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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.spi;

	import java.io.IOException;
	import java.nio.channels.*;
	import jdk.internal.misc.SharedSecrets;
	import sun.nio.ch.Interruptible;


	/**
	* Base implementation class for interruptible channels.
	*
	* <p> This class encapsulates the low-level machinery required to implement
	* the asynchronous closing and interruption of channels. A concrete channel
	* class must invoke the {@link #begin begin} and {@link #end end} methods
	* before and after, respectively, invoking an I/O operation that might block
	* indefinitely. In order to ensure that the {@link #end end} method is always
	* invoked, these methods should be used within a
	* {@code try} ... {@code finally} block:
	*
	* <blockquote><pre id="be">
	* boolean completed = false;
	* try {
	* begin();
	* completed = ...; // Perform blocking I/O operation
	* return ...; // Return result
	* } finally {
	* end(completed);
	* }</pre></blockquote>
	*
	* <p> The {@code completed} argument to the {@link #end end} method tells
	* whether or not the I/O operation actually completed, that is, whether it had
	* any effect that would be visible to the invoker. In the case of an
	* operation that reads bytes, for example, this argument should be
	* {@code true} if, and only if, some bytes were actually transferred into the
	* invoker's target buffer.
	*
	* <p> A concrete channel class must also implement the {@link
	* #implCloseChannel implCloseChannel} method in such a way that if it is
	* invoked while another thread is blocked in a native I/O operation upon the
	* channel then that operation will immediately return, either by throwing an
	* exception or by returning normally. If a thread is interrupted or the
	* channel upon which it is blocked is asynchronously closed then the channel's
	* {@link #end end} method will throw the appropriate exception.
	*
	* <p> This class performs the synchronization required to implement the {@link
	* java.nio.channels.Channel} specification. Implementations of the {@link
	* #implCloseChannel implCloseChannel} method need not synchronize against
	* other threads that might be attempting to close the channel. </p>
	*
	*
	* @author Mark Reinhold
	* @author JSR-51 Expert Group
	* @since 1.4
	*/

	public abstract class AbstractInterruptibleChannel
	implements Channel, InterruptibleChannel
	{

	private final Object closeLock = new Object();
	private volatile boolean closed;

	/**
	* Initializes a new instance of this class.
	*/
	protected AbstractInterruptibleChannel() { }

	/**
	* Closes this channel.
	*
	* <p> If the channel has already been closed then this method returns
	* immediately. Otherwise it marks the channel as closed and then invokes
	* the {@link #implCloseChannel implCloseChannel} method in order to
	* complete the close operation. </p>
	*
	* @throws IOException
	* If an I/O error occurs
	*/
	public final void close() throws IOException {
	synchronized (closeLock) {
	if (closed)
	return;
	closed = true;
	implCloseChannel();
	}
	}

	/**
	* Closes this channel.
	*
	* <p> This method is invoked by the {@link #close close} method in order
	* to perform the actual work of closing the channel. This method is only
	* invoked if the channel has not yet been closed, and it is never invoked
	* more than once.
	*
	* <p> An implementation of this method must arrange for any other thread
	* that is blocked in an I/O operation upon this channel to return
	* immediately, either by throwing an exception or by returning normally.
	* </p>
	*
	* @throws IOException
	* If an I/O error occurs while closing the channel
	*/
	protected abstract void implCloseChannel() throws IOException;

	public final boolean isOpen() {
	return !closed;
	}


	// -- Interruption machinery --

	private Interruptible interruptor;
	private volatile Thread interrupted;

	/**
	* Marks the beginning of an I/O operation that might block indefinitely.
	*
	* <p> This method should be invoked in tandem with the {@link #end end}
	* method, using a {@code try} ... {@code finally} block as
	* shown <a href="#be">above</a>, in order to implement asynchronous
	* closing and interruption for this channel. </p>
	*/
	protected final void begin() {
	if (interruptor == null) {
	interruptor = new Interruptible() {
	public void interrupt(Thread target) {
	synchronized (closeLock) {
	if (closed)
	return;
	closed = true;
	interrupted = target;
	try {
	AbstractInterruptibleChannel.this.implCloseChannel();
	} catch (IOException x) { }
	}
	}};
	}
	blockedOn(interruptor);
	Thread me = Thread.currentThread();
	if (me.isInterrupted())
	interruptor.interrupt(me);
	}

	/**
	* Marks the end of an I/O operation that might block indefinitely.
	*
	* <p> This method should be invoked in tandem with the {@link #begin
	* begin} method, using a {@code try} ... {@code finally} block
	* as shown <a href="#be">above</a>, in order to implement asynchronous
	* closing and interruption for this channel. </p>
	*
	* @param completed
	* {@code true} if, and only if, the I/O operation completed
	* successfully, that is, had some effect that would be visible to
	* the operation's invoker
	*
	* @throws AsynchronousCloseException
	* If the channel was asynchronously closed
	*
	* @throws ClosedByInterruptException
	* If the thread blocked in the I/O operation was interrupted
	*/
	protected final void end(boolean completed)
	throws AsynchronousCloseException
	{
	blockedOn(null);
	Thread interrupted = this.interrupted;
	if (interrupted != null && interrupted == Thread.currentThread()) {
	this.interrupted = null;
	throw new ClosedByInterruptException();
	}
	if (!completed && closed)
	throw new AsynchronousCloseException();
	}


	// -- jdk.internal.misc.SharedSecrets --
	static void blockedOn(Interruptible intr) { // package-private
	SharedSecrets.getJavaLangAccess().blockedOn(intr);
	}
	}

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