1、An abstract IPC service.  IPC calls take a single {@link Writable} as a parameter, and return a {@link Writable} as their value.  A service runs on a port and is defined by a parameter class and a value class.

2、共有5个内部类ExceptionsHandler，Call，Listener，Responder，Connection,Handler

3、很多内部属性，位置比较散乱

private final boolean authorize;
private boolean isSecurityEnabled;
private ExceptionsHandler exceptionsHandler = new ExceptionsHandler();

  private String bindAddress;
  private int port;                               // port we listen on
  private int handlerCount;                       // number of handler threads
  private int readThreads;                        // number of read threads
  private Class<? extends Writable> paramClass;   // class of call parameters
  private int maxIdleTime;                        // the maximum idle time after  which a client may be disconnected
  private int thresholdIdleConnections;           // the number of idle connections after which we will start cleaning up idle   connections
  int maxConnectionsToNuke;                       // the max number of connections to nuke during a cleanup
  protected RpcInstrumentation rpcMetrics;
  private Configuration conf;
  private SecretManager<TokenIdentifier> secretManager;

  private int maxQueueSize;
  private final int maxRespSize;
  private int socketSendBufferSize;
  private final boolean tcpNoDelay; // if T then disable Nagle‘s Algorithm

  volatile private boolean running = true;         // true while server runs
  private BlockingQueue<Call> callQueue; // queued calls

  private List<Connection> connectionList =
    Collections.synchronizedList(new LinkedList<Connection>());
  //maintain a list of client connections
  private Listener listener = null;
  private Responder responder = null;
  private int numConnections = 0;
  private Handler[] handlers = null;

4、这个Call和Client里边的Call是不一样的，

A call queued for handling.

private Writable param;                       // the parameter passed
private Connection connection;                // connection to client
private long timestamp;     // the time received when response is null ； the time served when response is not null
private ByteBuffer response;                      // the response for this call

5、Connection

Reads calls from a connection and queues them for handling.

private boolean rpcHeaderRead = false; // if initial rpc header is read
  private boolean headerRead = false;  //if the connection header that follows version is read.

  private SocketChannel channel;
  private ByteBuffer data;
  private ByteBuffer dataLengthBuffer;
  private LinkedList<Call> responseQueue;
  private volatile int rpcCount = 0; // number of outstanding rpcs
  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;
  public UserGroupInformation attemptingUser = null; // user name before auth

  // Fake ‘call‘ for failed authorization response
  private final int AUTHROIZATION_FAILED_CALLID = -1;
  private final Call authFailedCall =
    new Call(AUTHROIZATION_FAILED_CALLID, null, this);
  private ByteArrayOutputStream authFailedResponse = new ByteArrayOutputStream();
  // Fake ‘call‘ for SASL context setup
  private static final int SASL_CALLID = -33;
  private final Call saslCall = new Call(SASL_CALLID, null, this);
  private final ByteArrayOutputStream saslResponse = new ByteArrayOutputStream();
 
  private boolean useWrap = false;

6、ExceptionsHandler manages Exception groups for special handling e.g., terse exception group for concise logging messages

7、Handles queued calls .

8、Listens on the socket. Creates jobs for the handler threads

Listener里边有一个内部类，Reader

相应的属性有

 
private ServerSocketChannel acceptChannel = null; //the accept channel
private Selector selector = null; //the selector that we use for the server
private Reader[] readers = null;
private int currentReader = 0;
private InetSocketAddress address; //the address we bind at
private Random rand = new Random();
private long lastCleanupRunTime = 0; //the last time when a cleanup connec-
                                     //-tion (for idle connections) ran
private long cleanupInterval = 10000; //the minimum interval between
                                      //two cleanup runs
private int backlogLength = conf.getInt("ipc.server.listen.queue.size", 128);
private ExecutorService readPool;

9、Responder

Sends responses of RPC back to clients

相应的属性有

private Selector writeSelector;
    private int pending;         // connections waiting to register
   
    final static int PURGE_INTERVAL = 900000; // 15mins

踏着前人的脚印学hadoop——ipc中的Server