Java example source code file (Port.java)

This example Java source code file (Port.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

asynchronouschannelgroupimpl, filedescriptor, integer, ioexception, map, max_batch_size, override, pollablechannel, pollin, pollout, port, readwritelock, reentrantreadwritelock, shutdownchannelgroupexception, util

The Port.java Java example source code

/*
 * Copyright (c) 2008, 2009, 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.nio.channels.spi.AsynchronousChannelProvider;
import java.nio.channels.*;
import java.io.IOException;
import java.io.Closeable;
import java.io.FileDescriptor;
import java.util.Map;
import java.util.HashMap;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

/**
 * Base implementation of AsynchronousChannelGroupImpl for Unix systems.
 */

abstract class Port extends AsynchronousChannelGroupImpl {
    static final short POLLIN       = 0x0001;
    static final short POLLOUT      = 0x0004;
    static final short POLLERR      = 0x0008;
    static final short POLLHUP      = 0x0010;

    /**
     * Implemented by clients registered with this port.
     */
    interface PollableChannel extends Closeable {
        void onEvent(int events, boolean mayInvokeDirect);
    }

    // maps fd to "pollable" channel
    protected final ReadWriteLock fdToChannelLock = new ReentrantReadWriteLock();
    protected final Map<Integer,PollableChannel> fdToChannel =
        new HashMap<Integer,PollableChannel>();


    Port(AsynchronousChannelProvider provider, ThreadPool pool) {
        super(provider, pool);
    }

    /**
     * Register channel identified by its file descriptor
     */
    final void register(int fd, PollableChannel ch) {
        fdToChannelLock.writeLock().lock();
        try {
            if (isShutdown())
                throw new ShutdownChannelGroupException();
            fdToChannel.put(Integer.valueOf(fd), ch);
        } finally {
            fdToChannelLock.writeLock().unlock();
        }
    }

    /**
     * Unregister channel identified by its file descriptor
     */
    final void unregister(int fd) {
        boolean checkForShutdown = false;

        fdToChannelLock.writeLock().lock();
        try {
            fdToChannel.remove(Integer.valueOf(fd));

            // last key to be removed so check if group is shutdown
            if (fdToChannel.isEmpty())
                checkForShutdown = true;

        } finally {
            fdToChannelLock.writeLock().unlock();
        }

        // continue shutdown
        if (checkForShutdown && isShutdown()) {
            try {
                shutdownNow();
            } catch (IOException ignore) { }
        }
    }
    /**
     * Register file descriptor with polling mechanism for given events.
     * The implementation should translate the events as required.
     */
    abstract void startPoll(int fd, int events);

    @Override
    final boolean isEmpty() {
        fdToChannelLock.writeLock().lock();
        try {
            return fdToChannel.isEmpty();
        } finally {
            fdToChannelLock.writeLock().unlock();
        }
    }

    @Override
    final Object attachForeignChannel(final Channel channel, FileDescriptor fd) {
        int fdVal = IOUtil.fdVal(fd);
        register(fdVal, new PollableChannel() {
            public void onEvent(int events, boolean mayInvokeDirect) { }
            public void close() throws IOException {
                channel.close();
            }
        });
        return Integer.valueOf(fdVal);
    }

    @Override
    final void detachForeignChannel(Object key) {
        unregister((Integer)key);
    }

    @Override
    final void closeAllChannels() {
        /**
         * Close channels in batches of up to 128 channels. This allows close
         * to remove the channel from the map without interference.
         */
        final int MAX_BATCH_SIZE = 128;
        PollableChannel channels[] = new PollableChannel[MAX_BATCH_SIZE];
        int count;
        do {
            // grab a batch of up to 128 channels
            fdToChannelLock.writeLock().lock();
            count = 0;
            try {
                for (Integer fd: fdToChannel.keySet()) {
                    channels[count++] = fdToChannel.get(fd);
                    if (count >= MAX_BATCH_SIZE)
                        break;
                }
            } finally {
                fdToChannelLock.writeLock().unlock();
            }

            // close them
            for (int i=0; i<count; i++) {
                try {
                    channels[i].close();
                } catch (IOException ignore) { }
            }
        } while (count > 0);
    }
}