@Override
  public DatagramChannel bind(SocketAddress local) throws IOException {
    synchronized (readLock) {
      synchronized (writeLock) {
        synchronized (stateLock) {
          ensureOpen();
          if (localAddress != null) throw new AlreadyBoundException();
          InetSocketAddress isa;
          if (local == null) {
            // only Inet4Address allowed with IPv4 socket
            if (family == StandardProtocolFamily.INET) {
              isa = new InetSocketAddress(InetAddress.getByName("0.0.0.0"), 0);
            } else {
              isa = new InetSocketAddress(0);
            }
          } else {
            isa = Net.checkAddress(local);

            // only Inet4Address allowed with IPv4 socket
            if (family == StandardProtocolFamily.INET) {
              InetAddress addr = isa.getAddress();
              if (!(addr instanceof Inet4Address)) throw new UnsupportedAddressTypeException();
            }
          }
          SecurityManager sm = System.getSecurityManager();
          if (sm != null) {
            sm.checkListen(isa.getPort());
          }
          Net.bind(family, fd, isa.getAddress(), isa.getPort());
          localAddress = Net.localAddress(fd);
        }
      }
    }
    return this;
  }
  public DatagramChannel connect(SocketAddress sa) throws IOException {
    int localPort = 0;

    synchronized (readLock) {
      synchronized (writeLock) {
        synchronized (stateLock) {
          ensureOpenAndUnconnected();
          InetSocketAddress isa = Net.checkAddress(sa);
          SecurityManager sm = System.getSecurityManager();
          if (sm != null) sm.checkConnect(isa.getAddress().getHostAddress(), isa.getPort());
          int n = Net.connect(family, fd, isa.getAddress(), isa.getPort());
          if (n <= 0) throw new Error(); // Can't happen

          // Connection succeeded; disallow further invocation
          state = ST_CONNECTED;
          remoteAddress = sa;
          sender = isa;
          cachedSenderInetAddress = isa.getAddress();
          cachedSenderPort = isa.getPort();

          // set or refresh local address
          localAddress = Net.localAddress(fd);
        }
      }
    }
    return this;
  }
 public DatagramChannelImpl(SelectorProvider sp, FileDescriptor fd) throws IOException {
   super(sp);
   this.family =
       Net.isIPv6Available() ? StandardProtocolFamily.INET6 : StandardProtocolFamily.INET;
   this.fd = fd;
   this.fdVal = IOUtil.fdVal(fd);
   this.state = ST_UNCONNECTED;
   this.localAddress = Net.localAddress(fd);
 }
 public SocketAddress localAddress() {
   synchronized (stateLock) {
     if (state == ST_CONNECTED
         && (localAddress == null
             || ((InetSocketAddress) localAddress).getAddress().isAnyLocalAddress())) {
       // Socket was not bound before connecting or
       // Socket was bound with an "anyLocalAddress"
       localAddress = Net.localAddress(fd);
     }
     return localAddress;
   }
 }
 public void bind(SocketAddress local) throws IOException {
   synchronized (readLock) {
     synchronized (writeLock) {
       synchronized (stateLock) {
         ensureOpenAndUnconnected();
         if (localAddress != null) throw new AlreadyBoundException();
         InetSocketAddress isa = Net.checkAddress(local);
         Net.bind(fd, isa.getAddress(), isa.getPort());
         localAddress = Net.localAddress(fd);
       }
     }
   }
 }
  public int send(ByteBuffer src, SocketAddress target) throws IOException {
    if (src == null) throw new NullPointerException();

    synchronized (writeLock) {
      ensureOpen();
      InetSocketAddress isa = Net.checkAddress(target);
      InetAddress ia = isa.getAddress();
      if (ia == null) throw new IOException("Target address not resolved");
      synchronized (stateLock) {
        if (!isConnected()) {
          if (target == null) throw new NullPointerException();
          SecurityManager sm = System.getSecurityManager();
          if (sm != null) {
            if (ia.isMulticastAddress()) {
              sm.checkMulticast(ia);
            } else {
              sm.checkConnect(ia.getHostAddress(), isa.getPort());
            }
          }
        } else { // Connected case; Check address then write
          if (!target.equals(remoteAddress)) {
            throw new IllegalArgumentException("Connected address not equal to target address");
          }
          return write(src);
        }
      }

      int n = 0;
      try {
        begin();
        if (!isOpen()) return 0;
        writerThread = NativeThread.current();
        do {
          n = send(fd, src, isa);
        } while ((n == IOStatus.INTERRUPTED) && isOpen());

        synchronized (stateLock) {
          if (isOpen() && (localAddress == null)) {
            localAddress = Net.localAddress(fd);
          }
        }
        return IOStatus.normalize(n);
      } finally {
        writerThread = 0;
        end((n > 0) || (n == IOStatus.UNAVAILABLE));
        assert IOStatus.check(n);
      }
    }
  }
  @Override
  public DatagramChannel connect(SocketAddress sa) throws IOException {
    int localPort = 0;

    synchronized (readLock) {
      synchronized (writeLock) {
        synchronized (stateLock) {
          ensureOpenAndUnconnected();
          InetSocketAddress isa = Net.checkAddress(sa);
          SecurityManager sm = System.getSecurityManager();
          if (sm != null) sm.checkConnect(isa.getAddress().getHostAddress(), isa.getPort());
          int n = Net.connect(family, fd, isa.getAddress(), isa.getPort());
          if (n <= 0) throw new Error(); // Can't happen

          // Connection succeeded; disallow further invocation
          state = ST_CONNECTED;
          remoteAddress = isa;
          sender = isa;
          cachedSenderInetAddress = isa.getAddress();
          cachedSenderPort = isa.getPort();

          // set or refresh local address
          localAddress = Net.localAddress(fd);

          // flush any packets already received.
          boolean blocking = false;
          synchronized (blockingLock()) {
            try {
              blocking = isBlocking();
              // remainder of each packet thrown away
              ByteBuffer tmpBuf = ByteBuffer.allocate(1);
              if (blocking) {
                configureBlocking(false);
              }
              do {
                tmpBuf.clear();
              } while (receive(tmpBuf) != null);
            } finally {
              if (blocking) {
                configureBlocking(true);
              }
            }
          }
        }
      }
    }
    return this;
  }
  public DatagramChannel disconnect() throws IOException {
    synchronized (readLock) {
      synchronized (writeLock) {
        synchronized (stateLock) {
          if (!isConnected() || !isOpen()) return this;
          InetSocketAddress isa = (InetSocketAddress) remoteAddress;
          SecurityManager sm = System.getSecurityManager();
          if (sm != null) sm.checkConnect(isa.getAddress().getHostAddress(), isa.getPort());
          disconnect0(fd);
          remoteAddress = null;
          state = ST_UNCONNECTED;

          // refresh local address
          localAddress = Net.localAddress(fd);
        }
      }
    }
    return this;
  }