Java example source code file (AbstractSelectableChannel.java)

This example Java source code file (AbstractSelectableChannel.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

abstractselectablechannel, closedchannelexception, illegalargumentexception, illegalblockingmodeexception, ioexception, object, selectablechannel, selectionkey, selectorprovider

The AbstractSelectableChannel.java Java example source code

/*
 * Copyright (c) 2000, 2013, 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 java.nio.channels.spi;

import java.io.IOException;
import java.nio.channels.*;


/**
 * Base implementation class for selectable channels.
 *
 * <p> This class defines methods that handle the mechanics of channel
 * registration, deregistration, and closing.  It maintains the current
 * blocking mode of this channel as well as its current set of selection keys.
 * It performs all of the synchronization required to implement the {@link
 * java.nio.channels.SelectableChannel} specification.  Implementations of the
 * abstract protected methods defined in this class need not synchronize
 * against other threads that might be engaged in the same operations.  </p>
 *
 *
 * @author Mark Reinhold
 * @author Mike McCloskey
 * @author JSR-51 Expert Group
 * @since 1.4
 */

public abstract class AbstractSelectableChannel
    extends SelectableChannel
{

    // The provider that created this channel
    private final SelectorProvider provider;

    // Keys that have been created by registering this channel with selectors.
    // They are saved because if this channel is closed the keys must be
    // deregistered.  Protected by keyLock.
    //
    private SelectionKey[] keys = null;
    private int keyCount = 0;

    // Lock for key set and count
    private final Object keyLock = new Object();

    // Lock for registration and configureBlocking operations
    private final Object regLock = new Object();

    // Blocking mode, protected by regLock
    boolean blocking = true;

    /**
     * Initializes a new instance of this class.
     *
     * @param  provider
     *         The provider that created this channel
     */
    protected AbstractSelectableChannel(SelectorProvider provider) {
        this.provider = provider;
    }

    /**
     * Returns the provider that created this channel.
     *
     * @return  The provider that created this channel
     */
    public final SelectorProvider provider() {
        return provider;
    }


    // -- Utility methods for the key set --

    private void addKey(SelectionKey k) {
        assert Thread.holdsLock(keyLock);
        int i = 0;
        if ((keys != null) && (keyCount < keys.length)) {
            // Find empty element of key array
            for (i = 0; i < keys.length; i++)
                if (keys[i] == null)
                    break;
        } else if (keys == null) {
            keys =  new SelectionKey[3];
        } else {
            // Grow key array
            int n = keys.length * 2;
            SelectionKey[] ks =  new SelectionKey[n];
            for (i = 0; i < keys.length; i++)
                ks[i] = keys[i];
            keys = ks;
            i = keyCount;
        }
        keys[i] = k;
        keyCount++;
    }

    private SelectionKey findKey(Selector sel) {
        synchronized (keyLock) {
            if (keys == null)
                return null;
            for (int i = 0; i < keys.length; i++)
                if ((keys[i] != null) && (keys[i].selector() == sel))
                    return keys[i];
            return null;
        }
    }

    void removeKey(SelectionKey k) {                    // package-private
        synchronized (keyLock) {
            for (int i = 0; i < keys.length; i++)
                if (keys[i] == k) {
                    keys[i] = null;
                    keyCount--;
                }
            ((AbstractSelectionKey)k).invalidate();
        }
    }

    private boolean haveValidKeys() {
        synchronized (keyLock) {
            if (keyCount == 0)
                return false;
            for (int i = 0; i < keys.length; i++) {
                if ((keys[i] != null) && keys[i].isValid())
                    return true;
            }
            return false;
        }
    }


    // -- Registration --

    public final boolean isRegistered() {
        synchronized (keyLock) {
            return keyCount != 0;
        }
    }

    public final SelectionKey keyFor(Selector sel) {
        return findKey(sel);
    }

    /**
     * Registers this channel with the given selector, returning a selection key.
     *
     * <p>  This method first verifies that this channel is open and that the
     * given initial interest set is valid.
     *
     * <p> If this channel is already registered with the given selector then
     * the selection key representing that registration is returned after
     * setting its interest set to the given value.
     *
     * <p> Otherwise this channel has not yet been registered with the given
     * selector, so the {@link AbstractSelector#register register} method of
     * the selector is invoked while holding the appropriate locks.  The
     * resulting key is added to this channel's key set before being returned.
     * </p>
     *
     * @throws  ClosedSelectorException {@inheritDoc}
     *
     * @throws  IllegalBlockingModeException {@inheritDoc}
     *
     * @throws  IllegalSelectorException {@inheritDoc}
     *
     * @throws  CancelledKeyException {@inheritDoc}
     *
     * @throws  IllegalArgumentException {@inheritDoc}
     */
    public final SelectionKey register(Selector sel, int ops,
                                       Object att)
        throws ClosedChannelException
    {
        synchronized (regLock) {
            if (!isOpen())
                throw new ClosedChannelException();
            if ((ops & ~validOps()) != 0)
                throw new IllegalArgumentException();
            if (blocking)
                throw new IllegalBlockingModeException();
            SelectionKey k = findKey(sel);
            if (k != null) {
                k.interestOps(ops);
                k.attach(att);
            }
            if (k == null) {
                // New registration
                synchronized (keyLock) {
                    if (!isOpen())
                        throw new ClosedChannelException();
                    k = ((AbstractSelector)sel).register(this, ops, att);
                    addKey(k);
                }
            }
            return k;
        }
    }


    // -- Closing --

    /**
     * Closes this channel.
     *
     * <p> This method, which is specified in the {@link
     * AbstractInterruptibleChannel} class and is invoked by the {@link
     * java.nio.channels.Channel#close close} method, in turn invokes the
     * {@link #implCloseSelectableChannel implCloseSelectableChannel} method in
     * order to perform the actual work of closing this channel.  It then
     * cancels all of this channel's keys.  </p>
     */
    protected final void implCloseChannel() throws IOException {
        implCloseSelectableChannel();
        synchronized (keyLock) {
            int count = (keys == null) ? 0 : keys.length;
            for (int i = 0; i < count; i++) {
                SelectionKey k = keys[i];
                if (k != null)
                    k.cancel();
            }
        }
    }

    /**
     * Closes this selectable channel.
     *
     * <p> This method is invoked by the {@link java.nio.channels.Channel#close
     * close} method in order to perform the actual work of closing the
     * channel.  This method is only invoked if the channel has not yet been
     * closed, and it is never invoked more than once.
     *
     * <p> An implementation of this method must arrange for any other thread
     * that is blocked in an I/O operation upon this channel to return
     * immediately, either by throwing an exception or by returning normally.
     * </p>
     *
     * @throws  IOException
     *          If an I/O error occurs
     */
    protected abstract void implCloseSelectableChannel() throws IOException;


    // -- Blocking --

    public final boolean isBlocking() {
        synchronized (regLock) {
            return blocking;
        }
    }

    public final Object blockingLock() {
        return regLock;
    }

    /**
     * Adjusts this channel's blocking mode.
     *
     * <p> If the given blocking mode is different from the current blocking
     * mode then this method invokes the {@link #implConfigureBlocking
     * implConfigureBlocking} method, while holding the appropriate locks, in
     * order to change the mode.  </p>
     */
    public final SelectableChannel configureBlocking(boolean block)
        throws IOException
    {
        synchronized (regLock) {
            if (!isOpen())
                throw new ClosedChannelException();
            if (blocking == block)
                return this;
            if (block && haveValidKeys())
                throw new IllegalBlockingModeException();
            implConfigureBlocking(block);
            blocking = block;
        }
        return this;
    }

    /**
     * Adjusts this channel's blocking mode.
     *
     * <p> This method is invoked by the {@link #configureBlocking
     * configureBlocking} method in order to perform the actual work of
     * changing the blocking mode.  This method is only invoked if the new mode
     * is different from the current mode.  </p>
     *
     * @param  block  If <tt>true then this channel will be placed in
     *                blocking mode; if <tt>false then it will be placed
     *                non-blocking mode
     *
     * @throws IOException
     *         If an I/O error occurs
     */
    protected abstract void implConfigureBlocking(boolean block)
        throws IOException;

}