320 lines
12 KiB
Java
320 lines
12 KiB
Java
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/*
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* Copyright (c) 2000, 2018, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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package java.nio.channels;
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import java.io.IOException;
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import java.nio.channels.spi.AbstractInterruptibleChannel;
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import java.nio.channels.spi.SelectorProvider;
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/**
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* A channel that can be multiplexed via a {@link Selector}.
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*
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* <p> In order to be used with a selector, an instance of this class must
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* first be <i>registered</i> via the {@link #register(Selector,int,Object)
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* register} method. This method returns a new {@link SelectionKey} object
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* that represents the channel's registration with the selector.
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*
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* <p> Once registered with a selector, a channel remains registered until it
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* is <i>deregistered</i>. This involves deallocating whatever resources were
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* allocated to the channel by the selector.
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*
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* <p> A channel cannot be deregistered directly; instead, the key representing
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* its registration must be <i>cancelled</i>. Cancelling a key requests that
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* the channel be deregistered during the selector's next selection operation.
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* A key may be cancelled explicitly by invoking its {@link
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* SelectionKey#cancel() cancel} method. All of a channel's keys are cancelled
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* implicitly when the channel is closed, whether by invoking its {@link
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* Channel#close close} method or by interrupting a thread blocked in an I/O
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* operation upon the channel.
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*
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* <p> If the selector itself is closed then the channel will be deregistered,
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* and the key representing its registration will be invalidated, without
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* further delay.
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*
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* <p> A channel may be registered at most once with any particular selector.
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*
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* <p> Whether or not a channel is registered with one or more selectors may be
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* determined by invoking the {@link #isRegistered isRegistered} method.
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*
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* <p> Selectable channels are safe for use by multiple concurrent
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* threads. </p>
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*
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*
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* <a id="bm"></a>
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* <h2>Blocking mode</h2>
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*
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* A selectable channel is either in <i>blocking</i> mode or in
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* <i>non-blocking</i> mode. In blocking mode, every I/O operation invoked
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* upon the channel will block until it completes. In non-blocking mode an I/O
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* operation will never block and may transfer fewer bytes than were requested
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* or possibly no bytes at all. The blocking mode of a selectable channel may
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* be determined by invoking its {@link #isBlocking isBlocking} method.
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*
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* <p> Newly-created selectable channels are always in blocking mode.
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* Non-blocking mode is most useful in conjunction with selector-based
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* multiplexing. A channel must be placed into non-blocking mode before being
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* registered with a selector, and may not be returned to blocking mode until
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* it has been deregistered.
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*
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*
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* @author Mark Reinhold
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* @author JSR-51 Expert Group
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* @since 1.4
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*
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* @see SelectionKey
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* @see Selector
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*/
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public abstract class SelectableChannel
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extends AbstractInterruptibleChannel
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implements Channel
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{
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/**
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* Initializes a new instance of this class.
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*/
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protected SelectableChannel() { }
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/**
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* Returns the provider that created this channel.
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*
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* @return The provider that created this channel
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*/
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public abstract SelectorProvider provider();
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/**
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* Returns an <a href="SelectionKey.html#opsets">operation set</a>
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* identifying this channel's supported operations. The bits that are set
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* in this integer value denote exactly the operations that are valid for
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* this channel. This method always returns the same value for a given
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* concrete channel class.
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*
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* @return The valid-operation set
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*/
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public abstract int validOps();
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/**
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* Tells whether or not this channel is currently registered with any
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* selectors. A newly-created channel is not registered.
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*
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* <p> Due to the inherent delay between key cancellation and channel
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* deregistration, a channel may remain registered for some time after all
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* of its keys have been cancelled. A channel may also remain registered
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* for some time after it is closed. </p>
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*
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* @return {@code true} if, and only if, this channel is registered
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*/
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public abstract boolean isRegistered();
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/**
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* Retrieves the key representing the channel's registration with the given
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* selector.
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*
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* @param sel
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* The selector
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*
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* @return The key returned when this channel was last registered with the
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* given selector, or {@code null} if this channel is not
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* currently registered with that selector
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*/
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public abstract SelectionKey keyFor(Selector sel);
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/**
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* Registers this channel with the given selector, returning a selection
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* key.
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*
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* <p> If this channel is currently registered with the given selector then
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* the selection key representing that registration is returned. The key's
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* interest set will have been changed to {@code ops}, as if by invoking
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* the {@link SelectionKey#interestOps(int) interestOps(int)} method. If
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* the {@code att} argument is not {@code null} then the key's attachment
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* will have been set to that value. A {@link CancelledKeyException} will
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* be thrown if the key has already been cancelled.
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*
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* <p> Otherwise this channel has not yet been registered with the given
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* selector, so it is registered and the resulting new key is returned.
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* The key's initial interest set will be {@code ops} and its attachment
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* will be {@code att}.
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*
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* <p> This method may be invoked at any time. If this method is invoked
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* while a selection operation is in progress then it has no effect upon
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* that operation; the new registration or change to the key's interest set
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* will be seen by the next selection operation. If this method is invoked
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* while an invocation of {@link #configureBlocking(boolean) configureBlocking}
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* is in progress then it will block until the channel's blocking mode has
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* been adjusted.
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*
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* <p> If this channel is closed while this operation is in progress then
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* the key returned by this method will have been cancelled and will
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* therefore be invalid. </p>
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*
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* @param sel
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* The selector with which this channel is to be registered
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*
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* @param ops
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* The interest set for the resulting key
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*
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* @param att
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* The attachment for the resulting key; may be {@code null}
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*
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* @throws ClosedChannelException
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* If this channel is closed
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*
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* @throws ClosedSelectorException
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* If the selector is closed
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*
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* @throws IllegalBlockingModeException
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* If this channel is in blocking mode
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*
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* @throws IllegalSelectorException
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* If this channel was not created by the same provider
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* as the given selector
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*
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* @throws CancelledKeyException
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* If this channel is currently registered with the given selector
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* but the corresponding key has already been cancelled
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*
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* @throws IllegalArgumentException
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* If a bit in the {@code ops} set does not correspond to an
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* operation that is supported by this channel, that is, if
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* {@code set & ~validOps() != 0}
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*
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* @return A key representing the registration of this channel with
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* the given selector
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*/
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public abstract SelectionKey register(Selector sel, int ops, Object att)
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throws ClosedChannelException;
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/**
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* Registers this channel with the given selector, returning a selection
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* key.
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*
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* <p> An invocation of this convenience method of the form
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*
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* <blockquote>{@code sc.register(sel, ops)}</blockquote>
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*
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* behaves in exactly the same way as the invocation
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*
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* <blockquote>{@code sc.}{@link
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* #register(java.nio.channels.Selector,int,java.lang.Object)
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* register(sel, ops, null)}</blockquote>
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*
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* @param sel
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* The selector with which this channel is to be registered
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*
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* @param ops
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* The interest set for the resulting key
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*
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* @throws ClosedChannelException
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* If this channel is closed
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*
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* @throws ClosedSelectorException
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* If the selector is closed
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*
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* @throws IllegalBlockingModeException
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* If this channel is in blocking mode
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*
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* @throws IllegalSelectorException
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* If this channel was not created by the same provider
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* as the given selector
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*
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* @throws CancelledKeyException
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* If this channel is currently registered with the given selector
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* but the corresponding key has already been cancelled
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*
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* @throws IllegalArgumentException
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* If a bit in {@code ops} does not correspond to an operation
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* that is supported by this channel, that is, if {@code set &
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* ~validOps() != 0}
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*
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* @return A key representing the registration of this channel with
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* the given selector
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*/
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public final SelectionKey register(Selector sel, int ops)
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throws ClosedChannelException
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{
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return register(sel, ops, null);
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}
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/**
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* Adjusts this channel's blocking mode.
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*
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* <p> If this channel is registered with one or more selectors then an
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* attempt to place it into blocking mode will cause an {@link
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* IllegalBlockingModeException} to be thrown.
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*
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* <p> This method may be invoked at any time. The new blocking mode will
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* only affect I/O operations that are initiated after this method returns.
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* For some implementations this may require blocking until all pending I/O
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* operations are complete.
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*
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* <p> If this method is invoked while another invocation of this method or
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* of the {@link #register(Selector, int) register} method is in progress
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* then it will first block until the other operation is complete. </p>
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*
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* @param block If {@code true} then this channel will be placed in
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* blocking mode; if {@code false} then it will be placed
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* non-blocking mode
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*
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* @return This selectable channel
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*
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* @throws ClosedChannelException
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* If this channel is closed
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*
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* @throws IllegalBlockingModeException
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* If {@code block} is {@code true} and this channel is
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* registered with one or more selectors
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*
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* @throws IOException
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* If an I/O error occurs
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*/
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public abstract SelectableChannel configureBlocking(boolean block)
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throws IOException;
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/**
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* Tells whether or not every I/O operation on this channel will block
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* until it completes. A newly-created channel is always in blocking mode.
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*
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* <p> If this channel is closed then the value returned by this method is
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* not specified. </p>
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*
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* @return {@code true} if, and only if, this channel is in blocking mode
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*/
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public abstract boolean isBlocking();
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/**
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* Retrieves the object upon which the {@link #configureBlocking
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* configureBlocking} and {@link #register register} methods synchronize.
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* This is often useful in the implementation of adaptors that require a
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* specific blocking mode to be maintained for a short period of time.
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*
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* @return The blocking-mode lock object
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*/
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public abstract Object blockingLock();
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}
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