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345 lines
12 KiB
345 lines
12 KiB
/*
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* Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.
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* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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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 name="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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// Internal state:
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// keySet, may be empty but is never null, typ. a tiny array
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// boolean isRegistered, protected by key set
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// regLock, lock object to prevent duplicate registrations
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// boolean isBlocking, protected by regLock
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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 <tt>true</tt> 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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// sync(keySet) { return 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 <tt>null</tt> 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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// sync(keySet) { return findKey(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 <tt>ops</tt>, as if by invoking
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* the {@link SelectionKey#interestOps(int) interestOps(int)} method. If
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* the <tt>att</tt> argument is not <tt>null</tt> 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 <tt>ops</tt> and its attachment
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* will be <tt>att</tt>.
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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 another invocation of this method or of the {@link
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* #configureBlocking(boolean) configureBlocking} method is in progress
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* then it will first block until the other operation is complete. This
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* method will then synchronize on the selector's key set and therefore may
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* block if invoked concurrently with another registration or selection
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* operation involving the same selector. </p>
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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 <tt>null</tt>
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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 <tt>ops</tt> 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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// sync(regLock) {
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// sync(keySet) { look for selector }
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// if (channel found) { set interest ops -- may block in selector;
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// return key; }
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// create new key -- may block somewhere in selector;
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// sync(keySet) { add key; }
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// attach(attachment);
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// return key;
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// }
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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><tt>sc.register(sel, ops)</tt></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><tt>sc.{@link
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* #register(java.nio.channels.Selector,int,java.lang.Object)
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* register}(sel, ops, null)</tt></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 <tt>ops</tt> 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 <tt>true</tt> then this channel will be placed in
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* blocking mode; if <tt>false</tt> 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 <tt>block</tt> is <tt>true</tt> 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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// sync(regLock) {
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// sync(keySet) { throw IBME if block && isRegistered; }
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// change mode;
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// }
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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 <tt>true</tt> 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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