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/*
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* Copyright 2000-2004 Sun Microsystems, Inc. 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. Sun designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
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* CA 95054 USA or visit www.sun.com if you need additional information or
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* have any questions.
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*/
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package java.nio.channels.spi;
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import java.io.IOException;
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import java.nio.channels.SelectionKey;
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import java.nio.channels.Selector;
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import java.util.HashSet;
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import java.util.Set;
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import sun.nio.ch.Interruptible;
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import java.util.concurrent.atomic.AtomicBoolean;
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/**
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* Base implementation class for selectors.
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*
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* <p> This class encapsulates the low-level machinery required to implement
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* the interruption of selection operations. A concrete selector class must
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* invoke the {@link #begin begin} and {@link #end end} methods before and
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* after, respectively, invoking an I/O operation that might block
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* indefinitely. In order to ensure that the {@link #end end} method is always
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* invoked, these methods should be used within a
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* <tt>try</tt> ... <tt>finally</tt> block: <a name="be">
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*
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* <blockquote><pre>
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* try {
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* begin();
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* // Perform blocking I/O operation here
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* ...
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* } finally {
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* end();
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* }</pre></blockquote>
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*
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* <p> This class also defines methods for maintaining a selector's
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* cancelled-key set and for removing a key from its channel's key set, and
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* declares the abstract {@link #register register} method that is invoked by a
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* selectable channel's {@link AbstractSelectableChannel#register register}
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* method in order to perform the actual work of registering a channel. </p>
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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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public abstract class AbstractSelector
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extends Selector
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{
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private AtomicBoolean selectorOpen = new AtomicBoolean(true);
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// The provider that created this selector
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private final SelectorProvider provider;
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/**
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* Initializes a new instance of this class. </p>
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*/
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protected AbstractSelector(SelectorProvider provider) {
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this.provider = provider;
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}
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private final Set<SelectionKey> cancelledKeys = new HashSet<SelectionKey>();
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void cancel(SelectionKey k) { // package-private
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synchronized (cancelledKeys) {
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cancelledKeys.add(k);
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}
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}
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/**
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* Closes this selector.
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*
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* <p> If the selector has already been closed then this method returns
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* immediately. Otherwise it marks the selector as closed and then invokes
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* the {@link #implCloseSelector implCloseSelector} method in order to
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* complete the close operation. </p>
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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 final void close() throws IOException {
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boolean open = selectorOpen.getAndSet(false);
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if (!open)
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return;
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implCloseSelector();
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}
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/**
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* Closes this selector.
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*
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* <p> This method is invoked by the {@link #close close} method in order
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* to perform the actual work of closing the selector. This method is only
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* invoked if the selector has not yet been closed, and it is never invoked
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* more than once.
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*
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* <p> An implementation of this method must arrange for any other thread
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* that is blocked in a selection operation upon this selector to return
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* immediately as if by invoking the {@link
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* java.nio.channels.Selector#wakeup wakeup} method. </p>
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*
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* @throws IOException
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* If an I/O error occurs while closing the selector
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*/
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protected abstract void implCloseSelector() throws IOException;
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public final boolean isOpen() {
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return selectorOpen.get();
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}
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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 final SelectorProvider provider() {
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return provider;
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}
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/**
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* Retrieves this selector's cancelled-key set.
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*
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* <p> This set should only be used while synchronized upon it. </p>
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*
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* @return The cancelled-key set
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*/
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protected final Set<SelectionKey> cancelledKeys() {
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return cancelledKeys;
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}
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/**
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* Registers the given channel with this selector.
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*
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* <p> This method is invoked by a channel's {@link
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* AbstractSelectableChannel#register register} method in order to perform
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* the actual work of registering the channel with this selector. </p>
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*
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* @param ch
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* The channel to be registered
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*
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* @param ops
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* The initial interest set, which must be valid
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*
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* @param att
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* The initial attachment for the resulting key
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*
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* @return A new key representing the registration of the given channel
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* with this selector
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*/
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protected abstract SelectionKey register(AbstractSelectableChannel ch,
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int ops, Object att);
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/**
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* Removes the given key from its channel's key set.
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*
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* <p> This method must be invoked by the selector for each channel that it
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* deregisters. </p>
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*
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* @param key
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* The selection key to be removed
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*/
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protected final void deregister(AbstractSelectionKey key) {
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((AbstractSelectableChannel)key.channel()).removeKey(key);
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}
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// -- Interruption machinery --
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private Interruptible interruptor = null;
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/**
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* Marks the beginning of an I/O operation that might block indefinitely.
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*
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* <p> This method should be invoked in tandem with the {@link #end end}
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* method, using a <tt>try</tt> ... <tt>finally</tt> block as
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* shown <a href="#be">above</a>, in order to implement interruption for
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* this selector.
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*
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* <p> Invoking this method arranges for the selector's {@link
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* Selector#wakeup wakeup} method to be invoked if a thread's {@link
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* Thread#interrupt interrupt} method is invoked while the thread is
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* blocked in an I/O operation upon the selector. </p>
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*/
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protected final void begin() {
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if (interruptor == null) {
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interruptor = new Interruptible() {
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public void interrupt() {
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AbstractSelector.this.wakeup();
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}};
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}
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AbstractInterruptibleChannel.blockedOn(interruptor);
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if (Thread.currentThread().isInterrupted())
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interruptor.interrupt();
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}
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/**
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* Marks the end of an I/O operation that might block indefinitely.
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*
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* <p> This method should be invoked in tandem with the {@link #begin begin}
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* method, using a <tt>try</tt> ... <tt>finally</tt> block as
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* shown <a href="#be">above</a>, in order to implement interruption for
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* this selector. </p>
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*/
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protected final void end() {
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AbstractInterruptibleChannel.blockedOn(null);
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}
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}
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