
private volatile boolean sendRequestSucceed = false;
@Setter
@Getter
private volatile Throwable cause;
@Getter
private volatile ResponseMessagePacket response;

private final CountDownLatch latch = new CountDownLatch(1);

public ResponseFuture(String requestId, long timeoutMilliseconds) {
this.requestId = requestId;
this.timeoutMilliseconds = timeoutMilliseconds;
}

public boolean timeout() {
return System.currentTimeMillis() - beginTimestamp > timeoutMilliseconds;
}

public ResponseMessagePacket waitResponse(final long timeoutMilliseconds) throws InterruptedException {
latch.await(timeoutMilliseconds, TimeUnit.MILLISECONDS);
return response;
}

public void putResponse(ResponseMessagePacket response) throws InterruptedException {
this.response = response;
latch.countDown();
}
}

接着需要新增一个HashMap去缓存这些返送成功但是未得到响应处理的ResponseFuture

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Map<String /* request id */, ResponseFuture> RESPONSE_FUTURE_TABLE = Maps.newConcurrentMap();

这里的KEY选用requestId,而requestId之前已经定义为UUID,确保每个请求不会重复。为了简单起见,目前所有的逻辑都编写在契约代理工厂ContractProxyFactory,添加下面的功能:

  • 添加一个同步发送方法sendRequestSync()处理消息包的发送和同步响应,RequestMessagePacket转换为调用代理目标方法返回值类型的逻辑暂时也编写在此方法中。
  • 添加一个核心线程数量为逻辑核心数量 * 2的线程池用于处理请求。
  • 添加一个单线程的调度线程池用于定时清理那些过期的ResponseFuture,清理方法为scanResponseFutureTable()

修改后的ContractProxyFactory如下:

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@Slf4j
public class ContractProxyFactory {

private static final RequestArgumentExtractor EXTRACTOR = new DefaultRequestArgumentExtractor();
private static final ConcurrentMap<Class<?>, Object> CACHE = Maps.newConcurrentMap();
static final ConcurrentMap<String /* request id */, ResponseFuture> RESPONSE_FUTURE_TABLE = Maps.newConcurrentMap();
// 定义请求的最大超时时间为3秒
private static final long REQUEST_TIMEOUT_MS = 3000;
private static final ExecutorService EXECUTOR;
private static final ScheduledExecutorService CLIENT_HOUSE_KEEPER;
private static final Serializer SERIALIZER = FastJsonSerializer.X;


@SuppressWarnings("unchecked")
public static <T> T ofProxy(Class<T> interfaceKlass) {
// 缓存契约接口的代理类实例
return (T) CACHE.computeIfAbsent(interfaceKlass, x ->
Proxy.newProxyInstance(interfaceKlass.getClassLoader(), new Class[]{interfaceKlass}, (target, method, args) -> {
RequestArgumentExtractInput input = new RequestArgumentExtractInput();
input.setInterfaceKlass(interfaceKlass);
input.setMethod(method);
RequestArgumentExtractOutput output = EXTRACTOR.extract(input);
// 封装请求参数
RequestMessagePacket packet = new RequestMessagePacket();
packet.setMagicNumber(ProtocolConstant.MAGIC_NUMBER);
packet.setVersion(ProtocolConstant.VERSION);
packet.setSerialNumber(SerialNumberUtils.X.generateSerialNumber());
packet.setMessageType(MessageType.REQUEST);
packet.setInterfaceName(output.getInterfaceName());
packet.setMethodName(output.getMethodName());
packet.setMethodArgumentSignatures(output.getMethodArgumentSignatures().toArray(new String[0]));
packet.setMethodArguments(args);
Channel channel = ClientChannelHolder.CHANNEL_REFERENCE.get();
return sendRequestSync(channel, packet, method.getReturnType());
}));
}

/**
* 同步发送请求
*
* @param channel channel
* @param packet packet
* @return Object
*/
static Object sendRequestSync(Channel channel, RequestMessagePacket packet, Class<?> returnType) {
long beginTimestamp = System.currentTimeMillis();
ResponseFuture responseFuture = new ResponseFuture(packet.getSerialNumber(), REQUEST_TIMEOUT_MS);
RESPONSE_FUTURE_TABLE.put(packet.getSerialNumber(), responseFuture);
try {
// 获取到承载响应Packet的Future
Future<ResponseMessagePacket> packetFuture = EXECUTOR.submit(() -> {
channel.writeAndFlush(packet).addListener((ChannelFutureListener)
future -> responseFuture.setSendRequestSucceed(true));
return responseFuture.waitResponse(REQUEST_TIMEOUT_MS - (System.currentTimeMillis() - beginTimestamp));
});
ResponseMessagePacket responsePacket = packetFuture.get(
REQUEST_TIMEOUT_MS - (System.currentTimeMillis() - beginTimestamp), TimeUnit.MILLISECONDS);
if (null == responsePacket) {
// 超时导致响应包获取失败
throw new SendRequestException(String.format("ResponseMessagePacket获取超时,请求ID:%s", packet.getSerialNumber()));
} else {
ByteBuf payload = (ByteBuf) responsePacket.getPayload();
byte[] bytes = ByteBufferUtils.X.readBytes(payload);
return SERIALIZER.decode(bytes, returnType);
}
} catch (Exception e) {
log.error("同步发送请求异常,请求包:{}", JSON.toJSONString(packet), e);
if (e instanceof RuntimeException) {
throw (RuntimeException) e;
} else {
throw new SendRequestException(e);
}
}
}

static void scanResponseFutureTable() {
log.info("开始执行ResponseFutureTable清理任务......");
Iterator<Map.Entry<String, ResponseFuture>> iterator = RESPONSE_FUTURE_TABLE.entrySet().iterator();
while (iterator.hasNext()) {
Map.Entry<String, ResponseFuture> entry = iterator.next();
ResponseFuture responseFuture = entry.getValue();
if (responseFuture.timeout()) {
iterator.remove();
log.warn("移除过期的请求ResponseFuture,请求ID:{}", entry.getKey());
}
}
log.info("执行ResponseFutureTable清理任务结束......");
}

static {
int n = Runtime.getRuntime().availableProcessors();
EXECUTOR = new ThreadPoolExecutor(n * 2, n * 2, 0, TimeUnit.SECONDS,
new ArrayBlockingQueue<>(50), runnable -> {
Thread thread = new Thread(runnable);
thread.setDaemon(true);
thread.setName("CLIENT_REQUEST_EXECUTOR");
return thread;
});
CLIENT_HOUSE_KEEPER = new ScheduledThreadPoolExecutor(1, runnable -> {
Thread thread = new Thread(runnable);
thread.setDaemon(true);
thread.setName("CLIENT_HOUSE_KEEPER");
return thread;
});
CLIENT_HOUSE_KEEPER.scheduleWithFixedDelay(ContractProxyFactory::scanResponseFutureTable, 5, 5, TimeUnit.SECONDS);
}
}

接着添加一个客户端入站处理器,用于通过reuqestId匹配目标ResponseFuture实例,同时设置ResponseFuture实例中的response属性为响应包,同时释放闭锁:

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@Slf4j
public class ClientHandler extends SimpleChannelInboundHandler<ResponseMessagePacket> {

@Override
protected void channelRead0(ChannelHandlerContext ctx, ResponseMessagePacket packet) throws Exception {
log.info("接收到响应包,内容:{}", JSON.toJSONString(packet));
ResponseFuture responseFuture = ContractProxyFactory.RESPONSE_FUTURE_TABLE.get(packet.getSerialNumber());
if (null != responseFuture) {
responseFuture.putResponse(packet);
} else {
log.warn("接收响应包查询ResponseFuture不存在,请求ID:{}", packet.getSerialNumber());
}
}
}

最后,客户端启动类ClientApplication中添加ClientHandlerNetty的处理器流水线中即可:

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bootstrap.handler(new ChannelInitializer<SocketChannel>() {

@Override
protected void initChannel(SocketChannel ch) throws Exception {
ch.pipeline().addLast(new LengthFieldBasedFrameDecoder(1024, 0, 4, 0, 4));
ch.pipeline().addLast(new LengthFieldPrepender(4));
ch.pipeline().addLast(new LoggingHandler(LogLevel.DEBUG));
ch.pipeline().addLast(new RequestMessagePacketEncoder(FastJsonSerializer.X));
ch.pipeline().addLast(new ResponseMessagePacketDecoder());
ch.pipeline().addLast(new ClientHandler());
}
});

先运行之前- 《基于Netty和SpringBoot实现一个轻量级RPC框架-Server篇》中编写好的ServerApplication,再启动ClientApplication,日志输出如下:

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// 服务端
2020-01-18 14:32:59 [nioEventLoopGroup-3-2] INFO club.throwable.server.ServerHandler - 服务端接收到:RequestMessagePacket(interfaceName=club.throwable.contract.HelloService, methodName=sayHello, methodArgumentSignatures=[java.lang.String], methodArguments=[PooledUnsafeDirectByteBuf(ridx: 0, widx: 11, cap: 11/144)])
2020-01-18 14:32:59 [nioEventLoopGroup-3-2] INFO club.throwable.server.ServerHandler - 查找目标实现方法成功,目标类:club.throwable.server.contract.DefaultHelloService,宿主类:club.throwable.server.contract.DefaultHelloService,宿主方法:sayHello
2020-01-18 14:32:59 [nioEventLoopGroup-3-2] INFO club.throwable.server.ServerHandler - 服务端输出:{"attachments":{},"errorCode":200,"magicNumber":10086,"message":"Success","messageType":"RESPONSE","payload":"\"throwable say hello!\"","serialNumber":"21d131d26fc74f91b4691e0207826b90","version":1}

// 客户端
2020-01-18 14:32:59 [nioEventLoopGroup-2-1] INFO club.throwable.client.ClientHandler - 接收到响应包,内容:{"attachments":{},"errorCode":200,"magicNumber":10086,"message":"Success","messageType":"RESPONSE","payload":{"contiguous":true,"direct":true,"readOnly":false,"readable":true,"writable":false},"serialNumber":"21d131d26fc74f91b4691e0207826b90","version":1}
2020-01-18 14:32:59 [main] INFO c.throwable.client.ClientApplication - HelloService[throwable]调用结果:"throwable say hello!"
2020-01-18 14:33:04 [CLIENT_HOUSE_KEEPER] INFO c.t.client.ContractProxyFactory - 开始执行ResponseFutureTable清理任务......
2020-01-18 14:33:04 [CLIENT_HOUSE_KEEPER] WARN c.t.client.ContractProxyFactory - 移除过期的请求ResponseFuture,请求ID:21d131d26fc74f91b4691e0207826b90

可见异步线程模型已经被改造为同步化,现在可以通过契约接口通过RPC同步调用服务端。

小结

Client端的请求-响应同步化处理基本改造完毕,到此为止,一个RPC框架大致已经完成,接下来会对Client端和Server端进行一些改造,让契约相关组件托管到IOC容器,实现契约接口自动注入等等功能。

Demo项目地址:

(本文完e-a-20200118 c-2-d)



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