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	/*
	* 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();

	}

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