java/6 : sun/rmi/transport/tcp/TCPEndpoint.java

TCPEndpoint
https://openjdk.java.net/
GPLv2 + Classpath Exception
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
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 * 2 along with this work; if not, write to the Free Software Foundation,
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 *
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package sun.rmi.transport.tcp;

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import java.io.ObjectInput;
import java.io.ObjectOutput;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.rmi.ConnectIOException;
import java.rmi.RemoteException;
import java.rmi.server.RMIClientSocketFactory;
import java.rmi.server.RMIServerSocketFactory;
import java.rmi.server.RMISocketFactory;
import java.security.AccessController;
import java.util.Collection;
import java.util.HashMap;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.Map;
import java.util.Set;
import sun.rmi.runtime.Log;
import sun.rmi.runtime.NewThreadAction;
import sun.rmi.transport.Channel;
import sun.rmi.transport.Endpoint;
import sun.rmi.transport.Target;
import sun.rmi.transport.Transport;
import sun.security.action.GetBooleanAction;
import sun.security.action.GetIntegerAction;
import sun.security.action.GetPropertyAction;

TCPEndpoint represents some communication endpoint for an address
space (VM).
Author: Ann Wollrath/**
 * TCPEndpoint represents some communication endpoint for an address
 * space (VM).
 *
 * @author Ann Wollrath
 */
public class TCPEndpoint implements Endpoint {
    IP address or host name /** IP address or host name */
    private String host;
    port number /** port number */
    private int port;
    custom client socket factory (null if not custom factory) /** custom client socket factory (null if not custom factory) */
    private final RMIClientSocketFactory csf;
    custom server socket factory (null if not custom factory) /** custom server socket factory (null if not custom factory) */
    private final RMIServerSocketFactory ssf;

    if local, the port number to listen on /** if local, the port number to listen on */
    private int listenPort = -1;
    if local, the transport object associated with this endpoint /** if local, the transport object associated with this endpoint */
    private TCPTransport transport = null;

    the local host name /** the local host name */
    private static String localHost;
    true if real local host name is known yet /** true if real local host name is known yet */
    private static boolean localHostKnown;

    // this should be a *private* method since it is privileged
    private static int getInt(String name, int def) {
        return AccessController.doPrivileged(new GetIntegerAction(name, def));
    }

    // this should be a *private* method since it is privileged
    private static boolean getBoolean(String name) {
        return AccessController.doPrivileged(new GetBooleanAction(name));
    }

    Returns the value of the java.rmi.server.hostname property.
/**
     * Returns the value of the java.rmi.server.hostname property.
     */
    private static String getHostnameProperty() {
        return AccessController.doPrivileged(
            new GetPropertyAction("java.rmi.server.hostname"));
    }

    Find host name of local machine.  Property "java.rmi.server.hostname"
is used if set, so server administrator can compensate for the possible
inablility to get fully qualified host name from VM.
/**
     * Find host name of local machine.  Property "java.rmi.server.hostname"
     * is used if set, so server administrator can compensate for the possible
     * inablility to get fully qualified host name from VM.
     */
    static {
        localHostKnown = true;
        localHost = getHostnameProperty();

        // could try querying CGI program here?
        if (localHost == null) {
            try {
                InetAddress localAddr = InetAddress.getLocalHost();
                byte[] raw = localAddr.getAddress();
                if ((raw[0] == 127) &&
                    (raw[1] ==   0) &&
                    (raw[2] ==   0) &&
                    (raw[3] ==   1)) {
                    localHostKnown = false;
                }

                /* if the user wishes to use a fully qualified domain
                 * name then attempt to find one.
                 */
                if (getBoolean("java.rmi.server.useLocalHostName")) {
                    localHost = FQDN.attemptFQDN(localAddr);
                } else {
                    /* default to using ip addresses, names will
                     * work across seperate domains.
                     */
                    localHost = localAddr.getHostAddress();
                }
            } catch (Exception e) {
                localHostKnown = false;
                localHost = null;
            }
        }

        if (TCPTransport.tcpLog.isLoggable(Log.BRIEF)) {
            TCPTransport.tcpLog.log(Log.BRIEF,
                "localHostKnown = " + localHostKnown +
                ", localHost = " + localHost);
        }
    }

    maps an endpoint key containing custom socket factories to
their own unique endpoint /** maps an endpoint key containing custom socket factories to
     * their own unique endpoint */
    // TBD: should this be a weak hash table?
    private static final
        Map<TCPEndpoint,LinkedList<TCPEndpoint>> localEndpoints =
        new HashMap<TCPEndpoint,LinkedList<TCPEndpoint>>();

    Create an endpoint for a specified host and port.
This should not be used by external classes to create endpoints
for servers in this VM; use getLocalEndpoint instead.
/**
     * Create an endpoint for a specified host and port.
     * This should not be used by external classes to create endpoints
     * for servers in this VM; use getLocalEndpoint instead.
     */
    public TCPEndpoint(String host, int port) {
        this(host, port, null, null);
    }

    Create a custom socket factory endpoint for a specified host and port.
This should not be used by external classes to create endpoints
for servers in this VM; use getLocalEndpoint instead.
/**
     * Create a custom socket factory endpoint for a specified host and port.
     * This should not be used by external classes to create endpoints
     * for servers in this VM; use getLocalEndpoint instead.
     */
    public TCPEndpoint(String host, int port, RMIClientSocketFactory csf,
                       RMIServerSocketFactory ssf)
    {
        if (host == null)
            host = "";
        this.host = host;
        this.port = port;
        this.csf = csf;
        this.ssf = ssf;
    }

    Get an endpoint for the local address space on specified port.
If port number is 0, it returns shared default endpoint object
whose host name and port may or may not have been determined.
/**
     * Get an endpoint for the local address space on specified port.
     * If port number is 0, it returns shared default endpoint object
     * whose host name and port may or may not have been determined.
     */
    public static TCPEndpoint getLocalEndpoint(int port) {
        return getLocalEndpoint(port, null, null);
    }

    public static TCPEndpoint getLocalEndpoint(int port,
                                               RMIClientSocketFactory csf,
                                               RMIServerSocketFactory ssf)
    {
        /*
         * Find mapping for an endpoint key to the list of local unique
         * endpoints for this client/server socket factory pair (perhaps
         * null) for the specific port.
         */
        TCPEndpoint ep = null;

        synchronized (localEndpoints) {
            TCPEndpoint endpointKey = new TCPEndpoint(null, port, csf, ssf);
            LinkedList<TCPEndpoint> epList = localEndpoints.get(endpointKey);
            String localHost = resampleLocalHost();

            if (epList == null) {
                /*
                 * Create new endpoint list.
                 */
                ep = new TCPEndpoint(localHost, port, csf, ssf);
                epList = new LinkedList<TCPEndpoint>();
                epList.add(ep);
                ep.listenPort = port;
                ep.transport = new TCPTransport(epList);
                localEndpoints.put(endpointKey, epList);

                if (TCPTransport.tcpLog.isLoggable(Log.BRIEF)) {
                    TCPTransport.tcpLog.log(Log.BRIEF,
                        "created local endpoint for socket factory " + ssf +
                        " on port " + port);
                }
            } else {
                synchronized (epList) {
                    ep = epList.getLast();
                    String lastHost = ep.host;
                    int lastPort =  ep.port;
                    TCPTransport lastTransport = ep.transport;
                    // assert (localHost == null ^ lastHost != null)
                    if (localHost != null && !localHost.equals(lastHost)) {
                        /*
                         * Hostname has been updated; add updated endpoint
                         * to list.
                         */
                        if (lastPort != 0) {
                            /*
                             * Remove outdated endpoints only if the
                             * port has already been set on those endpoints.
                             */
                            epList.clear();
                        }
                        ep = new TCPEndpoint(localHost, lastPort, csf, ssf);
                        ep.listenPort = port;
                        ep.transport = lastTransport;
                        epList.add(ep);
                    }
                }
            }
        }

        return ep;
    }

    Resamples the local hostname and returns the possibly-updated
local hostname.
/**
     * Resamples the local hostname and returns the possibly-updated
     * local hostname.
     */
    private static String resampleLocalHost() {

        String hostnameProperty = getHostnameProperty();

        synchronized (localEndpoints) {
            // assert(localHostKnown ^ (localHost == null))

            if (hostnameProperty != null) {
                if (!localHostKnown) {
                    /*
                     * If the local hostname is unknown, update ALL
                     * existing endpoints with the new hostname.
                     */
                    setLocalHost(hostnameProperty);
                } else if (!hostnameProperty.equals(localHost)) {
                    /*
                     * Only update the localHost field for reference
                     * in future endpoint creation.
                     */
                    localHost = hostnameProperty;

                    if (TCPTransport.tcpLog.isLoggable(Log.BRIEF)) {
                        TCPTransport.tcpLog.log(Log.BRIEF,
                            "updated local hostname to: " + localHost);
                    }
                }
            }
            return localHost;
        }
    }

    Set the local host name, if currently unknown.
/**
     * Set the local host name, if currently unknown.
     */
    static void setLocalHost(String host) {
        // assert (host != null)

        synchronized (localEndpoints) {
            /*
             * If host is not known, change the host field of ALL
             * the local endpoints.
             */
            if (!localHostKnown) {
                localHost = host;
                localHostKnown = true;

                if (TCPTransport.tcpLog.isLoggable(Log.BRIEF)) {
                    TCPTransport.tcpLog.log(Log.BRIEF,
                        "local host set to " + host);
                }
                for (LinkedList<TCPEndpoint> epList : localEndpoints.values())
                {
                    synchronized (epList) {
                        for (TCPEndpoint ep : epList) {
                            ep.host = host;
                        }
                    }
                }
            }
        }
    }

    Set the port of the (shared) default endpoint object.
When first created, it contains port 0 because the transport
hasn't tried to listen to get assigned a port, or if listening
failed, a port hasn't been assigned from the server.
/**
     * Set the port of the (shared) default endpoint object.
     * When first created, it contains port 0 because the transport
     * hasn't tried to listen to get assigned a port, or if listening
     * failed, a port hasn't been assigned from the server.
     */
    static void setDefaultPort(int port, RMIClientSocketFactory csf,
                               RMIServerSocketFactory ssf)
    {
        TCPEndpoint endpointKey = new TCPEndpoint(null, 0, csf, ssf);

        synchronized (localEndpoints) {
            LinkedList<TCPEndpoint> epList = localEndpoints.get(endpointKey);

            synchronized (epList) {
                int size = epList.size();
                TCPEndpoint lastEp = epList.getLast();

                for (TCPEndpoint ep : epList) {
                    ep.port = port;
                }
                if (size > 1) {
                    /*
                     * Remove all but the last element of the list
                     * (which contains the most recent hostname).
                     */
                    epList.clear();
                    epList.add(lastEp);
                }
            }

            /*
             * Allow future exports to use the actual bound port
             * explicitly (see 6269166).
             */
            TCPEndpoint newEndpointKey = new TCPEndpoint(null, port, csf, ssf);
            localEndpoints.put(newEndpointKey, epList);

            if (TCPTransport.tcpLog.isLoggable(Log.BRIEF)) {
                TCPTransport.tcpLog.log(Log.BRIEF,
                    "default port for server socket factory " + ssf +
                    " and client socket factory " + csf +
                    " set to " + port);
            }
        }
    }

    Returns transport for making connections to remote endpoints;
(here, the default transport at port 0 is used).
/**
     * Returns transport for making connections to remote endpoints;
     * (here, the default transport at port 0 is used).
     */
    public Transport getOutboundTransport() {
        TCPEndpoint localEndpoint = getLocalEndpoint(0, null, null);
        return localEndpoint.transport;
    }

    Returns the current list of known transports.
The returned list is an unshared collection of Transports,
including all transports which may have channels to remote
endpoints.
/**
     * Returns the current list of known transports.
     * The returned list is an unshared collection of Transports,
     * including all transports which may have channels to remote
     * endpoints.
     */
    private static Collection<TCPTransport> allKnownTransports() {
        // Loop through local endpoints, getting the transport of each one.
        Set<TCPTransport> s;
        synchronized (localEndpoints) {
            // presize s to number of localEndpoints
            s = new HashSet<TCPTransport>(localEndpoints.size());
            for (LinkedList<TCPEndpoint> epList : localEndpoints.values()) {
                /*
                 * Each local endpoint has its transport added to s.
                 * Note: the transport is the same for all endpoints
                 * in the list, so it is okay to pick any one of them.
                 */
                TCPEndpoint ep = epList.getFirst();
                s.add(ep.transport);
            }
        }
        return s;
    }

    Release idle outbound connections to reduce demand on I/O resources.
All transports are asked to release excess connections.
/**
     * Release idle outbound connections to reduce demand on I/O resources.
     * All transports are asked to release excess connections.
     */
    public static void shedConnectionCaches() {
        for (TCPTransport transport : allKnownTransports()) {
            transport.shedConnectionCaches();
        }
    }

    Export the object to accept incoming calls.
/**
     * Export the object to accept incoming calls.
     */
    public void exportObject(Target target) throws RemoteException {
        transport.exportObject(target);
    }

    Returns a channel for this (remote) endpoint.
/**
     * Returns a channel for this (remote) endpoint.
     */
    public Channel getChannel() {
        return getOutboundTransport().getChannel(this);
    }

    Returns address for endpoint
/**
     * Returns address for endpoint
     */
    public String getHost() {
        return host;
    }

    Returns the port for this endpoint.  If this endpoint was
created as a server endpoint (using getLocalEndpoint) for a
default/anonymous port and its inbound transport has started
listening, this method returns (instead of zero) the actual
bound port suitable for passing to clients.
/**
     * Returns the port for this endpoint.  If this endpoint was
     * created as a server endpoint (using getLocalEndpoint) for a
     * default/anonymous port and its inbound transport has started
     * listening, this method returns (instead of zero) the actual
     * bound port suitable for passing to clients.
     **/
    public int getPort() {
        return port;
    }

    Returns the port that this endpoint's inbound transport listens
on, if this endpoint was created as a server endpoint (using
getLocalEndpoint).  If this endpoint was created for the
default/anonymous port, then this method returns zero even if
the transport has started listening.
/**
     * Returns the port that this endpoint's inbound transport listens
     * on, if this endpoint was created as a server endpoint (using
     * getLocalEndpoint).  If this endpoint was created for the
     * default/anonymous port, then this method returns zero even if
     * the transport has started listening.
     **/
    public int getListenPort() {
        return listenPort;
    }

    Returns the transport for incoming connections to this
endpoint, if this endpoint was created as a server endpoint
(using getLocalEndpoint).
/**
     * Returns the transport for incoming connections to this
     * endpoint, if this endpoint was created as a server endpoint
     * (using getLocalEndpoint).
     **/
    public Transport getInboundTransport() {
        return transport;
    }

    Get the client socket factory associated with this endpoint.
/**
     * Get the client socket factory associated with this endpoint.
     */
    public RMIClientSocketFactory getClientSocketFactory() {
        return csf;
    }

    Get the server socket factory associated with this endpoint.
/**
     * Get the server socket factory associated with this endpoint.
     */
    public RMIServerSocketFactory getServerSocketFactory() {
        return ssf;
    }

    Return string representation for endpoint.
/**
     * Return string representation for endpoint.
     */
    public String toString() {
        return "[" + host + ":" + port +
            (ssf != null ? "," + ssf : "") +
            (csf != null ? "," + csf : "") +
            "]";
    }

    public int hashCode() {
        return port;
    }

    public boolean equals(Object obj) {
        if ((obj != null) && (obj instanceof TCPEndpoint)) {
            TCPEndpoint ep = (TCPEndpoint) obj;
            if (port != ep.port || !host.equals(ep.host))
                return false;
            if (((csf == null) ^ (ep.csf == null)) ||
                ((ssf == null) ^ (ep.ssf == null)))
                return false;
            /*
             * Fix for 4254510: perform socket factory *class* equality check
             * before socket factory equality check to avoid passing
             * a potentially naughty socket factory to this endpoint's
             * {client,server} socket factory equals method.
             */
            if ((csf != null) &&
                !(csf.getClass() == ep.csf.getClass() && csf.equals(ep.csf)))
                return false;
            if ((ssf != null) &&
                !(ssf.getClass() == ep.ssf.getClass() && ssf.equals(ep.ssf)))
                return false;
            return true;
        } else {
            return false;
        }
    }

    /* codes for the self-describing formats of wire representation */
    private static final int FORMAT_HOST_PORT           = 0;
    private static final int FORMAT_HOST_PORT_FACTORY   = 1;

    Write endpoint to output stream.
/**
     * Write endpoint to output stream.
     */
    public void write(ObjectOutput out) throws IOException {
        if (csf == null) {
            out.writeByte(FORMAT_HOST_PORT);
            out.writeUTF(host);
            out.writeInt(port);
        } else {
            out.writeByte(FORMAT_HOST_PORT_FACTORY);
            out.writeUTF(host);
            out.writeInt(port);
            out.writeObject(csf);
        }
    }

    Get the endpoint from the input stream.
Params: in – the input stream
Throws: IOException – If id could not be read (due to stream failure)/**
     * Get the endpoint from the input stream.
     * @param in the input stream
     * @exception IOException If id could not be read (due to stream failure)
     */
    public static TCPEndpoint read(ObjectInput in)
        throws IOException, ClassNotFoundException
    {
        String host;
        int port;
        RMIClientSocketFactory csf = null;

        byte format = in.readByte();
        switch (format) {
          case FORMAT_HOST_PORT:
            host = in.readUTF();
            port = in.readInt();
            break;

          case FORMAT_HOST_PORT_FACTORY:
            host = in.readUTF();
            port = in.readInt();
            csf = (RMIClientSocketFactory) in.readObject();
          break;

          default:
            throw new IOException("invalid endpoint format");
        }
        return new TCPEndpoint(host, port, csf, null);
    }

    Write endpoint to output stream in older format used by
UnicastRef for JDK1.1 compatibility.
/**
     * Write endpoint to output stream in older format used by
     * UnicastRef for JDK1.1 compatibility.
     */
    public void writeHostPortFormat(DataOutput out) throws IOException {
        if (csf != null) {
            throw new InternalError("TCPEndpoint.writeHostPortFormat: " +
                "called for endpoint with non-null socket factory");
        }
        out.writeUTF(host);
        out.writeInt(port);
    }

    Create a new endpoint from input stream data.
Params: in – the input stream/**
     * Create a new endpoint from input stream data.
     * @param in the input stream
     */
    public static TCPEndpoint readHostPortFormat(DataInput in)
        throws IOException
    {
        String host = in.readUTF();
        int port = in.readInt();
        return new TCPEndpoint(host, port);
    }

    private static RMISocketFactory chooseFactory() {
        RMISocketFactory sf = RMISocketFactory.getSocketFactory();
        if (sf == null) {
            sf = TCPTransport.defaultSocketFactory;
        }
        return sf;
    }

    Open and return new client socket connection to endpoint.
/**
     * Open and return new client socket connection to endpoint.
     */
    Socket newSocket() throws RemoteException {
        if (TCPTransport.tcpLog.isLoggable(Log.VERBOSE)) {
            TCPTransport.tcpLog.log(Log.VERBOSE,
                "opening socket to " + this);
        }

        Socket socket;

        try {
            RMIClientSocketFactory clientFactory = csf;
            if (clientFactory == null) {
                clientFactory = chooseFactory();
            }
            socket = clientFactory.createSocket(host, port);

        } catch (java.net.UnknownHostException e) {
            throw new java.rmi.UnknownHostException(
                "Unknown host: " + host, e);
        } catch (java.net.ConnectException e) {
            throw new java.rmi.ConnectException(
                "Connection refused to host: " + host, e);
        } catch (IOException e) {
            // We might have simply run out of file descriptors
            try {
                TCPEndpoint.shedConnectionCaches();
                // REMIND: should we retry createSocket?
            } catch (OutOfMemoryError mem) {
                // don't quit if out of memory
            } catch (Exception ex) {
                // don't quit if shed fails non-catastrophically
            }

            throw new ConnectIOException("Exception creating connection to: " +
                host, e);
        }

        // set socket to disable Nagle's algorithm (always send immediately)
        // TBD: should this be left up to socket factory instead?
        try {
            socket.setTcpNoDelay(true);
        } catch (Exception e) {
            // if we fail to set this, ignore and proceed anyway
        }

        // fix 4187495: explicitly set SO_KEEPALIVE to prevent client hangs
        try {
            socket.setKeepAlive(true);
        } catch (Exception e) {
            // ignore and proceed
        }

        return socket;
    }

    Return new server socket to listen for connections on this endpoint.
/**
     * Return new server socket to listen for connections on this endpoint.
     */
    ServerSocket newServerSocket() throws IOException {
        if (TCPTransport.tcpLog.isLoggable(Log.VERBOSE)) {
            TCPTransport.tcpLog.log(Log.VERBOSE,
                "creating server socket on " + this);
        }

        RMIServerSocketFactory serverFactory = ssf;
        if (serverFactory == null) {
            serverFactory = chooseFactory();
        }
        ServerSocket server = serverFactory.createServerSocket(listenPort);

        // if we listened on an anonymous port, set the default port
        // (for this socket factory)
        if (listenPort == 0)
            setDefaultPort(server.getLocalPort(), csf, ssf);

        return server;
    }

    The class FQDN encapsulates a routine that makes a best effort
attempt to retrieve the fully qualified domain name of the local
host.
Author:  Laird Dornin/**
     * The class FQDN encapsulates a routine that makes a best effort
     * attempt to retrieve the fully qualified domain name of the local
     * host.
     *
     * @author  Laird Dornin
     */
    private static class FQDN implements Runnable {

        strings in which we can store discovered fqdn
/**
         * strings in which we can store discovered fqdn
         */
        private String reverseLookup;

        private String hostAddress;

        private FQDN(String hostAddress) {
            this.hostAddress = hostAddress;
        }

        Do our best to obtain a fully qualified hostname for the local
host.  Perform the following steps to get a localhostname:
1. InetAddress.getLocalHost().getHostName() - if contains
   '.' use as FQDN
2. if no '.' query name service for FQDN in a thread
   Note: We query the name service for an FQDN by creating
   an InetAddress via a stringified copy of the local ip
   address; this creates an InetAddress with a null hostname.
   Asking for the hostname of this InetAddress causes a name
   service lookup.
3. if name service takes too long to return, use ip address
4. if name service returns but response contains no '.'
   default to ipaddress.
/**
         * Do our best to obtain a fully qualified hostname for the local
         * host.  Perform the following steps to get a localhostname:
         *
         * 1. InetAddress.getLocalHost().getHostName() - if contains
         *    '.' use as FQDN
         * 2. if no '.' query name service for FQDN in a thread
         *    Note: We query the name service for an FQDN by creating
         *    an InetAddress via a stringified copy of the local ip
         *    address; this creates an InetAddress with a null hostname.
         *    Asking for the hostname of this InetAddress causes a name
         *    service lookup.
         *
         * 3. if name service takes too long to return, use ip address
         * 4. if name service returns but response contains no '.'
         *    default to ipaddress.
         */
        static String attemptFQDN(InetAddress localAddr)
            throws java.net.UnknownHostException
        {

            String hostName = localAddr.getHostName();

            if (hostName.indexOf('.') < 0 ) {

                String hostAddress = localAddr.getHostAddress();
                FQDN f = new FQDN(hostAddress);

                int nameServiceTimeOut =
                    TCPEndpoint.getInt("sun.rmi.transport.tcp.localHostNameTimeOut",
                                       10000);

                try {
                    synchronized(f) {
                        f.getFQDN();

                        /* wait to obtain an FQDN */
                        f.wait(nameServiceTimeOut);
                    }
                } catch (InterruptedException e) {
                    /* propagate the exception to the caller */
                    Thread.currentThread().interrupt();
                }
                hostName = f.getHost();

                if ((hostName == null) || (hostName.equals(""))
                    || (hostName.indexOf('.') < 0 )) {

                    hostName = hostAddress;
                }
            }
            return hostName;
        }

        Method that that will start a thread to wait to retrieve a
fully qualified domain name from a name service.  The spawned
thread may never return but we have marked it as a daemon so the vm
will terminate appropriately.
/**
         * Method that that will start a thread to wait to retrieve a
         * fully qualified domain name from a name service.  The spawned
         * thread may never return but we have marked it as a daemon so the vm
         * will terminate appropriately.
         */
        private void getFQDN() {

            /* FQDN finder will run in RMI threadgroup. */
            Thread t = AccessController.doPrivileged(
                new NewThreadAction(FQDN.this, "FQDN Finder", true));
            t.start();
        }

        private synchronized String getHost() {
            return reverseLookup;
        }

        thread to query a name service for the fqdn of this host.
/**
         * thread to query a name service for the fqdn of this host.
         */
        public void run()  {

            String name = null;

            try {
                name = InetAddress.getByName(hostAddress).getHostName();
            } catch (java.net.UnknownHostException e) {
            } finally {
                synchronized(this) {
                    reverseLookup = name;
                    this.notify();
                }
            }
        }
    }
}
Params:	in – the input stream
Throws:	IOException – If id could not be read (due to stream failure)
/

java/ 6/ sun/rmi/transport/tcp/TCPEndpoint.java
