src/java.base/share/classes/sun/nio/ch/DatagramChannelImpl.java
changeset 47216 71c04702a3d5
parent 44534 a076dffbc2c1
child 48750 ffbb784a8873
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/java.base/share/classes/sun/nio/ch/DatagramChannelImpl.java	Tue Sep 12 19:03:39 2017 +0200
@@ -0,0 +1,1152 @@
+/*
+ * Copyright (c) 2001, 2017, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * 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).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package sun.nio.ch;
+
+import java.io.FileDescriptor;
+import java.io.IOException;
+import java.net.*;
+import java.nio.ByteBuffer;
+import java.nio.channels.*;
+import java.nio.channels.spi.*;
+import java.util.*;
+import sun.net.ResourceManager;
+import sun.net.ext.ExtendedSocketOptions;
+
+/**
+ * An implementation of DatagramChannels.
+ */
+
+class DatagramChannelImpl
+    extends DatagramChannel
+    implements SelChImpl
+{
+
+    // Used to make native read and write calls
+    private static NativeDispatcher nd = new DatagramDispatcher();
+
+    // Our file descriptor
+    private final FileDescriptor fd;
+
+    // fd value needed for dev/poll. This value will remain valid
+    // even after the value in the file descriptor object has been set to -1
+    private final int fdVal;
+
+    // The protocol family of the socket
+    private final ProtocolFamily family;
+
+    // IDs of native threads doing reads and writes, for signalling
+    private volatile long readerThread;
+    private volatile long writerThread;
+
+    // Cached InetAddress and port for unconnected DatagramChannels
+    // used by receive0
+    private InetAddress cachedSenderInetAddress;
+    private int cachedSenderPort;
+
+    // Lock held by current reading or connecting thread
+    private final Object readLock = new Object();
+
+    // Lock held by current writing or connecting thread
+    private final Object writeLock = new Object();
+
+    // Lock held by any thread that modifies the state fields declared below
+    // DO NOT invoke a blocking I/O operation while holding this lock!
+    private final Object stateLock = new Object();
+
+    // -- The following fields are protected by stateLock
+
+    // State (does not necessarily increase monotonically)
+    private static final int ST_UNINITIALIZED = -1;
+    private static final int ST_UNCONNECTED = 0;
+    private static final int ST_CONNECTED = 1;
+    private static final int ST_KILLED = 2;
+    private int state = ST_UNINITIALIZED;
+
+    // Binding
+    private InetSocketAddress localAddress;
+    private InetSocketAddress remoteAddress;
+
+    // Our socket adaptor, if any
+    private DatagramSocket socket;
+
+    // Multicast support
+    private MembershipRegistry registry;
+
+    // set true when socket is bound and SO_REUSEADDRESS is emulated
+    private boolean reuseAddressEmulated;
+
+    // set true/false when socket is already bound and SO_REUSEADDR is emulated
+    private boolean isReuseAddress;
+
+    // -- End of fields protected by stateLock
+
+
+    public DatagramChannelImpl(SelectorProvider sp)
+        throws IOException
+    {
+        super(sp);
+        ResourceManager.beforeUdpCreate();
+        try {
+            this.family = Net.isIPv6Available() ?
+                StandardProtocolFamily.INET6 : StandardProtocolFamily.INET;
+            this.fd = Net.socket(family, false);
+            this.fdVal = IOUtil.fdVal(fd);
+            this.state = ST_UNCONNECTED;
+        } catch (IOException ioe) {
+            ResourceManager.afterUdpClose();
+            throw ioe;
+        }
+    }
+
+    public DatagramChannelImpl(SelectorProvider sp, ProtocolFamily family)
+        throws IOException
+    {
+        super(sp);
+        if ((family != StandardProtocolFamily.INET) &&
+            (family != StandardProtocolFamily.INET6))
+        {
+            if (family == null)
+                throw new NullPointerException("'family' is null");
+            else
+                throw new UnsupportedOperationException("Protocol family not supported");
+        }
+        if (family == StandardProtocolFamily.INET6) {
+            if (!Net.isIPv6Available()) {
+                throw new UnsupportedOperationException("IPv6 not available");
+            }
+        }
+        this.family = family;
+        this.fd = Net.socket(family, false);
+        this.fdVal = IOUtil.fdVal(fd);
+        this.state = ST_UNCONNECTED;
+    }
+
+    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 DatagramSocket socket() {
+        synchronized (stateLock) {
+            if (socket == null)
+                socket = DatagramSocketAdaptor.create(this);
+            return socket;
+        }
+    }
+
+    @Override
+    public SocketAddress getLocalAddress() throws IOException {
+        synchronized (stateLock) {
+            if (!isOpen())
+                throw new ClosedChannelException();
+            // Perform security check before returning address
+            return Net.getRevealedLocalAddress(localAddress);
+        }
+    }
+
+    @Override
+    public SocketAddress getRemoteAddress() throws IOException {
+        synchronized (stateLock) {
+            if (!isOpen())
+                throw new ClosedChannelException();
+            return remoteAddress;
+        }
+    }
+
+    @Override
+    public <T> DatagramChannel setOption(SocketOption<T> name, T value)
+        throws IOException
+    {
+        if (name == null)
+            throw new NullPointerException();
+        if (!supportedOptions().contains(name))
+            throw new UnsupportedOperationException("'" + name + "' not supported");
+
+        synchronized (stateLock) {
+            ensureOpen();
+
+            if (name == StandardSocketOptions.IP_TOS ||
+                name == StandardSocketOptions.IP_MULTICAST_TTL ||
+                name == StandardSocketOptions.IP_MULTICAST_LOOP)
+            {
+                // options are protocol dependent
+                Net.setSocketOption(fd, family, name, value);
+                return this;
+            }
+
+            if (name == StandardSocketOptions.IP_MULTICAST_IF) {
+                if (value == null)
+                    throw new IllegalArgumentException("Cannot set IP_MULTICAST_IF to 'null'");
+                NetworkInterface interf = (NetworkInterface)value;
+                if (family == StandardProtocolFamily.INET6) {
+                    int index = interf.getIndex();
+                    if (index == -1)
+                        throw new IOException("Network interface cannot be identified");
+                    Net.setInterface6(fd, index);
+                } else {
+                    // need IPv4 address to identify interface
+                    Inet4Address target = Net.anyInet4Address(interf);
+                    if (target == null)
+                        throw new IOException("Network interface not configured for IPv4");
+                    int targetAddress = Net.inet4AsInt(target);
+                    Net.setInterface4(fd, targetAddress);
+                }
+                return this;
+            }
+            if (name == StandardSocketOptions.SO_REUSEADDR &&
+                    Net.useExclusiveBind() && localAddress != null)
+            {
+                reuseAddressEmulated = true;
+                this.isReuseAddress = (Boolean)value;
+            }
+
+            // remaining options don't need any special handling
+            Net.setSocketOption(fd, Net.UNSPEC, name, value);
+            return this;
+        }
+    }
+
+    @Override
+    @SuppressWarnings("unchecked")
+    public <T> T getOption(SocketOption<T> name)
+        throws IOException
+    {
+        if (name == null)
+            throw new NullPointerException();
+        if (!supportedOptions().contains(name))
+            throw new UnsupportedOperationException("'" + name + "' not supported");
+
+        synchronized (stateLock) {
+            ensureOpen();
+
+            if (name == StandardSocketOptions.IP_TOS ||
+                name == StandardSocketOptions.IP_MULTICAST_TTL ||
+                name == StandardSocketOptions.IP_MULTICAST_LOOP)
+            {
+                return (T) Net.getSocketOption(fd, family, name);
+            }
+
+            if (name == StandardSocketOptions.IP_MULTICAST_IF) {
+                if (family == StandardProtocolFamily.INET) {
+                    int address = Net.getInterface4(fd);
+                    if (address == 0)
+                        return null;    // default interface
+
+                    InetAddress ia = Net.inet4FromInt(address);
+                    NetworkInterface ni = NetworkInterface.getByInetAddress(ia);
+                    if (ni == null)
+                        throw new IOException("Unable to map address to interface");
+                    return (T) ni;
+                } else {
+                    int index = Net.getInterface6(fd);
+                    if (index == 0)
+                        return null;    // default interface
+
+                    NetworkInterface ni = NetworkInterface.getByIndex(index);
+                    if (ni == null)
+                        throw new IOException("Unable to map index to interface");
+                    return (T) ni;
+                }
+            }
+
+            if (name == StandardSocketOptions.SO_REUSEADDR &&
+                    reuseAddressEmulated)
+            {
+                return (T)Boolean.valueOf(isReuseAddress);
+            }
+
+            // no special handling
+            return (T) Net.getSocketOption(fd, Net.UNSPEC, name);
+        }
+    }
+
+    private static class DefaultOptionsHolder {
+        static final Set<SocketOption<?>> defaultOptions = defaultOptions();
+
+        private static Set<SocketOption<?>> defaultOptions() {
+            HashSet<SocketOption<?>> set = new HashSet<>(8);
+            set.add(StandardSocketOptions.SO_SNDBUF);
+            set.add(StandardSocketOptions.SO_RCVBUF);
+            set.add(StandardSocketOptions.SO_REUSEADDR);
+            if (Net.isReusePortAvailable()) {
+                set.add(StandardSocketOptions.SO_REUSEPORT);
+            }
+            set.add(StandardSocketOptions.SO_BROADCAST);
+            set.add(StandardSocketOptions.IP_TOS);
+            set.add(StandardSocketOptions.IP_MULTICAST_IF);
+            set.add(StandardSocketOptions.IP_MULTICAST_TTL);
+            set.add(StandardSocketOptions.IP_MULTICAST_LOOP);
+            ExtendedSocketOptions extendedOptions =
+                    ExtendedSocketOptions.getInstance();
+            set.addAll(extendedOptions.options());
+            return Collections.unmodifiableSet(set);
+        }
+    }
+
+    @Override
+    public final Set<SocketOption<?>> supportedOptions() {
+        return DefaultOptionsHolder.defaultOptions;
+    }
+
+    private void ensureOpen() throws ClosedChannelException {
+        if (!isOpen())
+            throw new ClosedChannelException();
+    }
+
+    private SocketAddress sender;       // Set by receive0 (## ugh)
+
+    public SocketAddress receive(ByteBuffer dst) throws IOException {
+        if (dst.isReadOnly())
+            throw new IllegalArgumentException("Read-only buffer");
+        synchronized (readLock) {
+            ensureOpen();
+            // Socket was not bound before attempting receive
+            if (localAddress() == null)
+                bind(null);
+            int n = 0;
+            ByteBuffer bb = null;
+            try {
+                begin();
+                if (!isOpen())
+                    return null;
+                SecurityManager security = System.getSecurityManager();
+                readerThread = NativeThread.current();
+                if (isConnected() || (security == null)) {
+                    do {
+                        n = receive(fd, dst);
+                    } while ((n == IOStatus.INTERRUPTED) && isOpen());
+                    if (n == IOStatus.UNAVAILABLE)
+                        return null;
+                } else {
+                    bb = Util.getTemporaryDirectBuffer(dst.remaining());
+                    for (;;) {
+                        do {
+                            n = receive(fd, bb);
+                        } while ((n == IOStatus.INTERRUPTED) && isOpen());
+                        if (n == IOStatus.UNAVAILABLE)
+                            return null;
+                        InetSocketAddress isa = (InetSocketAddress)sender;
+                        try {
+                            security.checkAccept(
+                                isa.getAddress().getHostAddress(),
+                                isa.getPort());
+                        } catch (SecurityException se) {
+                            // Ignore packet
+                            bb.clear();
+                            n = 0;
+                            continue;
+                        }
+                        bb.flip();
+                        dst.put(bb);
+                        break;
+                    }
+                }
+                return sender;
+            } finally {
+                if (bb != null)
+                    Util.releaseTemporaryDirectBuffer(bb);
+                readerThread = 0;
+                end((n > 0) || (n == IOStatus.UNAVAILABLE));
+                assert IOStatus.check(n);
+            }
+        }
+    }
+
+    private int receive(FileDescriptor fd, ByteBuffer dst)
+        throws IOException
+    {
+        int pos = dst.position();
+        int lim = dst.limit();
+        assert (pos <= lim);
+        int rem = (pos <= lim ? lim - pos : 0);
+        if (dst instanceof DirectBuffer && rem > 0)
+            return receiveIntoNativeBuffer(fd, dst, rem, pos);
+
+        // Substitute a native buffer. If the supplied buffer is empty
+        // we must instead use a nonempty buffer, otherwise the call
+        // will not block waiting for a datagram on some platforms.
+        int newSize = Math.max(rem, 1);
+        ByteBuffer bb = Util.getTemporaryDirectBuffer(newSize);
+        try {
+            int n = receiveIntoNativeBuffer(fd, bb, newSize, 0);
+            bb.flip();
+            if (n > 0 && rem > 0)
+                dst.put(bb);
+            return n;
+        } finally {
+            Util.releaseTemporaryDirectBuffer(bb);
+        }
+    }
+
+    private int receiveIntoNativeBuffer(FileDescriptor fd, ByteBuffer bb,
+                                        int rem, int pos)
+        throws IOException
+    {
+        int n = receive0(fd, ((DirectBuffer)bb).address() + pos, rem,
+                         isConnected());
+        if (n > 0)
+            bb.position(pos + n);
+        return n;
+    }
+
+    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);
+            }
+        }
+    }
+
+    private int send(FileDescriptor fd, ByteBuffer src, InetSocketAddress target)
+        throws IOException
+    {
+        if (src instanceof DirectBuffer)
+            return sendFromNativeBuffer(fd, src, target);
+
+        // Substitute a native buffer
+        int pos = src.position();
+        int lim = src.limit();
+        assert (pos <= lim);
+        int rem = (pos <= lim ? lim - pos : 0);
+
+        ByteBuffer bb = Util.getTemporaryDirectBuffer(rem);
+        try {
+            bb.put(src);
+            bb.flip();
+            // Do not update src until we see how many bytes were written
+            src.position(pos);
+
+            int n = sendFromNativeBuffer(fd, bb, target);
+            if (n > 0) {
+                // now update src
+                src.position(pos + n);
+            }
+            return n;
+        } finally {
+            Util.releaseTemporaryDirectBuffer(bb);
+        }
+    }
+
+    private int sendFromNativeBuffer(FileDescriptor fd, ByteBuffer bb,
+                                     InetSocketAddress target)
+        throws IOException
+    {
+        int pos = bb.position();
+        int lim = bb.limit();
+        assert (pos <= lim);
+        int rem = (pos <= lim ? lim - pos : 0);
+
+        boolean preferIPv6 = (family != StandardProtocolFamily.INET);
+        int written;
+        try {
+            written = send0(preferIPv6, fd, ((DirectBuffer)bb).address() + pos,
+                            rem, target.getAddress(), target.getPort());
+        } catch (PortUnreachableException pue) {
+            if (isConnected())
+                throw pue;
+            written = rem;
+        }
+        if (written > 0)
+            bb.position(pos + written);
+        return written;
+    }
+
+    public int read(ByteBuffer buf) throws IOException {
+        if (buf == null)
+            throw new NullPointerException();
+        synchronized (readLock) {
+            synchronized (stateLock) {
+                ensureOpen();
+                if (!isConnected())
+                    throw new NotYetConnectedException();
+            }
+            int n = 0;
+            try {
+                begin();
+                if (!isOpen())
+                    return 0;
+                readerThread = NativeThread.current();
+                do {
+                    n = IOUtil.read(fd, buf, -1, nd);
+                } while ((n == IOStatus.INTERRUPTED) && isOpen());
+                return IOStatus.normalize(n);
+            } finally {
+                readerThread = 0;
+                end((n > 0) || (n == IOStatus.UNAVAILABLE));
+                assert IOStatus.check(n);
+            }
+        }
+    }
+
+    public long read(ByteBuffer[] dsts, int offset, int length)
+        throws IOException
+    {
+        if ((offset < 0) || (length < 0) || (offset > dsts.length - length))
+            throw new IndexOutOfBoundsException();
+        synchronized (readLock) {
+            synchronized (stateLock) {
+                ensureOpen();
+                if (!isConnected())
+                    throw new NotYetConnectedException();
+            }
+            long n = 0;
+            try {
+                begin();
+                if (!isOpen())
+                    return 0;
+                readerThread = NativeThread.current();
+                do {
+                    n = IOUtil.read(fd, dsts, offset, length, nd);
+                } while ((n == IOStatus.INTERRUPTED) && isOpen());
+                return IOStatus.normalize(n);
+            } finally {
+                readerThread = 0;
+                end((n > 0) || (n == IOStatus.UNAVAILABLE));
+                assert IOStatus.check(n);
+            }
+        }
+    }
+
+    public int write(ByteBuffer buf) throws IOException {
+        if (buf == null)
+            throw new NullPointerException();
+        synchronized (writeLock) {
+            synchronized (stateLock) {
+                ensureOpen();
+                if (!isConnected())
+                    throw new NotYetConnectedException();
+            }
+            int n = 0;
+            try {
+                begin();
+                if (!isOpen())
+                    return 0;
+                writerThread = NativeThread.current();
+                do {
+                    n = IOUtil.write(fd, buf, -1, nd);
+                } while ((n == IOStatus.INTERRUPTED) && isOpen());
+                return IOStatus.normalize(n);
+            } finally {
+                writerThread = 0;
+                end((n > 0) || (n == IOStatus.UNAVAILABLE));
+                assert IOStatus.check(n);
+            }
+        }
+    }
+
+    public long write(ByteBuffer[] srcs, int offset, int length)
+        throws IOException
+    {
+        if ((offset < 0) || (length < 0) || (offset > srcs.length - length))
+            throw new IndexOutOfBoundsException();
+        synchronized (writeLock) {
+            synchronized (stateLock) {
+                ensureOpen();
+                if (!isConnected())
+                    throw new NotYetConnectedException();
+            }
+            long n = 0;
+            try {
+                begin();
+                if (!isOpen())
+                    return 0;
+                writerThread = NativeThread.current();
+                do {
+                    n = IOUtil.write(fd, srcs, offset, length, nd);
+                } while ((n == IOStatus.INTERRUPTED) && isOpen());
+                return IOStatus.normalize(n);
+            } finally {
+                writerThread = 0;
+                end((n > 0) || (n == IOStatus.UNAVAILABLE));
+                assert IOStatus.check(n);
+            }
+        }
+    }
+
+    protected void implConfigureBlocking(boolean block) throws IOException {
+        IOUtil.configureBlocking(fd, block);
+    }
+
+    public SocketAddress localAddress() {
+        synchronized (stateLock) {
+            return localAddress;
+        }
+    }
+
+    public SocketAddress remoteAddress() {
+        synchronized (stateLock) {
+            return remoteAddress;
+        }
+    }
+
+    @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 boolean isConnected() {
+        synchronized (stateLock) {
+            return (state == ST_CONNECTED);
+        }
+    }
+
+    void ensureOpenAndUnconnected() throws IOException { // package-private
+        synchronized (stateLock) {
+            if (!isOpen())
+                throw new ClosedChannelException();
+            if (state != ST_UNCONNECTED)
+                throw new IllegalStateException("Connect already invoked");
+        }
+    }
+
+    @Override
+    public DatagramChannel connect(SocketAddress sa) throws IOException {
+        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();
+                            ByteBuffer tmpBuf = ByteBuffer.allocate(100);
+                            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 = remoteAddress;
+                    SecurityManager sm = System.getSecurityManager();
+                    if (sm != null)
+                        sm.checkConnect(isa.getAddress().getHostAddress(),
+                                        isa.getPort());
+                    boolean isIPv6 = (family == StandardProtocolFamily.INET6);
+                    disconnect0(fd, isIPv6);
+                    remoteAddress = null;
+                    state = ST_UNCONNECTED;
+
+                    // refresh local address
+                    localAddress = Net.localAddress(fd);
+                }
+            }
+        }
+        return this;
+    }
+
+    /**
+     * Joins channel's socket to the given group/interface and
+     * optional source address.
+     */
+    private MembershipKey innerJoin(InetAddress group,
+                                    NetworkInterface interf,
+                                    InetAddress source)
+        throws IOException
+    {
+        if (!group.isMulticastAddress())
+            throw new IllegalArgumentException("Group not a multicast address");
+
+        // check multicast address is compatible with this socket
+        if (group instanceof Inet4Address) {
+            if (family == StandardProtocolFamily.INET6 && !Net.canIPv6SocketJoinIPv4Group())
+                throw new IllegalArgumentException("IPv6 socket cannot join IPv4 multicast group");
+        } else if (group instanceof Inet6Address) {
+            if (family != StandardProtocolFamily.INET6)
+                throw new IllegalArgumentException("Only IPv6 sockets can join IPv6 multicast group");
+        } else {
+            throw new IllegalArgumentException("Address type not supported");
+        }
+
+        // check source address
+        if (source != null) {
+            if (source.isAnyLocalAddress())
+                throw new IllegalArgumentException("Source address is a wildcard address");
+            if (source.isMulticastAddress())
+                throw new IllegalArgumentException("Source address is multicast address");
+            if (source.getClass() != group.getClass())
+                throw new IllegalArgumentException("Source address is different type to group");
+        }
+
+        SecurityManager sm = System.getSecurityManager();
+        if (sm != null)
+            sm.checkMulticast(group);
+
+        synchronized (stateLock) {
+            if (!isOpen())
+                throw new ClosedChannelException();
+
+            // check the registry to see if we are already a member of the group
+            if (registry == null) {
+                registry = new MembershipRegistry();
+            } else {
+                // return existing membership key
+                MembershipKey key = registry.checkMembership(group, interf, source);
+                if (key != null)
+                    return key;
+            }
+
+            MembershipKeyImpl key;
+            if ((family == StandardProtocolFamily.INET6) &&
+                ((group instanceof Inet6Address) || Net.canJoin6WithIPv4Group()))
+            {
+                int index = interf.getIndex();
+                if (index == -1)
+                    throw new IOException("Network interface cannot be identified");
+
+                // need multicast and source address as byte arrays
+                byte[] groupAddress = Net.inet6AsByteArray(group);
+                byte[] sourceAddress = (source == null) ? null :
+                    Net.inet6AsByteArray(source);
+
+                // join the group
+                int n = Net.join6(fd, groupAddress, index, sourceAddress);
+                if (n == IOStatus.UNAVAILABLE)
+                    throw new UnsupportedOperationException();
+
+                key = new MembershipKeyImpl.Type6(this, group, interf, source,
+                                                  groupAddress, index, sourceAddress);
+
+            } else {
+                // need IPv4 address to identify interface
+                Inet4Address target = Net.anyInet4Address(interf);
+                if (target == null)
+                    throw new IOException("Network interface not configured for IPv4");
+
+                int groupAddress = Net.inet4AsInt(group);
+                int targetAddress = Net.inet4AsInt(target);
+                int sourceAddress = (source == null) ? 0 : Net.inet4AsInt(source);
+
+                // join the group
+                int n = Net.join4(fd, groupAddress, targetAddress, sourceAddress);
+                if (n == IOStatus.UNAVAILABLE)
+                    throw new UnsupportedOperationException();
+
+                key = new MembershipKeyImpl.Type4(this, group, interf, source,
+                                                  groupAddress, targetAddress, sourceAddress);
+            }
+
+            registry.add(key);
+            return key;
+        }
+    }
+
+    @Override
+    public MembershipKey join(InetAddress group,
+                              NetworkInterface interf)
+        throws IOException
+    {
+        return innerJoin(group, interf, null);
+    }
+
+    @Override
+    public MembershipKey join(InetAddress group,
+                              NetworkInterface interf,
+                              InetAddress source)
+        throws IOException
+    {
+        if (source == null)
+            throw new NullPointerException("source address is null");
+        return innerJoin(group, interf, source);
+    }
+
+    // package-private
+    void drop(MembershipKeyImpl key) {
+        assert key.channel() == this;
+
+        synchronized (stateLock) {
+            if (!key.isValid())
+                return;
+
+            try {
+                if (key instanceof MembershipKeyImpl.Type6) {
+                    MembershipKeyImpl.Type6 key6 =
+                        (MembershipKeyImpl.Type6)key;
+                    Net.drop6(fd, key6.groupAddress(), key6.index(), key6.source());
+                } else {
+                    MembershipKeyImpl.Type4 key4 = (MembershipKeyImpl.Type4)key;
+                    Net.drop4(fd, key4.groupAddress(), key4.interfaceAddress(),
+                        key4.source());
+                }
+            } catch (IOException ioe) {
+                // should not happen
+                throw new AssertionError(ioe);
+            }
+
+            key.invalidate();
+            registry.remove(key);
+        }
+    }
+
+    /**
+     * Block datagrams from given source if a memory to receive all
+     * datagrams.
+     */
+    void block(MembershipKeyImpl key, InetAddress source)
+        throws IOException
+    {
+        assert key.channel() == this;
+        assert key.sourceAddress() == null;
+
+        synchronized (stateLock) {
+            if (!key.isValid())
+                throw new IllegalStateException("key is no longer valid");
+            if (source.isAnyLocalAddress())
+                throw new IllegalArgumentException("Source address is a wildcard address");
+            if (source.isMulticastAddress())
+                throw new IllegalArgumentException("Source address is multicast address");
+            if (source.getClass() != key.group().getClass())
+                throw new IllegalArgumentException("Source address is different type to group");
+
+            int n;
+            if (key instanceof MembershipKeyImpl.Type6) {
+                 MembershipKeyImpl.Type6 key6 =
+                    (MembershipKeyImpl.Type6)key;
+                n = Net.block6(fd, key6.groupAddress(), key6.index(),
+                               Net.inet6AsByteArray(source));
+            } else {
+                MembershipKeyImpl.Type4 key4 =
+                    (MembershipKeyImpl.Type4)key;
+                n = Net.block4(fd, key4.groupAddress(), key4.interfaceAddress(),
+                               Net.inet4AsInt(source));
+            }
+            if (n == IOStatus.UNAVAILABLE) {
+                // ancient kernel
+                throw new UnsupportedOperationException();
+            }
+        }
+    }
+
+    /**
+     * Unblock given source.
+     */
+    void unblock(MembershipKeyImpl key, InetAddress source) {
+        assert key.channel() == this;
+        assert key.sourceAddress() == null;
+
+        synchronized (stateLock) {
+            if (!key.isValid())
+                throw new IllegalStateException("key is no longer valid");
+
+            try {
+                if (key instanceof MembershipKeyImpl.Type6) {
+                    MembershipKeyImpl.Type6 key6 =
+                        (MembershipKeyImpl.Type6)key;
+                    Net.unblock6(fd, key6.groupAddress(), key6.index(),
+                                 Net.inet6AsByteArray(source));
+                } else {
+                    MembershipKeyImpl.Type4 key4 =
+                        (MembershipKeyImpl.Type4)key;
+                    Net.unblock4(fd, key4.groupAddress(), key4.interfaceAddress(),
+                                 Net.inet4AsInt(source));
+                }
+            } catch (IOException ioe) {
+                // should not happen
+                throw new AssertionError(ioe);
+            }
+        }
+    }
+
+    protected void implCloseSelectableChannel() throws IOException {
+        synchronized (stateLock) {
+            if (state != ST_KILLED)
+                nd.preClose(fd);
+            ResourceManager.afterUdpClose();
+
+            // if member of mulitcast group then invalidate all keys
+            if (registry != null)
+                registry.invalidateAll();
+
+            long th;
+            if ((th = readerThread) != 0)
+                NativeThread.signal(th);
+            if ((th = writerThread) != 0)
+                NativeThread.signal(th);
+            if (!isRegistered())
+                kill();
+        }
+    }
+
+    public void kill() throws IOException {
+        synchronized (stateLock) {
+            if (state == ST_KILLED)
+                return;
+            if (state == ST_UNINITIALIZED) {
+                state = ST_KILLED;
+                return;
+            }
+            assert !isOpen() && !isRegistered();
+            nd.close(fd);
+            state = ST_KILLED;
+        }
+    }
+
+    @SuppressWarnings("deprecation")
+    protected void finalize() throws IOException {
+        // fd is null if constructor threw exception
+        if (fd != null)
+            close();
+    }
+
+    /**
+     * Translates native poll revent set into a ready operation set
+     */
+    public boolean translateReadyOps(int ops, int initialOps,
+                                     SelectionKeyImpl sk) {
+        int intOps = sk.nioInterestOps(); // Do this just once, it synchronizes
+        int oldOps = sk.nioReadyOps();
+        int newOps = initialOps;
+
+        if ((ops & Net.POLLNVAL) != 0) {
+            // This should only happen if this channel is pre-closed while a
+            // selection operation is in progress
+            // ## Throw an error if this channel has not been pre-closed
+            return false;
+        }
+
+        if ((ops & (Net.POLLERR | Net.POLLHUP)) != 0) {
+            newOps = intOps;
+            sk.nioReadyOps(newOps);
+            return (newOps & ~oldOps) != 0;
+        }
+
+        if (((ops & Net.POLLIN) != 0) &&
+            ((intOps & SelectionKey.OP_READ) != 0))
+            newOps |= SelectionKey.OP_READ;
+
+        if (((ops & Net.POLLOUT) != 0) &&
+            ((intOps & SelectionKey.OP_WRITE) != 0))
+            newOps |= SelectionKey.OP_WRITE;
+
+        sk.nioReadyOps(newOps);
+        return (newOps & ~oldOps) != 0;
+    }
+
+    public boolean translateAndUpdateReadyOps(int ops, SelectionKeyImpl sk) {
+        return translateReadyOps(ops, sk.nioReadyOps(), sk);
+    }
+
+    public boolean translateAndSetReadyOps(int ops, SelectionKeyImpl sk) {
+        return translateReadyOps(ops, 0, sk);
+    }
+
+    // package-private
+    int poll(int events, long timeout) throws IOException {
+        assert Thread.holdsLock(blockingLock()) && !isBlocking();
+
+        synchronized (readLock) {
+            int n = 0;
+            try {
+                begin();
+                synchronized (stateLock) {
+                    if (!isOpen())
+                        return 0;
+                    readerThread = NativeThread.current();
+                }
+                n = Net.poll(fd, events, timeout);
+            } finally {
+                readerThread = 0;
+                end(n > 0);
+            }
+            return n;
+        }
+    }
+
+    /**
+     * Translates an interest operation set into a native poll event set
+     */
+    public void translateAndSetInterestOps(int ops, SelectionKeyImpl sk) {
+        int newOps = 0;
+
+        if ((ops & SelectionKey.OP_READ) != 0)
+            newOps |= Net.POLLIN;
+        if ((ops & SelectionKey.OP_WRITE) != 0)
+            newOps |= Net.POLLOUT;
+        if ((ops & SelectionKey.OP_CONNECT) != 0)
+            newOps |= Net.POLLIN;
+        sk.selector.putEventOps(sk, newOps);
+    }
+
+    public FileDescriptor getFD() {
+        return fd;
+    }
+
+    public int getFDVal() {
+        return fdVal;
+    }
+
+
+    // -- Native methods --
+
+    private static native void initIDs();
+
+    private static native void disconnect0(FileDescriptor fd, boolean isIPv6)
+        throws IOException;
+
+    private native int receive0(FileDescriptor fd, long address, int len,
+                                boolean connected)
+        throws IOException;
+
+    private native int send0(boolean preferIPv6, FileDescriptor fd, long address,
+                             int len, InetAddress addr, int port)
+        throws IOException;
+
+    static {
+        IOUtil.load();
+        initIDs();
+    }
+
+}