Java tutorial
/* * Copyright (c) 2000, 2018, 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</i> 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</i>. 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</i>. 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 id="bm"></a> * <h2>Blocking mode</h2> * * A selectable channel is either in <i>blocking</i> mode or in * <i>non-blocking</i> 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</a> * 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(); /** * 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 {@code true} if, and only if, this channel is registered */ public abstract boolean 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 {@code null} if this channel is not * currently registered with that selector */ public abstract SelectionKey keyFor(Selector 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 {@code ops}, as if by invoking * the {@link SelectionKey#interestOps(int) interestOps(int)} method. If * the {@code att} argument is not {@code 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 {@code ops} and its attachment * will be {@code att}. * * <p> This method may be invoked at any time. If this method is invoked * while a selection operation is in progress then it has no effect upon * that operation; the new registration or change to the key's interest set * will be seen by the next selection operation. If this method is invoked * while an invocation of {@link #configureBlocking(boolean) configureBlocking} * is in progress then it will block until the channel's blocking mode has * been adjusted. * * <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 {@code 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 {@code 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; /** * Registers this channel with the given selector, returning a selection * key. * * <p> An invocation of this convenience method of the form * * <blockquote>{@code sc.register(sel, ops)}</blockquote> * * behaves in exactly the same way as the invocation * * <blockquote>{@code sc.}{@link * #register(java.nio.channels.Selector,int,java.lang.Object) * register(sel, ops, null)}</blockquote> * * @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 {@code 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 {@code true} then this channel will be placed in * blocking mode; if {@code false} then it will be placed * non-blocking mode * * @return This selectable channel * * @throws ClosedChannelException * If this channel is closed * * @throws IllegalBlockingModeException * If {@code block} is {@code 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; /** * 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 {@code 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(); }