Hadoop-远程过程调用

 

 

 

Hadoop IPC类图如下

 
 

 

连接

//为了提高通讯效率，连接是可以复用的，通过ConnectionId来区分不同的连接
class ConnectionId {
     InetSocketAddress address;         //远端服务器的地址
     UserGroupInformation ticket;       //用户和用户组的信息
     Class protocol;                     //IPC接口对应的类对象
}

//ConnectionHeader类是客户端和服务端TCP连接建立之后交换的第一条消息，包括ConnectionId中的
//用户信息和IPC接口信息，用于确认用户是否有权利连接
ConnectionHeader


//服务端连接对象
public class Connection {
    private boolean rpcHeaderRead = false; //是否已读如入了RPC版本号
    private boolean headerRead = false;  //是否读入了连接消息头

    private SocketChannel channel;
    private ByteBuffer data;
    private ByteBuffer dataLengthBuffer;
    private LinkedList responseQueue;
    private volatile int rpcCount = 0; //当前正在处理的RPC数量
    private long lastContact;
    private int dataLength;
    private Socket socket;
    // Cache the remote host & port info so that even if the socket is 
    // disconnected, we can say where it used to connect to.
    private String hostAddress;
    private int remotePort;
    private InetAddress addr;
    
    ConnectionHeader header = new ConnectionHeader();
    Class protocol;
    boolean useSasl;
    SaslServer saslServer;
    private AuthMethod authMethod;
    private boolean saslContextEstablished;
    private boolean skipInitialSaslHandshake;
    private ByteBuffer rpcHeaderBuffer;
    private ByteBuffer unwrappedData;
    private ByteBuffer unwrappedDataLengthBuffer;
    UserGroupInformation user = null;
}

//客户端连接
  private class Connection extends Thread {
    private InetSocketAddress server;             //IPC服务端地址
    private String serverPrincipal;  // server's krb5 principal name
    private ConnectionHeader header;              //连接消息头
    private final ConnectionId remoteId;                //IPC连接标识
    private AuthMethod authMethod; // authentication method
    private boolean useSasl;
    private Token token;
    private SaslRpcClient saslRpcClient;
    
    private Socket socket = null;                 // connected socket
    private DataInputStream in;
    private DataOutputStream out;
    private int rpcTimeout;
    private int maxIdleTime; //connections will be culled if it was idle for
         //maxIdleTime msecs
    private int maxRetries; //the max. no. of retries for socket connections
    private boolean tcpNoDelay; // if T then disable Nagle's Algorithm
    private int pingInterval; // how often sends ping to the server in msecs
    
    // currently active calls
    private Hashtable calls = new Hashtable();
    private AtomicLong lastActivity = new AtomicLong();// last I/O activity time
    private AtomicBoolean shouldCloseConnection = new AtomicBoolean();  // indicate if the connection is closed
    private IOException closeException; // close reason
}

 

Call

//客户端
  private class Call {
    int id;                                       // call id
    Writable param;                               // parameter
    Writable value;                               // value, null if error
    IOException error;                            // exception, null if value
    boolean done;    
}

//服务端
  private static class Call {
    private int id;                               // the client's call id
    private Writable param;                       // the parameter passed
    private Connection connection;                // connection to client
    private long timestamp; 
}

//客户端和服务端通过各自的Call对象发送调用
客户端还有ParallelCall 用于同时发送多个远程IPC调用

 

 

服务端处理

//处理监听事件的线程
class Listener extends Thread {
	//创建SeverSocketChannel，并注册ACCEPT事件
	public Listener() {
		acceptChannel = ServerSocketChannel.open();	
		acceptChannel.configureBlocking(false);

      	// Bind the server socket to the local host and port
      	bind(acceptChannel.socket(), address, backlogLength);
      	port = acceptChannel.socket().getLocalPort(); //Could be an ephemeral port
      	// create a selector;
      	selector= Selector.open();
      	readers = new Reader[readThreads];
      	readPool = Executors.newFixedThreadPool(readThreads);
      	for (int i = 0; i < readThreads; i++) {
        	Selector readSelector = Selector.open();
        	Reader reader = new Reader(readSelector);
        	readers[i] = reader;
        	readPool.execute(reader);
      	}
      	acceptChannel.register(selector, SelectionKey.OP_ACCEPT);	
	}

	//处理ACCEPT事件
	public void run() {
	selector.select();
	Iterator iter = selector.selectedKeys().iterator();
	while (iter.hasNext()) {
		key = iter.next();
		iter.remove();
		if (key.isValid()) {
	    	if (key.isAcceptable())
	      		doAccept(key);
	  		}
		}            	
	}

}

//Reader线程，用于处理读事件并交由Handler线程处理
class Reader implements Runnable {
	public void run() {
		readSelector.select();
		while (adding) {
			this.wait(1000);
		}
		Iterator iter = readSelector.selectedKeys().iterator();
		while (iter.hasNext()) {
			key = iter.next();
			iter.remove();
			if (key.isValid()) {
	  			if (key.isReadable()) {
	    			doRead(key);
	  			}
			}
		}		              	
	}
}

//异步的处理写事件
class Responder extends Thread {
	public void run() {
		waitPending();     // If a channel is being registered, wait.
		writeSelector.select(PURGE_INTERVAL);
		Iterator iter = writeSelector.selectedKeys().iterator();
		while (iter.hasNext()) {
			SelectionKey key = iter.next();
            iter.remove();
			if (key.isValid() && key.isWritable()) {
				doAsyncWrite(key);
			}            
		}
		
		synchronized (writeSelector.keys()) {
			calls = new ArrayList(writeSelector.keys().size());
			iter = writeSelector.keys().iterator();
			while (iter.hasNext()) {
				SelectionKey key = iter.next();
				Call call = (Call)key.attachment();
				if (call != null && key.channel() == call.connection.channel) { 
					calls.add(call);
				}
			}
		}		
	}

}



void doAsyncWrite(SelectionKey key) {
	synchronized(call.connection.responseQueue) {
		processResponse(call.connection.responseQueue, false);
	}
}


//inHandler用于表示是Handler中直接调用写操作
//还是Responer线程的异步写操作
void processResponse(LinkedList responseQueue,boolean inHandler) {
	call = responseQueue.removeFirst();
          SocketChannel channel = call.connection.channel;
	int count =  (buffer.remaining() <= NIO_BUFFER_LIMIT) ?
                 channel.write(buffer) : channelIO(null, channel, buffer);          
}


void doRead(SelectionKey key) {
	Connection c = (Connection)key.attachment();
	count = c.readAndProcess();
}