Java example source code file (SelectableChannel.java)

This example Java source code file (SelectableChannel.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

abstractinterruptiblechannel, closedchannelexception, ioexception, object, selectablechannel, selectionkey, selectorprovider

The SelectableChannel.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;

import java.io.IOException;
import java.nio.channels.spi.AbstractInterruptibleChannel;
import java.nio.channels.spi.SelectorProvider;


/**
 * A channel that can be multiplexed via a {@link Selector}.
 *
 * <p> In order to be used with a selector, an instance of this class must
 * first be <i>registered via the {@link #register(Selector,int,Object)
 * register} method.  This method returns a new {@link SelectionKey} object
 * that represents the channel's registration with the selector.
 *
 * <p> Once registered with a selector, a channel remains registered until it
 * is <i>deregistered.  This involves deallocating whatever resources were
 * allocated to the channel by the selector.
 *
 * <p> A channel cannot be deregistered directly; instead, the key representing
 * its registration must be <i>cancelled.  Cancelling a key requests that
 * the channel be deregistered during the selector's next selection operation.
 * A key may be cancelled explicitly by invoking its {@link
 * SelectionKey#cancel() cancel} method.  All of a channel's keys are cancelled
 * implicitly when the channel is closed, whether by invoking its {@link
 * Channel#close close} method or by interrupting a thread blocked in an I/O
 * operation upon the channel.
 *
 * <p> If the selector itself is closed then the channel will be deregistered,
 * and the key representing its registration will be invalidated, without
 * further delay.
 *
 * <p> A channel may be registered at most once with any particular selector.
 *
 * <p> Whether or not a channel is registered with one or more selectors may be
 * determined by invoking the {@link #isRegistered isRegistered} method.
 *
 * <p> Selectable channels are safe for use by multiple concurrent
 * threads. </p>
 *
 *
 * <a name="bm">
 * <h2>Blocking mode
 *
 * A selectable channel is either in <i>blocking mode or in
 * <i>non-blocking mode.  In blocking mode, every I/O operation invoked
 * upon the channel will block until it completes.  In non-blocking mode an I/O
 * operation will never block and may transfer fewer bytes than were requested
 * or possibly no bytes at all.  The blocking mode of a selectable channel may
 * be determined by invoking its {@link #isBlocking isBlocking} method.
 *
 * <p> Newly-created selectable channels are always in blocking mode.
 * Non-blocking mode is most useful in conjunction with selector-based
 * multiplexing.  A channel must be placed into non-blocking mode before being
 * registered with a selector, and may not be returned to blocking mode until
 * it has been deregistered.
 *
 *
 * @author Mark Reinhold
 * @author JSR-51 Expert Group
 * @since 1.4
 *
 * @see SelectionKey
 * @see Selector
 */

public abstract class SelectableChannel
    extends AbstractInterruptibleChannel
    implements Channel
{

    /**
     * Initializes a new instance of this class.
     */
    protected SelectableChannel() { }

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

    /**
     * Returns an <a href="SelectionKey.html#opsets">operation set
     * identifying this channel's supported operations.  The bits that are set
     * in this integer value denote exactly the operations that are valid for
     * this channel.  This method always returns the same value for a given
     * concrete channel class.
     *
     * @return  The valid-operation set
     */
    public abstract int validOps();

    // Internal state:
    //   keySet, may be empty but is never null, typ. a tiny array
    //   boolean isRegistered, protected by key set
    //   regLock, lock object to prevent duplicate registrations
    //   boolean isBlocking, protected by regLock

    /**
     * Tells whether or not this channel is currently registered with any
     * selectors.  A newly-created channel is not registered.
     *
     * <p> Due to the inherent delay between key cancellation and channel
     * deregistration, a channel may remain registered for some time after all
     * of its keys have been cancelled.  A channel may also remain registered
     * for some time after it is closed.  </p>
     *
     * @return <tt>true if, and only if, this channel is registered
     */
    public abstract boolean isRegistered();
    //
    // sync(keySet) { return isRegistered; }

    /**
     * Retrieves the key representing the channel's registration with the given
     * selector.
     *
     * @param   sel
     *          The selector
     *
     * @return  The key returned when this channel was last registered with the
     *          given selector, or <tt>null if this channel is not
     *          currently registered with that selector
     */
    public abstract SelectionKey keyFor(Selector sel);
    //
    // sync(keySet) { return findKey(sel); }

    /**
     * Registers this channel with the given selector, returning a selection
     * key.
     *
     * <p> If this channel is currently registered with the given selector then
     * the selection key representing that registration is returned.  The key's
     * interest set will have been changed to <tt>ops, as if by invoking
     * the {@link SelectionKey#interestOps(int) interestOps(int)} method.  If
     * the <tt>att argument is not null then the key's attachment
     * will have been set to that value.  A {@link CancelledKeyException} will
     * be thrown if the key has already been cancelled.
     *
     * <p> Otherwise this channel has not yet been registered with the given
     * selector, so it is registered and the resulting new key is returned.
     * The key's initial interest set will be <tt>ops and its attachment
     * will be <tt>att.
     *
     * <p> This method may be invoked at any time.  If this method is invoked
     * while another invocation of this method or of the {@link
     * #configureBlocking(boolean) configureBlocking} method is in progress
     * then it will first block until the other operation is complete.  This
     * method will then synchronize on the selector's key set and therefore may
     * block if invoked concurrently with another registration or selection
     * operation involving the same selector. </p>
     *
     * <p> If this channel is closed while this operation is in progress then
     * the key returned by this method will have been cancelled and will
     * therefore be invalid. </p>
     *
     * @param  sel
     *         The selector with which this channel is to be registered
     *
     * @param  ops
     *         The interest set for the resulting key
     *
     * @param  att
     *         The attachment for the resulting key; may be <tt>null
     *
     * @throws  ClosedChannelException
     *          If this channel is closed
     *
     * @throws  ClosedSelectorException
     *          If the selector is closed
     *
     * @throws  IllegalBlockingModeException
     *          If this channel is in blocking mode
     *
     * @throws  IllegalSelectorException
     *          If this channel was not created by the same provider
     *          as the given selector
     *
     * @throws  CancelledKeyException
     *          If this channel is currently registered with the given selector
     *          but the corresponding key has already been cancelled
     *
     * @throws  IllegalArgumentException
     *          If a bit in the <tt>ops set does not correspond to an
     *          operation that is supported by this channel, that is, if
     *          {@code set & ~validOps() != 0}
     *
     * @return  A key representing the registration of this channel with
     *          the given selector
     */
    public abstract SelectionKey register(Selector sel, int ops, Object att)
        throws ClosedChannelException;
    //
    // sync(regLock) {
    //   sync(keySet) { look for selector }
    //   if (channel found) { set interest ops -- may block in selector;
    //                        return key; }
    //   create new key -- may block somewhere in selector;
    //   sync(keySet) { add key; }
    //   attach(attachment);
    //   return key;
    // }

    /**
     * Registers this channel with the given selector, returning a selection
     * key.
     *
     * <p> An invocation of this convenience method of the form
     *
     * <blockquote>sc.register(sel, ops)
     *
     * behaves in exactly the same way as the invocation
     *
     * <blockquote>sc.{@link
     * #register(java.nio.channels.Selector,int,java.lang.Object)
     * register}(sel, ops, null)</tt>
     *
     * @param  sel
     *         The selector with which this channel is to be registered
     *
     * @param  ops
     *         The interest set for the resulting key
     *
     * @throws  ClosedChannelException
     *          If this channel is closed
     *
     * @throws  ClosedSelectorException
     *          If the selector is closed
     *
     * @throws  IllegalBlockingModeException
     *          If this channel is in blocking mode
     *
     * @throws  IllegalSelectorException
     *          If this channel was not created by the same provider
     *          as the given selector
     *
     * @throws  CancelledKeyException
     *          If this channel is currently registered with the given selector
     *          but the corresponding key has already been cancelled
     *
     * @throws  IllegalArgumentException
     *          If a bit in <tt>ops does not correspond to an operation
     *          that is supported by this channel, that is, if {@code set &
     *          ~validOps() != 0}
     *
     * @return  A key representing the registration of this channel with
     *          the given selector
     */
    public final SelectionKey register(Selector sel, int ops)
        throws ClosedChannelException
    {
        return register(sel, ops, null);
    }

    /**
     * Adjusts this channel's blocking mode.
     *
     * <p> If this channel is registered with one or more selectors then an
     * attempt to place it into blocking mode will cause an {@link
     * IllegalBlockingModeException} to be thrown.
     *
     * <p> This method may be invoked at any time.  The new blocking mode will
     * only affect I/O operations that are initiated after this method returns.
     * For some implementations this may require blocking until all pending I/O
     * operations are complete.
     *
     * <p> If this method is invoked while another invocation of this method or
     * of the {@link #register(Selector, int) register} method is in progress
     * then it will first block until the other operation is complete. </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
     *
     * @return  This selectable channel
     *
     * @throws  ClosedChannelException
     *          If this channel is closed
     *
     * @throws  IllegalBlockingModeException
     *          If <tt>block is true and this channel is
     *          registered with one or more selectors
     *
     * @throws IOException
     *         If an I/O error occurs
     */
    public abstract SelectableChannel configureBlocking(boolean block)
        throws IOException;
    //
    // sync(regLock) {
    //   sync(keySet) { throw IBME if block && isRegistered; }
    //   change mode;
    // }

    /**
     * Tells whether or not every I/O operation on this channel will block
     * until it completes.  A newly-created channel is always in blocking mode.
     *
     * <p> If this channel is closed then the value returned by this method is
     * not specified. </p>
     *
     * @return <tt>true if, and only if, this channel is in blocking mode
     */
    public abstract boolean isBlocking();

    /**
     * Retrieves the object upon which the {@link #configureBlocking
     * configureBlocking} and {@link #register register} methods synchronize.
     * This is often useful in the implementation of adaptors that require a
     * specific blocking mode to be maintained for a short period of time.
     *
     * @return  The blocking-mode lock object
     */
    public abstract Object blockingLock();

}