hadoop ipc.RPC

Hadoop IPC分析 (基于v0.1.0)

IPC - Inter-Process Communication

定义了Invocation类，该类封装了调用的方法和参数信息。

其余代码整体上主要分两部分，一部分为client call server，一部分为server启动监听服务。后面按实际用法进行分析。

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Usage 1: 调用远程服务

XXXProtocol xxx = (XXXProtocol) RPC.getProxy(XXXProtocol.class, 
        new InetSocketAddress(port), conf);

public static Object getProxy(Class protocol, InetSocketAddress addr, 
            Configuration conf) {
    return Proxy.newProxyInstance(protocol.getClassLoader(),
            new Class[] { protocol },
            new Invoker(addr, conf));
}

定义了Invoker类，该类实现了InvocationHandler接口，为具体调用类。

封装了地址信息和客户端信息，有configuration的get/set保证Client的单例

InetSocketAddress address; // IP|hostname + port
Client CLIENT; // new Client(ObjectWritable.class, conf); 并set回conf保证唯一的CLIENT实例

以下是InvocationHandler的具体实现方法

public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    // 此处调用Client的call方法，其会建立远程connection，发起call，不断监听以获取返回值
    ObjectWritable value = (ObjectWritable) CLIENT.call(
            new Invocation(method, args), address);            
    return value.get();
}

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Usage 2: 启动服务，监听端口

Server server = RPC.getServer(...);
server.start();

public static Server getServer(final Object instance, final int port, 
        Configuration conf);
public static Server getServer(final Object instance, final int port, 
        final int numHandlers, final boolean verbose, Configuration conf);

以上两个方法返回Server的实例，new Server(...)

Server类继承自org.apache.hadoop.ipc.Server，实现了Writable call(Writable param)方法。该方法反射调用了Server的具体方法

Method method = implementation.getMethod(call.getMethodName(), 
        call.getParameterClasses());
Object value = method.invoke(instance, call.getParameters());
return new ObjectWritable(method.getReturnType(), value);

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/** Expert: Make multiple, parallel calls to a set of servers. */

public static Object[] call(Method method, Object[][] params, 
        InetSocketAddress[] addrs, Configuration conf) {
    ......
}